aboutsummaryrefslogtreecommitdiff
path: root/drivers/block/xen-blkfront.c
blob: c4a4c900628891c31fec541277cb7ffea9a3e68b (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
/*
 * blkfront.c
 *
 * XenLinux virtual block device driver.
 *
 * Copyright (c) 2003-2004, Keir Fraser & Steve Hand
 * Modifications by Mark A. Williamson are (c) Intel Research Cambridge
 * Copyright (c) 2004, Christian Limpach
 * Copyright (c) 2004, Andrew Warfield
 * Copyright (c) 2005, Christopher Clark
 * Copyright (c) 2005, XenSource Ltd
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License version 2
 * as published by the Free Software Foundation; or, when distributed
 * separately from the Linux kernel or incorporated into other
 * software packages, subject to the following license:
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this source file (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#include <linux/interrupt.h>
#include <linux/blkdev.h>
#include <linux/hdreg.h>
#include <linux/cdrom.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/mutex.h>
#include <linux/scatterlist.h>
#include <linux/bitmap.h>
#include <linux/list.h>

#include <xen/xen.h>
#include <xen/xenbus.h>
#include <xen/grant_table.h>
#include <xen/events.h>
#include <xen/page.h>
#include <xen/platform_pci.h>

#include <xen/interface/grant_table.h>
#include <xen/interface/io/blkif.h>
#include <xen/interface/io/protocols.h>

#include <asm/xen/hypervisor.h>

enum blkif_state {
	BLKIF_STATE_DISCONNECTED,
	BLKIF_STATE_CONNECTED,
	BLKIF_STATE_SUSPENDED,
};

struct grant {
	grant_ref_t gref;
	unsigned long pfn;
	struct list_head node;
};

struct blk_shadow {
	struct blkif_request req;
	struct request *request;
	struct grant **grants_used;
	struct grant **indirect_grants;
	struct scatterlist *sg;
};

struct split_bio {
	struct bio *bio;
	atomic_t pending;
	int err;
};

static DEFINE_MUTEX(blkfront_mutex);
static const struct block_device_operations xlvbd_block_fops;

/*
 * Maximum number of segments in indirect requests, the actual value used by
 * the frontend driver is the minimum of this value and the value provided
 * by the backend driver.
 */

static unsigned int xen_blkif_max_segments = 32;
module_param_named(max, xen_blkif_max_segments, int, S_IRUGO);
MODULE_PARM_DESC(max, "Maximum amount of segments in indirect requests (default is 32)");

#define BLK_RING_SIZE __CONST_RING_SIZE(blkif, PAGE_SIZE)

/*
 * We have one of these per vbd, whether ide, scsi or 'other'.  They
 * hang in private_data off the gendisk structure. We may end up
 * putting all kinds of interesting stuff here :-)
 */
struct blkfront_info
{
	spinlock_t io_lock;
	struct mutex mutex;
	struct xenbus_device *xbdev;
	struct gendisk *gd;
	int vdevice;
	blkif_vdev_t handle;
	enum blkif_state connected;
	int ring_ref;
	struct blkif_front_ring ring;
	unsigned int evtchn, irq;
	struct request_queue *rq;
	struct work_struct work;
	struct gnttab_free_callback callback;
	struct blk_shadow shadow[BLK_RING_SIZE];
	struct list_head grants;
	struct list_head indirect_pages;
	unsigned int persistent_gnts_c;
	unsigned long shadow_free;
	unsigned int feature_flush;
	unsigned int flush_op;
	unsigned int feature_discard:1;
	unsigned int feature_secdiscard:1;
	unsigned int discard_granularity;
	unsigned int discard_alignment;
	unsigned int feature_persistent:1;
	unsigned int max_indirect_segments;
	int is_ready;
};

static unsigned int nr_minors;
static unsigned long *minors;
static DEFINE_SPINLOCK(minor_lock);

#define MAXIMUM_OUTSTANDING_BLOCK_REQS \
	(BLKIF_MAX_SEGMENTS_PER_REQUEST * BLK_RING_SIZE)
#define GRANT_INVALID_REF	0

#define PARTS_PER_DISK		16
#define PARTS_PER_EXT_DISK      256

#define BLKIF_MAJOR(dev) ((dev)>>8)
#define BLKIF_MINOR(dev) ((dev) & 0xff)

#define EXT_SHIFT 28
#define EXTENDED (1<<EXT_SHIFT)
#define VDEV_IS_EXTENDED(dev) ((dev)&(EXTENDED))
#define BLKIF_MINOR_EXT(dev) ((dev)&(~EXTENDED))
#define EMULATED_HD_DISK_MINOR_OFFSET (0)
#define EMULATED_HD_DISK_NAME_OFFSET (EMULATED_HD_DISK_MINOR_OFFSET / 256)
#define EMULATED_SD_DISK_MINOR_OFFSET (0)
#define EMULATED_SD_DISK_NAME_OFFSET (EMULATED_SD_DISK_MINOR_OFFSET / 256)

#define DEV_NAME	"xvd"	/* name in /dev */

#define SEGS_PER_INDIRECT_FRAME \
	(PAGE_SIZE/sizeof(struct blkif_request_segment_aligned))
#define INDIRECT_GREFS(_segs) \
	((_segs + SEGS_PER_INDIRECT_FRAME - 1)/SEGS_PER_INDIRECT_FRAME)

static int blkfront_setup_indirect(struct blkfront_info *info);

static int get_id_from_freelist(struct blkfront_info *info)
{
	unsigned long free = info->shadow_free;
	BUG_ON(free >= BLK_RING_SIZE);
	info->shadow_free = info->shadow[free].req.u.rw.id;
	info->shadow[free].req.u.rw.id = 0x0fffffee; /* debug */
	return free;
}

static int add_id_to_freelist(struct blkfront_info *info,
			       unsigned long id)
{
	if (info->shadow[id].req.u.rw.id != id)
		return -EINVAL;
	if (info->shadow[id].request == NULL)
		return -EINVAL;
	info->shadow[id].req.u.rw.id  = info->shadow_free;
	info->shadow[id].request = NULL;
	info->shadow_free = id;
	return 0;
}

static int fill_grant_buffer(struct blkfront_info *info, int num)
{
	struct page *granted_page;
	struct grant *gnt_list_entry, *n;
	int i = 0;

	while(i < num) {
		gnt_list_entry = kzalloc(sizeof(struct grant), GFP_NOIO);
		if (!gnt_list_entry)
			goto out_of_memory;

		if (info->feature_persistent) {
			granted_page = alloc_page(GFP_NOIO);
			if (!granted_page) {
				kfree(gnt_list_entry);
				goto out_of_memory;
			}
			gnt_list_entry->pfn = page_to_pfn(granted_page);
		}

		gnt_list_entry->gref = GRANT_INVALID_REF;
		list_add(&gnt_list_entry->node, &info->grants);
		i++;
	}

	return 0;

out_of_memory:
	list_for_each_entry_safe(gnt_list_entry, n,
	                         &info->grants, node) {
		list_del(&gnt_list_entry->node);
		if (info->feature_persistent)
			__free_page(pfn_to_page(gnt_list_entry->pfn));
		kfree(gnt_list_entry);
		i--;
	}
	BUG_ON(i != 0);
	return -ENOMEM;
}

static struct grant *get_grant(grant_ref_t *gref_head,
                               unsigned long pfn,
                               struct blkfront_info *info)
{
	struct grant *gnt_list_entry;
	unsigned long buffer_mfn;

	BUG_ON(list_empty(&info->grants));
	gnt_list_entry = list_first_entry(&info->grants, struct grant,
	                                  node);
	list_del(&gnt_list_entry->node);

	if (gnt_list_entry->gref != GRANT_INVALID_REF) {
		info->persistent_gnts_c--;
		return gnt_list_entry;
	}

