Home Home > GIT Browse
summaryrefslogtreecommitdiff
blob: 3ed642e0a0c2a5cf935f31c81ff733afbd89bcac (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
3431
3432
3433
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
/*
 * fs/dcache.c
 *
 * Complete reimplementation
 * (C) 1997 Thomas Schoebel-Theuer,
 * with heavy changes by Linus Torvalds
 */

/*
 * Notes on the allocation strategy:
 *
 * The dcache is a master of the icache - whenever a dcache entry
 * exists, the inode will always exist. "iput()" is done either when
 * the dcache entry is deleted or garbage collected.
 */

#include <linux/syscalls.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/fs.h>
#include <linux/fsnotify.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/hash.h>
#include <linux/cache.h>
#include <linux/export.h>
#include <linux/mount.h>
#include <linux/file.h>
#include <asm/uaccess.h>
#include <linux/security.h>
#include <linux/seqlock.h>
#include <linux/swap.h>
#include <linux/bootmem.h>
#include <linux/fs_struct.h>
#include <linux/hardirq.h>
#include <linux/bit_spinlock.h>
#include <linux/rculist_bl.h>
#include <linux/prefetch.h>
#include <linux/ratelimit.h>
#include <linux/list_lru.h>
#include <linux/kasan.h>

#include "internal.h"
#include "mount.h"

/*
 * Usage:
 * dcache->d_inode->i_lock protects:
 *   - i_dentry, d_u.d_alias, d_inode of aliases
 * dcache_hash_bucket lock protects:
 *   - the dcache hash table
 * s_anon bl list spinlock protects:
 *   - the s_anon list (see __d_drop)
 * dentry->d_sb->s_dentry_lru_lock protects:
 *   - the dcache lru lists and counters
 * d_lock protects:
 *   - d_flags
 *   - d_name
 *   - d_lru
 *   - d_count
 *   - d_unhashed()
 *   - d_parent and d_subdirs
 *   - childrens' d_child and d_parent
 *   - d_u.d_alias, d_inode
 *
 * Ordering:
 * dentry->d_inode->i_lock
 *   dentry->d_lock
 *     dentry->d_sb->s_dentry_lru_lock
 *     dcache_hash_bucket lock
 *     s_anon lock
 *
 * If there is an ancestor relationship:
 * dentry->d_parent->...->d_parent->d_lock
 *   ...
 *     dentry->d_parent->d_lock
 *       dentry->d_lock
 *
 * If no ancestor relationship:
 * if (dentry1 < dentry2)
 *   dentry1->d_lock
 *     dentry2->d_lock
 */
int sysctl_vfs_cache_pressure __read_mostly = 100;
EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);

__cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);

EXPORT_SYMBOL(rename_lock);

static struct kmem_cache *dentry_cache __read_mostly;

/*
 * This is the single most critical data structure when it comes
 * to the dcache: the hashtable for lookups. Somebody should try
 * to make this good - I've just made it work.
 *
 * This hash-function tries to avoid losing too many bits of hash
 * information, yet avoid using a prime hash-size or similar.
 */

static unsigned int d_hash_mask __read_mostly;
static unsigned int d_hash_shift __read_mostly;

static struct hlist_bl_head *dentry_hashtable __read_mostly;

static inline struct hlist_bl_head *d_hash(const struct dentry *parent,
					unsigned int hash)
{
	hash += (unsigned long) parent / L1_CACHE_BYTES;
	return dentry_hashtable + hash_32(hash, d_hash_shift);
}

/* Statistics gathering. */
struct dentry_stat_t dentry_stat = {
	.age_limit = 45,
};

static DEFINE_PER_CPU(long, nr_dentry);
static DEFINE_PER_CPU(long, nr_dentry_unused);

#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)

/*
 * Here we resort to our own counters instead of using generic per-cpu counters
 * for consistency with what the vfs inode code does. We are expected to harvest
 * better code and performance by having our own specialized counters.
 *
 * Please note that the loop is done over all possible CPUs, not over all online
 * CPUs. The reason for this is that we don't want to play games with CPUs going
 * on and off. If one of them goes off, we will just keep their counters.
 *
 * glommer: See cffbc8a for details, and if you ever intend to change this,
 * please update all vfs counters to match.
 */
static long get_nr_dentry(void)
{
	int i;
	long sum = 0;
	for_each_possible_cpu(i)
		sum += per_cpu(nr_dentry, i);
	return sum < 0 ? 0 : sum;
}

static long get_nr_dentry_unused(void)
{
	int i;
	long sum = 0;
	for_each_possible_cpu(i)
		sum += per_cpu(nr_dentry_unused, i);
	return sum < 0 ? 0 : sum;
}

int proc_nr_dentry(struct ctl_table *table, int write, void __user *buffer,
		   size_t *lenp, loff_t *ppos)
{
	dentry_stat.nr_dentry = get_nr_dentry();
	dentry_stat.nr_unused = get_nr_dentry_unused();
	return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
}
#endif

/*
 * Compare 2 name strings, return 0 if they match, otherwise non-zero.
 * The strings are both count bytes long, and count is non-zero.
 */
#ifdef CONFIG_DCACHE_WORD_ACCESS

#include <asm/word-at-a-time.h>
/*
 * NOTE! 'cs' and 'scount' come from a dentry, so it has a
 * aligned allocation for this particular component. We don't
 * strictly need the load_unaligned_zeropad() safety, but it
 * doesn't hurt either.
 *
 * In contrast, 'ct' and 'tcount' can be from a pathname, and do
 * need the careful unaligned handling.
 */
static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
{
	unsigned long a,b,mask;

	for (;;) {
		a = *(unsigned long *)cs;
		b = load_unaligned_zeropad(ct);
		if (tcount < sizeof(unsigned long))
			break;
		if (unlikely(a != b))
			return 1;
		cs += sizeof(unsigned long);
		ct += sizeof(unsigned long);
		tcount -= sizeof(unsigned long);
		if (!tcount)
			return 0;
	}
	mask = bytemask_from_count(tcount);
	return unlikely(!!((a ^ b) & mask));
}

#else

static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
{
	do {
		if (*cs != *ct)
			return 1;
		cs++;
		ct++;
		tcount--;
	} while (tcount);
	return 0;
}

#endif

static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
{
	const unsigned char *cs;
	/*
	 * Be careful about RCU walk racing with rename:
	 * use ACCESS_ONCE to fetch the name pointer.
	 *
	 * NOTE! Even if a rename will mean that the length
	 * was not loaded atomically, we don't care. The
	 * RCU walk will check the sequence count eventually,
	 * and catch it. And we won't overrun the buffer,
	 * because we're reading the name pointer atomically,
	 * and a dentry name is guaranteed to be properly
	 * terminated with a NUL byte.
	 *
	 * End result: even if 'len' is wrong, we'll exit
	 * early because the data cannot match (there can
	 * be no NUL in the ct/tcount data)
	 */
	cs = ACCESS_ONCE(dentry->d_name.name);
	smp_read_barrier_depends();
	return dentry_string_cmp(cs, ct, tcount);
}

struct external_name {
	union {
		atomic_t count;
		struct rcu_head head;
	} u;
	unsigned char name[];
};

static inline struct external_name *external_name(struct dentry *dentry)
{
	return container_of(dentry->d_name.name, struct external_name, name[0]);
}

static void __d_free(struct rcu_head *head)
{
	struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);

	kmem_cache_free(dentry_cache, dentry); 
}

static void __d_free_external(struct rcu_head *head)
{
	struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
	kfree(external_name(dentry));
	kmem_cache_free(dentry_cache, dentry); 
}

static inline int dname_external(const struct dentry *dentry)
{
	return dentry->d_name.name != dentry->d_iname;
}

void take_dentry_name_snapshot(struct name_snapshot *name, struct dentry *dentry)
{
	spin_lock(&dentry->d_lock);
	if (unlikely(dname_external(dentry))) {
		struct external_name *p = external_name(dentry);
		atomic_inc(&p->u.count);
		spin_unlock(&dentry->d_lock);
		name->name = p->name;
	} else {
		memcpy(name->inline_name, dentry->d_iname, DNAME_INLINE_LEN);
		spin_unlock(&dentry->d_lock);
		name->name = name->inline_name;
	}
}
EXPORT_SYMBOL(take_dentry_name_snapshot);

void release_dentry_name_snapshot(struct name_snapshot *name)
{
	if (unlikely(name->name != name->inline_name)) {
		struct external_name *p;
		p = container_of(name->name, struct external_name, name[0]);
		if (unlikely(atomic_dec_and_test(&p->u.count)))
			kfree_rcu(p, u.head);
	}
}
EXPORT_SYMBOL(release_dentry_name_snapshot);

static inline void __d_set_inode_and_type(struct dentry *dentry,
					  struct inode *inode,
					  unsigned type_flags)
{
	unsigned flags;

	dentry->d_inode = inode;
	flags = READ_ONCE(dentry->d_flags);
	flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
	flags |= type_flags;
	WRITE_ONCE(dentry->d_flags, flags);
}

static inline void __d_clear_type_and_inode(struct dentry *dentry)
{
	unsigned flags = READ_ONCE(dentry->d_flags);

	flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
	WRITE_ONCE(dentry->d_flags, flags);
	dentry->d_inode = NULL;
}

static void dentry_free(struct dentry *dentry)
{
	WARN_ON(!hlist_unhashed(&dentry->d_u.d_alias));
	if (unlikely(dname_external(dentry))) {
		struct external_name *p = external_name(dentry);
		if (likely(atomic_dec_and_test(&p->u.count))) {
			call_rcu(&dentry->d_u.d_rcu, __d_free_external);
			return;
		}
	}
	/* if dentry was never visible to RCU, immediate free is OK */
	if (!(dentry->d_flags & DCACHE_RCUACCESS))
		__d_free(&dentry->d_u.d_rcu);
	else
		call_rcu(&dentry->d_u.d_rcu, __d_free);
}

/**
 * dentry_rcuwalk_invalidate - invalidate in-progress rcu-walk lookups
 * @dentry: the target dentry
 * After this call, in-progress rcu-walk path lookup will fail. This
 * should be called after unhashing, and after changing d_inode (if
 * the dentry has not already been unhashed).
 */
static inline void dentry_rcuwalk_invalidate(struct dentry *dentry)
{
	lockdep_assert_held(&dentry->d_lock);
	/* Go through am invalidation barrier */
	write_seqcount_invalidate(&dentry->d_seq);
}

/*
 * Release the dentry's inode, using the filesystem
 * d_iput() operation if defined. Dentry has no refcount
 * and is unhashed.
 */
static void dentry_iput(struct dentry * dentry)
	__releases(dentry->d_lock)
	__releases(dentry->d_inode->i_lock)
{
	struct inode *inode = dentry->d_inode;
	if (inode) {
		__d_clear_type_and_inode(dentry);
		hlist_del_init(&dentry->d_u.d_alias);
		spin_unlock(&dentry->d_lock);
		spin_unlock(&inode->i_lock);
		if (!inode->i_nlink)
			fsnotify_inoderemove(inode);
		if (dentry->d_op && dentry->d_op->d_iput)
			dentry->d_op->d_iput(dentry, inode);
		else
			iput(inode);
	} else {
		spin_unlock(&dentry->d_lock);
	}
}

/*
 * Release the dentry's inode, using the filesystem
 * d_iput() operation if defined. dentry remains in-use.
 */
static void dentry_unlink_inode(struct dentry * dentry)
	__releases(dentry->d_lock)
	__releases(dentry->d_inode->i_lock)
{
	struct inode *inode = dentry->d_inode;

	raw_write_seqcount_begin(&dentry->d_seq);
	__d_clear_type_and_inode(dentry);
	hlist_del_init(&dentry->d_u.d_alias);
	raw_write_seqcount_end(&dentry->d_seq);
	spin_unlock(&dentry->d_lock);
	spin_unlock(&inode->i_lock);
	if (!inode->i_nlink)
		fsnotify_inoderemove(inode);
	if (dentry->d_op && dentry->d_op->d_iput)
		dentry->d_op->d_iput(dentry, inode);
	else
		iput(inode);
}

/*
 * The DCACHE_LRU_LIST bit is set whenever the 'd_lru' entry
 * is in use - which includes both the "real" per-superblock
 * LRU list _and_ the DCACHE_SHRINK_LIST use.
 *
 * The DCACHE_SHRINK_LIST bit is set whenever the dentry is
 * on the shrink list (ie not on the superblock LRU list).
 *
 * The per-cpu "nr_dentry_unused" counters are updated with
 * the DCACHE_LRU_LIST bit.
 *
 * These helper functions make sure we always follow the
 * rules. d_lock must be held by the caller.
 */
#define D_FLAG_VERIFY(dentry,x) WARN_ON_ONCE(((dentry)->d_flags & (DCACHE_LRU_LIST | DCACHE_SHRINK_LIST)) != (x))
static void d_lru_add(struct dentry *dentry)
{
	D_FLAG_VERIFY(dentry, 0);
	dentry->d_flags |= DCACHE_LRU_LIST;
	this_cpu_inc(nr_dentry_unused);
	WARN_ON_ONCE(!list_lru_add(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
}

static void d_lru_del(struct dentry *dentry)
{
	D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
	dentry->d_flags &= ~DCACHE_LRU_LIST;
	this_cpu_dec(nr_dentry_unused);
	WARN_ON_ONCE(!list_lru_del(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
}

static void d_shrink_del(struct dentry *dentry)
{
	D_FLAG_VERIFY(dentry, DCACHE_SHRINK_LIST | DCACHE_LRU_LIST);
	list_del_init(&dentry->d_lru);
	dentry->d_flags &= ~(DCACHE_SHRINK_LIST | DCACHE_LRU_LIST);
	this_cpu_dec(nr_dentry_unused);
}

static void d_shrink_add(struct dentry *dentry, struct list_head *list)
{
	D_FLAG_VERIFY(dentry, 0);
	list_add(&dentry->d_lru, list);
	dentry->d_flags |= DCACHE_SHRINK_LIST | DCACHE_LRU_LIST;
	this_cpu_inc(nr_dentry_unused);
}

