summaryrefslogtreecommitdiff
path: root/OvmfPkg/VirtioBlkDxe/VirtioBlk.c
blob: 9969aab66fe425adee41aab5fb201adcf81bf354 (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
/** @file

  This driver produces Block I/O Protocol instances for virtio-blk devices.

  The implementation is basic:

  - No attach/detach (ie. removable media).

  - Although the non-blocking interfaces of EFI_BLOCK_IO2_PROTOCOL could be a
    good match for multiple in-flight virtio-blk requests, we stick to
    synchronous requests and EFI_BLOCK_IO_PROTOCOL for now.

  Copyright (C) 2012, Red Hat, Inc.

  This program and the accompanying materials are licensed and made available
  under the terms and conditions of the BSD License which accompanies this
  distribution. The full text of the license may be found at
  http://opensource.org/licenses/bsd-license.php

  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, WITHOUT
  WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.

**/

#include <IndustryStandard/Pci.h>
#include <Library/BaseMemoryLib.h>
#include <Library/DebugLib.h>
#include <Library/MemoryAllocationLib.h>
#include <Library/UefiBootServicesTableLib.h>
#include <Library/UefiLib.h>

#include "VirtioBlk.h"

/**

  Write a word into Region 0 of the device specified by PciIo.

  Region 0 must be an iomem region. This is an internal function for the
  VIRTIO_CFG_WRITE() macro below.

  @param[in] PciIo        Target PCI device.

  @param[in] FieldOffset  Destination offset.

  @param[in] FieldSize    Destination field size, must be in { 1, 2, 4, 8 }.

  @param[in] Value        Little endian value to write, converted to UINT64.
                          The least significant FieldSize bytes will be used.


  @return  Status code returned by PciIo->Io.Write().

**/
STATIC
EFIAPI
EFI_STATUS
VirtioWrite (
  IN EFI_PCI_IO_PROTOCOL *PciIo,
  IN UINTN               FieldOffset,
  IN UINTN               FieldSize,
  IN UINT64              Value
  )
{
  UINTN                     Count;
  EFI_PCI_IO_PROTOCOL_WIDTH Width;

  Count = 1;
  switch (FieldSize) {
    case 1:
      Width = EfiPciIoWidthUint8;
      break;

    case 2:
      Width = EfiPciIoWidthUint16;
      break;

    case 8:
      Count = 2;
      // fall through

    case 4:
      Width = EfiPciIoWidthUint32;
      break;

    default:
      ASSERT (FALSE);
  }

  return PciIo->Io.Write (
                     PciIo,
                     Width,
                     PCI_BAR_IDX0,
                     FieldOffset,
                     Count,
                     &Value
                     );
}


/**

  Read a word from Region 0 of the device specified by PciIo.

  Region 0 must be an iomem region. This is an internal function for the
  VIRTIO_CFG_READ() macro below.

  @param[in] PciIo        Source PCI device.

  @param[in] FieldOffset  Source offset.

  @param[in] FieldSize    Source field size, must be in { 1, 2, 4, 8 }.

  @param[in] BufferSize   Number of bytes available in the target buffer. Must
                          equal FieldSize.

  @param[out] Buffer      Target buffer.


  @return  Status code returned by PciIo->Io.Read().

**/
STATIC
EFIAPI
EFI_STATUS
VirtioRead (
  IN  EFI_PCI_IO_PROTOCOL *PciIo,
  IN  UINTN               FieldOffset,
  IN  UINTN               FieldSize,
  IN  UINTN               BufferSize,
  OUT VOID                *Buffer
  )
{
  UINTN                     Count;
  EFI_PCI_IO_PROTOCOL_WIDTH Width;

  ASSERT (FieldSize == BufferSize);

  Count = 1;
  switch (FieldSize) {
    case 1:
      Width = EfiPciIoWidthUint8;
      break;

    case 2:
      Width = EfiPciIoWidthUint16;
      break;

    case 8:
      Count = 2;
      // fall through

    case 4:
      Width = EfiPciIoWidthUint32;
      break;

    default:
      ASSERT (FALSE);
  }

  return PciIo->Io.Read (
                     PciIo,
                     Width,
                     PCI_BAR_IDX0,
                     FieldOffset,
                     Count,
                     Buffer
                     );
}


/**

  Convenience macros to read and write region 0 IO space elements of the
  virtio-blk PCI device, for configuration purposes.

  The following macros make it possible to specify only the "core parameters"
  for such accesses and to derive the rest. By the time VIRTIO_CFG_WRITE()
  returns, the transaction will have been completed.

  @param[in] Dev       Pointer to the VBLK_DEV structure whose PCI IO space
                       we're accessing. Dev->PciIo must be valid.

  @param[in] Field     A field name from VBLK_HDR, identifying the virtio-blk
                       configuration item to access.

  @param[in] Value     (VIRTIO_CFG_WRITE() only.) The value to write to the
                       selected configuration item.

  @param[out] Pointer  (VIRTIO_CFG_READ() only.) The object to receive the
                       value read from the configuration item. Its type must be
                       one of UINT8, UINT16, UINT32, UINT64.


  @return  Status code returned by VirtioWrite() / VirtioRead().

**/

#define VIRTIO_CFG_WRITE(Dev, Field, Value)  (VirtioWrite (             \
                                                (Dev)->PciIo,           \
                                                OFFSET_OF_VHDR (Field), \
                                                SIZE_OF_VHDR (Field),   \
                                                (Value)                 \
                                                ))

#define VIRTIO_CFG_READ(Dev, Field, Pointer) (VirtioRead (              \
                                                (Dev)->PciIo,           \
                                                OFFSET_OF_VHDR (Field), \
                                                SIZE_OF_VHDR (Field),   \
                                                sizeof *(Pointer),      \
                                                (Pointer)               \
                                                ))


//
// UEFI Spec 2.3.1 + Errata C, 12.8 EFI Block I/O Protocol
// Driver Writer's Guide for UEFI 2.3.1 v1.01,
//   24.2 Block I/O Protocol Implementations
//
EFI_STATUS
EFIAPI
VirtioBlkReset (
  IN EFI_BLOCK_IO_PROTOCOL *This,
  IN BOOLEAN               ExtendedVerification
  )
{
  //
  // If we managed to initialize and install the driver, then the device is
  // working correctly.
  //
  return EFI_SUCCESS;
}

/**

  Verify correctness of the read/write (not flush) request submitted to the
  EFI_BLOCK_IO_PROTOCOL instance.