	/* Assign a gref to this page */
	gnt_list_entry->gref = gnttab_claim_grant_reference(gref_head);
	BUG_ON(gnt_list_entry->gref == -ENOSPC);
	if (!info->feature_persistent) {
		BUG_ON(!pfn);
		gnt_list_entry->pfn = pfn;
	}
	buffer_mfn = pfn_to_mfn(gnt_list_entry->pfn);
	gnttab_grant_foreign_access_ref(gnt_list_entry->gref,
	                                info->xbdev->otherend_id,
	                                buffer_mfn, 0);
	return gnt_list_entry;
}

static const char *op_name(int op)
{
	static const char *const names[] = {
		[BLKIF_OP_READ] = "read",
		[BLKIF_OP_WRITE] = "write",
		[BLKIF_OP_WRITE_BARRIER] = "barrier",
		[BLKIF_OP_FLUSH_DISKCACHE] = "flush",
		[BLKIF_OP_DISCARD] = "discard" };

	if (op < 0 || op >= ARRAY_SIZE(names))
		return "unknown";

	if (!names[op])
		return "reserved";

	return names[op];
}
static int xlbd_reserve_minors(unsigned int minor, unsigned int nr)
{
	unsigned int end = minor + nr;
	int rc;

	if (end > nr_minors) {
		unsigned long *bitmap, *old;

		bitmap = kcalloc(BITS_TO_LONGS(end), sizeof(*bitmap),
				 GFP_KERNEL);
		if (bitmap == NULL)
			return -ENOMEM;

		spin_lock(&minor_lock);
		if (end > nr_minors) {
			old = minors;
			memcpy(bitmap, minors,
			       BITS_TO_LONGS(nr_minors) * sizeof(*bitmap));
			minors = bitmap;
			nr_minors = BITS_TO_LONGS(end) * BITS_PER_LONG;
		} else
			old = bitmap;
		spin_unlock(&minor_lock);
		kfree(old);
	}

	spin_lock(&minor_lock);
	if (find_next_bit(minors, end, minor) >= end) {
		bitmap_set(minors, minor, nr);
		rc = 0;
	} else
		rc = -EBUSY;
	spin_unlock(&minor_lock);

	return rc;
}

static void xlbd_release_minors(unsigned int minor, unsigned int nr)
{
	unsigned int end = minor + nr;

	BUG_ON(end > nr_minors);
	spin_lock(&minor_lock);
	bitmap_clear(minors,  minor, nr);
	spin_unlock(&minor_lock);
}

static void blkif_restart_queue_callback(void *arg)
{
	struct blkfront_info *info = (struct blkfront_info *)arg;
	schedule_work(&info->work);
}

static int blkif_getgeo(struct block_device *bd, struct hd_geometry *hg)
{
	/* We don't have real geometry info, but let's at least return
	   values consistent with the size of the device */
	sector_t nsect = get_capacity(bd->bd_disk);
	sector_t cylinders = nsect;

	hg->heads = 0xff;
	hg->sectors = 0x3f;
	sector_div(cylinders, hg->heads * hg->sectors);
	hg->cylinders = cylinders;
	if ((sector_t)(hg->cylinders + 1) * hg->heads * hg->sectors < nsect)
		hg->cylinders = 0xffff;
	return 0;
}

static int blkif_ioctl(struct block_device *bdev, fmode_t mode,
		       unsigned command, unsigned long argument)
{
	struct blkfront_info *info = bdev->bd_disk->private_data;
	int i;

	dev_dbg(&info->xbdev->dev, "command: 0x%x, argument: 0x%lx\n",
		command, (long)argument);

	switch (command) {
	case CDROMMULTISESSION:
		dev_dbg(&info->xbdev->dev, "FIXME: support multisession CDs later\n");
		for (i = 0; i < sizeof(struct cdrom_multisession); i++)
			if (put_user(0, (char __user *)(argument + i)))
				return -EFAULT;
		return 0;

	case CDROM_GET_CAPABILITY: {
		struct gendisk *gd = info->gd;
		if (gd->flags & GENHD_FL_CD)
			return 0;
		return -EINVAL;
	}

	default:
		/*printk(KERN_ALERT "ioctl %08x not supported by Xen blkdev\n",
		  command);*/
		return -EINVAL; /* same return as native Linux */
	}

	return 0;
}

/*
 * Generate a Xen blkfront IO request from a blk layer request.  Reads
 * and writes are handled as expected.
 *
 * @req: a request struct
 */
static int blkif_queue_request(struct request *req)
{
	struct blkfront_info *info = req->rq_disk->private_data;
	struct blkif_request *ring_req;
	unsigned long id;
	unsigned int fsect, lsect;
	int i, ref, n;
	struct blkif_request_segment_aligned *segments = NULL;

	/*
	 * Used to store if we are able to queue the request by just using
	 * existing persistent grants, or if we have to get new grants,
	 * as there are not sufficiently many free.
	 */
	bool new_persistent_gnts;
	grant_ref_t gref_head;
	struct grant *gnt_list_entry = NULL;
	struct scatterlist *sg;
	int nseg, max_grefs;

	if (unlikely(info->connected != BLKIF_STATE_CONNECTED))
		return 1;

	max_grefs = req->nr_phys_segments;
	if (max_grefs > BLKIF_MAX_SEGMENTS_PER_REQUEST)
		/*
		 * If we are using indirect segments we need to account
		 * for the indirect grefs used in the request.
		 */
		max_grefs += INDIRECT_GREFS(req->nr_phys_segments);

	/* Check if we have enough grants to allocate a requests */
	if (info->persistent_gnts_c < max_grefs) {
		new_persistent_gnts = 1;
		if (gnttab_alloc_grant_references(
		    max_grefs - info->persistent_gnts_c,
		    &gref_head) < 0) {
			gnttab_request_free_callback(
				&info->callback,
				blkif_restart_queue_callback,
				info,
				max_grefs);
			return 1;
		}
	} else
		new_persistent_gnts = 0;

	/* Fill out a communications ring structure. */
	ring_req = RING_GET_REQUEST(&info->ring, info->ring.req_prod_pvt);
	id = get_id_from_freelist(info);
	info->shadow[id].request = req;

	if (unlikely(req->cmd_flags & (REQ_DISCARD | REQ_SECURE))) {
		ring_req->operation = BLKIF_OP_DISCARD;
		ring_req->u.discard.nr_sectors = blk_rq_sectors(req);
		ring_req->u.discard.id = id;
		ring_req->u.discard.sector_number = (blkif_sector_t)blk_rq_pos(req);
		if ((req->cmd_flags & REQ_SECURE) && info->feature_secdiscard)
			ring_req->u.discard.flag = BLKIF_DISCARD_SECURE;
		else
			ring_req->u.discard.flag = 0;
	} else {
		BUG_ON(info->max_indirect_segments == 0 &&
		       req->nr_phys_segments > BLKIF_MAX_SEGMENTS_PER_REQUEST);
		BUG_ON(info->max_indirect_segments &&
		       req->nr_phys_segments > info->max_indirect_segments);
		nseg = blk_rq_map_sg(req->q, req, info->shadow[id].sg);
		ring_req->u.rw.id = id;
		if (nseg > BLKIF_MAX_SEGMENTS_PER_REQUEST) {
			/*
			 * The indirect operation can only be a BLKIF_OP_READ or
			 * BLKIF_OP_WRITE
			 */
			BUG_ON(req->cmd_flags & (REQ_FLUSH | REQ_FUA));
			ring_req->operation = BLKIF_OP_INDIRECT;
			ring_req->u.indirect.indirect_op = rq_data_dir(req) ?
				BLKIF_OP_WRITE : BLKIF_OP_READ;
			ring_req->u.indirect.sector_number = (blkif_sector_t)blk_rq_pos(req);
			ring_req->u.indirect.handle = info->handle;
			ring_req->u.indirect.nr_segments = nseg;
		} else {
			ring_req->u.rw.sector_number = (blkif_sector_t)blk_rq_pos(req);
			ring_req->u.rw.handle = info->handle;
			ring_req->operation = rq_data_dir(req) ?
				BLKIF_OP_WRITE : BLKIF_OP_READ;
			if (req->cmd_flags & (REQ_FLUSH | REQ_FUA)) {
				/*
				 * Ideally we can do an unordered flush-to-disk. In case the
				 * backend onlysupports barriers, use that. A barrier request
				 * a superset of FUA, so we can implement it the same
				 * way.  (It's also a FLUSH+FUA, since it is
				 * guaranteed ordered WRT previous writes.)
				 */
				ring_req->operation = info->flush_op;
			}
			ring_req->u.rw.nr_segments = nseg;
		}
		for_each_sg(info->shadow[id].sg, sg, nseg, i) {
			fsect = sg->offset >> 9;
			lsect = fsect + (sg->length >> 9) - 1;

			if ((ring_req->operation == BLKIF_OP_INDIRECT) &&
			    (i % SEGS_PER_INDIRECT_FRAME == 0)) {
				unsigned long uninitialized_var(pfn);

				if (segments)
					kunmap_atomic(segments);

				n = i / SEGS_PER_INDIRECT_FRAME;
				if (!info->feature_persistent) {
					struct page *indirect_page;