/*
 * These can only be called under the global LRU lock, ie during the
 * callback for freeing the LRU list. "isolate" removes it from the
 * LRU lists entirely, while shrink_move moves it to the indicated
 * private list.
 */
static void d_lru_isolate(struct list_lru_one *lru, struct dentry *dentry)
{
	D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
	dentry->d_flags &= ~DCACHE_LRU_LIST;
	this_cpu_dec(nr_dentry_unused);
	list_lru_isolate(lru, &dentry->d_lru);
}

static void d_lru_shrink_move(struct list_lru_one *lru, struct dentry *dentry,
			      struct list_head *list)
{
	D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
	dentry->d_flags |= DCACHE_SHRINK_LIST;
	list_lru_isolate_move(lru, &dentry->d_lru, list);
}

/*
 * dentry_lru_(add|del)_list) must be called with d_lock held.
 */
static void dentry_lru_add(struct dentry *dentry)
{
	if (unlikely(!(dentry->d_flags & DCACHE_LRU_LIST)))
		d_lru_add(dentry);
}

/**
 * d_drop - drop a dentry
 * @dentry: dentry to drop
 *
 * d_drop() unhashes the entry from the parent dentry hashes, so that it won't
 * be found through a VFS lookup any more. Note that this is different from
 * deleting the dentry - d_delete will try to mark the dentry negative if
 * possible, giving a successful _negative_ lookup, while d_drop will
 * just make the cache lookup fail.
 *
 * d_drop() is used mainly for stuff that wants to invalidate a dentry for some
 * reason (NFS timeouts or autofs deletes).
 *
 * __d_drop requires dentry->d_lock.
 */
void __d_drop(struct dentry *dentry)
{
	if (!d_unhashed(dentry)) {
		struct hlist_bl_head *b;
		/*
		 * Hashed dentries are normally on the dentry hashtable,
		 * with the exception of those newly allocated by
		 * d_obtain_alias, which are always IS_ROOT:
		 */
		if (unlikely(IS_ROOT(dentry)))
			b = &dentry->d_sb->s_anon;
		else
			b = d_hash(dentry->d_parent, dentry->d_name.hash);

		hlist_bl_lock(b);
		__hlist_bl_del(&dentry->d_hash);
		dentry->d_hash.pprev = NULL;
		hlist_bl_unlock(b);
		dentry_rcuwalk_invalidate(dentry);
	}
}
EXPORT_SYMBOL(__d_drop);

void d_drop(struct dentry *dentry)
{
	spin_lock(&dentry->d_lock);
	__d_drop(dentry);
	spin_unlock(&dentry->d_lock);
}
EXPORT_SYMBOL(d_drop);

static void __dentry_kill(struct dentry *dentry)
{
	struct dentry *parent = NULL;
	bool can_free = true;
	if (!IS_ROOT(dentry))
		parent = dentry->d_parent;

	/*
	 * The dentry is now unrecoverably dead to the world.
	 */
	lockref_mark_dead(&dentry->d_lockref);

	/*
	 * inform the fs via d_prune that this dentry is about to be
	 * unhashed and destroyed.
	 */
	if (dentry->d_flags & DCACHE_OP_PRUNE)
		dentry->d_op->d_prune(dentry);

	if (dentry->d_flags & DCACHE_LRU_LIST) {
		if (!(dentry->d_flags & DCACHE_SHRINK_LIST))
			d_lru_del(dentry);
	}
	/* if it was on the hash then remove it */
	__d_drop(dentry);
	__list_del_entry(&dentry->d_child);
	/*
	 * Inform d_walk() that we are no longer attached to the
	 * dentry tree
	 */
	dentry->d_flags |= DCACHE_DENTRY_KILLED;
	if (parent)
		spin_unlock(&parent->d_lock);
	dentry_iput(dentry);
	/*
	 * dentry_iput drops the locks, at which point nobody (except
	 * transient RCU lookups) can reach this dentry.
	 */
	BUG_ON(dentry->d_lockref.count > 0);
	this_cpu_dec(nr_dentry);
	if (dentry->d_op && dentry->d_op->d_release)
		dentry->d_op->d_release(dentry);

	spin_lock(&dentry->d_lock);
	if (dentry->d_flags & DCACHE_SHRINK_LIST) {
		dentry->d_flags |= DCACHE_MAY_FREE;
		can_free = false;
	}
	spin_unlock(&dentry->d_lock);
	if (likely(can_free))
		dentry_free(dentry);
}

/*
 * Finish off a dentry we've decided to kill.
 * dentry->d_lock must be held, returns with it unlocked.
 * If ref is non-zero, then decrement the refcount too.
 * Returns dentry requiring refcount drop, or NULL if we're done.
 */
static struct dentry *dentry_kill(struct dentry *dentry)
	__releases(dentry->d_lock)
{
	struct inode *inode = dentry->d_inode;
	struct dentry *parent = NULL;

	if (inode && unlikely(!spin_trylock(&inode->i_lock)))
		goto failed;

	if (!IS_ROOT(dentry)) {
		parent = dentry->d_parent;
		if (unlikely(!spin_trylock(&parent->d_lock))) {
			if (inode)
				spin_unlock(&inode->i_lock);
			goto failed;
		}
	}

	__dentry_kill(dentry);
	return parent;

failed:
	spin_unlock(&dentry->d_lock);
	return dentry; /* try again with same dentry */
}

static inline struct dentry *lock_parent(struct dentry *dentry)
{
	struct dentry *parent = dentry->d_parent;
	if (IS_ROOT(dentry))
		return NULL;
	if (unlikely(dentry->d_lockref.count < 0))
		return NULL;
	if (likely(spin_trylock(&parent->d_lock)))
		return parent;
	rcu_read_lock();
	spin_unlock(&dentry->d_lock);
again:
	parent = ACCESS_ONCE(dentry->d_parent);
	spin_lock(&parent->d_lock);
	/*
	 * We can't blindly lock dentry until we are sure
	 * that we won't violate the locking order.
	 * Any changes of dentry->d_parent must have
	 * been done with parent->d_lock held, so
	 * spin_lock() above is enough of a barrier
	 * for checking if it's still our child.
	 */
	if (unlikely(parent != dentry->d_parent)) {
		spin_unlock(&parent->d_lock);
		goto again;
	}
	rcu_read_unlock();
	if (parent != dentry)
		spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
	else
		parent = NULL;
	return parent;
}

/*
 * Try to do a lockless dput(), and return whether that was successful.
 *
 * If unsuccessful, we return false, having already taken the dentry lock.
 *
 * The caller needs to hold the RCU read lock, so that the dentry is
 * guaranteed to stay around even if the refcount goes down to zero!
 */
static inline bool fast_dput(struct dentry *dentry)
{
	int ret;
	unsigned int d_flags;

	/*
	 * If we have a d_op->d_delete() operation, we sould not
	 * let the dentry count go to zero, so use "put_or_lock".
	 */
	if (unlikely(dentry->d_flags & DCACHE_OP_DELETE))
		return lockref_put_or_lock(&dentry->d_lockref);

	/*
	 * .. otherwise, we can try to just decrement the
	 * lockref optimistically.
	 */
	ret = lockref_put_return(&dentry->d_lockref);

	/*
	 * If the lockref_put_return() failed due to the lock being held
	 * by somebody else, the fast path has failed. We will need to
	 * get the lock, and then check the count again.
	 */
	if (unlikely(ret < 0)) {
		spin_lock(&dentry->d_lock);
		if (dentry->d_lockref.count > 1) {
			dentry->d_lockref.count--;
			spin_unlock(&dentry->d_lock);
			return 1;
		}
		return 0;
	}

	/*
	 * If we weren't the last ref, we're done.
	 */
	if (ret)
		return 1;

	/*
	 * Careful, careful. The reference count went down
	 * to zero, but we don't hold the dentry lock, so
	 * somebody else could get it again, and do another
	 * dput(), and we need to not race with that.
	 *
	 * However, there is a very special and common case
	 * where we don't care, because there is nothing to
	 * do: the dentry is still hashed, it does not have
	 * a 'delete' op, and it's referenced and already on
	 * the LRU list.
	 *
	 * NOTE! Since we aren't locked, these values are
	 * not "stable". However, it is sufficient that at
	 * some point after we dropped the reference the
	 * dentry was hashed and the flags had the proper
	 * value. Other dentry users may have re-gotten
	 * a reference to the dentry and change that, but
	 * our work is done - we can leave the dentry
	 * around with a zero refcount.
	 */
	smp_rmb();
	d_flags = ACCESS_ONCE(dentry->d_flags);
	d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | DCACHE_DISCONNECTED;

	/* Nothing to do? Dropping the reference was all we needed? */
	if (d_flags == (DCACHE_REFERENCED | DCACHE_LRU_LIST) && !d_unhashed(dentry))
		return 1;

	/*
	 * Not the fast normal case? Get the lock. We've already decremented
	 * the refcount, but we'll need to re-check the situation after
	 * getting the lock.
	 */
	spin_lock(&dentry->d_lock);

	/*
	 * Did somebody else grab a reference to it in the meantime, and
	 * we're no longer the last user after all? Alternatively, somebody
	 * else could have killed it and marked it dead. Either way, we
	 * don't need to do anything else.
	 */
	if (dentry->d_lockref.count) {
		spin_unlock(&dentry->d_lock);
		return 1;
	}

	/*
	 * Re-get the reference we optimistically dropped. We hold the
	 * lock, and we just tested that it was zero, so we can just
	 * set it to 1.
	 */
	dentry->d_lockref.count = 1;
	return 0;
}


/* 
 * This is dput
 *
 * This is complicated by the fact that we do not want to put
 * dentries that are no longer on any hash chain on the unused
 * list: we'd much rather just get rid of them immediately.
 *
 * However, that implies that we have to traverse the dentry
 * tree upwards to the parents which might _also_ now be
 * scheduled for deletion (it may have been only waiting for
 * its last child to go away).
 *
 * This tail recursion is done by hand as we don't want to depend
 * on the compiler to always get this right (gcc generally doesn't).
 * Real recursion would eat up our stack space.
 */

/*
 * dput - release a dentry
 * @dentry: dentry to release 
 *
 * Release a dentry. This will drop the usage count and if appropriate
 * call the dentry unlink method as well as removing it from the queues and
 * releasing its resources. If the parent dentries were scheduled for release
 * they too may now get deleted.
 */
void dput(struct dentry *dentry)
{
	if (unlikely(!dentry))
		return;

repeat:
	might_sleep();

	rcu_read_lock();
	if (likely(fast_dput(dentry))) {
		rcu_read_unlock();
		return;
	}

	/* Slow case: now with the dentry lock held */
	rcu_read_unlock();

	/* Unreachable? Get rid of it */
	if (unlikely(d_unhashed(dentry)))
		goto kill_it;

	if (unlikely(dentry->d_flags & DCACHE_DISCONNECTED))
		goto kill_it;

	if (unlikely(dentry->d_flags & DCACHE_OP_DELETE)) {
		if (dentry->d_op->d_delete(dentry))
			goto kill_it;
	}

	if (!(dentry->d_flags & DCACHE_REFERENCED))
		dentry->d_flags |= DCACHE_REFERENCED;
	dentry_lru_add(dentry);

	dentry->d_lockref.count--;
	spin_unlock(&dentry->d_lock);
	return;

kill_it:
	dentry = dentry_kill(dentry);
	if (dentry) {
		cond_resched();
		goto repeat;
	}
}
EXPORT_SYMBOL(dput);


/* This must be called with d_lock held */
static inline void __dget_dlock(struct dentry *dentry)
{
	dentry->d_lockref.count++;
}

static inline void __dget(struct dentry *dentry)
{
	lockref_get(&dentry->d_lockref);
}

struct dentry *dget_parent(struct dentry *dentry)
{
	int gotref;
	struct dentry *ret;

	/*
	 * Do optimistic parent lookup without any
	 * locking.
	 */
	rcu_read_lock();
	ret = ACCESS_ONCE(dentry->d_parent);
	gotref = lockref_get_not_zero(&ret->d_lockref);
	rcu_read_unlock();
	if (likely(gotref)) {
		if (likely(ret == ACCESS_ONCE(dentry->d_parent)))
			return ret;
		dput(ret);
	}

repeat:
	/*
	 * Don't need rcu_dereference because we re-check it was correct under
	 * the lock.
	 */
	rcu_read_lock();
	ret = dentry->d_parent;
	spin_lock(&ret->d_lock);
	if (unlikely(ret != dentry->d_parent)) {
		spin_unlock(&ret->d_lock);
		rcu_read_unlock();
		goto repeat;
	}
	rcu_read_unlock();
	BUG_ON(!ret->d_lockref.count);
	ret->d_lockref.count++;
	spin_unlock(&ret->d_lock);
	return ret;
}
EXPORT_SYMBOL(dget_parent);