  This function provides most verification steps described in:

    UEFI Spec 2.3.1 + Errata C, 12.8 EFI Block I/O Protocol, 12.8 EFI Block I/O
    Protocol,
    - EFI_BLOCK_IO_PROTOCOL.ReadBlocks()
    - EFI_BLOCK_IO_PROTOCOL.WriteBlocks()

    Driver Writer's Guide for UEFI 2.3.1 v1.01,
    - 24.2.2. ReadBlocks() and ReadBlocksEx() Implementation
    - 24.2.3 WriteBlocks() and WriteBlockEx() Implementation

  Request sizes are limited to 1 GB (checked). This is not a practical
  limitation, just conformance to virtio-0.9.5, 2.3.2 Descriptor Table: "no
  descriptor chain may be more than 2^32 bytes long in total".

  Some Media characteristics are hardcoded in VirtioBlkInit() below (like
  non-removable media, no restriction on buffer alignment etc); we rely on
  those here without explicit mention.

  @param[in] Media               The EFI_BLOCK_IO_MEDIA characteristics for
                                 this driver instance, extracted from the
                                 underlying virtio-blk device at initialization
                                 time. We validate the request against this set
                                 of attributes.


  @param[in] Lba                 Logical Block Address: number of logical
                                 blocks to skip from the beginning of the
                                 device.

  @param[in] PositiveBufferSize  Size of buffer to transfer, in bytes. The
                                 caller is responsible to ensure this parameter
                                 is positive.

  @param[in] RequestIsWrite      TRUE iff data transfer goes from guest to
                                 device.


  @@return                       Validation result to be forwarded outwards by
                                 ReadBlocks() and WriteBlocks, as required by
                                 the specs above.

**/
STATIC
EFI_STATUS
EFIAPI
VerifyReadWriteRequest (
  IN  EFI_BLOCK_IO_MEDIA *Media,
  IN  EFI_LBA            Lba,
  IN  UINTN              PositiveBufferSize,
  IN  BOOLEAN            RequestIsWrite
  )
{
  UINTN BlockCount;

  ASSERT (PositiveBufferSize > 0);

  if (PositiveBufferSize > SIZE_1GB ||
      PositiveBufferSize % Media->BlockSize > 0) {
    return EFI_BAD_BUFFER_SIZE;
  }
  BlockCount = PositiveBufferSize / Media->BlockSize;

  //
  // Avoid unsigned wraparound on either side in the second comparison.
  //
  if (Lba > Media->LastBlock || BlockCount - 1 > Media->LastBlock - Lba) {
    return EFI_INVALID_PARAMETER;
  }

  if (RequestIsWrite && Media->ReadOnly) {
    return EFI_WRITE_PROTECTED;
  }

  return EFI_SUCCESS;
}


/**

  Append a contiguous buffer for transmission / reception via the virtio ring.

  This function implements the following sections from virtio-0.9.5:
  - 2.4.1.1 Placing Buffers into the Descriptor Table
  - 2.4.1.2 Updating the Available Ring

  Free space is taken as granted, since this driver supports only synchronous
  requests and host side status is processed in lock-step with request
  submission. VirtioBlkInit() verifies the ring size in advance.

  @param[in out] Ring           The virtio ring to append the buffer to, as a
                                descriptor.

  @param [in] BufferPhysAddr    (Guest pseudo-physical) start address of the
                                transmit / receive buffer

  @param [in] BufferSize        Number of bytes to transmit or receive.

  @param [in] Flags             A bitmask of VRING_DESC_F_* flags. The caller
                                computes this mask dependent on further buffers
                                to append and transfer direction.
                                VRING_DESC_F_INDIRECT is unsupported. The
                                VRING_DESC.Next field is always set, but the
                                host only interprets it dependent on
                                VRING_DESC_F_NEXT.

  @param [in] HeadIdx           The index identifying the head buffer (first
                                buffer appended) belonging to this same
                                request.

  @param [in out] NextAvailIdx  On input, the index identifying the next
                                descriptor available to carry the buffer. On
                                output, incremented by one, modulo 2^16.

**/

STATIC
VOID
EFIAPI
AppendDesc (
  IN OUT          VRING  *Ring,
  IN              UINTN  BufferPhysAddr,
  IN              UINT32 BufferSize,
  IN              UINT16 Flags,
  IN              UINT16 HeadIdx,
  IN OUT          UINT16 *NextAvailIdx
  )
{
  volatile VRING_DESC *Desc;

  Desc        = &Ring->Desc[*NextAvailIdx % Ring->QueueSize];
  Desc->Addr  = BufferPhysAddr;
  Desc->Len   = BufferSize;
  Desc->Flags = Flags;
  Ring->Avail.Ring[(*NextAvailIdx)++ % Ring->QueueSize] =
    HeadIdx % Ring->QueueSize;
  Desc->Next  = *NextAvailIdx % Ring->QueueSize;
}


/**

  Format a read / write / flush request as three consecutive virtio
  descriptors, push them to the host, and poll for the response.

  This is the main workhorse function. Two use cases are supported, read/write
  and flush. The function may only be called after the request parameters have
  been verified by
  - specific checks in ReadBlocks() / WriteBlocks() / FlushBlocks(), and
  - VerifyReadWriteRequest() (for read/write only).

  Parameters handled commonly:

    @param[in] Dev             The virtio-blk device the request is targeted
                               at.

  Flush request:

    @param[in] Lba             Must be zero.

    @param[in] BufferSize      Must be zero.

    @param[in out] Buffer      Ignored by the function.