					/* Fetch a pre-allocated page to use for indirect grefs */
					BUG_ON(list_empty(&info->indirect_pages));
					indirect_page = list_first_entry(&info->indirect_pages,
					                                 struct page, lru);
					list_del(&indirect_page->lru);
					pfn = page_to_pfn(indirect_page);
				}
				gnt_list_entry = get_grant(&gref_head, pfn, info);
				info->shadow[id].indirect_grants[n] = gnt_list_entry;
				segments = kmap_atomic(pfn_to_page(gnt_list_entry->pfn));
				ring_req->u.indirect.indirect_grefs[n] = gnt_list_entry->gref;
			}

			gnt_list_entry = get_grant(&gref_head, page_to_pfn(sg_page(sg)), info);
			ref = gnt_list_entry->gref;

			info->shadow[id].grants_used[i] = gnt_list_entry;

			if (rq_data_dir(req) && info->feature_persistent) {
				char *bvec_data;
				void *shared_data;

				BUG_ON(sg->offset + sg->length > PAGE_SIZE);

				shared_data = kmap_atomic(pfn_to_page(gnt_list_entry->pfn));
				bvec_data = kmap_atomic(sg_page(sg));

				/*
				 * this does not wipe data stored outside the
				 * range sg->offset..sg->offset+sg->length.
				 * Therefore, blkback *could* see data from
				 * previous requests. This is OK as long as
				 * persistent grants are shared with just one
				 * domain. It may need refactoring if this
				 * changes
				 */
				memcpy(shared_data + sg->offset,
				       bvec_data   + sg->offset,
				       sg->length);

				kunmap_atomic(bvec_data);
				kunmap_atomic(shared_data);
			}
			if (ring_req->operation != BLKIF_OP_INDIRECT) {
				ring_req->u.rw.seg[i] =
						(struct blkif_request_segment) {
							.gref       = ref,
							.first_sect = fsect,
							.last_sect  = lsect };
			} else {
				n = i % SEGS_PER_INDIRECT_FRAME;
				segments[n] =
					(struct blkif_request_segment_aligned) {
							.gref       = ref,
							.first_sect = fsect,
							.last_sect  = lsect };
			}
		}
		if (segments)
			kunmap_atomic(segments);
	}

	info->ring.req_prod_pvt++;

	/* Keep a private copy so we can reissue requests when recovering. */
	info->shadow[id].req = *ring_req;

	if (new_persistent_gnts)
		gnttab_free_grant_references(gref_head);

	return 0;
}


static inline void flush_requests(struct blkfront_info *info)
{
	int notify;

	RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&info->ring, notify);

	if (notify)
		notify_remote_via_irq(info->irq);
}

/*
 * do_blkif_request
 *  read a block; request is in a request queue
 */
static void do_blkif_request(struct request_queue *rq)
{
	struct blkfront_info *info = NULL;
	struct request *req;
	int queued;

	pr_debug("Entered do_blkif_request\n");

	queued = 0;

	while ((req = blk_peek_request(rq)) != NULL) {
		info = req->rq_disk->private_data;

		if (RING_FULL(&info->ring))
			goto wait;

		blk_start_request(req);

		if ((req->cmd_type != REQ_TYPE_FS) ||
		    ((req->cmd_flags & (REQ_FLUSH | REQ_FUA)) &&
		    !info->flush_op)) {
			__blk_end_request_all(req, -EIO);
			continue;
		}

		pr_debug("do_blk_req %p: cmd %p, sec %lx, "
			 "(%u/%u) buffer:%p [%s]\n",
			 req, req->cmd, (unsigned long)blk_rq_pos(req),
			 blk_rq_cur_sectors(req), blk_rq_sectors(req),
			 req->buffer, rq_data_dir(req) ? "write" : "read");

		if (blkif_queue_request(req)) {
			blk_requeue_request(rq, req);
wait:
			/* Avoid pointless unplugs. */
			blk_stop_queue(rq);
			break;
		}

		queued++;
	}

	if (queued != 0)
		flush_requests(info);
}

static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size,
				unsigned int physical_sector_size,
				unsigned int segments)
{
	struct request_queue *rq;
	struct blkfront_info *info = gd->private_data;

	rq = blk_init_queue(do_blkif_request, &info->io_lock);
	if (rq == NULL)
		return -1;

	queue_flag_set_unlocked(QUEUE_FLAG_VIRT, rq);

	if (info->feature_discard) {
		queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, rq);
		blk_queue_max_discard_sectors(rq, get_capacity(gd));
		rq->limits.discard_granularity = info->discard_granularity;
		rq->limits.discard_alignment = info->discard_alignment;
		if (info->feature_secdiscard)
			queue_flag_set_unlocked(QUEUE_FLAG_SECDISCARD, rq);
	}

	/* Hard sector size and max sectors impersonate the equiv. hardware. */
	blk_queue_logical_block_size(rq, sector_size);
	blk_queue_physical_block_size(rq, physical_sector_size);
	blk_queue_max_hw_sectors(rq, (segments * PAGE_SIZE) / 512);

	/* Each segment in a request is up to an aligned page in size. */
	blk_queue_segment_boundary(rq, PAGE_SIZE - 1);
	blk_queue_max_segment_size(rq, PAGE_SIZE);

	/* Ensure a merged request will fit in a single I/O ring slot. */
	blk_queue_max_segments(rq, segments);

	/* Make sure buffer addresses are sector-aligned. */
	blk_queue_dma_alignment(rq, 511);

	/* Make sure we don't use bounce buffers. */
	blk_queue_bounce_limit(rq, BLK_BOUNCE_ANY);

	gd->queue = rq;

	return 0;
}


static void xlvbd_flush(struct blkfront_info *info)
{
	blk_queue_flush(info->rq, info->feature_flush);
	printk(KERN_INFO "blkfront: %s: %s: %s %s %s %s %s\n",
	       info->gd->disk_name,
	       info->flush_op == BLKIF_OP_WRITE_BARRIER ?
		"barrier" : (info->flush_op == BLKIF_OP_FLUSH_DISKCACHE ?
		"flush diskcache" : "barrier or flush"),
	       info->feature_flush ? "enabled;" : "disabled;",
	       "persistent grants:",
	       info->feature_persistent ? "enabled;" : "disabled;",
	       "indirect descriptors:",
	       info->max_indirect_segments ? "enabled;" : "disabled;");
}

static int xen_translate_vdev(int vdevice, int *minor, unsigned int *offset)
{
	int major;
	major = BLKIF_MAJOR(vdevice);
	*minor = BLKIF_MINOR(vdevice);
	switch (major) {
		case XEN_IDE0_MAJOR:
			*offset = (*minor / 64) + EMULATED_HD_DISK_NAME_OFFSET;
			*minor = ((*minor / 64) * PARTS_PER_DISK) +
				EMULATED_HD_DISK_MINOR_OFFSET;
			break;
		case XEN_IDE1_MAJOR:
			*offset = (*minor / 64) + 2 + EMULATED_HD_DISK_NAME_OFFSET;
			*minor = (((*minor / 64) + 2) * PARTS_PER_DISK) +
				EMULATED_HD_DISK_MINOR_OFFSET;
			break;
		case XEN_SCSI_DISK0_MAJOR:
			*offset = (*minor / PARTS_PER_DISK) + EMULATED_SD_DISK_NAME_OFFSET;
			*minor = *minor + EMULATED_SD_DISK_MINOR_OFFSET;
			break;
		case XEN_SCSI_DISK1_MAJOR:
		case XEN_SCSI_DISK2_MAJOR:
		case XEN_SCSI_DISK3_MAJOR:
		case XEN_SCSI_DISK4_MAJOR:
		case XEN_SCSI_DISK5_MAJOR:
		case XEN_SCSI_DISK6_MAJOR:
		case XEN_SCSI_DISK7_MAJOR:
			*offset = (*minor / PARTS_PER_DISK) + 
				((major - XEN_SCSI_DISK1_MAJOR + 1) * 16) +
				EMULATED_SD_DISK_NAME_OFFSET;
			*minor = *minor +
				((major - XEN_SCSI_DISK1_MAJOR + 1) * 16 * PARTS_PER_DISK) +
				EMULATED_SD_DISK_MINOR_OFFSET;
			break;
		case XEN_SCSI_DISK8_MAJOR:
		case XEN_SCSI_DISK9_MAJOR:
		case XEN_SCSI_DISK10_MAJOR:
		case XEN_SCSI_DISK11_MAJOR:
		case XEN_SCSI_DISK12_MAJOR:
		case XEN_SCSI_DISK13_MAJOR:
		case XEN_SCSI_DISK14_MAJOR:
		case XEN_SCSI_DISK15_MAJOR:
			*offset = (*minor / PARTS_PER_DISK) + 
				((major - XEN_SCSI_DISK8_MAJOR + 8) * 16) +
				EMULATED_SD_DISK_NAME_OFFSET;
			*minor = *minor +
				((major - XEN_SCSI_DISK8_MAJOR + 8) * 16 * PARTS_PER_DISK) +
				EMULATED_SD_DISK_MINOR_OFFSET;
			break;
		case XENVBD_MAJOR:
			*offset = *minor / PARTS_PER_DISK;
			break;
		default:
			printk(KERN_WARNING "blkfront: your disk configuration is "
					"incorrect, please use an xvd device instead\n");
			return -ENODEV;
	}
	return 0;
}

static char *encode_disk_name(char *ptr, unsigned int n)
{
	if (n >= 26)
		ptr = encode_disk_name(ptr, n / 26 - 1);
	*ptr = 'a' + n % 26;
	return ptr + 1;
}

static int xlvbd_alloc_gendisk(blkif_sector_t capacity,
			       struct blkfront_info *info,
			       u16 vdisk_info, u16 sector_size,
			       unsigned int physical_sector_size)
{
	struct gendisk *gd;
	int nr_minors = 1;
	int err;
	unsigned int offset;
	int minor;
	int nr_parts;
	char *ptr;