/**
 * d_find_alias - grab a hashed alias of inode
 * @inode: inode in question
 *
 * If inode has a hashed alias, or is a directory and has any alias,
 * acquire the reference to alias and return it. Otherwise return NULL.
 * Notice that if inode is a directory there can be only one alias and
 * it can be unhashed only if it has no children, or if it is the root
 * of a filesystem, or if the directory was renamed and d_revalidate
 * was the first vfs operation to notice.
 *
 * If the inode has an IS_ROOT, DCACHE_DISCONNECTED alias, then prefer
 * any other hashed alias over that one.
 */
static struct dentry *__d_find_alias(struct inode *inode)
{
	struct dentry *alias, *discon_alias;

again:
	discon_alias = NULL;
	hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
		spin_lock(&alias->d_lock);
 		if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
			if (IS_ROOT(alias) &&
			    (alias->d_flags & DCACHE_DISCONNECTED)) {
				discon_alias = alias;
			} else {
				__dget_dlock(alias);
				spin_unlock(&alias->d_lock);
				return alias;
			}
		}
		spin_unlock(&alias->d_lock);
	}
	if (discon_alias) {
		alias = discon_alias;
		spin_lock(&alias->d_lock);
		if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) {
			__dget_dlock(alias);
			spin_unlock(&alias->d_lock);
			return alias;
		}
		spin_unlock(&alias->d_lock);
		goto again;
	}
	return NULL;
}

struct dentry *d_find_alias(struct inode *inode)
{
	struct dentry *de = NULL;

	if (!hlist_empty(&inode->i_dentry)) {
		spin_lock(&inode->i_lock);
		de = __d_find_alias(inode);
		spin_unlock(&inode->i_lock);
	}
	return de;
}
EXPORT_SYMBOL(d_find_alias);

/*
 *	Try to kill dentries associated with this inode.
 * WARNING: you must own a reference to inode.
 */
void d_prune_aliases(struct inode *inode)
{
	struct dentry *dentry;
restart:
	spin_lock(&inode->i_lock);
	hlist_for_each_entry(dentry, &inode->i_dentry, d_u.d_alias) {
		spin_lock(&dentry->d_lock);
		if (!dentry->d_lockref.count) {
			struct dentry *parent = lock_parent(dentry);
			if (likely(!dentry->d_lockref.count)) {
				__dentry_kill(dentry);
				dput(parent);
				goto restart;
			}
			if (parent)
				spin_unlock(&parent->d_lock);
		}
		spin_unlock(&dentry->d_lock);
	}
	spin_unlock(&inode->i_lock);
}
EXPORT_SYMBOL(d_prune_aliases);

static void shrink_dentry_list(struct list_head *list)
{
	struct dentry *dentry, *parent;

	while (!list_empty(list)) {
		struct inode *inode;
		dentry = list_entry(list->prev, struct dentry, d_lru);
		spin_lock(&dentry->d_lock);
		parent = lock_parent(dentry);

		/*
		 * The dispose list is isolated and dentries are not accounted
		 * to the LRU here, so we can simply remove it from the list
		 * here regardless of whether it is referenced or not.
		 */
		d_shrink_del(dentry);

		/*
		 * We found an inuse dentry which was not removed from
		 * the LRU because of laziness during lookup. Do not free it.
		 */
		if (dentry->d_lockref.count > 0) {
			spin_unlock(&dentry->d_lock);
			if (parent)
				spin_unlock(&parent->d_lock);
			continue;
		}


		if (unlikely(dentry->d_flags & DCACHE_DENTRY_KILLED)) {
			bool can_free = dentry->d_flags & DCACHE_MAY_FREE;
			spin_unlock(&dentry->d_lock);
			if (parent)
				spin_unlock(&parent->d_lock);
			if (can_free)
				dentry_free(dentry);
			continue;
		}

		inode = dentry->d_inode;
		if (inode && unlikely(!spin_trylock(&inode->i_lock))) {
			d_shrink_add(dentry, list);
			spin_unlock(&dentry->d_lock);
			if (parent)
				spin_unlock(&parent->d_lock);
			continue;
		}

		__dentry_kill(dentry);

		/*
		 * We need to prune ancestors too. This is necessary to prevent
		 * quadratic behavior of shrink_dcache_parent(), but is also
		 * expected to be beneficial in reducing dentry cache
		 * fragmentation.
		 */
		dentry = parent;
		while (dentry && !lockref_put_or_lock(&dentry->d_lockref)) {
			parent = lock_parent(dentry);
			if (dentry->d_lockref.count != 1) {
				dentry->d_lockref.count--;
				spin_unlock(&dentry->d_lock);
				if (parent)
					spin_unlock(&parent->d_lock);
				break;
			}
			inode = dentry->d_inode;	/* can't be NULL */
			if (unlikely(!spin_trylock(&inode->i_lock))) {
				spin_unlock(&dentry->d_lock);
				if (parent)
					spin_unlock(&parent->d_lock);
				cpu_relax();
				continue;
			}
			__dentry_kill(dentry);
			dentry = parent;
		}
	}
}

static enum lru_status dentry_lru_isolate(struct list_head *item,
		struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
{
	struct list_head *freeable = arg;
	struct dentry	*dentry = container_of(item, struct dentry, d_lru);


	/*
	 * we are inverting the lru lock/dentry->d_lock here,
	 * so use a trylock. If we fail to get the lock, just skip
	 * it
	 */
	if (!spin_trylock(&dentry->d_lock))
		return LRU_SKIP;

	/*
	 * Referenced dentries are still in use. If they have active
	 * counts, just remove them from the LRU. Otherwise give them
	 * another pass through the LRU.
	 */
	if (dentry->d_lockref.count) {
		d_lru_isolate(lru, dentry);
		spin_unlock(&dentry->d_lock);
		return LRU_REMOVED;
	}

	if (dentry->d_flags & DCACHE_REFERENCED) {
		dentry->d_flags &= ~DCACHE_REFERENCED;
		spin_unlock(&dentry->d_lock);

		/*
		 * The list move itself will be made by the common LRU code. At
		 * this point, we've dropped the dentry->d_lock but keep the
		 * lru lock. This is safe to do, since every list movement is
		 * protected by the lru lock even if both locks are held.
		 *
		 * This is guaranteed by the fact that all LRU management
		 * functions are intermediated by the LRU API calls like
		 * list_lru_add and list_lru_del. List movement in this file
		 * only ever occur through this functions or through callbacks
		 * like this one, that are called from the LRU API.
		 *
		 * The only exceptions to this are functions like
		 * shrink_dentry_list, and code that first checks for the
		 * DCACHE_SHRINK_LIST flag.  Those are guaranteed to be
		 * operating only with stack provided lists after they are
		 * properly isolated from the main list.  It is thus, always a
		 * local access.
		 */
		return LRU_ROTATE;
	}

	d_lru_shrink_move(lru, dentry, freeable);
	spin_unlock(&dentry->d_lock);

	return LRU_REMOVED;
}

/**
 * prune_dcache_sb - shrink the dcache
 * @sb: superblock
 * @sc: shrink control, passed to list_lru_shrink_walk()
 *
 * Attempt to shrink the superblock dcache LRU by @sc->nr_to_scan entries. This
 * is done when we need more memory and called from the superblock shrinker
 * function.
 *
 * This function may fail to free any resources if all the dentries are in
 * use.
 */
long prune_dcache_sb(struct super_block *sb, struct shrink_control *sc)
{
	LIST_HEAD(dispose);
	long freed;

	freed = list_lru_shrink_walk(&sb->s_dentry_lru, sc,
				     dentry_lru_isolate, &dispose);
	shrink_dentry_list(&dispose);
	return freed;
}

static enum lru_status dentry_lru_isolate_shrink(struct list_head *item,
		struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
{
	struct list_head *freeable = arg;
	struct dentry	*dentry = container_of(item, struct dentry, d_lru);

	/*
	 * we are inverting the lru lock/dentry->d_lock here,
	 * so use a trylock. If we fail to get the lock, just skip
	 * it
	 */
	if (!spin_trylock(&dentry->d_lock))
		return LRU_SKIP;

	d_lru_shrink_move(lru, dentry, freeable);
	spin_unlock(&dentry->d_lock);

	return LRU_REMOVED;
}


/**
 * shrink_dcache_sb - shrink dcache for a superblock
 * @sb: superblock
 *
 * Shrink the dcache for the specified super block. This is used to free
 * the dcache before unmounting a file system.
 */
void shrink_dcache_sb(struct super_block *sb)
{
	long freed;

	do {
		LIST_HEAD(dispose);

		freed = list_lru_walk(&sb->s_dentry_lru,
			dentry_lru_isolate_shrink, &dispose, 1024);

		this_cpu_sub(nr_dentry_unused, freed);
		shrink_dentry_list(&dispose);
		cond_resched();
	} while (list_lru_count(&sb->s_dentry_lru) > 0);
}
EXPORT_SYMBOL(shrink_dcache_sb);

/**
 * enum d_walk_ret - action to talke during tree walk
 * @D_WALK_CONTINUE:	contrinue walk
 * @D_WALK_QUIT:	quit walk
 * @D_WALK_NORETRY:	quit when retry is needed
 * @D_WALK_SKIP:	skip this dentry and its children
 */
enum d_walk_ret {
	D_WALK_CONTINUE,
	D_WALK_QUIT,
	D_WALK_NORETRY,
	D_WALK_SKIP,
};

/**
 * d_walk - walk the dentry tree
 * @parent:	start of walk
 * @data:	data passed to @enter() and @finish()
 * @enter:	callback when first entering the dentry
 * @finish:	callback when successfully finished the walk
 *
 * The @enter() and @finish() callbacks are called with d_lock held.
 */
static void d_walk(struct dentry *parent, void *data,
		   enum d_walk_ret (*enter)(void *, struct dentry *),
		   void (*finish)(void *))
{
	struct dentry *this_parent;
	struct list_head *next;
	unsigned seq = 0;
	enum d_walk_ret ret;
	bool retry = true;

again:
	read_seqbegin_or_lock(&rename_lock, &seq);
	this_parent = parent;
	spin_lock(&this_parent->d_lock);

	ret = enter(data, this_parent);
	switch (ret) {
	case D_WALK_CONTINUE:
		break;
	case D_WALK_QUIT:
	case D_WALK_SKIP:
		goto out_unlock;
	case D_WALK_NORETRY:
		retry = false;
		break;
	}
repeat:
	next = this_parent->d_subdirs.next;
resume:
	while (next != &this_parent->d_subdirs) {
		struct list_head *tmp = next;
		struct dentry *dentry = list_entry(tmp, struct dentry, d_child);
		next = tmp->next;

		spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);

		ret = enter(data, dentry);
		switch (ret) {
		case D_WALK_CONTINUE:
			break;
		case D_WALK_QUIT:
			spin_unlock(&dentry->d_lock);
			goto out_unlock;
		case D_WALK_NORETRY:
			retry = false;
			break;
		case D_WALK_SKIP:
			spin_unlock(&dentry->d_lock);
			continue;
		}

		if (!list_empty(&dentry->d_subdirs)) {
			spin_unlock(&this_parent->d_lock);
			spin_release(&dentry->d_lock.dep_map, 1, _RET_IP_);
			this_parent = dentry;
			spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
			goto repeat;
		}
		spin_unlock(&dentry->d_lock);
	}
	/*
	 * All done at this level ... ascend and resume the search.
	 */
	rcu_read_lock();
ascend:
	if (this_parent != parent) {
		struct dentry *child = this_parent;
		this_parent = child->d_parent;

		spin_unlock(&child->d_lock);
		spin_lock(&this_parent->d_lock);

		/* might go back up the wrong parent if we have had a rename. */
		if (need_seqretry(&rename_lock, seq))
			goto rename_retry;
		/* go into the first sibling still alive */
		do {
			next = child->d_child.next;
			if (next == &this_parent->d_subdirs)
				goto ascend;
			child = list_entry(next, struct dentry, d_child);
		} while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED));
		rcu_read_unlock();
		goto resume;
	}
	if (need_seqretry(&rename_lock, seq))
		goto rename_retry;
	rcu_read_unlock();
	if (finish)
		finish(data);

out_unlock:
	spin_unlock(&this_parent->d_lock);
	done_seqretry(&rename_lock, seq);
	return;

rename_retry:
	spin_unlock(&this_parent->d_lock);
	rcu_read_unlock();
	BUG_ON(seq & 1);
	if (!retry)
		return;
	seq = 1;
	goto again;
}

/*
 * Search for at least 1 mount point in the dentry's subdirs.
 * We descend to the next level whenever the d_subdirs
 * list is non-empty and continue searching.
 */

static enum d_walk_ret check_mount(void *data, struct dentry *dentry)
{
	int *ret = data;
	if (d_mountpoint(dentry)) {
		*ret = 1;
		return D_WALK_QUIT;
	}
	return D_WALK_CONTINUE;
}