    @param[in] RequestIsWrite  Must be TRUE.

  Read/Write request:

    @param[in] Lba             Logical Block Address: number of logical blocks
                               to skip from the beginning of the device.

    @param[in] BufferSize      Size of buffer to transfer, in bytes. The caller
                               is responsible to ensure this parameter is
                               positive.

    @param[in out] Buffer      The guest side area to read data from the device
                               into, or write data to the device from.

    @param[in] RequestIsWrite  TRUE iff data transfer goes from guest to
                               device.

  Return values are common to both use cases, and are appropriate to be
  forwarded by the EFI_BLOCK_IO_PROTOCOL functions (ReadBlocks(),
  WriteBlocks(), FlushBlocks()).


  @retval EFI_SUCCESS          Transfer complete.

  @retval EFI_DEVICE_ERROR     Failed to notify host side via PCI write, or
                               unable to parse host response, or host response
                               is not VIRTIO_BLK_S_OK.

**/

STATIC
EFI_STATUS
EFIAPI
SynchronousRequest (
  IN              VBLK_DEV *Dev,
  IN              EFI_LBA  Lba,
  IN              UINTN    BufferSize,
  IN OUT volatile VOID     *Buffer,
  IN              BOOLEAN  RequestIsWrite
  )
{
  UINT32                  BlockSize;
  volatile VIRTIO_BLK_REQ Request;
  volatile UINT8          HostStatus;
  UINT16                  FirstAvailIdx;
  UINT16                  NextAvailIdx;
  UINTN                   PollPeriodUsecs;

  BlockSize = Dev->BlockIoMedia.BlockSize;

  //
  // ensured by VirtioBlkInit()
  //
  ASSERT (BlockSize > 0);
  ASSERT (BlockSize % 512 == 0);

  //
  // ensured by contract above, plus VerifyReadWriteRequest()
  //
  ASSERT (BufferSize % BlockSize == 0);

  //
  // Prepare virtio-blk request header, setting zero size for flush.
  // IO Priority is homogeneously 0.
  //
  Request.Type   = RequestIsWrite ?
                   (BufferSize == 0 ? VIRTIO_BLK_T_FLUSH : VIRTIO_BLK_T_OUT) :
                   VIRTIO_BLK_T_IN;
  Request.IoPrio = 0;
  Request.Sector = Lba * (BlockSize / 512);

  //
  // Prepare for virtio-0.9.5, 2.4.2 Receiving Used Buffers From the Device.
  // We're going to poll the answer, the host should not send an interrupt.
  //
  *Dev->Ring.Avail.Flags = (UINT16) VRING_AVAIL_F_NO_INTERRUPT;

  //
  // preset a host status for ourselves that we do not accept as success
  //
  HostStatus = VIRTIO_BLK_S_IOERR;

  //
  // ensured by VirtioBlkInit() -- this predicate, in combination with the
  // lock-step progress, ensures we don't have to track free descriptors.
  //
  ASSERT (Dev->Ring.QueueSize >= 3);

  //
  // Implement virtio-0.9.5, 2.4.1 Supplying Buffers to the Device.
  //
  FirstAvailIdx = *Dev->Ring.Avail.Idx;
  NextAvailIdx  = FirstAvailIdx;

  //
  // virtio-blk header in first desc
  //
  AppendDesc (&Dev->Ring, (UINTN) &Request, sizeof Request, VRING_DESC_F_NEXT,
    FirstAvailIdx, &NextAvailIdx);

  //
  // data buffer for read/write in second desc
  //
  if (BufferSize > 0) {
    //
    // From virtio-0.9.5, 2.3.2 Descriptor Table:
    // "no descriptor chain may be more than 2^32 bytes long in total".
    //
    // The predicate is ensured by the call contract above (for flush), or
    // VerifyReadWriteRequest() (for read/write). It also implies that
    // converting BufferSize to UINT32 will not truncate it.
    //
    ASSERT (BufferSize <= SIZE_1GB);

    //
    // VRING_DESC_F_WRITE is interpreted from the host's point of view.
    //
    AppendDesc (&Dev->Ring, (UINTN) Buffer, (UINT32) BufferSize,
      VRING_DESC_F_NEXT | (RequestIsWrite ? 0 : VRING_DESC_F_WRITE),
      FirstAvailIdx, &NextAvailIdx);
  }

  //
  // host status in last (second or third) desc
  //
  AppendDesc (&Dev->Ring, (UINTN) &HostStatus, sizeof HostStatus,
    VRING_DESC_F_WRITE, FirstAvailIdx, &NextAvailIdx);

  //
  // virtio-0.9.5, 2.4.1.3 Updating the Index Field
  //
  MemoryFence();
  *Dev->Ring.Avail.Idx = NextAvailIdx;

  //
  // virtio-0.9.5, 2.4.1.4 Notifying the Device -- gratuitous notifications are
  // OK. virtio-blk's only virtqueue is #0, called "requestq" (see Appendix D).
  //
  MemoryFence();
  if (EFI_ERROR (VIRTIO_CFG_WRITE (Dev, VhdrQueueNotify, 0))) {
    return EFI_DEVICE_ERROR;
  }

  //
  // virtio-0.9.5, 2.4.2 Receiving Used Buffers From the Device
  // Wait until the host processes and acknowledges our 3-part descriptor
  // chain. The condition we use for polling is greatly simplified and relies
  // on synchronous, the lock-step progress.
  //
  // Keep slowing down until we reach a poll period of slightly above 1 ms.
  //
  PollPeriodUsecs = 1;
  MemoryFence();
  while (*Dev->Ring.Used.Idx != NextAvailIdx) {
    gBS->Stall (PollPeriodUsecs); // calls AcpiTimerLib::MicroSecondDelay

    if (PollPeriodUsecs < 1024) {
      PollPeriodUsecs *= 2;
    }
    MemoryFence();
  }

  if (HostStatus == VIRTIO_BLK_S_OK) {
    return EFI_SUCCESS;
  }

  return EFI_DEVICE_ERROR;
}


/**

  ReadBlocks() operation for virtio-blk.