	BUG_ON(info->gd != NULL);
	BUG_ON(info->rq != NULL);

	if ((info->vdevice>>EXT_SHIFT) > 1) {
		/* this is above the extended range; something is wrong */
		printk(KERN_WARNING "blkfront: vdevice 0x%x is above the extended range; ignoring\n", info->vdevice);
		return -ENODEV;
	}

	if (!VDEV_IS_EXTENDED(info->vdevice)) {
		err = xen_translate_vdev(info->vdevice, &minor, &offset);
		if (err)
			return err;		
 		nr_parts = PARTS_PER_DISK;
	} else {
		minor = BLKIF_MINOR_EXT(info->vdevice);
		nr_parts = PARTS_PER_EXT_DISK;
		offset = minor / nr_parts;
		if (xen_hvm_domain() && offset < EMULATED_HD_DISK_NAME_OFFSET + 4)
			printk(KERN_WARNING "blkfront: vdevice 0x%x might conflict with "
					"emulated IDE disks,\n\t choose an xvd device name"
					"from xvde on\n", info->vdevice);
	}
	if (minor >> MINORBITS) {
		pr_warn("blkfront: %#x's minor (%#x) out of range; ignoring\n",
			info->vdevice, minor);
		return -ENODEV;
	}

	if ((minor % nr_parts) == 0)
		nr_minors = nr_parts;

	err = xlbd_reserve_minors(minor, nr_minors);
	if (err)
		goto out;
	err = -ENODEV;

	gd = alloc_disk(nr_minors);
	if (gd == NULL)
		goto release;

	strcpy(gd->disk_name, DEV_NAME);
	ptr = encode_disk_name(gd->disk_name + sizeof(DEV_NAME) - 1, offset);
	BUG_ON(ptr >= gd->disk_name + DISK_NAME_LEN);
	if (nr_minors > 1)
		*ptr = 0;
	else
		snprintf(ptr, gd->disk_name + DISK_NAME_LEN - ptr,
			 "%d", minor & (nr_parts - 1));

	gd->major = XENVBD_MAJOR;
	gd->first_minor = minor;
	gd->fops = &xlvbd_block_fops;
	gd->private_data = info;
	gd->driverfs_dev = &(info->xbdev->dev);
	set_capacity(gd, capacity);

	if (xlvbd_init_blk_queue(gd, sector_size, physical_sector_size,
				 info->max_indirect_segments ? :
				 BLKIF_MAX_SEGMENTS_PER_REQUEST)) {
		del_gendisk(gd);
		goto release;
	}

	info->rq = gd->queue;
	info->gd = gd;

	xlvbd_flush(info);

	if (vdisk_info & VDISK_READONLY)
		set_disk_ro(gd, 1);

	if (vdisk_info & VDISK_REMOVABLE)
		gd->flags |= GENHD_FL_REMOVABLE;

	if (vdisk_info & VDISK_CDROM)
		gd->flags |= GENHD_FL_CD;

	return 0;

 release:
	xlbd_release_minors(minor, nr_minors);
 out:
	return err;
}

static void xlvbd_release_gendisk(struct blkfront_info *info)
{
	unsigned int minor, nr_minors;
	unsigned long flags;

	if (info->rq == NULL)
		return;

	spin_lock_irqsave(&info->io_lock, flags);

	/* No more blkif_request(). */
	blk_stop_queue(info->rq);

	/* No more gnttab callback work. */
	gnttab_cancel_free_callback(&info->callback);
	spin_unlock_irqrestore(&info->io_lock, flags);

	/* Flush gnttab callback work. Must be done with no locks held. */
	flush_work(&info->work);

	del_gendisk(info->gd);

	minor = info->gd->first_minor;
	nr_minors = info->gd->minors;
	xlbd_release_minors(minor, nr_minors);

	blk_cleanup_queue(info->rq);
	info->rq = NULL;

	put_disk(info->gd);
	info->gd = NULL;
}

static void kick_pending_request_queues(struct blkfront_info *info)
{
	if (!RING_FULL(&info->ring)) {
		/* Re-enable calldowns. */
		blk_start_queue(info->rq);
		/* Kick things off immediately. */
		do_blkif_request(info->rq);
	}
}

static void blkif_restart_queue(struct work_struct *work)
{
	struct blkfront_info *info = container_of(work, struct blkfront_info, work);

	spin_lock_irq(&info->io_lock);
	if (info->connected == BLKIF_STATE_CONNECTED)
		kick_pending_request_queues(info);
	spin_unlock_irq(&info->io_lock);
}

static void blkif_free(struct blkfront_info *info, int suspend)
{
	struct grant *persistent_gnt;
	struct grant *n;
	int i, j, segs;

	/* Prevent new requests being issued until we fix things up. */
	spin_lock_irq(&info->io_lock);
	info->connected = suspend ?
		BLKIF_STATE_SUSPENDED : BLKIF_STATE_DISCONNECTED;
	/* No more blkif_request(). */
	if (info->rq)
		blk_stop_queue(info->rq);

	/* Remove all persistent grants */
	if (!list_empty(&info->grants)) {
		list_for_each_entry_safe(persistent_gnt, n,
		                         &info->grants, node) {
			list_del(&persistent_gnt->node);
			if (persistent_gnt->gref != GRANT_INVALID_REF) {
				gnttab_end_foreign_access(persistent_gnt->gref,
				                          0, 0UL);
				info->persistent_gnts_c--;
			}
			if (info->feature_persistent)
				__free_page(pfn_to_page(persistent_gnt->pfn));
			kfree(persistent_gnt);
		}
	}
	BUG_ON(info->persistent_gnts_c != 0);

	/*
	 * Remove indirect pages, this only happens when using indirect
	 * descriptors but not persistent grants
	 */
	if (!list_empty(&info->indirect_pages)) {
		struct page *indirect_page, *n;

		BUG_ON(info->feature_persistent);
		list_for_each_entry_safe(indirect_page, n, &info->indirect_pages, lru) {
			list_del(&indirect_page->lru);
			__free_page(indirect_page);
		}
	}

	for (i = 0; i < BLK_RING_SIZE; i++) {
		/*
		 * Clear persistent grants present in requests already
		 * on the shared ring
		 */
		if (!info->shadow[i].request)
			goto free_shadow;

		segs = info->shadow[i].req.operation == BLKIF_OP_INDIRECT ?
		       info->shadow[i].req.u.indirect.nr_segments :
		       info->shadow[i].req.u.rw.nr_segments;
		for (j = 0; j < segs; j++) {
			persistent_gnt = info->shadow[i].grants_used[j];
			gnttab_end_foreign_access(persistent_gnt->gref, 0, 0UL);
			if (info->feature_persistent)
				__free_page(pfn_to_page(persistent_gnt->pfn));
			kfree(persistent_gnt);
		}

		if (info->shadow[i].req.operation != BLKIF_OP_INDIRECT)
			/*
			 * If this is not an indirect operation don't try to
			 * free indirect segments
			 */
			goto free_shadow;

		for (j = 0; j < INDIRECT_GREFS(segs); j++) {
			persistent_gnt = info->shadow[i].indirect_grants[j];
			gnttab_end_foreign_access(persistent_gnt->gref, 0, 0UL);
			__free_page(pfn_to_page(persistent_gnt->pfn));
			kfree(persistent_gnt);
		}

free_shadow:
		kfree(info->shadow[i].grants_used);
		info->shadow[i].grants_used = NULL;
		kfree(info->shadow[i].indirect_grants);
		info->shadow[i].indirect_grants = NULL;
		kfree(info->shadow[i].sg);
		info->shadow[i].sg = NULL;
	}

	/* No more gnttab callback work. */
	gnttab_cancel_free_callback(&info->callback);
	spin_unlock_irq(&info->io_lock);

	/* Flush gnttab callback work. Must be done with no locks held. */
	flush_work(&info->work);