/**
 * have_submounts - check for mounts over a dentry
 * @parent: dentry to check.
 *
 * Return true if the parent or its subdirectories contain
 * a mount point
 */
int have_submounts(struct dentry *parent)
{
	int ret = 0;

	d_walk(parent, &ret, check_mount, NULL);

	return ret;
}
EXPORT_SYMBOL(have_submounts);

/*
 * Called by mount code to set a mountpoint and check if the mountpoint is
 * reachable (e.g. NFS can unhash a directory dentry and then the complete
 * subtree can become unreachable).
 *
 * Only one of d_invalidate() and d_set_mounted() must succeed.  For
 * this reason take rename_lock and d_lock on dentry and ancestors.
 */
int d_set_mounted(struct dentry *dentry)
{
	struct dentry *p;
	int ret = -ENOENT;
	write_seqlock(&rename_lock);
	for (p = dentry->d_parent; !IS_ROOT(p); p = p->d_parent) {
		/* Need exclusion wrt. d_invalidate() */
		spin_lock(&p->d_lock);
		if (unlikely(d_unhashed(p))) {
			spin_unlock(&p->d_lock);
			goto out;
		}
		spin_unlock(&p->d_lock);
	}
	spin_lock(&dentry->d_lock);
	if (!d_unlinked(dentry)) {
		ret = -EBUSY;
		if (!d_mountpoint(dentry)) {
			dentry->d_flags |= DCACHE_MOUNTED;
			ret = 0;
		}
	}
 	spin_unlock(&dentry->d_lock);
out:
	write_sequnlock(&rename_lock);
	return ret;
}

/*
 * Search the dentry child list of the specified parent,
 * and move any unused dentries to the end of the unused
 * list for prune_dcache(). We descend to the next level
 * whenever the d_subdirs list is non-empty and continue
 * searching.
 *
 * It returns zero iff there are no unused children,
 * otherwise  it returns the number of children moved to
 * the end of the unused list. This may not be the total
 * number of unused children, because select_parent can
 * drop the lock and return early due to latency
 * constraints.
 */

struct select_data {
	struct dentry *start;
	struct list_head dispose;
	int found;
};

static enum d_walk_ret select_collect(void *_data, struct dentry *dentry)
{
	struct select_data *data = _data;
	enum d_walk_ret ret = D_WALK_CONTINUE;

	if (data->start == dentry)
		goto out;

	if (dentry->d_flags & DCACHE_SHRINK_LIST) {
		data->found++;
	} else {
		if (dentry->d_flags & DCACHE_LRU_LIST)
			d_lru_del(dentry);
		if (!dentry->d_lockref.count) {
			d_shrink_add(dentry, &data->dispose);
			data->found++;
		}
	}
	/*
	 * We can return to the caller if we have found some (this
	 * ensures forward progress). We'll be coming back to find
	 * the rest.
	 */
	if (!list_empty(&data->dispose))
		ret = need_resched() ? D_WALK_QUIT : D_WALK_NORETRY;
out:
	return ret;
}

/**
 * shrink_dcache_parent - prune dcache
 * @parent: parent of entries to prune
 *
 * Prune the dcache to remove unused children of the parent dentry.
 */
void shrink_dcache_parent(struct dentry *parent)
{
	for (;;) {
		struct select_data data;

		INIT_LIST_HEAD(&data.dispose);
		data.start = parent;
		data.found = 0;

		d_walk(parent, &data, select_collect, NULL);
		if (!data.found)
			break;

		shrink_dentry_list(&data.dispose);
		cond_resched();
	}
}
EXPORT_SYMBOL(shrink_dcache_parent);

static enum d_walk_ret umount_check(void *_data, struct dentry *dentry)
{
	/* it has busy descendents; complain about those instead */
	if (!list_empty(&dentry->d_subdirs))
		return D_WALK_CONTINUE;

	/* root with refcount 1 is fine */
	if (dentry == _data && dentry->d_lockref.count == 1)
		return D_WALK_CONTINUE;

	printk(KERN_ERR "BUG: Dentry %p{i=%lx,n=%pd} "
			" still in use (%d) [unmount of %s %s]\n",
		       dentry,
		       dentry->d_inode ?
		       dentry->d_inode->i_ino : 0UL,
		       dentry,
		       dentry->d_lockref.count,
		       dentry->d_sb->s_type->name,
		       dentry->d_sb->s_id);
	WARN_ON(1);
	return D_WALK_CONTINUE;
}

static void do_one_tree(struct dentry *dentry)
{
	shrink_dcache_parent(dentry);
	d_walk(dentry, dentry, umount_check, NULL);
	d_drop(dentry);
	dput(dentry);
}

/*
 * destroy the dentries attached to a superblock on unmounting
 */
void shrink_dcache_for_umount(struct super_block *sb)
{
	struct dentry *dentry;

	WARN(down_read_trylock(&sb->s_umount), "s_umount should've been locked");

	dentry = sb->s_root;
	sb->s_root = NULL;
	do_one_tree(dentry);

	while (!hlist_bl_empty(&sb->s_anon)) {
		dentry = dget(hlist_bl_entry(hlist_bl_first(&sb->s_anon), struct dentry, d_hash));
		do_one_tree(dentry);
	}
}

struct detach_data {
	struct select_data select;
	struct dentry *mountpoint;
};
static enum d_walk_ret detach_and_collect(void *_data, struct dentry *dentry)
{
	struct detach_data *data = _data;

	if (d_mountpoint(dentry)) {
		__dget_dlock(dentry);
		data->mountpoint = dentry;
		return D_WALK_QUIT;
	}

	return select_collect(&data->select, dentry);
}

static void check_and_drop(void *_data)
{
	struct detach_data *data = _data;

	if (!data->mountpoint && !data->select.found)
		__d_drop(data->select.start);
}

/**
 * d_invalidate - detach submounts, prune dcache, and drop
 * @dentry: dentry to invalidate (aka detach, prune and drop)
 *
 * no dcache lock.
 *
 * The final d_drop is done as an atomic operation relative to
 * rename_lock ensuring there are no races with d_set_mounted.  This
 * ensures there are no unhashed dentries on the path to a mountpoint.
 */
void d_invalidate(struct dentry *dentry)
{
	/*
	 * If it's already been dropped, return OK.
	 */
	spin_lock(&dentry->d_lock);
	if (d_unhashed(dentry)) {
		spin_unlock(&dentry->d_lock);
		return;
	}
	spin_unlock(&dentry->d_lock);

	/* Negative dentries can be dropped without further checks */
	if (!dentry->d_inode) {
		d_drop(dentry);
		return;
	}

	for (;;) {
		struct detach_data data;

		data.mountpoint = NULL;
		INIT_LIST_HEAD(&data.select.dispose);
		data.select.start = dentry;
		data.select.found = 0;

		d_walk(dentry, &data, detach_and_collect, check_and_drop);

		if (data.select.found)
			shrink_dentry_list(&data.select.dispose);

		if (data.mountpoint) {
			detach_mounts(data.mountpoint);
			dput(data.mountpoint);
		}

		if (!data.mountpoint && !data.select.found)
			break;

		cond_resched();
	}
}
EXPORT_SYMBOL(d_invalidate);

/**
 * __d_alloc	-	allocate a dcache entry
 * @sb: filesystem it will belong to
 * @name: qstr of the name
 *
 * Allocates a dentry. It returns %NULL if there is insufficient memory
 * available. On a success the dentry is returned. The name passed in is
 * copied and the copy passed in may be reused after this call.
 */
 
struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
{
	struct dentry *dentry;
	char *dname;

	dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL);
	if (!dentry)
		return NULL;

	/*
	 * We guarantee that the inline name is always NUL-terminated.
	 * This way the memcpy() done by the name switching in rename
	 * will still always have a NUL at the end, even if we might
	 * be overwriting an internal NUL character
	 */
	dentry->d_iname[DNAME_INLINE_LEN-1] = 0;
	if (name->len > DNAME_INLINE_LEN-1) {
		size_t size = offsetof(struct external_name, name[1]);
		struct external_name *p = kmalloc(size + name->len, GFP_KERNEL);
		if (!p) {
			kmem_cache_free(dentry_cache, dentry); 
			return NULL;
		}
		atomic_set(&p->u.count, 1);
		dname = p->name;
		if (IS_ENABLED(CONFIG_DCACHE_WORD_ACCESS))
			kasan_unpoison_shadow(dname,
				round_up(name->len + 1,	sizeof(unsigned long)));
	} else  {
		dname = dentry->d_iname;
	}	

	dentry->d_name.len = name->len;
	dentry->d_name.hash = name->hash;
	memcpy(dname, name->name, name->len);
	dname[name->len] = 0;

	/* Make sure we always see the terminating NUL character */
	smp_wmb();
	dentry->d_name.name = dname;

	dentry->d_lockref.count = 1;
	dentry->d_flags = 0;
	spin_lock_init(&dentry->d_lock);
	seqcount_init(&dentry->d_seq);
	dentry->d_inode = NULL;
	dentry->d_parent = dentry;
	dentry->d_sb = sb;
	dentry->d_op = NULL;
	dentry->d_fsdata = NULL;
	INIT_HLIST_BL_NODE(&dentry->d_hash);
	INIT_LIST_HEAD(&dentry->d_lru);
	INIT_LIST_HEAD(&dentry->d_subdirs);
	INIT_HLIST_NODE(&dentry->d_u.d_alias);
	INIT_LIST_HEAD(&dentry->d_child);
	d_set_d_op(dentry, dentry->d_sb->s_d_op);

	this_cpu_inc(nr_dentry);

	return dentry;
}

/**
 * d_alloc	-	allocate a dcache entry
 * @parent: parent of entry to allocate
 * @name: qstr of the name
 *
 * Allocates a dentry. It returns %NULL if there is insufficient memory
 * available. On a success the dentry is returned. The name passed in is
 * copied and the copy passed in may be reused after this call.
 */
struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
{
	struct dentry *dentry = __d_alloc(parent->d_sb, name);
	if (!dentry)
		return NULL;
	dentry->d_flags |= DCACHE_RCUACCESS;
	spin_lock(&parent->d_lock);
	/*
	 * don't need child lock because it is not subject
	 * to concurrency here
	 */
	__dget_dlock(parent);
	dentry->d_parent = parent;
	list_add(&dentry->d_child, &parent->d_subdirs);
	spin_unlock(&parent->d_lock);

	return dentry;
}
EXPORT_SYMBOL(d_alloc);

/**
 * d_alloc_pseudo - allocate a dentry (for lookup-less filesystems)
 * @sb: the superblock
 * @name: qstr of the name
 *
 * For a filesystem that just pins its dentries in memory and never
 * performs lookups at all, return an unhashed IS_ROOT dentry.
 */
struct dentry *d_alloc_pseudo(struct super_block *sb, const struct qstr *name)
{
	return __d_alloc(sb, name);
}
EXPORT_SYMBOL(d_alloc_pseudo);

struct dentry *d_alloc_name(struct dentry *parent, const char *name)
{
	struct qstr q;

	q.name = name;
	q.len = strlen(name);
	q.hash = full_name_hash(q.name, q.len);
	return d_alloc(parent, &q);
}
EXPORT_SYMBOL(d_alloc_name);

void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
{
	WARN_ON_ONCE(dentry->d_op);
	WARN_ON_ONCE(dentry->d_flags & (DCACHE_OP_HASH	|
				DCACHE_OP_COMPARE	|
				DCACHE_OP_REVALIDATE	|
				DCACHE_OP_WEAK_REVALIDATE	|
				DCACHE_OP_DELETE	|
				DCACHE_OP_SELECT_INODE	|
				DCACHE_OP_REAL));
	dentry->d_op = op;
	if (!op)
		return;
	if (op->d_hash)
		dentry->d_flags |= DCACHE_OP_HASH;
	if (op->d_compare)
		dentry->d_flags |= DCACHE_OP_COMPARE;
	if (op->d_revalidate)
		dentry->d_flags |= DCACHE_OP_REVALIDATE;
	if (op->d_weak_revalidate)
		dentry->d_flags |= DCACHE_OP_WEAK_REVALIDATE;
	if (op->d_delete)
		dentry->d_flags |= DCACHE_OP_DELETE;
	if (op->d_prune)
		dentry->d_flags |= DCACHE_OP_PRUNE;
	if (op->d_select_inode)
		dentry->d_flags |= DCACHE_OP_SELECT_INODE;
	if (op->d_real)
		dentry->d_flags |= DCACHE_OP_REAL;

}
EXPORT_SYMBOL(d_set_d_op);