  See
  - UEFI Spec 2.3.1 + Errata C, 12.8 EFI Block I/O Protocol, 12.8 EFI Block I/O
    Protocol, EFI_BLOCK_IO_PROTOCOL.ReadBlocks().
  - Driver Writer's Guide for UEFI 2.3.1 v1.01, 24.2.2. ReadBlocks() and
    ReadBlocksEx() Implementation.

  Parameter checks and conformant return values are implemented in
  VerifyReadWriteRequest() and SynchronousRequest().

  A zero BufferSize doesn't seem to be prohibited, so do nothing in that case,
  successfully.

**/

EFI_STATUS
EFIAPI
VirtioBlkReadBlocks (
  IN  EFI_BLOCK_IO_PROTOCOL *This,
  IN  UINT32                MediaId,
  IN  EFI_LBA               Lba,
  IN  UINTN                 BufferSize,
  OUT VOID                  *Buffer
  )
{
  VBLK_DEV   *Dev;
  EFI_STATUS Status;

  if (BufferSize == 0) {
    return EFI_SUCCESS;
  }

  Dev = VIRTIO_BLK_FROM_BLOCK_IO (This);
  Status = VerifyReadWriteRequest (
             &Dev->BlockIoMedia,
             Lba,
             BufferSize,
             FALSE               // RequestIsWrite
             );
  if (EFI_ERROR (Status)) {
    return Status;
  }

  return SynchronousRequest (
           Dev,
           Lba,
           BufferSize,
           Buffer,
           FALSE       // RequestIsWrite
           );
}

/**

  WriteBlocks() operation for virtio-blk.

  See
  - UEFI Spec 2.3.1 + Errata C, 12.8 EFI Block I/O Protocol, 12.8 EFI Block I/O
    Protocol, EFI_BLOCK_IO_PROTOCOL.WriteBlocks().
  - Driver Writer's Guide for UEFI 2.3.1 v1.01, 24.2.3 WriteBlocks() and
    WriteBlockEx() Implementation.

  Parameter checks and conformant return values are implemented in
  VerifyReadWriteRequest() and SynchronousRequest().

  A zero BufferSize doesn't seem to be prohibited, so do nothing in that case,
  successfully.

**/

EFI_STATUS
EFIAPI
VirtioBlkWriteBlocks (
  IN EFI_BLOCK_IO_PROTOCOL *This,
  IN UINT32                MediaId,
  IN EFI_LBA               Lba,
  IN UINTN                 BufferSize,
  IN VOID                  *Buffer
  )
{
  VBLK_DEV   *Dev;
  EFI_STATUS Status;

  if (BufferSize == 0) {
    return EFI_SUCCESS;
  }

  Dev = VIRTIO_BLK_FROM_BLOCK_IO (This);
  Status = VerifyReadWriteRequest (
             &Dev->BlockIoMedia,
             Lba,
             BufferSize,
             TRUE                // RequestIsWrite
             );
  if (EFI_ERROR (Status)) {
    return Status;
  }

  return SynchronousRequest (
           Dev,
           Lba,
           BufferSize,
           Buffer,
           TRUE        // RequestIsWrite
           );
}


/**

  FlushBlocks() operation for virtio-blk.

  See
  - UEFI Spec 2.3.1 + Errata C, 12.8 EFI Block I/O Protocol, 12.8 EFI Block I/O
    Protocol, EFI_BLOCK_IO_PROTOCOL.FlushBlocks().
  - Driver Writer's Guide for UEFI 2.3.1 v1.01, 24.2.4 FlushBlocks() and
    FlushBlocksEx() Implementation.

  If the underlying virtio-blk device doesn't support flushing (ie.
  write-caching), then this function should not be called by higher layers,
  according to EFI_BLOCK_IO_MEDIA characteristics set in VirtioBlkInit().
  Should they do nonetheless, we do nothing, successfully.

**/

EFI_STATUS
EFIAPI
VirtioBlkFlushBlocks (
  IN EFI_BLOCK_IO_PROTOCOL *This
  )
{
  VBLK_DEV *Dev;

  Dev = VIRTIO_BLK_FROM_BLOCK_IO (This);
  return Dev->BlockIoMedia.WriteCaching ?
           SynchronousRequest (
             Dev,
             0,    // Lba
             0,    // BufferSize
             NULL, // Buffer
             TRUE  // RequestIsWrite
             ) :
           EFI_SUCCESS;
}


/**

  Device probe function for this driver.

  The DXE core calls this function for any given device in order to see if the
  driver can drive the device.

  Specs relevant in the general sense:

  - UEFI Spec 2.3.1 + Errata C:
    - 6.3 Protocol Handler Services -- for accessing the underlying device
    - 10.1 EFI Driver Binding Protocol -- for exporting ourselves

  - Driver Writer's Guide for UEFI 2.3.1 v1.01:
    - 5.1.3.4 OpenProtocol() and CloseProtocol() -- for accessing the
      underlying device
    - 9 Driver Binding Protocol -- for exporting ourselves

  Specs relevant in the specific sense:
  - UEFI Spec 2.3.1 + Errata C, 13.4 EFI PCI I/O Protocol
  - Driver Writer's Guide for UEFI 2.3.1 v1.01, 18 PCI Driver Design
    Guidelines, 18.3 PCI drivers.

  @param[in]  This                The EFI_DRIVER_BINDING_PROTOCOL object
                                  incorporating this driver (independently of
                                  any device).

  @param[in] DeviceHandle         The device to probe.

  @param[in] RemainingDevicePath  Relevant only for bus drivers, ignored.


  @retval EFI_SUCCESS      The driver supports the device being probed.

  @retval EFI_UNSUPPORTED  Based on virtio-blk PCI discovery, we do not support
                           the device.

  @return                  Error codes from the OpenProtocol() boot service or
                           the PciIo protocol.