	/* Free resources associated with old device channel. */
	if (info->ring_ref != GRANT_INVALID_REF) {
		gnttab_end_foreign_access(info->ring_ref, 0,
					  (unsigned long)info->ring.sring);
		info->ring_ref = GRANT_INVALID_REF;
		info->ring.sring = NULL;
	}
	if (info->irq)
		unbind_from_irqhandler(info->irq, info);
	info->evtchn = info->irq = 0;

}

static void blkif_completion(struct blk_shadow *s, struct blkfront_info *info,
			     struct blkif_response *bret)
{
	int i = 0;
	struct scatterlist *sg;
	char *bvec_data;
	void *shared_data;
	int nseg;

	nseg = s->req.operation == BLKIF_OP_INDIRECT ?
		s->req.u.indirect.nr_segments : s->req.u.rw.nr_segments;

	if (bret->operation == BLKIF_OP_READ && info->feature_persistent) {
		/*
		 * Copy the data received from the backend into the bvec.
		 * Since bv_offset can be different than 0, and bv_len different
		 * than PAGE_SIZE, we have to keep track of the current offset,
		 * to be sure we are copying the data from the right shared page.
		 */
		for_each_sg(s->sg, sg, nseg, i) {
			BUG_ON(sg->offset + sg->length > PAGE_SIZE);
			shared_data = kmap_atomic(
				pfn_to_page(s->grants_used[i]->pfn));
			bvec_data = kmap_atomic(sg_page(sg));
			memcpy(bvec_data   + sg->offset,
			       shared_data + sg->offset,
			       sg->length);
			kunmap_atomic(bvec_data);
			kunmap_atomic(shared_data);
		}
	}
	/* Add the persistent grant into the list of free grants */
	for (i = 0; i < nseg; i++) {
		if (gnttab_query_foreign_access(s->grants_used[i]->gref)) {
			/*
			 * If the grant is still mapped by the backend (the
			 * backend has chosen to make this grant persistent)
			 * we add it at the head of the list, so it will be
			 * reused first.
			 */
			if (!info->feature_persistent)
				pr_alert_ratelimited("backed has not unmapped grant: %u\n",
						     s->grants_used[i]->gref);
			list_add(&s->grants_used[i]->node, &info->grants);
			info->persistent_gnts_c++;
		} else {
			/*
			 * If the grant is not mapped by the backend we end the
			 * foreign access and add it to the tail of the list,
			 * so it will not be picked again unless we run out of
			 * persistent grants.
			 */
			gnttab_end_foreign_access(s->grants_used[i]->gref, 0, 0UL);
			s->grants_used[i]->gref = GRANT_INVALID_REF;
			list_add_tail(&s->grants_used[i]->node, &info->grants);
		}
	}
	if (s->req.operation == BLKIF_OP_INDIRECT) {
		for (i = 0; i < INDIRECT_GREFS(nseg); i++) {
			if (gnttab_query_foreign_access(s->indirect_grants[i]->gref)) {
				if (!info->feature_persistent)
					pr_alert_ratelimited("backed has not unmapped grant: %u\n",
							     s->indirect_grants[i]->gref);
				list_add(&s->indirect_grants[i]->node, &info->grants);
				info->persistent_gnts_c++;
			} else {
				struct page *indirect_page;

				gnttab_end_foreign_access(s->indirect_grants[i]->gref, 0, 0UL);
				/*
				 * Add the used indirect page back to the list of
				 * available pages for indirect grefs.
				 */
				indirect_page = pfn_to_page(s->indirect_grants[i]->pfn);
				list_add(&indirect_page->lru, &info->indirect_pages);
				s->indirect_grants[i]->gref = GRANT_INVALID_REF;
				list_add_tail(&s->indirect_grants[i]->node, &info->grants);
			}
		}
	}
}

static irqreturn_t blkif_interrupt(int irq, void *dev_id)
{
	struct request *req;
	struct blkif_response *bret;
	RING_IDX i, rp;
	unsigned long flags;
	struct blkfront_info *info = (struct blkfront_info *)dev_id;
	int error;

	spin_lock_irqsave(&info->io_lock, flags);

	if (unlikely(info->connected != BLKIF_STATE_CONNECTED)) {
		spin_unlock_irqrestore(&info->io_lock, flags);
		return IRQ_HANDLED;
	}

 again:
	rp = info->ring.sring->rsp_prod;
	rmb(); /* Ensure we see queued responses up to 'rp'. */

	for (i = info->ring.rsp_cons; i != rp; i++) {
		unsigned long id;

		bret = RING_GET_RESPONSE(&info->ring, i);
		id   = bret->id;
		/*
		 * The backend has messed up and given us an id that we would
		 * never have given to it (we stamp it up to BLK_RING_SIZE -
		 * look in get_id_from_freelist.
		 */
		if (id >= BLK_RING_SIZE) {
			WARN(1, "%s: response to %s has incorrect id (%ld)\n",
			     info->gd->disk_name, op_name(bret->operation), id);
			/* We can't safely get the 'struct request' as
			 * the id is busted. */
			continue;
		}
		req  = info->shadow[id].request;

		if (bret->operation != BLKIF_OP_DISCARD)
			blkif_completion(&info->shadow[id], info, bret);

		if (add_id_to_freelist(info, id)) {
			WARN(1, "%s: response to %s (id %ld) couldn't be recycled!\n",
			     info->gd->disk_name, op_name(bret->operation), id);
			continue;
		}

		error = (bret->status == BLKIF_RSP_OKAY) ? 0 : -EIO;
		switch (bret->operation) {
		case BLKIF_OP_DISCARD:
			if (unlikely(bret->status == BLKIF_RSP_EOPNOTSUPP)) {
				struct request_queue *rq = info->rq;
				printk(KERN_WARNING "blkfront: %s: %s op failed\n",
					   info->gd->disk_name, op_name(bret->operation));
				error = -EOPNOTSUPP;
				info->feature_discard = 0;
				info->feature_secdiscard = 0;
				queue_flag_clear(QUEUE_FLAG_DISCARD, rq);
				queue_flag_clear(QUEUE_FLAG_SECDISCARD, rq);
			}
			__blk_end_request_all(req, error);
			break;
		case BLKIF_OP_FLUSH_DISKCACHE:
		case BLKIF_OP_WRITE_BARRIER:
			if (unlikely(bret->status == BLKIF_RSP_EOPNOTSUPP)) {
				printk(KERN_WARNING "blkfront: %s: %s op failed\n",
				       info->gd->disk_name, op_name(bret->operation));
				error = -EOPNOTSUPP;
			}
			if (unlikely(bret->status == BLKIF_RSP_ERROR &&
				     info->shadow[id].req.u.rw.nr_segments == 0)) {
				printk(KERN_WARNING "blkfront: %s: empty %s op failed\n",
				       info->gd->disk_name, op_name(bret->operation));
				error = -EOPNOTSUPP;
			}
			if (unlikely(error)) {
				if (error == -EOPNOTSUPP)
					error = 0;
				info->feature_flush = 0;
				info->flush_op = 0;
				xlvbd_flush(info);
			}
			/* fall through */
		case BLKIF_OP_READ:
		case BLKIF_OP_WRITE:
			if (unlikely(bret->status != BLKIF_RSP_OKAY))
				dev_dbg(&info->xbdev->dev, "Bad return from blkdev data "
					"request: %x\n", bret->status);

			__blk_end_request_all(req, error);
			break;
		default:
			BUG();
		}
	}

	info->ring.rsp_cons = i;

	if (i != info->ring.req_prod_pvt) {
		int more_to_do;
		RING_FINAL_CHECK_FOR_RESPONSES(&info->ring, more_to_do);
		if (more_to_do)
			goto again;
	} else
		info->ring.sring->rsp_event = i + 1;

	kick_pending_request_queues(info);

	spin_unlock_irqrestore(&info->io_lock, flags);

	return IRQ_HANDLED;
}


static int setup_blkring(struct xenbus_device *dev,
			 struct blkfront_info *info)
{
	struct blkif_sring *sring;
	int err;

	info->ring_ref = GRANT_INVALID_REF;

	sring = (struct blkif_sring *)__get_free_page(GFP_NOIO | __GFP_HIGH);
	if (!sring) {
		xenbus_dev_fatal(dev, -ENOMEM, "allocating shared ring");
		return -ENOMEM;
	}
	SHARED_RING_INIT(sring);
	FRONT_RING_INIT(&info->ring, sring, PAGE_SIZE);

	err = xenbus_grant_ring(dev, virt_to_mfn(info->ring.sring));
	if (err < 0) {
		free_page((unsigned long)sring);
		info->ring.sring = NULL;
		goto fail;
	}
	info->ring_ref = err;

	err = xenbus_alloc_evtchn(dev, &info->evtchn);
	if (err)
		goto fail;

	err = bind_evtchn_to_irqhandler(info->evtchn, blkif_interrupt, 0,
					"blkif", info);
	if (err <= 0) {
		xenbus_dev_fatal(dev, err,
				 "bind_evtchn_to_irqhandler failed");
		goto fail;
	}
	info->irq = err;

	return 0;
fail:
	blkif_free(info, 0);
	return err;
}


/* Common code used when first setting up, and when resuming. */
static int talk_to_blkback(struct xenbus_device *dev,
			   struct blkfront_info *info)
{
	const char *message = NULL;
	struct xenbus_transaction xbt;
	int err;