/*
 * d_set_fallthru - Mark a dentry as falling through to a lower layer
 * @dentry - The dentry to mark
 *
 * Mark a dentry as falling through to the lower layer (as set with
 * d_pin_lower()).  This flag may be recorded on the medium.
 */
void d_set_fallthru(struct dentry *dentry)
{
	spin_lock(&dentry->d_lock);
	dentry->d_flags |= DCACHE_FALLTHRU;
	spin_unlock(&dentry->d_lock);
}
EXPORT_SYMBOL(d_set_fallthru);

static unsigned d_flags_for_inode(struct inode *inode)
{
	unsigned add_flags = DCACHE_REGULAR_TYPE;

	if (!inode)
		return DCACHE_MISS_TYPE;

	if (S_ISDIR(inode->i_mode)) {
		add_flags = DCACHE_DIRECTORY_TYPE;
		if (unlikely(!(inode->i_opflags & IOP_LOOKUP))) {
			if (unlikely(!inode->i_op->lookup))
				add_flags = DCACHE_AUTODIR_TYPE;
			else
				inode->i_opflags |= IOP_LOOKUP;
		}
		goto type_determined;
	}

	if (unlikely(!(inode->i_opflags & IOP_NOFOLLOW))) {
		if (unlikely(inode->i_op->follow_link)) {
			add_flags = DCACHE_SYMLINK_TYPE;
			goto type_determined;
		}
		inode->i_opflags |= IOP_NOFOLLOW;
	}

	if (unlikely(!S_ISREG(inode->i_mode)))
		add_flags = DCACHE_SPECIAL_TYPE;

type_determined:
	if (unlikely(IS_AUTOMOUNT(inode)))
		add_flags |= DCACHE_NEED_AUTOMOUNT;
	return add_flags;
}

static void __d_instantiate(struct dentry *dentry, struct inode *inode)
{
	unsigned add_flags = d_flags_for_inode(inode);

	spin_lock(&dentry->d_lock);
	if (inode)
		hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
	raw_write_seqcount_begin(&dentry->d_seq);
	__d_set_inode_and_type(dentry, inode, add_flags);
	raw_write_seqcount_end(&dentry->d_seq);
	spin_unlock(&dentry->d_lock);
	fsnotify_d_instantiate(dentry, inode);
}

/**
 * d_instantiate - fill in inode information for a dentry
 * @entry: dentry to complete
 * @inode: inode to attach to this dentry
 *
 * Fill in inode information in the entry.
 *
 * This turns negative dentries into productive full members
 * of society.
 *
 * NOTE! This assumes that the inode count has been incremented
 * (or otherwise set) by the caller to indicate that it is now
 * in use by the dcache.
 */
 
void d_instantiate(struct dentry *entry, struct inode * inode)
{
	BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
	if (inode)
		spin_lock(&inode->i_lock);
	__d_instantiate(entry, inode);
	if (inode)
		spin_unlock(&inode->i_lock);
	security_d_instantiate(entry, inode);
}
EXPORT_SYMBOL(d_instantiate);

/**
 * d_instantiate_unique - instantiate a non-aliased dentry
 * @entry: dentry to instantiate
 * @inode: inode to attach to this dentry
 *
 * Fill in inode information in the entry. On success, it returns NULL.
 * If an unhashed alias of "entry" already exists, then we return the
 * aliased dentry instead and drop one reference to inode.
 *
 * Note that in order to avoid conflicts with rename() etc, the caller
 * had better be holding the parent directory semaphore.
 *
 * This also assumes that the inode count has been incremented
 * (or otherwise set) by the caller to indicate that it is now
 * in use by the dcache.
 */
static struct dentry *__d_instantiate_unique(struct dentry *entry,
					     struct inode *inode)
{
	struct dentry *alias;
	int len = entry->d_name.len;
	const char *name = entry->d_name.name;
	unsigned int hash = entry->d_name.hash;

	if (!inode) {
		__d_instantiate(entry, NULL);
		return NULL;
	}

	hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
		/*
		 * Don't need alias->d_lock here, because aliases with
		 * d_parent == entry->d_parent are not subject to name or
		 * parent changes, because the parent inode i_mutex is held.
		 */
		if (alias->d_name.hash != hash)
			continue;
		if (alias->d_parent != entry->d_parent)
			continue;
		if (alias->d_name.len != len)
			continue;
		if (dentry_cmp(alias, name, len))
			continue;
		__dget(alias);
		return alias;
	}

	__d_instantiate(entry, inode);
	return NULL;
}

struct dentry *d_instantiate_unique(struct dentry *entry, struct inode *inode)
{
	struct dentry *result;

	BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));

	if (inode)
		spin_lock(&inode->i_lock);
	result = __d_instantiate_unique(entry, inode);
	if (inode)
		spin_unlock(&inode->i_lock);

	if (!result) {
		security_d_instantiate(entry, inode);
		return NULL;
	}

	BUG_ON(!d_unhashed(result));
	iput(inode);
	return result;
}

EXPORT_SYMBOL(d_instantiate_unique);

/**
 * d_instantiate_no_diralias - instantiate a non-aliased dentry
 * @entry: dentry to complete
 * @inode: inode to attach to this dentry
 *
 * Fill in inode information in the entry.  If a directory alias is found, then
 * return an error (and drop inode).  Together with d_materialise_unique() this
 * guarantees that a directory inode may never have more than one alias.
 */
int d_instantiate_no_diralias(struct dentry *entry, struct inode *inode)
{
	BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));

	spin_lock(&inode->i_lock);
	if (S_ISDIR(inode->i_mode) && !hlist_empty(&inode->i_dentry)) {
		spin_unlock(&inode->i_lock);
		iput(inode);
		return -EBUSY;
	}
	__d_instantiate(entry, inode);
	spin_unlock(&inode->i_lock);
	security_d_instantiate(entry, inode);

	return 0;
}
EXPORT_SYMBOL(d_instantiate_no_diralias);

struct dentry *d_make_root(struct inode *root_inode)
{
	struct dentry *res = NULL;

	if (root_inode) {
		static const struct qstr name = QSTR_INIT("/", 1);

		res = __d_alloc(root_inode->i_sb, &name);
		if (res)
			d_instantiate(res, root_inode);
		else
			iput(root_inode);
	}
	return res;
}
EXPORT_SYMBOL(d_make_root);

static struct dentry * __d_find_any_alias(struct inode *inode)
{
	struct dentry *alias;

	if (hlist_empty(&inode->i_dentry))
		return NULL;
	alias = hlist_entry(inode->i_dentry.first, struct dentry, d_u.d_alias);
	__dget(alias);
	return alias;
}

/**
 * d_find_any_alias - find any alias for a given inode
 * @inode: inode to find an alias for
 *
 * If any aliases exist for the given inode, take and return a
 * reference for one of them.  If no aliases exist, return %NULL.
 */
struct dentry *d_find_any_alias(struct inode *inode)
{
	struct dentry *de;

	spin_lock(&inode->i_lock);
	de = __d_find_any_alias(inode);
	spin_unlock(&inode->i_lock);
	return de;
}
EXPORT_SYMBOL(d_find_any_alias);

static struct dentry *__d_obtain_alias(struct inode *inode, int disconnected)
{
	static const struct qstr anonstring = QSTR_INIT("/", 1);
	struct dentry *tmp;
	struct dentry *res;
	unsigned add_flags;

	if (!inode)
		return ERR_PTR(-ESTALE);
	if (IS_ERR(inode))
		return ERR_CAST(inode);

	res = d_find_any_alias(inode);
	if (res)
		goto out_iput;

	tmp = __d_alloc(inode->i_sb, &anonstring);
	if (!tmp) {
		res = ERR_PTR(-ENOMEM);
		goto out_iput;
	}

	spin_lock(&inode->i_lock);
	res = __d_find_any_alias(inode);
	if (res) {
		spin_unlock(&inode->i_lock);
		dput(tmp);
		goto out_iput;
	}

	/* attach a disconnected dentry */
	add_flags = d_flags_for_inode(inode);

	if (disconnected)
		add_flags |= DCACHE_DISCONNECTED;

	spin_lock(&tmp->d_lock);
	__d_set_inode_and_type(tmp, inode, add_flags);
	hlist_add_head(&tmp->d_u.d_alias, &inode->i_dentry);
	hlist_bl_lock(&tmp->d_sb->s_anon);
	hlist_bl_add_head(&tmp->d_hash, &tmp->d_sb->s_anon);
	hlist_bl_unlock(&tmp->d_sb->s_anon);
	spin_unlock(&tmp->d_lock);
	spin_unlock(&inode->i_lock);
	security_d_instantiate(tmp, inode);

	return tmp;

 out_iput:
	if (res && !IS_ERR(res))
		security_d_instantiate(res, inode);
	iput(inode);
	return res;
}

/**
 * d_obtain_alias - find or allocate a DISCONNECTED dentry for a given inode
 * @inode: inode to allocate the dentry for
 *
 * Obtain a dentry for an inode resulting from NFS filehandle conversion or
 * similar open by handle operations.  The returned dentry may be anonymous,
 * or may have a full name (if the inode was already in the cache).
 *
 * When called on a directory inode, we must ensure that the inode only ever
 * has one dentry.  If a dentry is found, that is returned instead of
 * allocating a new one.
 *
 * On successful return, the reference to the inode has been transferred
 * to the dentry.  In case of an error the reference on the inode is released.
 * To make it easier to use in export operations a %NULL or IS_ERR inode may
 * be passed in and the error will be propagated to the return value,
 * with a %NULL @inode replaced by ERR_PTR(-ESTALE).
 */
struct dentry *d_obtain_alias(struct inode *inode)
{
	return __d_obtain_alias(inode, 1);
}
EXPORT_SYMBOL(d_obtain_alias);

/**
 * d_obtain_root - find or allocate a dentry for a given inode
 * @inode: inode to allocate the dentry for
 *
 * Obtain an IS_ROOT dentry for the root of a filesystem.
 *
 * We must ensure that directory inodes only ever have one dentry.  If a
 * dentry is found, that is returned instead of allocating a new one.
 *
 * On successful return, the reference to the inode has been transferred
 * to the dentry.  In case of an error the reference on the inode is
 * released.  A %NULL or IS_ERR inode may be passed in and will be the
 * error will be propagate to the return value, with a %NULL @inode
 * replaced by ERR_PTR(-ESTALE).
 */
struct dentry *d_obtain_root(struct inode *inode)
{
	return __d_obtain_alias(inode, 0);
}
EXPORT_SYMBOL(d_obtain_root);

/**
 * d_add_ci - lookup or allocate new dentry with case-exact name
 * @inode:  the inode case-insensitive lookup has found
 * @dentry: the negative dentry that was passed to the parent's lookup func
 * @name:   the case-exact name to be associated with the returned dentry
 *
 * This is to avoid filling the dcache with case-insensitive names to the
 * same inode, only the actual correct case is stored in the dcache for
 * case-insensitive filesystems.
 *
 * For a case-insensitive lookup match and if the the case-exact dentry
 * already exists in in the dcache, use it and return it.
 *
 * If no entry exists with the exact case name, allocate new dentry with
 * the exact case, and return the spliced entry.
 */
struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode,
			struct qstr *name)
{
	struct dentry *found;
	struct dentry *new;

	/*
	 * First check if a dentry matching the name already exists,
	 * if not go ahead and create it now.
	 */
	found = d_hash_and_lookup(dentry->d_parent, name);
	if (!found) {
		new = d_alloc(dentry->d_parent, name);
		if (!new) {
			found = ERR_PTR(-ENOMEM);
		} else {
			found = d_splice_alias(inode, new);
			if (found) {
				dput(new);
				return found;
			}
			return new;
		}
	}
	iput(inode);
	return found;
}
EXPORT_SYMBOL(d_add_ci);

/*
 * Do the slow-case of the dentry name compare.
 *
 * Unlike the dentry_cmp() function, we need to atomically
 * load the name and length information, so that the
 * filesystem can rely on them, and can use the 'name' and
 * 'len' information without worrying about walking off the
 * end of memory etc.
 *
 * Thus the read_seqcount_retry() and the "duplicate" info
 * in arguments (the low-level filesystem should not look
 * at the dentry inode or name contents directly, since
 * rename can change them while we're in RCU mode).
 */
enum slow_d_compare {
	D_COMP_OK,
	D_COMP_NOMATCH,
	D_COMP_SEQRETRY,
};

static noinline enum slow_d_compare slow_dentry_cmp(
		const struct dentry *parent,
		struct dentry *dentry,
		unsigned int seq,
		const struct qstr *name)
{
	int tlen = dentry->d_name.len;
	const char *tname = dentry->d_name.name;

	if (read_seqcount_retry(&dentry->d_seq, seq)) {
		cpu_relax();
		return D_COMP_SEQRETRY;
	}
	if (parent->d_op->d_compare(parent, dentry, tlen, tname, name))
		return D_COMP_NOMATCH;
	return D_COMP_OK;
}

/**
 * __d_lookup_rcu - search for a dentry (racy, store-free)
 * @parent: parent dentry
 * @name: qstr of name we wish to find
 * @seqp: returns d_seq value at the point where the dentry was found
 * Returns: dentry, or NULL
 *
 * __d_lookup_rcu is the dcache lookup function for rcu-walk name
 * resolution (store-free path walking) design described in
 * Documentation/filesystems/path-lookup.txt.
 *
 * This is not to be used outside core vfs.
 *
 * __d_lookup_rcu must only be used in rcu-walk mode, ie. with vfsmount lock
 * held, and rcu_read_lock held. The returned dentry must not be stored into
 * without taking d_lock and checking d_seq sequence count against @seq
 * returned here.
 *
 * A refcount may be taken on the found dentry with the d_rcu_to_refcount
 * function.
 *
 * Alternatively, __d_lookup_rcu may be called again to look up the child of
 * the returned dentry, so long as its parent's seqlock is checked after the
 * child is looked up. Thus, an interlocking stepping of sequence lock checks
 * is formed, giving integrity down the path walk.
 *
 * NOTE! The caller *has* to check the resulting dentry against the sequence
 * number we've returned before using any of the resulting dentry state!
 */
struct dentry *__d_lookup_rcu(const struct dentry *parent,
				const struct qstr *name,
				unsigned *seqp)
{
	u64 hashlen = name->hash_len;
	const unsigned char *str = name->name;
	struct hlist_bl_head *b = d_hash(parent, hashlen_hash(hashlen));
	struct hlist_bl_node *node;
	struct dentry *dentry;