**/

EFI_STATUS
EFIAPI
VirtioBlkDriverBindingSupported (
  IN EFI_DRIVER_BINDING_PROTOCOL *This,
  IN EFI_HANDLE                  DeviceHandle,
  IN EFI_DEVICE_PATH_PROTOCOL    *RemainingDevicePath
  )
{
  EFI_STATUS          Status;
  EFI_PCI_IO_PROTOCOL *PciIo;
  PCI_TYPE00          Pci;

  //
  // Attempt to open the device with the PciIo set of interfaces. On success,
  // the protocol is "instantiated" for the PCI device. Covers duplicate open
  // attempts (EFI_ALREADY_STARTED).
  //
  Status = gBS->OpenProtocol (
                  DeviceHandle,               // candidate device
                  &gEfiPciIoProtocolGuid,     // for generic PCI access
                  (VOID **)&PciIo,            // handle to instantiate
                  This->DriverBindingHandle,  // requestor driver identity
                  DeviceHandle,               // ControllerHandle, according to
                                              // the UEFI Driver Model
                  EFI_OPEN_PROTOCOL_BY_DRIVER // get exclusive PciIo access to
                                              // the device; to be released
                  );
  if (EFI_ERROR (Status)) {
    return Status;
  }

  //
  // Read entire PCI configuration header for more extensive check ahead.
  //
  Status = PciIo->Pci.Read (
                        PciIo,                        // (protocol, device)
                                                      // handle
                        EfiPciIoWidthUint32,          // access width & copy
                                                      // mode
                        0,                            // Offset
                        sizeof Pci / sizeof (UINT32), // Count
                        &Pci                          // target buffer
                        );

  if (Status == EFI_SUCCESS) {
    //
    // virtio-0.9.5, 2.1 PCI Discovery
    //
    Status = (Pci.Hdr.VendorId == 0x1AF4 &&
              Pci.Hdr.DeviceId >= 0x1000 && Pci.Hdr.DeviceId <= 0x103F &&
              Pci.Hdr.RevisionID == 0x00 &&
              Pci.Device.SubsystemID == 0x02) ? EFI_SUCCESS : EFI_UNSUPPORTED;
  }

  //
  // We needed PCI IO access only transitorily, to see whether we support the
  // device or not.
  //
  gBS->CloseProtocol (DeviceHandle, &gEfiPciIoProtocolGuid,
         This->DriverBindingHandle, DeviceHandle);
  return Status;
}


/**

  Configure a virtio ring.

  This function sets up internal storage (the guest-host communication area)
  and lays out several "navigation" (ie. no-ownership) pointers to parts of
  that storage.

  Relevant sections from the virtio-0.9.5 spec:
  - 1.1 Virtqueues,
  - 2.3 Virtqueue Configuration.

  @param[in]                    The number of descriptors to allocate for the
                                virtio ring, as requested by the host.

  @param[out] Ring              The virtio ring to set up.

  @retval EFI_OUT_OF_RESOURCES  AllocatePages() failed to allocate contiguous
                                pages for the requested QueueSize. Fields of
                                Ring have indeterminate value.

  @retval EFI_SUCCESS           Allocation and setup successful. Ring->Base
                                (and nothing else) is responsible for
                                deallocation.

**/

STATIC
EFI_STATUS
EFIAPI
VirtioRingInit (
  IN  UINT16 QueueSize,
  OUT VRING  *Ring
  )
{
  UINTN          RingSize;
  volatile UINT8 *RingPagesPtr;

  RingSize = ALIGN_VALUE (
               sizeof *Ring->Desc            * QueueSize +
               sizeof *Ring->Avail.Flags                 +
               sizeof *Ring->Avail.Idx                   +
               sizeof *Ring->Avail.Ring      * QueueSize +
               sizeof *Ring->Avail.UsedEvent,
               EFI_PAGE_SIZE);

  RingSize += ALIGN_VALUE (
                sizeof *Ring->Used.Flags                  +
                sizeof *Ring->Used.Idx                    +
                sizeof *Ring->Used.UsedElem   * QueueSize +
                sizeof *Ring->Used.AvailEvent,
                EFI_PAGE_SIZE);

  Ring->NumPages = EFI_SIZE_TO_PAGES (RingSize);
  Ring->Base = AllocatePages (Ring->NumPages);
  if (Ring->Base == NULL) {
    return EFI_OUT_OF_RESOURCES;
  }
  SetMem (Ring->Base, RingSize, 0x00);
  RingPagesPtr = Ring->Base;

  Ring->Desc = (volatile VOID *) RingPagesPtr;
  RingPagesPtr += sizeof *Ring->Desc * QueueSize;

  Ring->Avail.Flags = (volatile VOID *) RingPagesPtr;
  RingPagesPtr += sizeof *Ring->Avail.Flags;

  Ring->Avail.Idx = (volatile VOID *) RingPagesPtr;
  RingPagesPtr += sizeof *Ring->Avail.Idx;

  Ring->Avail.Ring = (volatile VOID *) RingPagesPtr;
  RingPagesPtr += sizeof *Ring->Avail.Ring * QueueSize;

  Ring->Avail.UsedEvent = (volatile VOID *) RingPagesPtr;
  RingPagesPtr += sizeof *Ring->Avail.UsedEvent;

  RingPagesPtr = (volatile UINT8 *) Ring->Base +
                 ALIGN_VALUE (RingPagesPtr - (volatile UINT8 *) Ring->Base,
                   EFI_PAGE_SIZE);

  Ring->Used.Flags = (volatile VOID *) RingPagesPtr;
  RingPagesPtr += sizeof *Ring->Used.Flags;

  Ring->Used.Idx = (volatile VOID *) RingPagesPtr;
  RingPagesPtr += sizeof *Ring->Used.Idx;

  Ring->Used.UsedElem = (volatile VOID *) RingPagesPtr;
  RingPagesPtr += sizeof *Ring->Used.UsedElem * QueueSize;

  Ring->Used.AvailEvent = (volatile VOID *) RingPagesPtr;
  RingPagesPtr += sizeof *Ring->Used.AvailEvent;

  Ring->QueueSize = QueueSize;
  return EFI_SUCCESS;
}


/**

  Tear down the internal resources of a configured virtio ring.