	/* Create shared ring, alloc event channel. */
	err = setup_blkring(dev, info);
	if (err)
		goto out;

again:
	err = xenbus_transaction_start(&xbt);
	if (err) {
		xenbus_dev_fatal(dev, err, "starting transaction");
		goto destroy_blkring;
	}

	err = xenbus_printf(xbt, dev->nodename,
			    "ring-ref", "%u", info->ring_ref);
	if (err) {
		message = "writing ring-ref";
		goto abort_transaction;
	}
	err = xenbus_printf(xbt, dev->nodename,
			    "event-channel", "%u", info->evtchn);
	if (err) {
		message = "writing event-channel";
		goto abort_transaction;
	}
	err = xenbus_printf(xbt, dev->nodename, "protocol", "%s",
			    XEN_IO_PROTO_ABI_NATIVE);
	if (err) {
		message = "writing protocol";
		goto abort_transaction;
	}
	err = xenbus_printf(xbt, dev->nodename,
			    "feature-persistent", "%u", 1);
	if (err)
		dev_warn(&dev->dev,
			 "writing persistent grants feature to xenbus");

	err = xenbus_transaction_end(xbt, 0);
	if (err) {
		if (err == -EAGAIN)
			goto again;
		xenbus_dev_fatal(dev, err, "completing transaction");
		goto destroy_blkring;
	}

	xenbus_switch_state(dev, XenbusStateInitialised);

	return 0;

 abort_transaction:
	xenbus_transaction_end(xbt, 1);
	if (message)
		xenbus_dev_fatal(dev, err, "%s", message);
 destroy_blkring:
	blkif_free(info, 0);
 out:
	return err;
}

/**
 * Entry point to this code when a new device is created.  Allocate the basic
 * structures and the ring buffer for communication with the backend, and
 * inform the backend of the appropriate details for those.  Switch to
 * Initialised state.
 */
static int blkfront_probe(struct xenbus_device *dev,
			  const struct xenbus_device_id *id)
{
	int err, vdevice, i;
	struct blkfront_info *info;

	/* FIXME: Use dynamic device id if this is not set. */
	err = xenbus_scanf(XBT_NIL, dev->nodename,
			   "virtual-device", "%i", &vdevice);
	if (err != 1) {
		/* go looking in the extended area instead */
		err = xenbus_scanf(XBT_NIL, dev->nodename, "virtual-device-ext",
				   "%i", &vdevice);
		if (err != 1) {
			xenbus_dev_fatal(dev, err, "reading virtual-device");
			return err;
		}
	}

	if (xen_hvm_domain()) {
		char *type;
		int len;
		/* no unplug has been done: do not hook devices != xen vbds */
		if (xen_platform_pci_unplug & XEN_UNPLUG_UNNECESSARY) {
			int major;

			if (!VDEV_IS_EXTENDED(vdevice))
				major = BLKIF_MAJOR(vdevice);
			else
				major = XENVBD_MAJOR;

			if (major != XENVBD_MAJOR) {
				printk(KERN_INFO
						"%s: HVM does not support vbd %d as xen block device\n",
						__FUNCTION__, vdevice);
				return -ENODEV;
			}
		}
		/* do not create a PV cdrom device if we are an HVM guest */
		type = xenbus_read(XBT_NIL, dev->nodename, "device-type", &len);
		if (IS_ERR(type))
			return -ENODEV;
		if (strncmp(type, "cdrom", 5) == 0) {
			kfree(type);
			return -ENODEV;
		}
		kfree(type);
	}
	info = kzalloc(sizeof(*info), GFP_KERNEL);
	if (!info) {
		xenbus_dev_fatal(dev, -ENOMEM, "allocating info structure");
		return -ENOMEM;
	}

	mutex_init(&info->mutex);
	spin_lock_init(&info->io_lock);
	info->xbdev = dev;
	info->vdevice = vdevice;
	INIT_LIST_HEAD(&info->grants);
	INIT_LIST_HEAD(&info->indirect_pages);
	info->persistent_gnts_c = 0;
	info->connected = BLKIF_STATE_DISCONNECTED;
	INIT_WORK(&info->work, blkif_restart_queue);

	for (i = 0; i < BLK_RING_SIZE; i++)
		info->shadow[i].req.u.rw.id = i+1;
	info->shadow[BLK_RING_SIZE-1].req.u.rw.id = 0x0fffffff;

	/* Front end dir is a number, which is used as the id. */
	info->handle = simple_strtoul(strrchr(dev->nodename, '/')+1, NULL, 0);
	dev_set_drvdata(&dev->dev, info);

	err = talk_to_blkback(dev, info);
	if (err) {
		kfree(info);
		dev_set_drvdata(&dev->dev, NULL);
		return err;
	}

	return 0;
}

static void split_bio_end(struct bio *bio, int error)
{
	struct split_bio *split_bio = bio->bi_private;

	if (error)
		split_bio->err = error;

	if (atomic_dec_and_test(&split_bio->pending)) {
		split_bio->bio->bi_phys_segments = 0;
		bio_endio(split_bio->bio, split_bio->err);
		kfree(split_bio);
	}
	bio_put(bio);
}

static int blkif_recover(struct blkfront_info *info)
{
	int i;
	struct request *req, *n;
	struct blk_shadow *copy;
	int rc;
	struct bio *bio, *cloned_bio;
	struct bio_list bio_list, merge_bio;
	unsigned int segs, offset;
	int pending, size;
	struct split_bio *split_bio;
	struct list_head requests;

	/* Stage 1: Make a safe copy of the shadow state. */
	copy = kmemdup(info->shadow, sizeof(info->shadow),
		       GFP_NOIO | __GFP_REPEAT | __GFP_HIGH);
	if (!copy)
		return -ENOMEM;

	/* Stage 2: Set up free list. */
	memset(&info->shadow, 0, sizeof(info->shadow));
	for (i = 0; i < BLK_RING_SIZE; i++)
		info->shadow[i].req.u.rw.id = i+1;
	info->shadow_free = info->ring.req_prod_pvt;
	info->shadow[BLK_RING_SIZE-1].req.u.rw.id = 0x0fffffff;

	rc = blkfront_setup_indirect(info);
	if (rc) {
		kfree(copy);
		return rc;
	}

	segs = info->max_indirect_segments ? : BLKIF_MAX_SEGMENTS_PER_REQUEST;
	blk_queue_max_segments(info->rq, segs);
	bio_list_init(&bio_list);
	INIT_LIST_HEAD(&requests);
	for (i = 0; i < BLK_RING_SIZE; i++) {
		/* Not in use? */
		if (!copy[i].request)
			continue;

		/*
		 * Get the bios in the request so we can re-queue them.
		 */
		if (copy[i].request->cmd_flags &
		    (REQ_FLUSH | REQ_FUA | REQ_DISCARD | REQ_SECURE)) {
			/*
			 * Flush operations don't contain bios, so
			 * we need to requeue the whole request
			 */
			list_add(&copy[i].request->queuelist, &requests);
			continue;
		}
		merge_bio.head = copy[i].request->bio;
		merge_bio.tail = copy[i].request->biotail;
		bio_list_merge(&bio_list, &merge_bio);
		copy[i].request->bio = NULL;
		blk_put_request(copy[i].request);
	}

	kfree(copy);

	/*
	 * Empty the queue, this is important because we might have
	 * requests in the queue with more segments than what we
	 * can handle now.
	 */
	spin_lock_irq(&info->io_lock);
	while ((req = blk_fetch_request(info->rq)) != NULL) {
		if (req->cmd_flags &
		    (REQ_FLUSH | REQ_FUA | REQ_DISCARD | REQ_SECURE)) {
			list_add(&req->queuelist, &requests);
			continue;
		}
		merge_bio.head = req->bio;
		merge_bio.tail = req->biotail;
		bio_list_merge(&bio_list, &merge_bio);
		req->bio = NULL;
		if (req->cmd_flags & (REQ_FLUSH | REQ_FUA))
			pr_alert("diskcache flush request found!\n");
		__blk_put_request(info->rq, req);
	}
	spin_unlock_irq(&info->io_lock);

	xenbus_switch_state(info->xbdev, XenbusStateConnected);

	spin_lock_irq(&info->io_lock);