	/*
	 * Note: There is significant duplication with __d_lookup_rcu which is
	 * required to prevent single threaded performance regressions
	 * especially on architectures where smp_rmb (in seqcounts) are costly.
	 * Keep the two functions in sync.
	 */

	/*
	 * The hash list is protected using RCU.
	 *
	 * Carefully use d_seq when comparing a candidate dentry, to avoid
	 * races with d_move().
	 *
	 * It is possible that concurrent renames can mess up our list
	 * walk here and result in missing our dentry, resulting in the
	 * false-negative result. d_lookup() protects against concurrent
	 * renames using rename_lock seqlock.
	 *
	 * See Documentation/filesystems/path-lookup.txt for more details.
	 */
	hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
		unsigned seq;

seqretry:
		/*
		 * The dentry sequence count protects us from concurrent
		 * renames, and thus protects parent and name fields.
		 *
		 * The caller must perform a seqcount check in order
		 * to do anything useful with the returned dentry.
		 *
		 * NOTE! We do a "raw" seqcount_begin here. That means that
		 * we don't wait for the sequence count to stabilize if it
		 * is in the middle of a sequence change. If we do the slow
		 * dentry compare, we will do seqretries until it is stable,
		 * and if we end up with a successful lookup, we actually
		 * want to exit RCU lookup anyway.
		 */
		seq = raw_seqcount_begin(&dentry->d_seq);
		if (dentry->d_parent != parent)
			continue;
		if (d_unhashed(dentry))
			continue;

		if (unlikely(parent->d_flags & DCACHE_OP_COMPARE)) {
			if (dentry->d_name.hash != hashlen_hash(hashlen))
				continue;
			*seqp = seq;
			switch (slow_dentry_cmp(parent, dentry, seq, name)) {
			case D_COMP_OK:
				return dentry;
			case D_COMP_NOMATCH:
				continue;
			default:
				goto seqretry;
			}
		}

		if (dentry->d_name.hash_len != hashlen)
			continue;
		*seqp = seq;
		if (!dentry_cmp(dentry, str, hashlen_len(hashlen)))
			return dentry;
	}
	return NULL;
}

/**
 * d_lookup - search for a dentry
 * @parent: parent dentry
 * @name: qstr of name we wish to find
 * Returns: dentry, or NULL
 *
 * d_lookup searches the children of the parent dentry for the name in
 * question. If the dentry is found its reference count is incremented and the
 * dentry is returned. The caller must use dput to free the entry when it has
 * finished using it. %NULL is returned if the dentry does not exist.
 */
struct dentry *d_lookup(const struct dentry *parent, const struct qstr *name)
{
	struct dentry *dentry;
	unsigned seq;

	do {
		seq = read_seqbegin(&rename_lock);
		dentry = __d_lookup(parent, name);
		if (dentry)
			break;
	} while (read_seqretry(&rename_lock, seq));
	return dentry;
}
EXPORT_SYMBOL(d_lookup);

/**
 * __d_lookup - search for a dentry (racy)
 * @parent: parent dentry
 * @name: qstr of name we wish to find
 * Returns: dentry, or NULL
 *
 * __d_lookup is like d_lookup, however it may (rarely) return a
 * false-negative result due to unrelated rename activity.
 *
 * __d_lookup is slightly faster by avoiding rename_lock read seqlock,
 * however it must be used carefully, eg. with a following d_lookup in
 * the case of failure.
 *
 * __d_lookup callers must be commented.
 */
struct dentry *__d_lookup(const struct dentry *parent, const struct qstr *name)
{
	unsigned int len = name->len;
	unsigned int hash = name->hash;
	const unsigned char *str = name->name;
	struct hlist_bl_head *b = d_hash(parent, hash);
	struct hlist_bl_node *node;
	struct dentry *found = NULL;
	struct dentry *dentry;

	/*
	 * Note: There is significant duplication with __d_lookup_rcu which is
	 * required to prevent single threaded performance regressions
	 * especially on architectures where smp_rmb (in seqcounts) are costly.
	 * Keep the two functions in sync.
	 */

	/*
	 * The hash list is protected using RCU.
	 *
	 * Take d_lock when comparing a candidate dentry, to avoid races
	 * with d_move().
	 *
	 * It is possible that concurrent renames can mess up our list
	 * walk here and result in missing our dentry, resulting in the
	 * false-negative result. d_lookup() protects against concurrent
	 * renames using rename_lock seqlock.
	 *
	 * See Documentation/filesystems/path-lookup.txt for more details.
	 */
	rcu_read_lock();
	
	hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {

		if (dentry->d_name.hash != hash)
			continue;

		spin_lock(&dentry->d_lock);
		if (dentry->d_parent != parent)
			goto next;
		if (d_unhashed(dentry))
			goto next;

		/*
		 * It is safe to compare names since d_move() cannot
		 * change the qstr (protected by d_lock).
		 */
		if (parent->d_flags & DCACHE_OP_COMPARE) {
			int tlen = dentry->d_name.len;
			const char *tname = dentry->d_name.name;
			if (parent->d_op->d_compare(parent, dentry, tlen, tname, name))
				goto next;
		} else {
			if (dentry->d_name.len != len)
				goto next;
			if (dentry_cmp(dentry, str, len))
				goto next;
		}

		dentry->d_lockref.count++;
		found = dentry;
		spin_unlock(&dentry->d_lock);
		break;
next:
		spin_unlock(&dentry->d_lock);
 	}
 	rcu_read_unlock();

 	return found;
}

/**
 * d_hash_and_lookup - hash the qstr then search for a dentry
 * @dir: Directory to search in
 * @name: qstr of name we wish to find
 *
 * On lookup failure NULL is returned; on bad name - ERR_PTR(-error)
 */
struct dentry *d_hash_and_lookup(struct dentry *dir, struct qstr *name)
{
	/*
	 * Check for a fs-specific hash function. Note that we must
	 * calculate the standard hash first, as the d_op->d_hash()
	 * routine may choose to leave the hash value unchanged.
	 */
	name->hash = full_name_hash(name->name, name->len);
	if (dir->d_flags & DCACHE_OP_HASH) {
		int err = dir->d_op->d_hash(dir, name);
		if (unlikely(err < 0))
			return ERR_PTR(err);
	}
	return d_lookup(dir, name);
}
EXPORT_SYMBOL(d_hash_and_lookup);

/*
 * When a file is deleted, we have two options:
 * - turn this dentry into a negative dentry
 * - unhash this dentry and free it.
 *
 * Usually, we want to just turn this into
 * a negative dentry, but if anybody else is
 * currently using the dentry or the inode
 * we can't do that and we fall back on removing
 * it from the hash queues and waiting for
 * it to be deleted later when it has no users
 */
 
/**
 * d_delete - delete a dentry
 * @dentry: The dentry to delete
 *
 * Turn the dentry into a negative dentry if possible, otherwise
 * remove it from the hash queues so it can be deleted later
 */
 
void d_delete(struct dentry * dentry)
{
	struct inode *inode;
	int isdir = 0;
	/*
	 * Are we the only user?
	 */
again:
	spin_lock(&dentry->d_lock);
	inode = dentry->d_inode;
	isdir = S_ISDIR(inode->i_mode);
	if (dentry->d_lockref.count == 1) {
		if (!spin_trylock(&inode->i_lock)) {
			spin_unlock(&dentry->d_lock);
			cpu_relax();
			goto again;
		}
		dentry->d_flags &= ~DCACHE_CANT_MOUNT;
		dentry_unlink_inode(dentry);
		fsnotify_nameremove(dentry, isdir);
		return;
	}

	if (!d_unhashed(dentry))
		__d_drop(dentry);

	spin_unlock(&dentry->d_lock);

	fsnotify_nameremove(dentry, isdir);
}
EXPORT_SYMBOL(d_delete);

static void __d_rehash(struct dentry * entry, struct hlist_bl_head *b)
{
	BUG_ON(!d_unhashed(entry));
	hlist_bl_lock(b);
	hlist_bl_add_head_rcu(&entry->d_hash, b);
	hlist_bl_unlock(b);
}

static void _d_rehash(struct dentry * entry)
{
	__d_rehash(entry, d_hash(entry->d_parent, entry->d_name.hash));
}

/**
 * d_rehash	- add an entry back to the hash
 * @entry: dentry to add to the hash
 *
 * Adds a dentry to the hash according to its name.
 */
 
void d_rehash(struct dentry * entry)
{
	spin_lock(&entry->d_lock);
	_d_rehash(entry);
	spin_unlock(&entry->d_lock);
}
EXPORT_SYMBOL(d_rehash);

/**
 * dentry_update_name_case - update case insensitive dentry with a new name
 * @dentry: dentry to be updated
 * @name: new name
 *
 * Update a case insensitive dentry with new case of name.
 *
 * dentry must have been returned by d_lookup with name @name. Old and new
 * name lengths must match (ie. no d_compare which allows mismatched name
 * lengths).
 *
 * Parent inode i_mutex must be held over d_lookup and into this call (to
 * keep renames and concurrent inserts, and readdir(2) away).
 */
void dentry_update_name_case(struct dentry *dentry, struct qstr *name)
{
	BUG_ON(!mutex_is_locked(&dentry->d_parent->d_inode->i_mutex));
	BUG_ON(dentry->d_name.len != name->len); /* d_lookup gives this */

	spin_lock(&dentry->d_lock);
	write_seqcount_begin(&dentry->d_seq);
	memcpy((unsigned char *)dentry->d_name.name, name->name, name->len);
	write_seqcount_end(&dentry->d_seq);
	spin_unlock(&dentry->d_lock);
}
EXPORT_SYMBOL(dentry_update_name_case);

static void swap_names(struct dentry *dentry, struct dentry *target)
{
	if (unlikely(dname_external(target))) {
		if (unlikely(dname_external(dentry))) {
			/*
			 * Both external: swap the pointers
			 */
			swap(target->d_name.name, dentry->d_name.name);
		} else {
			/*
			 * dentry:internal, target:external.  Steal target's
			 * storage and make target internal.
			 */
			memcpy(target->d_iname, dentry->d_name.name,
					dentry->d_name.len + 1);
			dentry->d_name.name = target->d_name.name;
			target->d_name.name = target->d_iname;
		}
	} else {
		if (unlikely(dname_external(dentry))) {
			/*
			 * dentry:external, target:internal.  Give dentry's
			 * storage to target and make dentry internal
			 */
			memcpy(dentry->d_iname, target->d_name.name,
					target->d_name.len + 1);
			target->d_name.name = dentry->d_name.name;
			dentry->d_name.name = dentry->d_iname;
		} else {
			/*
			 * Both are internal.
			 */
			unsigned int i;
			BUILD_BUG_ON(!IS_ALIGNED(DNAME_INLINE_LEN, sizeof(long)));
			kmemcheck_mark_initialized(dentry->d_iname, DNAME_INLINE_LEN);
			kmemcheck_mark_initialized(target->d_iname, DNAME_INLINE_LEN);
			for (i = 0; i < DNAME_INLINE_LEN / sizeof(long); i++) {
				swap(((long *) &dentry->d_iname)[i],
				     ((long *) &target->d_iname)[i]);
			}
		}
	}
	swap(dentry->d_name.hash_len, target->d_name.hash_len);
}

static void copy_name(struct dentry *dentry, struct dentry *target)
{
	struct external_name *old_name = NULL;
	if (unlikely(dname_external(dentry)))
		old_name = external_name(dentry);
	if (unlikely(dname_external(target))) {
		atomic_inc(&external_name(target)->u.count);
		dentry->d_name = target->d_name;
	} else {
		memcpy(dentry->d_iname, target->d_name.name,
				target->d_name.len + 1);
		dentry->d_name.name = dentry->d_iname;
		dentry->d_name.hash_len = target->d_name.hash_len;
	}
	if (old_name && likely(atomic_dec_and_test(&old_name->u.count)))
		kfree_rcu(old_name, u.head);
}

static void dentry_lock_for_move(struct dentry *dentry, struct dentry *target)
{
	/*
	 * XXXX: do we really need to take target->d_lock?
	 */
	if (IS_ROOT(dentry) || dentry->d_parent == target->d_parent)
		spin_lock(&target->d_parent->d_lock);
	else {
		if (d_ancestor(dentry->d_parent, target->d_parent)) {
			spin_lock(&dentry->d_parent->d_lock);
			spin_lock_nested(&target->d_parent->d_lock,
						DENTRY_D_LOCK_NESTED);
		} else {
			spin_lock(&target->d_parent->d_lock);
			spin_lock_nested(&dentry->d_parent->d_lock,
						DENTRY_D_LOCK_NESTED);
		}
	}
	if (target < dentry) {
		spin_lock_nested(&target->d_lock, 2);
		spin_lock_nested(&dentry->d_lock, 3);
	} else {
		spin_lock_nested(&dentry->d_lock, 2);
		spin_lock_nested(&target->d_lock, 3);
	}
}

static void dentry_unlock_for_move(struct dentry *dentry, struct dentry *target)
{
	if (target->d_parent != dentry->d_parent)
		spin_unlock(&dentry->d_parent->d_lock);
	if (target->d_parent != target)
		spin_unlock(&target->d_parent->d_lock);
	spin_unlock(&target->d_lock);
	spin_unlock(&dentry->d_lock);
}