  The caller is responsible to stop the host from using this ring before
  invoking this function: the VSTAT_DRIVER_OK bit must be clear in
  VhdrDeviceStatus.

  @param[out] Ring  The virtio ring to clean up.

**/


STATIC
VOID
EFIAPI
VirtioRingUninit (
  IN OUT VRING *Ring
  )
{
  FreePages (Ring->Base, Ring->NumPages);
  SetMem (Ring, sizeof *Ring, 0x00);
}


/**

  Set up all BlockIo and virtio-blk aspects of this driver for the specified
  device.

  @param[in out] Dev  The driver instance to configure. The caller is
                      responsible for Dev->PciIo's validity (ie. working IO
                      access to the underlying virtio-blk PCI device).

  @retval EFI_SUCCESS      Setup complete.

  @retval EFI_UNSUPPORTED  The driver is unable to work with the virtio ring or
                           virtio-blk attributes the host provides.

  @return                  Error codes from VirtioRingInit() or
                           VIRTIO_CFG_READ() / VIRTIO_CFG_WRITE().

**/

STATIC
EFI_STATUS
EFIAPI
VirtioBlkInit (
  IN OUT VBLK_DEV *Dev
  )
{
  UINT8      NextDevStat;
  EFI_STATUS Status;

  UINT32     Features;
  UINT64     NumSectors;
  UINT32     BlockSize;
  UINT16     QueueSize;

  //
  // Execute virtio-0.9.5, 2.2.1 Device Initialization Sequence.
  //
  NextDevStat = 0;             // step 1 -- reset device
  Status = VIRTIO_CFG_WRITE (Dev, VhdrDeviceStatus, NextDevStat);
  if (EFI_ERROR (Status)) {
    goto Failed;
  }

  NextDevStat |= VSTAT_ACK;    // step 2 -- acknowledge device presence
  Status = VIRTIO_CFG_WRITE (Dev, VhdrDeviceStatus, NextDevStat);
  if (EFI_ERROR (Status)) {
    goto Failed;
  }

  NextDevStat |= VSTAT_DRIVER; // step 3 -- we know how to drive it
  Status = VIRTIO_CFG_WRITE (Dev, VhdrDeviceStatus, NextDevStat);
  if (EFI_ERROR (Status)) {
    goto Failed;
  }

  //
  // step 4a -- retrieve and validate features
  //
  Status = VIRTIO_CFG_READ (Dev, VhdrDeviceFeatureBits, &Features);
  if (EFI_ERROR (Status)) {
    goto Failed;
  }
  Status = VIRTIO_CFG_READ (Dev, VhdrCapacity, &NumSectors);
  if (EFI_ERROR (Status)) {
    goto Failed;
  }
  if (NumSectors == 0) {
    Status = EFI_UNSUPPORTED;
    goto Failed;
  }

  if (Features & VIRTIO_BLK_F_BLK_SIZE) {
    Status = VIRTIO_CFG_READ (Dev, VhdrBlkSize, &BlockSize);
    if (EFI_ERROR (Status)) {
      goto Failed;
    }
    if (BlockSize == 0 || BlockSize % 512 != 0 ||
        NumSectors % (BlockSize / 512) != 0) {
      //
      // We can only handle a logical block consisting of whole sectors,
      // and only a disk composed of whole logical blocks.
      //
      Status = EFI_UNSUPPORTED;
      goto Failed;
    }
  }
  else {
    BlockSize = 512;
  }

  //
  // step 4b -- allocate virtqueue
  //
  Status = VIRTIO_CFG_WRITE (Dev, VhdrQueueSelect, 0);
  if (EFI_ERROR (Status)) {
    goto Failed;
  }
  Status = VIRTIO_CFG_READ (Dev, VhdrQueueSize, &QueueSize);
  if (EFI_ERROR (Status)) {
    goto Failed;
  }
  if (QueueSize < 3) { // SynchronousRequest() uses at most three descriptors
    Status = EFI_UNSUPPORTED;
    goto Failed;
  }

  Status = VirtioRingInit (QueueSize, &Dev->Ring);
  if (EFI_ERROR (Status)) {
    goto Failed;
  }

  //
  // step 4c -- Report GPFN (guest-physical frame number) of queue. If anything
  // fails from here on, we must release the ring resources.
  //
  Status = VIRTIO_CFG_WRITE (Dev, VhdrQueueAddress,
             (UINTN) Dev->Ring.Base >> EFI_PAGE_SHIFT);
  if (EFI_ERROR (Status)) {
    goto ReleaseQueue;
  }

  //
  // step 5 -- Report understood features. There are no virtio-blk specific
  // features to negotiate in virtio-0.9.5, plus we do not want any of the
  // device-independent (known or unknown) VIRTIO_F_* capabilities (see
  // Appendix B).
  //
  Status = VIRTIO_CFG_WRITE (Dev, VhdrGuestFeatureBits, 0);
  if (EFI_ERROR (Status)) {
    goto ReleaseQueue;
  }

  //
  // step 6 -- initialization complete
  //
  NextDevStat |= VSTAT_DRIVER_OK;
  Status = VIRTIO_CFG_WRITE (Dev, VhdrDeviceStatus, NextDevStat);
  if (EFI_ERROR (Status)) {
    goto ReleaseQueue;
  }