	/* Now safe for us to use the shared ring */
	info->connected = BLKIF_STATE_CONNECTED;

	/* Kick any other new requests queued since we resumed */
	kick_pending_request_queues(info);

	list_for_each_entry_safe(req, n, &requests, queuelist) {
		/* Requeue pending requests (flush or discard) */
		list_del_init(&req->queuelist);
		BUG_ON(req->nr_phys_segments > segs);
		blk_requeue_request(info->rq, req);
	}
	spin_unlock_irq(&info->io_lock);

	while ((bio = bio_list_pop(&bio_list)) != NULL) {
		/* Traverse the list of pending bios and re-queue them */
		if (bio_segments(bio) > segs) {
			/*
			 * This bio has more segments than what we can
			 * handle, we have to split it.
			 */
			pending = (bio_segments(bio) + segs - 1) / segs;
			split_bio = kzalloc(sizeof(*split_bio), GFP_NOIO);
			BUG_ON(split_bio == NULL);
			atomic_set(&split_bio->pending, pending);
			split_bio->bio = bio;
			for (i = 0; i < pending; i++) {
				offset = (i * segs * PAGE_SIZE) >> 9;
				size = min((unsigned int)(segs * PAGE_SIZE) >> 9,
					   (unsigned int)(bio->bi_size >> 9) - offset);
				cloned_bio = bio_clone(bio, GFP_NOIO);
				BUG_ON(cloned_bio == NULL);
				bio_trim(cloned_bio, offset, size);
				cloned_bio->bi_private = split_bio;
				cloned_bio->bi_end_io = split_bio_end;
				submit_bio(cloned_bio->bi_rw, cloned_bio);
			}
			/*
			 * Now we have to wait for all those smaller bios to
			 * end, so we can also end the "parent" bio.
			 */
			continue;
		}
		/* We don't need to split this bio */
		submit_bio(bio->bi_rw, bio);
	}

	return 0;
}

/**
 * We are reconnecting to the backend, due to a suspend/resume, or a backend
 * driver restart.  We tear down our blkif structure and recreate it, but
 * leave the device-layer structures intact so that this is transparent to the
 * rest of the kernel.
 */
static int blkfront_resume(struct xenbus_device *dev)
{
	struct blkfront_info *info = dev_get_drvdata(&dev->dev);
	int err;

	dev_dbg(&dev->dev, "blkfront_resume: %s\n", dev->nodename);

	blkif_free(info, info->connected == BLKIF_STATE_CONNECTED);

	err = talk_to_blkback(dev, info);

	/*
	 * We have to wait for the backend to switch to
	 * connected state, since we want to read which
	 * features it supports.
	 */

	return err;
}

static void
blkfront_closing(struct blkfront_info *info)
{
	struct xenbus_device *xbdev = info->xbdev;
	struct block_device *bdev = NULL;

	mutex_lock(&info->mutex);

	if (xbdev->state == XenbusStateClosing) {
		mutex_unlock(&info->mutex);
		return;
	}

	if (info->gd)
		bdev = bdget_disk(info->gd, 0);

	mutex_unlock(&info->mutex);

	if (!bdev) {
		xenbus_frontend_closed(xbdev);
		return;
	}

	mutex_lock(&bdev->bd_mutex);

	if (bdev->bd_openers) {
		xenbus_dev_error(xbdev, -EBUSY,
				 "Device in use; refusing to close");
		xenbus_switch_state(xbdev, XenbusStateClosing);
	} else {
		xlvbd_release_gendisk(info);
		xenbus_frontend_closed(xbdev);
	}

	mutex_unlock(&bdev->bd_mutex);
	bdput(bdev);
}

static void blkfront_setup_discard(struct blkfront_info *info)
{
	int err;
	char *type;
	unsigned int discard_granularity;
	unsigned int discard_alignment;
	unsigned int discard_secure;

	type = xenbus_read(XBT_NIL, info->xbdev->otherend, "type", NULL);
	if (IS_ERR(type))
		return;

	info->feature_secdiscard = 0;
	if (strncmp(type, "phy", 3) == 0) {
		err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
			"discard-granularity", "%u", &discard_granularity,
			"discard-alignment", "%u", &discard_alignment,
			NULL);
		if (!err) {
			info->feature_discard = 1;
			info->discard_granularity = discard_granularity;
			info->discard_alignment = discard_alignment;
		}
		err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
			    "discard-secure", "%d", &discard_secure,
			    NULL);
		if (!err)
			info->feature_secdiscard = discard_secure;

	} else if (strncmp(type, "file", 4) == 0)
		info->feature_discard = 1;

	kfree(type);
}

static int blkfront_setup_indirect(struct blkfront_info *info)
{
	unsigned int indirect_segments, segs;
	int err, i;

	err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
			    "feature-max-indirect-segments", "%u", &indirect_segments,
			    NULL);
	if (err) {
		info->max_indirect_segments = 0;
		segs = BLKIF_MAX_SEGMENTS_PER_REQUEST;
	} else {
		info->max_indirect_segments = min(indirect_segments,
						  xen_blkif_max_segments);
		segs = info->max_indirect_segments;
	}

	err = fill_grant_buffer(info, (segs + INDIRECT_GREFS(segs)) * BLK_RING_SIZE);
	if (err)
		goto out_of_memory;

	if (!info->feature_persistent && info->max_indirect_segments) {
		/*
		 * We are using indirect descriptors but not persistent
		 * grants, we need to allocate a set of pages that can be
		 * used for mapping indirect grefs
		 */
		int num = INDIRECT_GREFS(segs) * BLK_RING_SIZE;

		BUG_ON(!list_empty(&info->indirect_pages));
		for (i = 0; i < num; i++) {
			struct page *indirect_page = alloc_page(GFP_NOIO);
			if (!indirect_page)
				goto out_of_memory;
			list_add(&indirect_page->lru, &info->indirect_pages);
		}
	}

	for (i = 0; i < BLK_RING_SIZE; i++) {
		info->shadow[i].grants_used = kzalloc(
			sizeof(info->shadow[i].grants_used[0]) * segs,
			GFP_NOIO);
		info->shadow[i].sg = kzalloc(sizeof(info->shadow[i].sg[0]) * segs, GFP_NOIO);
		if (info->max_indirect_segments)
			info->shadow[i].indirect_grants = kzalloc(
				sizeof(info->shadow[i].indirect_grants[0]) *
				INDIRECT_GREFS(segs),
				GFP_NOIO);
		if ((info->shadow[i].grants_used == NULL) ||
			(info->shadow[i].sg == NULL) ||
		     (info->max_indirect_segments &&
		     (info->shadow[i].indirect_grants == NULL)))
			goto out_of_memory;
		sg_init_table(info->shadow[i].sg, segs);
	}


	return 0;

out_of_memory:
	for (i = 0; i < BLK_RING_SIZE; i++) {
		kfree(info->shadow[i].grants_used);
		info->shadow[i].grants_used = NULL;
		kfree(info->shadow[i].sg);
		info->shadow[i].sg = NULL;
		kfree(info->shadow[i].indirect_grants);
		info->shadow[i].indirect_grants = NULL;
	}
	if (!list_empty(&info->indirect_pages)) {
		struct page *indirect_page, *n;
		list_for_each_entry_safe(indirect_page, n, &info->indirect_pages, lru) {
			list_del(&indirect_page->lru);
			__free_page(indirect_page);
		}
	}
	return -ENOMEM;
}

/*
 * Invoked when the backend is finally 'ready' (and has told produced
 * the details about the physical device - #sectors, size, etc).
 */
static void blkfront_connect(struct blkfront_info *info)
{
	unsigned long long sectors;
	unsigned long sector_size;
	unsigned int physical_sector_size;
	unsigned int binfo;
	int err;
	int barrier, flush, discard, persistent;

	switch (info->connected) {
	case BLKIF_STATE_CONNECTED:
		/*
		 * Potentially, the back-end may be signalling
		 * a capacity change; update the capacity.
		 */
		err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
				   "sectors", "%Lu", &sectors);
		if (XENBUS_EXIST_ERR(err))
			return;
		printk(KERN_INFO "Setting capacity to %Lu\n",
		       sectors);
		set_capacity(info->gd, sectors);
		revalidate_disk(info->gd);

		return;
	case BLKIF_STATE_SUSPENDED:
		/*
		 * If we are recovering from suspension, we need to wait
		 * for the backend to announce it's features before
		 * reconnecting, at least we need to know if the backend
		 * supports indirect descriptors, and how many.
		 */
		blkif_recover(info);
		return;

	default:
		break;
	}

	dev_dbg(&info->xbdev->dev, "%s:%s.\n",
		__func__, info->xbdev->otherend);

	err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
			    "sectors", "%llu", &sectors,
			    "info", "%u", &binfo,
			    "sector-size", "%lu", &sector_size,
			    NULL);
	if (err) {
		xenbus_dev_fatal(info->xbdev, err,
				 "reading backend fields at %s",
				 info->xbdev->otherend);
		return;
	}