/*
 * When switching names, the actual string doesn't strictly have to
 * be preserved in the target - because we're dropping the target
 * anyway. As such, we can just do a simple memcpy() to copy over
 * the new name before we switch, unless we are going to rehash
 * it.  Note that if we *do* unhash the target, we are not allowed
 * to rehash it without giving it a new name/hash key - whether
 * we swap or overwrite the names here, resulting name won't match
 * the reality in filesystem; it's only there for d_path() purposes.
 * Note that all of this is happening under rename_lock, so the
 * any hash lookup seeing it in the middle of manipulations will
 * be discarded anyway.  So we do not care what happens to the hash
 * key in that case.
 */
/*
 * __d_move - move a dentry
 * @dentry: entry to move
 * @target: new dentry
 * @exchange: exchange the two dentries
 *
 * Update the dcache to reflect the move of a file name. Negative
 * dcache entries should not be moved in this way. Caller must hold
 * rename_lock, the i_mutex of the source and target directories,
 * and the sb->s_vfs_rename_mutex if they differ. See lock_rename().
 */
static void __d_move(struct dentry *dentry, struct dentry *target,
		     bool exchange)
{
	if (!dentry->d_inode)
		printk(KERN_WARNING "VFS: moving negative dcache entry\n");

	BUG_ON(d_ancestor(dentry, target));
	BUG_ON(d_ancestor(target, dentry));

	dentry_lock_for_move(dentry, target);

	write_seqcount_begin(&dentry->d_seq);
	write_seqcount_begin_nested(&target->d_seq, DENTRY_D_LOCK_NESTED);

	/* __d_drop does write_seqcount_barrier, but they're OK to nest. */

	/*
	 * Move the dentry to the target hash queue. Don't bother checking
	 * for the same hash queue because of how unlikely it is.
	 */
	__d_drop(dentry);
	__d_rehash(dentry, d_hash(target->d_parent, target->d_name.hash));

	/*
	 * Unhash the target (d_delete() is not usable here).  If exchanging
	 * the two dentries, then rehash onto the other's hash queue.
	 */
	__d_drop(target);
	if (exchange) {
		__d_rehash(target,
			   d_hash(dentry->d_parent, dentry->d_name.hash));
	}

	/* Switch the names.. */
	if (exchange)
		swap_names(dentry, target);
	else
		copy_name(dentry, target);

	/* ... and switch them in the tree */
	if (IS_ROOT(dentry)) {
		/* splicing a tree */
		dentry->d_flags |= DCACHE_RCUACCESS;
		dentry->d_parent = target->d_parent;
		target->d_parent = target;
		list_del_init(&target->d_child);
		list_move(&dentry->d_child, &dentry->d_parent->d_subdirs);
	} else {
		/* swapping two dentries */
		swap(dentry->d_parent, target->d_parent);
		list_move(&target->d_child, &target->d_parent->d_subdirs);
		list_move(&dentry->d_child, &dentry->d_parent->d_subdirs);
		if (exchange)
			fsnotify_d_move(target);
		fsnotify_d_move(dentry);
	}

	write_seqcount_end(&target->d_seq);
	write_seqcount_end(&dentry->d_seq);

	dentry_unlock_for_move(dentry, target);
}

/*
 * d_move - move a dentry
 * @dentry: entry to move
 * @target: new dentry
 *
 * Update the dcache to reflect the move of a file name. Negative
 * dcache entries should not be moved in this way. See the locking
 * requirements for __d_move.
 */
void d_move(struct dentry *dentry, struct dentry *target)
{
	write_seqlock(&rename_lock);
	__d_move(dentry, target, false);
	write_sequnlock(&rename_lock);
}
EXPORT_SYMBOL(d_move);

/*
 * d_exchange - exchange two dentries
 * @dentry1: first dentry
 * @dentry2: second dentry
 */
void d_exchange(struct dentry *dentry1, struct dentry *dentry2)
{
	write_seqlock(&rename_lock);

	WARN_ON(!dentry1->d_inode);
	WARN_ON(!dentry2->d_inode);
	WARN_ON(IS_ROOT(dentry1));
	WARN_ON(IS_ROOT(dentry2));

	__d_move(dentry1, dentry2, true);

	write_sequnlock(&rename_lock);
}

/**
 * d_ancestor - search for an ancestor
 * @p1: ancestor dentry
 * @p2: child dentry
 *
 * Returns the ancestor dentry of p2 which is a child of p1, if p1 is
 * an ancestor of p2, else NULL.
 */
struct dentry *d_ancestor(struct dentry *p1, struct dentry *p2)
{
	struct dentry *p;

	for (p = p2; !IS_ROOT(p); p = p->d_parent) {
		if (p->d_parent == p1)
			return p;
	}
	return NULL;
}

/*
 * This helper attempts to cope with remotely renamed directories
 *
 * It assumes that the caller is already holding
 * dentry->d_parent->d_inode->i_mutex, and rename_lock
 *
 * Note: If ever the locking in lock_rename() changes, then please
 * remember to update this too...
 */
static int __d_unalias(struct inode *inode,
		struct dentry *dentry, struct dentry *alias)
{
	struct mutex *m1 = NULL, *m2 = NULL;
	int ret = -ESTALE;

	/* If alias and dentry share a parent, then no extra locks required */
	if (alias->d_parent == dentry->d_parent)
		goto out_unalias;

	/* See lock_rename() */
	if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
		goto out_err;
	m1 = &dentry->d_sb->s_vfs_rename_mutex;
	if (!mutex_trylock(&alias->d_parent->d_inode->i_mutex))
		goto out_err;
	m2 = &alias->d_parent->d_inode->i_mutex;
out_unalias:
	__d_move(alias, dentry, false);
	ret = 0;
out_err:
	if (m2)
		mutex_unlock(m2);
	if (m1)
		mutex_unlock(m1);
	return ret;
}

/**
 * d_splice_alias - splice a disconnected dentry into the tree if one exists
 * @inode:  the inode which may have a disconnected dentry
 * @dentry: a negative dentry which we want to point to the inode.
 *
 * If inode is a directory and has an IS_ROOT alias, then d_move that in
 * place of the given dentry and return it, else simply d_add the inode
 * to the dentry and return NULL.
 *
 * If a non-IS_ROOT directory is found, the filesystem is corrupt, and
 * we should error out: directories can't have multiple aliases.
 *
 * This is needed in the lookup routine of any filesystem that is exportable
 * (via knfsd) so that we can build dcache paths to directories effectively.
 *
 * If a dentry was found and moved, then it is returned.  Otherwise NULL
 * is returned.  This matches the expected return value of ->lookup.
 *
 * Cluster filesystems may call this function with a negative, hashed dentry.
 * In that case, we know that the inode will be a regular file, and also this
 * will only occur during atomic_open. So we need to check for the dentry
 * being already hashed only in the final case.
 */
struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
{
	if (IS_ERR(inode))
		return ERR_CAST(inode);

	BUG_ON(!d_unhashed(dentry));

	if (!inode) {
		__d_instantiate(dentry, NULL);
		goto out;
	}
	spin_lock(&inode->i_lock);
	if (S_ISDIR(inode->i_mode)) {
		struct dentry *new = __d_find_any_alias(inode);
		if (unlikely(new)) {
			/* The reference to new ensures it remains an alias */
			spin_unlock(&inode->i_lock);
			write_seqlock(&rename_lock);
			if (unlikely(d_ancestor(new, dentry))) {
				write_sequnlock(&rename_lock);
				dput(new);
				new = ERR_PTR(-ELOOP);
				pr_warn_ratelimited(
					"VFS: Lookup of '%s' in %s %s"
					" would have caused loop\n",
					dentry->d_name.name,
					inode->i_sb->s_type->name,
					inode->i_sb->s_id);
			} else if (!IS_ROOT(new)) {
				int err = __d_unalias(inode, dentry, new);
				write_sequnlock(&rename_lock);
				if (err) {
					dput(new);
					new = ERR_PTR(err);
				}
			} else {
				__d_move(new, dentry, false);
				write_sequnlock(&rename_lock);
				security_d_instantiate(new, inode);
			}
			iput(inode);
			return new;
		}
	}
	/* already taking inode->i_lock, so d_add() by hand */
	__d_instantiate(dentry, inode);
	spin_unlock(&inode->i_lock);
out:
	security_d_instantiate(dentry, inode);
	d_rehash(dentry);
	return NULL;
}
EXPORT_SYMBOL(d_splice_alias);

static int prepend(char **buffer, int *buflen, const char *str, int namelen)
{
	*buflen -= namelen;
	if (*buflen < 0)
		return -ENAMETOOLONG;
	*buffer -= namelen;
	memcpy(*buffer, str, namelen);
	return 0;
}

/**
 * prepend_name - prepend a pathname in front of current buffer pointer
 * @buffer: buffer pointer
 * @buflen: allocated length of the buffer
 * @name:   name string and length qstr structure
 *
 * With RCU path tracing, it may race with d_move(). Use ACCESS_ONCE() to
 * make sure that either the old or the new name pointer and length are
 * fetched. However, there may be mismatch between length and pointer.
 * The length cannot be trusted, we need to copy it byte-by-byte until
 * the length is reached or a null byte is found. It also prepends "/" at
 * the beginning of the name. The sequence number check at the caller will
 * retry it again when a d_move() does happen. So any garbage in the buffer
 * due to mismatched pointer and length will be discarded.
 *
 * Data dependency barrier is needed to make sure that we see that terminating
 * NUL.  Alpha strikes again, film at 11...
 */
static int prepend_name(char **buffer, int *buflen, struct qstr *name)
{
	const char *dname = ACCESS_ONCE(name->name);
	u32 dlen = ACCESS_ONCE(name->len);
	char *p;

	smp_read_barrier_depends();

	*buflen -= dlen + 1;
	if (*buflen < 0)
		return -ENAMETOOLONG;
	p = *buffer -= dlen + 1;
	*p++ = '/';
	while (dlen--) {
		char c = *dname++;
		if (!c)
			break;
		*p++ = c;
	}
	return 0;
}

/**
 * prepend_path - Prepend path string to a buffer
 * @path: the dentry/vfsmount to report
 * @root: root vfsmnt/dentry
 * @buffer: pointer to the end of the buffer
 * @buflen: pointer to buffer length
 *
 * The function will first try to write out the pathname without taking any
 * lock other than the RCU read lock to make sure that dentries won't go away.
 * It only checks the sequence number of the global rename_lock as any change
 * in the dentry's d_seq will be preceded by changes in the rename_lock
 * sequence number. If the sequence number had been changed, it will restart
 * the whole pathname back-tracing sequence again by taking the rename_lock.
 * In this case, there is no need to take the RCU read lock as the recursive
 * parent pointer references will keep the dentry chain alive as long as no
 * rename operation is performed.
 */
static int prepend_path(const struct path *path,
			const struct path *root,
			char **buffer, int *buflen)
{
	struct dentry *dentry;
	struct vfsmount *vfsmnt;
	struct mount *mnt;
	int error = 0;
	unsigned seq, m_seq = 0;
	char *bptr;
	int blen;

	rcu_read_lock();
restart_mnt:
	read_seqbegin_or_lock(&mount_lock, &m_seq);
	seq = 0;
	rcu_read_lock();
restart:
	bptr = *buffer;
	blen = *buflen;
	error = 0;
	dentry = path->dentry;
	vfsmnt = path->mnt;
	mnt = real_mount(vfsmnt);
	read_seqbegin_or_lock(&rename_lock, &seq);
	while (dentry != root->dentry || vfsmnt != root->mnt) {
		struct dentry * parent;

		if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
			struct mount *parent = ACCESS_ONCE(mnt->mnt_parent);
			/* Escaped? */
			if (dentry != vfsmnt->mnt_root) {
				bptr = *buffer;
				blen = *buflen;
				error = 3;
				break;
			}
			/* Global root? */
			if (mnt != parent) {
				dentry = ACCESS_ONCE(mnt->mnt_mountpoint);
				mnt = parent;
				vfsmnt = &mnt->mnt;
				continue;
			}
			if (!error)
				error = is_mounted(vfsmnt) ? 1 : 2;
			break;
		}
		parent = dentry->d_parent;
		prefetch(parent);
		error = prepend_name(&bptr, &blen, &dentry->d_name);
		if (error)
			break;

		dentry = parent;
	}
	if (!(seq & 1))
		rcu_read_unlock();
	if (need_seqretry(&rename_lock, seq)) {
		seq = 1;
		goto restart;
	}
	done_seqretry(&rename_lock, seq);

	if (!(m_seq & 1))
		rcu_read_unlock();
	if (need_seqretry(&mount_lock, m_seq)) {
		m_seq = 1;
		goto restart_mnt;
	}
	done_seqretry(&mount_lock, m_seq);

	if (error >= 0 && bptr == *buffer) {
		if (--blen < 0)
			error = -ENAMETOOLONG;
		else
			*--bptr = '/';
	}
	*buffer = bptr;
	*buflen = blen;
	return error;
}