  //
  // Populate the exported interface's attributes; see UEFI spec v2.3.1 +
  // Errata C, 12.8 EFI Block I/O Protocol. We stick to the lowest possible
  // EFI_BLOCK_IO_PROTOCOL revision for now.
  //
  Dev->BlockIo.Revision              = 0;
  Dev->BlockIo.Media                 = &Dev->BlockIoMedia;
  Dev->BlockIo.Reset                 = &VirtioBlkReset;
  Dev->BlockIo.ReadBlocks            = &VirtioBlkReadBlocks;
  Dev->BlockIo.WriteBlocks           = &VirtioBlkWriteBlocks;
  Dev->BlockIo.FlushBlocks           = &VirtioBlkFlushBlocks;
  Dev->BlockIoMedia.MediaId          = 0;
  Dev->BlockIoMedia.RemovableMedia   = FALSE;
  Dev->BlockIoMedia.MediaPresent     = TRUE;
  Dev->BlockIoMedia.LogicalPartition = FALSE;
  Dev->BlockIoMedia.ReadOnly         = !!(Features & VIRTIO_BLK_F_RO);
  Dev->BlockIoMedia.WriteCaching     = !!(Features & VIRTIO_BLK_F_FLUSH);
  Dev->BlockIoMedia.BlockSize        = BlockSize;
  Dev->BlockIoMedia.IoAlign          = 0;
  Dev->BlockIoMedia.LastBlock        = NumSectors / (BlockSize / 512) - 1;
  return EFI_SUCCESS;

ReleaseQueue:
  VirtioRingUninit (&Dev->Ring);

Failed:
  //
  // Notify the host about our failure to setup: virtio-0.9.5, 2.2.2.1 Device
  // Status. PCI IO access failure here should not mask the original error.
  //
  NextDevStat |= VSTAT_FAILED;
  VIRTIO_CFG_WRITE (Dev, VhdrDeviceStatus, NextDevStat);

  return Status; // reached only via Failed above
}


/**

  Uninitialize the internals of a virtio-blk device that has been successfully
  set up with VirtioBlkInit().

  @param[in out]  Dev  The device to clean up.

**/

STATIC
VOID
EFIAPI
VirtioBlkUninit (
  IN OUT VBLK_DEV *Dev
  )
{
  //
  // Reset the virtual device -- see virtio-0.9.5, 2.2.2.1 Device Status. When
  // VIRTIO_CFG_WRITE() returns, the host will have learned to stay away from
  // the old comms area.
  //
  VIRTIO_CFG_WRITE (Dev, VhdrDeviceStatus, 0);

  VirtioRingUninit (&Dev->Ring);

  SetMem (&Dev->BlockIo,      sizeof Dev->BlockIo,      0x00);
  SetMem (&Dev->BlockIoMedia, sizeof Dev->BlockIoMedia, 0x00);
}


/**

  After we've pronounced support for a specific device in
  DriverBindingSupported(), we start managing said device (passed in by the
  Driver Exeuction Environment) with the following service.

  See DriverBindingSupported() for specification references.

  @param[in]  This                The EFI_DRIVER_BINDING_PROTOCOL object
                                  incorporating this driver (independently of
                                  any device).

  @param[in] DeviceHandle         The supported device to drive.

  @param[in] RemainingDevicePath  Relevant only for bus drivers, ignored.


  @retval EFI_SUCCESS           Driver instance has been created and
                                initialized  for the virtio-blk PCI device, it
                                is now accessibla via EFI_BLOCK_IO_PROTOCOL.

  @retval EFI_OUT_OF_RESOURCES  Memory allocation failed.

  @return                       Error codes from the OpenProtocol() boot
                                service, the PciIo protocol, VirtioBlkInit(),
                                or the InstallProtocolInterface() boot service.

**/

EFI_STATUS
EFIAPI
VirtioBlkDriverBindingStart (
  IN EFI_DRIVER_BINDING_PROTOCOL *This,
  IN EFI_HANDLE                  DeviceHandle,
  IN EFI_DEVICE_PATH_PROTOCOL    *RemainingDevicePath
  )
{
  VBLK_DEV   *Dev;
  EFI_STATUS Status;

  Dev = (VBLK_DEV *) AllocateZeroPool (sizeof *Dev);
  if (Dev == NULL) {
    return EFI_OUT_OF_RESOURCES;
  }

  Status = gBS->OpenProtocol (DeviceHandle, &gEfiPciIoProtocolGuid,
                  (VOID **)&Dev->PciIo, This->DriverBindingHandle,
                  DeviceHandle, EFI_OPEN_PROTOCOL_BY_DRIVER);
  if (EFI_ERROR (Status)) {
    goto FreeVirtioBlk;
  }

  //
  // We must retain and ultimately restore the original PCI attributes of the
  // device. See Driver Writer's Guide for UEFI 2.3.1 v1.01, 18.3 PCI drivers /
  // 18.3.2 Start() and Stop().
  //
  // The third parameter ("Attributes", input) is ignored by the Get operation.
  // The fourth parameter ("Result", output) is ignored by the Enable and Set
  // operations.
  //
  // For virtio-blk we only need IO space access.
  //
  Status = Dev->PciIo->Attributes (Dev->PciIo, EfiPciIoAttributeOperationGet,
                         0, &Dev->OriginalPciAttributes);
  if (EFI_ERROR (Status)) {
    goto ClosePciIo;
  }

  Status = Dev->PciIo->Attributes (Dev->PciIo,
                         EfiPciIoAttributeOperationEnable,
                         EFI_PCI_IO_ATTRIBUTE_IO, NULL);
  if (EFI_ERROR (Status)) {
    goto ClosePciIo;
  }

  //
  // PCI IO access granted, configure virtio-blk device.
  //
  Status = VirtioBlkInit (Dev);
  if (EFI_ERROR (Status)) {
    goto RestorePciAttributes;
  }

  //
  // Setup complete, attempt to export the driver instance's BlockIo interface.
  //
  Dev->Signature = VBLK_SIG;
  Status = gBS->InstallProtocolInterface (&DeviceHandle,
                  &gEfiBlockIoProtocolGuid, EFI_NATIVE_INTERFACE,
                  &Dev->BlockIo);
  if (EFI_ERROR (Status)) {
    goto UninitDev;
  }

  return EFI_SUCCESS;

UninitDev:
  VirtioBlkUninit (Dev);

RestorePciAttributes:
  Dev->PciIo->Attributes (Dev->PciIo, EfiPciIoAttributeOperationSet,
                Dev->OriginalPciAttributes, NULL);

ClosePciIo:
  gBS->CloseProtocol (DeviceHandle, &gEfiPciIoProtocolGuid,
         This->DriverBindingHandle, DeviceHandle);

FreeVirtioBlk:
  FreePool (Dev);

  return Status;
}


/**

  Stop driving a virtio-blk device and remove its BlockIo interface.