	/*
	 * physcial-sector-size is a newer field, so old backends may not
	 * provide this. Assume physical sector size to be the same as
	 * sector_size in that case.
	 */
	err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
			   "physical-sector-size", "%u", &physical_sector_size);
	if (err != 1)
		physical_sector_size = sector_size;

	info->feature_flush = 0;
	info->flush_op = 0;

	err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
			    "feature-barrier", "%d", &barrier,
			    NULL);

	/*
	 * If there's no "feature-barrier" defined, then it means
	 * we're dealing with a very old backend which writes
	 * synchronously; nothing to do.
	 *
	 * If there are barriers, then we use flush.
	 */
	if (!err && barrier) {
		info->feature_flush = REQ_FLUSH | REQ_FUA;
		info->flush_op = BLKIF_OP_WRITE_BARRIER;
	}
	/*
	 * And if there is "feature-flush-cache" use that above
	 * barriers.
	 */
	err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
			    "feature-flush-cache", "%d", &flush,
			    NULL);

	if (!err && flush) {
		info->feature_flush = REQ_FLUSH;
		info->flush_op = BLKIF_OP_FLUSH_DISKCACHE;
	}

	err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
			    "feature-discard", "%d", &discard,
			    NULL);

	if (!err && discard)
		blkfront_setup_discard(info);

	err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
			    "feature-persistent", "%u", &persistent,
			    NULL);
	if (err)
		info->feature_persistent = 0;
	else
		info->feature_persistent = persistent;

	err = blkfront_setup_indirect(info);
	if (err) {
		xenbus_dev_fatal(info->xbdev, err, "setup_indirect at %s",
				 info->xbdev->otherend);
		return;
	}

	err = xlvbd_alloc_gendisk(sectors, info, binfo, sector_size,
				  physical_sector_size);
	if (err) {
		xenbus_dev_fatal(info->xbdev, err, "xlvbd_add at %s",
				 info->xbdev->otherend);
		return;
	}

	xenbus_switch_state(info->xbdev, XenbusStateConnected);

	/* Kick pending requests. */
	spin_lock_irq(&info->io_lock);
	info->connected = BLKIF_STATE_CONNECTED;
	kick_pending_request_queues(info);
	spin_unlock_irq(&info->io_lock);

	add_disk(info->gd);

	info->is_ready = 1;
}

/**
 * Callback received when the backend's state changes.
 */
static void blkback_changed(struct xenbus_device *dev,
			    enum xenbus_state backend_state)
{
	struct blkfront_info *info = dev_get_drvdata(&dev->dev);

	dev_dbg(&dev->dev, "blkfront:blkback_changed to state %d.\n", backend_state);

	switch (backend_state) {
	case XenbusStateInitialising:
	case XenbusStateInitWait:
	case XenbusStateInitialised:
	case XenbusStateReconfiguring:
	case XenbusStateReconfigured:
	case XenbusStateUnknown:
	case XenbusStateClosed:
		break;

	case XenbusStateConnected:
		blkfront_connect(info);
		break;

	case XenbusStateClosing:
		blkfront_closing(info);
		break;
	}
}

static int blkfront_remove(struct xenbus_device *xbdev)
{
	struct blkfront_info *info = dev_get_drvdata(&xbdev->dev);
	struct block_device *bdev = NULL;
	struct gendisk *disk;

	dev_dbg(&xbdev->dev, "%s removed", xbdev->nodename);

	blkif_free(info, 0);

	mutex_lock(&info->mutex);

	disk = info->gd;
	if (disk)
		bdev = bdget_disk(disk, 0);

	info->xbdev = NULL;
	mutex_unlock(&info->mutex);

	if (!bdev) {
		kfree(info);
		return 0;
	}

	/*
	 * The xbdev was removed before we reached the Closed
	 * state. See if it's safe to remove the disk. If the bdev
	 * isn't closed yet, we let release take care of it.
	 */

	mutex_lock(&bdev->bd_mutex);
	info = disk->private_data;

	dev_warn(disk_to_dev(disk),
		 "%s was hot-unplugged, %d stale handles\n",
		 xbdev->nodename, bdev->bd_openers);

	if (info && !bdev->bd_openers) {
		xlvbd_release_gendisk(info);
		disk->private_data = NULL;
		kfree(info);
	}

	mutex_unlock(&bdev->bd_mutex);
	bdput(bdev);

	return 0;
}

static int blkfront_is_ready(struct xenbus_device *dev)
{
	struct blkfront_info *info = dev_get_drvdata(&dev->dev);

	return info->is_ready && info->xbdev;
}

static int blkif_open(struct block_device *bdev, fmode_t mode)
{
	struct gendisk *disk = bdev->bd_disk;
	struct blkfront_info *info;
	int err = 0;

	mutex_lock(&blkfront_mutex);

	info = disk->private_data;
	if (!info) {
		/* xbdev gone */
		err = -ERESTARTSYS;
		goto out;
	}

	mutex_lock(&info->mutex);

	if (!info->gd)
		/* xbdev is closed */
		err = -ERESTARTSYS;

	mutex_unlock(&info->mutex);

out:
	mutex_unlock(&blkfront_mutex);
	return err;
}

static void blkif_release(struct gendisk *disk, fmode_t mode)
{
	struct blkfront_info *info = disk->private_data;
	struct block_device *bdev;
	struct xenbus_device *xbdev;

	mutex_lock(&blkfront_mutex);

	bdev = bdget_disk(disk, 0);

	if (!bdev) {
		WARN(1, "Block device %s yanked out from us!\n", disk->disk_name);
		goto out_mutex;
	}
	if (bdev->bd_openers)
		goto out;

	/*
	 * Check if we have been instructed to close. We will have
	 * deferred this request, because the bdev was still open.
	 */

	mutex_lock(&info->mutex);
	xbdev = info->xbdev;

	if (xbdev && xbdev->state == XenbusStateClosing) {
		/* pending switch to state closed */
		dev_info(disk_to_dev(bdev->bd_disk), "releasing disk\n");
		xlvbd_release_gendisk(info);
		xenbus_frontend_closed(info->xbdev);
 	}

	mutex_unlock(&info->mutex);

	if (!xbdev) {
		/* sudden device removal */
		dev_info(disk_to_dev(bdev->bd_disk), "releasing disk\n");
		xlvbd_release_gendisk(info);
		disk->private_data = NULL;
		kfree(info);
	}

out:
	bdput(bdev);
out_mutex:
	mutex_unlock(&blkfront_mutex);
}

static const struct block_device_operations xlvbd_block_fops =
{
	.owner = THIS_MODULE,
	.open = blkif_open,
	.release = blkif_release,
	.getgeo = blkif_getgeo,
	.ioctl = blkif_ioctl,
};


static const struct xenbus_device_id blkfront_ids[] = {
	{ "vbd" },
	{ "" }
};

static DEFINE_XENBUS_DRIVER(blkfront, ,
	.probe = blkfront_probe,
	.remove = blkfront_remove,
	.resume = blkfront_resume,
	.otherend_changed = blkback_changed,
	.is_ready = blkfront_is_ready,
);

static int __init xlblk_init(void)
{
	int ret;

	if (!xen_domain())
		return -ENODEV;

	if (xen_hvm_domain() && !xen_platform_pci_unplug)
		return -ENODEV;

	if (register_blkdev(XENVBD_MAJOR, DEV_NAME)) {
		printk(KERN_WARNING "xen_blk: can't get major %d with name %s\n",
		       XENVBD_MAJOR, DEV_NAME);
		return -ENODEV;
	}

	ret = xenbus_register_frontend(&blkfront_driver);
	if (ret) {
		unregister_blkdev(XENVBD_MAJOR, DEV_NAME);
		return ret;
	}

	return 0;
}
module_init(xlblk_init);


static void __exit xlblk_exit(void)
{
	xenbus_unregister_driver(&blkfront_driver);
	unregister_blkdev(XENVBD_MAJOR, DEV_NAME);
	kfree(minors);
}
module_exit(xlblk_exit);

MODULE_DESCRIPTION("Xen virtual block device frontend");
MODULE_LICENSE("GPL");
MODULE_ALIAS_BLOCKDEV_MAJOR(XENVBD_MAJOR);
MODULE_ALIAS("xen:vbd");
MODULE_ALIAS("xenblk");