/**
 * __d_path - return the path of a dentry
 * @path: the dentry/vfsmount to report
 * @root: root vfsmnt/dentry
 * @buf: buffer to return value in
 * @buflen: buffer length
 *
 * Convert a dentry into an ASCII path name.
 *
 * Returns a pointer into the buffer or an error code if the
 * path was too long.
 *
 * "buflen" should be positive.
 *
 * If the path is not reachable from the supplied root, return %NULL.
 */
char *__d_path(const struct path *path,
	       const struct path *root,
	       char *buf, int buflen)
{
	char *res = buf + buflen;
	int error;

	prepend(&res, &buflen, "\0", 1);
	error = prepend_path(path, root, &res, &buflen);

	if (error < 0)
		return ERR_PTR(error);
	if (error > 0)
		return NULL;
	return res;
}

char *d_absolute_path(const struct path *path,
	       char *buf, int buflen)
{
	struct path root = {};
	char *res = buf + buflen;
	int error;

	prepend(&res, &buflen, "\0", 1);
	error = prepend_path(path, &root, &res, &buflen);

	if (error > 1)
		error = -EINVAL;
	if (error < 0)
		return ERR_PTR(error);
	return res;
}

/*
 * same as __d_path but appends "(deleted)" for unlinked files.
 */
static int path_with_deleted(const struct path *path,
			     const struct path *root,
			     char **buf, int *buflen)
{
	prepend(buf, buflen, "\0", 1);
	if (d_unlinked(path->dentry)) {
		int error = prepend(buf, buflen, " (deleted)", 10);
		if (error)
			return error;
	}

	return prepend_path(path, root, buf, buflen);
}

static int prepend_unreachable(char **buffer, int *buflen)
{
	return prepend(buffer, buflen, "(unreachable)", 13);
}

static void get_fs_root_rcu(struct fs_struct *fs, struct path *root)
{
	unsigned seq;

	do {
		seq = read_seqcount_begin(&fs->seq);
		*root = fs->root;
	} while (read_seqcount_retry(&fs->seq, seq));
}

/**
 * d_path - return the path of a dentry
 * @path: path to report
 * @buf: buffer to return value in
 * @buflen: buffer length
 *
 * Convert a dentry into an ASCII path name. If the entry has been deleted
 * the string " (deleted)" is appended. Note that this is ambiguous.
 *
 * Returns a pointer into the buffer or an error code if the path was
 * too long. Note: Callers should use the returned pointer, not the passed
 * in buffer, to use the name! The implementation often starts at an offset
 * into the buffer, and may leave 0 bytes at the start.
 *
 * "buflen" should be positive.
 */
char *d_path(const struct path *path, char *buf, int buflen)
{
	char *res = buf + buflen;
	struct path root;
	int error;

	/*
	 * We have various synthetic filesystems that never get mounted.  On
	 * these filesystems dentries are never used for lookup purposes, and
	 * thus don't need to be hashed.  They also don't need a name until a
	 * user wants to identify the object in /proc/pid/fd/.  The little hack
	 * below allows us to generate a name for these objects on demand:
	 *
	 * Some pseudo inodes are mountable.  When they are mounted
	 * path->dentry == path->mnt->mnt_root.  In that case don't call d_dname
	 * and instead have d_path return the mounted path.
	 */
	if (path->dentry->d_op && path->dentry->d_op->d_dname &&
	    (!IS_ROOT(path->dentry) || path->dentry != path->mnt->mnt_root))
		return path->dentry->d_op->d_dname(path->dentry, buf, buflen);

	rcu_read_lock();
	get_fs_root_rcu(current->fs, &root);
	error = path_with_deleted(path, &root, &res, &buflen);
	rcu_read_unlock();

	if (error < 0)
		res = ERR_PTR(error);
	return res;
}
EXPORT_SYMBOL(d_path);

/*
 * Helper function for dentry_operations.d_dname() members
 */
char *dynamic_dname(struct dentry *dentry, char *buffer, int buflen,
			const char *fmt, ...)
{
	va_list args;
	char temp[64];
	int sz;

	va_start(args, fmt);
	sz = vsnprintf(temp, sizeof(temp), fmt, args) + 1;
	va_end(args);

	if (sz > sizeof(temp) || sz > buflen)
		return ERR_PTR(-ENAMETOOLONG);

	buffer += buflen - sz;
	return memcpy(buffer, temp, sz);
}

char *simple_dname(struct dentry *dentry, char *buffer, int buflen)
{
	char *end = buffer + buflen;
	/* these dentries are never renamed, so d_lock is not needed */
	if (prepend(&end, &buflen, " (deleted)", 11) ||
	    prepend(&end, &buflen, dentry->d_name.name, dentry->d_name.len) ||
	    prepend(&end, &buflen, "/", 1))  
		end = ERR_PTR(-ENAMETOOLONG);
	return end;
}
EXPORT_SYMBOL(simple_dname);

/*
 * Write full pathname from the root of the filesystem into the buffer.
 */
static char *__dentry_path(struct dentry *d, char *buf, int buflen)
{
	struct dentry *dentry;
	char *end, *retval;
	int len, seq = 0;
	int error = 0;

	if (buflen < 2)
		goto Elong;

	rcu_read_lock();
restart:
	dentry = d;
	end = buf + buflen;
	len = buflen;
	prepend(&end, &len, "\0", 1);
	/* Get '/' right */
	retval = end-1;
	*retval = '/';
	read_seqbegin_or_lock(&rename_lock, &seq);
	while (!IS_ROOT(dentry)) {
		struct dentry *parent = dentry->d_parent;

		prefetch(parent);
		error = prepend_name(&end, &len, &dentry->d_name);
		if (error)
			break;

		retval = end;
		dentry = parent;
	}
	if (!(seq & 1))
		rcu_read_unlock();
	if (need_seqretry(&rename_lock, seq)) {
		seq = 1;
		goto restart;
	}
	done_seqretry(&rename_lock, seq);
	if (error)
		goto Elong;
	return retval;
Elong:
	return ERR_PTR(-ENAMETOOLONG);
}

char *dentry_path_raw(struct dentry *dentry, char *buf, int buflen)
{
	return __dentry_path(dentry, buf, buflen);
}
EXPORT_SYMBOL(dentry_path_raw);

char *dentry_path(struct dentry *dentry, char *buf, int buflen)
{
	char *p = NULL;
	char *retval;

	if (d_unlinked(dentry)) {
		p = buf + buflen;
		if (prepend(&p, &buflen, "//deleted", 10) != 0)
			goto Elong;
		buflen++;
	}
	retval = __dentry_path(dentry, buf, buflen);
	if (!IS_ERR(retval) && p)
		*p = '/';	/* restore '/' overriden with '\0' */
	return retval;
Elong:
	return ERR_PTR(-ENAMETOOLONG);
}

static void get_fs_root_and_pwd_rcu(struct fs_struct *fs, struct path *root,
				    struct path *pwd)
{
	unsigned seq;

	do {
		seq = read_seqcount_begin(&fs->seq);
		*root = fs->root;
		*pwd = fs->pwd;
	} while (read_seqcount_retry(&fs->seq, seq));
}

/*
 * NOTE! The user-level library version returns a
 * character pointer. The kernel system call just
 * returns the length of the buffer filled (which
 * includes the ending '\0' character), or a negative
 * error value. So libc would do something like
 *
 *	char *getcwd(char * buf, size_t size)
 *	{
 *		int retval;
 *
 *		retval = sys_getcwd(buf, size);
 *		if (retval >= 0)
 *			return buf;
 *		errno = -retval;
 *		return NULL;
 *	}
 */
SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
{
	int error;
	struct path pwd, root;
	char *page = __getname();

	if (!page)
		return -ENOMEM;

	rcu_read_lock();
	get_fs_root_and_pwd_rcu(current->fs, &root, &pwd);

	error = -ENOENT;
	if (!d_unlinked(pwd.dentry)) {
		unsigned long len;
		char *cwd = page + PATH_MAX;
		int buflen = PATH_MAX;

		prepend(&cwd, &buflen, "\0", 1);
		error = prepend_path(&pwd, &root, &cwd, &buflen);
		rcu_read_unlock();

		if (error < 0)
			goto out;

		/* Unreachable from current root */
		if (error > 0) {
			error = prepend_unreachable(&cwd, &buflen);
			if (error)
				goto out;
		}

		error = -ERANGE;
		len = PATH_MAX + page - cwd;
		if (len <= size) {
			error = len;
			if (copy_to_user(buf, cwd, len))
				error = -EFAULT;
		}
	} else {
		rcu_read_unlock();
	}

out:
	__putname(page);
	return error;
}

/*
 * Test whether new_dentry is a subdirectory of old_dentry.
 *
 * Trivially implemented using the dcache structure
 */

/**
 * is_subdir - is new dentry a subdirectory of old_dentry
 * @new_dentry: new dentry
 * @old_dentry: old dentry
 *
 * Returns 1 if new_dentry is a subdirectory of the parent (at any depth).
 * Returns 0 otherwise.
 * Caller must ensure that "new_dentry" is pinned before calling is_subdir()
 */
  
int is_subdir(struct dentry *new_dentry, struct dentry *old_dentry)
{
	int result;
	unsigned seq;

	if (new_dentry == old_dentry)
		return 1;

	do {
		/* for restarting inner loop in case of seq retry */
		seq = read_seqbegin(&rename_lock);
		/*
		 * Need rcu_readlock to protect against the d_parent trashing
		 * due to d_move
		 */
		rcu_read_lock();
		if (d_ancestor(old_dentry, new_dentry))
			result = 1;
		else
			result = 0;
		rcu_read_unlock();
	} while (read_seqretry(&rename_lock, seq));

	return result;
}

static enum d_walk_ret d_genocide_kill(void *data, struct dentry *dentry)
{
	struct dentry *root = data;
	if (dentry != root) {
		if (d_unhashed(dentry) || !dentry->d_inode)
			return D_WALK_SKIP;

		if (!(dentry->d_flags & DCACHE_GENOCIDE)) {
			dentry->d_flags |= DCACHE_GENOCIDE;
			dentry->d_lockref.count--;
		}
	}
	return D_WALK_CONTINUE;
}

void d_genocide(struct dentry *parent)
{
	d_walk(parent, parent, d_genocide_kill, NULL);
}

void d_tmpfile(struct dentry *dentry, struct inode *inode)
{
	inode_dec_link_count(inode);
	BUG_ON(dentry->d_name.name != dentry->d_iname ||
		!hlist_unhashed(&dentry->d_u.d_alias) ||
		!d_unlinked(dentry));
	spin_lock(&dentry->d_parent->d_lock);
	spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
	dentry->d_name.len = sprintf(dentry->d_iname, "#%llu",
				(unsigned long long)inode->i_ino);
	spin_unlock(&dentry->d_lock);
	spin_unlock(&dentry->d_parent->d_lock);
	d_instantiate(dentry, inode);
}
EXPORT_SYMBOL(d_tmpfile);

static __initdata unsigned long dhash_entries;
static int __init set_dhash_entries(char *str)
{
	if (!str)
		return 0;
	dhash_entries = simple_strtoul(str, &str, 0);
	return 1;
}
__setup("dhash_entries=", set_dhash_entries);

static void __init dcache_init_early(void)
{
	unsigned int loop;

	/* If hashes are distributed across NUMA nodes, defer
	 * hash allocation until vmalloc space is available.
	 */
	if (hashdist)
		return;

	dentry_hashtable =
		alloc_large_system_hash("Dentry cache",
					sizeof(struct hlist_bl_head),
					dhash_entries,
					13,
					HASH_EARLY,
					&d_hash_shift,
					&d_hash_mask,
					0,
					0);

	for (loop = 0; loop < (1U << d_hash_shift); loop++)
		INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
}

static void __init dcache_init(void)
{
	unsigned int loop;

	/* 
	 * A constructor could be added for stable state like the lists,
	 * but it is probably not worth it because of the cache nature
	 * of the dcache. 
	 */
	dentry_cache = KMEM_CACHE(dentry,
		SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD);

	/* Hash may have been set up in dcache_init_early */
	if (!hashdist)
		return;

	dentry_hashtable =
		alloc_large_system_hash("Dentry cache",
					sizeof(struct hlist_bl_head),
					dhash_entries,
					13,
					0,
					&d_hash_shift,
					&d_hash_mask,
					0,
					0);

	for (loop = 0; loop < (1U << d_hash_shift); loop++)
		INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
}

/* SLAB cache for __getname() consumers */
struct kmem_cache *names_cachep __read_mostly;
EXPORT_SYMBOL(names_cachep);

EXPORT_SYMBOL(d_genocide);

void __init vfs_caches_init_early(void)
{
	dcache_init_early();
	inode_init_early();
}

void __init vfs_caches_init(void)
{
	names_cachep = kmem_cache_create("names_cache", PATH_MAX, 0,
			SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);

	dcache_init();
	inode_init();
	files_init();
	files_maxfiles_init();
	mnt_init();
	bdev_cache_init();
	chrdev_init();
}