  This function replays the success path of DriverBindingStart() in reverse.
  The host side virtio-blk device is reset, so that the OS boot loader or the
  OS may reinitialize it.

  @param[in] This               The EFI_DRIVER_BINDING_PROTOCOL object
                                incorporating this driver (independently of any
                                device).

  @param[in] DeviceHandle       Stop driving this device.

  @param[in] NumberOfChildren   Since this function belongs to a device driver
                                only (as opposed to a bus driver), the caller
                                environment sets NumberOfChildren to zero, and
                                we ignore it.

  @param[in] ChildHandleBuffer  Ignored (corresponding to NumberOfChildren).

**/

EFI_STATUS
EFIAPI
VirtioBlkDriverBindingStop (
  IN EFI_DRIVER_BINDING_PROTOCOL *This,
  IN EFI_HANDLE                  DeviceHandle,
  IN UINTN                       NumberOfChildren,
  IN EFI_HANDLE                  *ChildHandleBuffer
  )
{
  VBLK_DEV   *Dev;
  EFI_STATUS Status;

  Dev = VIRTIO_BLK_FROM_BLOCK_IO (This);

  //
  // If DriverBindingStop() is called with the driver instance still in use,
  // or any of the parameters are invalid, we've caught a bug.
  //
  Status = gBS->UninstallProtocolInterface (DeviceHandle,
                  &gEfiBlockIoProtocolGuid, &Dev->BlockIo);
  ASSERT (Status == EFI_SUCCESS);

  VirtioBlkUninit (Dev);

  Dev->PciIo->Attributes (Dev->PciIo, EfiPciIoAttributeOperationSet,
                Dev->OriginalPciAttributes, NULL);

  gBS->CloseProtocol (DeviceHandle, &gEfiPciIoProtocolGuid,
         This->DriverBindingHandle, DeviceHandle);

  FreePool (Dev);

  return EFI_SUCCESS;
}


//
// The static object that groups the Supported() (ie. probe), Start() and
// Stop() functions of the driver together. Refer to UEFI Spec 2.3.1 + Errata
// C, 10.1 EFI Driver Binding Protocol.
//
STATIC EFI_DRIVER_BINDING_PROTOCOL gDriverBinding = {
  &VirtioBlkDriverBindingSupported,
  &VirtioBlkDriverBindingStart,
  &VirtioBlkDriverBindingStop,
  0x10, // Version, must be in [0x10 .. 0xFFFFFFEF] for IHV-developed drivers
  NULL, // ImageHandle, to be overwritten by
        // EfiLibInstallDriverBindingComponentName2() in VirtioBlkEntryPoint()
  NULL  // DriverBindingHandle, ditto
};


//
// The purpose of the following scaffolding (EFI_COMPONENT_NAME_PROTOCOL and
// EFI_COMPONENT_NAME2_PROTOCOL implementation) is to format the driver's name
// in English, for display on standard console devices. This is recommended for
// UEFI drivers that follow the UEFI Driver Model. Refer to the Driver Writer's
// Guide for UEFI 2.3.1 v1.01, 11 UEFI Driver and Controller Names.
//
// Device type names ("Virtio Block Device") are not formatted because the
// driver supports only that device type. Therefore the driver name suffices
// for unambiguous identification.
//

STATIC GLOBAL_REMOVE_IF_UNREFERENCED
EFI_UNICODE_STRING_TABLE mDriverNameTable[] = {
  { "eng;en", L"Virtio Block Driver" },
  { NULL,     NULL                   }
};

STATIC GLOBAL_REMOVE_IF_UNREFERENCED
EFI_COMPONENT_NAME_PROTOCOL gComponentName;

EFI_STATUS
EFIAPI
VirtioBlkGetDriverName (
  IN  EFI_COMPONENT_NAME_PROTOCOL *This,
  IN  CHAR8                       *Language,
  OUT CHAR16                      **DriverName
  )
{
  return LookupUnicodeString2 (
           Language,
           This->SupportedLanguages,
           mDriverNameTable,
           DriverName,
           (BOOLEAN)(This == &gComponentName) // Iso639Language
           );
}

EFI_STATUS
EFIAPI
VirtioBlkGetDeviceName (
  IN  EFI_COMPONENT_NAME_PROTOCOL *This,
  IN  EFI_HANDLE                  DeviceHandle,
  IN  EFI_HANDLE                  ChildHandle,
  IN  CHAR8                       *Language,
  OUT CHAR16                      **ControllerName
  )
{
  return EFI_UNSUPPORTED;
}

STATIC GLOBAL_REMOVE_IF_UNREFERENCED
EFI_COMPONENT_NAME_PROTOCOL gComponentName = {
  &VirtioBlkGetDriverName,
  &VirtioBlkGetDeviceName,
  "eng" // SupportedLanguages, ISO 639-2 language codes
};

STATIC GLOBAL_REMOVE_IF_UNREFERENCED
EFI_COMPONENT_NAME2_PROTOCOL gComponentName2 = {
  (EFI_COMPONENT_NAME2_GET_DRIVER_NAME)     &VirtioBlkGetDriverName,
  (EFI_COMPONENT_NAME2_GET_CONTROLLER_NAME) &VirtioBlkGetDeviceName,
  "en" // SupportedLanguages, RFC 4646 language codes
};


//
// Entry point of this driver.
//
EFI_STATUS
EFIAPI
VirtioBlkEntryPoint (
  IN EFI_HANDLE       ImageHandle,
  IN EFI_SYSTEM_TABLE *SystemTable
  )
{
  return EfiLibInstallDriverBindingComponentName2 (
           ImageHandle,
           SystemTable,
           &gDriverBinding,
           ImageHandle,
           &gComponentName,
           &gComponentName2
           );
}