forked from torvalds/linux
-
Notifications
You must be signed in to change notification settings - Fork 1
/
scsi_mid_low_api.txt
1279 lines (1137 loc) · 53 KB
/
scsi_mid_low_api.txt
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
Linux Kernel 2.6 series
SCSI mid_level - lower_level driver interface
=============================================
Introduction
============
This document outlines the interface between the Linux SCSI mid level and
SCSI lower level drivers. Lower level drivers (LLDs) are variously called
host bus adapter (HBA) drivers and host drivers (HD). A "host" in this
context is a bridge between a computer IO bus (e.g. PCI or ISA) and a
single SCSI initiator port on a SCSI transport. An "initiator" port
(SCSI terminology, see SAM-3 at http://www.t10.org) sends SCSI commands
to "target" SCSI ports (e.g. disks). There can be many LLDs in a running
system, but only one per hardware type. Most LLDs can control one or more
SCSI HBAs. Some HBAs contain multiple hosts.
In some cases the SCSI transport is an external bus that already has
its own subsystem in Linux (e.g. USB and ieee1394). In such cases the
SCSI subsystem LLD is a software bridge to the other driver subsystem.
Examples are the usb-storage driver (found in the drivers/usb/storage
directory) and the ieee1394/sbp2 driver (found in the drivers/ieee1394
directory).
For example, the aic7xxx LLD controls Adaptec SCSI parallel interface
(SPI) controllers based on that company's 7xxx chip series. The aic7xxx
LLD can be built into the kernel or loaded as a module. There can only be
one aic7xxx LLD running in a Linux system but it may be controlling many
HBAs. These HBAs might be either on PCI daughter-boards or built into
the motherboard (or both). Some aic7xxx based HBAs are dual controllers
and thus represent two hosts. Like most modern HBAs, each aic7xxx host
has its own PCI device address. [The one-to-one correspondence between
a SCSI host and a PCI device is common but not required (e.g. with
ISA adapters).]
The SCSI mid level isolates an LLD from other layers such as the SCSI
upper layer drivers and the block layer.
This version of the document roughly matches linux kernel version 2.6.8 .
Documentation
=============
There is a SCSI documentation directory within the kernel source tree,
typically Documentation/scsi . Most documents are in plain
(i.e. ASCII) text. This file is named scsi_mid_low_api.txt and can be
found in that directory. A more recent copy of this document may be found
at http://web.archive.org/web/20070107183357rn_1/sg.torque.net/scsi/.
Many LLDs are documented there (e.g. aic7xxx.txt). The SCSI mid-level is
briefly described in scsi.txt which contains a url to a document
describing the SCSI subsystem in the lk 2.4 series. Two upper level
drivers have documents in that directory: st.txt (SCSI tape driver) and
scsi-generic.txt (for the sg driver).
Some documentation (or urls) for LLDs may be found in the C source code
or in the same directory as the C source code. For example to find a url
about the USB mass storage driver see the
/usr/src/linux/drivers/usb/storage directory.
Driver structure
================
Traditionally an LLD for the SCSI subsystem has been at least two files in
the drivers/scsi directory. For example, a driver called "xyz" has a header
file "xyz.h" and a source file "xyz.c". [Actually there is no good reason
why this couldn't all be in one file; the header file is superfluous.] Some
drivers that have been ported to several operating systems have more than
two files. For example the aic7xxx driver has separate files for generic
and OS-specific code (e.g. FreeBSD and Linux). Such drivers tend to have
their own directory under the drivers/scsi directory.
When a new LLD is being added to Linux, the following files (found in the
drivers/scsi directory) will need some attention: Makefile and Kconfig .
It is probably best to study how existing LLDs are organized.
As the 2.5 series development kernels evolve into the 2.6 series
production series, changes are being introduced into this interface. An
example of this is driver initialization code where there are now 2 models
available. The older one, similar to what was found in the lk 2.4 series,
is based on hosts that are detected at HBA driver load time. This will be
referred to the "passive" initialization model. The newer model allows HBAs
to be hot plugged (and unplugged) during the lifetime of the LLD and will
be referred to as the "hotplug" initialization model. The newer model is
preferred as it can handle both traditional SCSI equipment that is
permanently connected as well as modern "SCSI" devices (e.g. USB or
IEEE 1394 connected digital cameras) that are hotplugged. Both
initialization models are discussed in the following sections.
An LLD interfaces to the SCSI subsystem several ways:
a) directly invoking functions supplied by the mid level
b) passing a set of function pointers to a registration function
supplied by the mid level. The mid level will then invoke these
functions at some point in the future. The LLD will supply
implementations of these functions.
c) direct access to instances of well known data structures maintained
by the mid level
Those functions in group a) are listed in a section entitled "Mid level
supplied functions" below.
Those functions in group b) are listed in a section entitled "Interface
functions" below. Their function pointers are placed in the members of
"struct scsi_host_template", an instance of which is passed to
scsi_host_alloc() ** . Those interface functions that the LLD does not
wish to supply should have NULL placed in the corresponding member of
struct scsi_host_template. Defining an instance of struct
scsi_host_template at file scope will cause NULL to be placed in function
pointer members not explicitly initialized.
Those usages in group c) should be handled with care, especially in a
"hotplug" environment. LLDs should be aware of the lifetime of instances
that are shared with the mid level and other layers.
All functions defined within an LLD and all data defined at file scope
should be static. For example the slave_alloc() function in an LLD
called "xxx" could be defined as
"static int xxx_slave_alloc(struct scsi_device * sdev) { /* code */ }"
** the scsi_host_alloc() function is a replacement for the rather vaguely
named scsi_register() function in most situations.
Hotplug initialization model
============================
In this model an LLD controls when SCSI hosts are introduced and removed
from the SCSI subsystem. Hosts can be introduced as early as driver
initialization and removed as late as driver shutdown. Typically a driver
will respond to a sysfs probe() callback that indicates an HBA has been
detected. After confirming that the new device is one that the LLD wants
to control, the LLD will initialize the HBA and then register a new host
with the SCSI mid level.
During LLD initialization the driver should register itself with the
appropriate IO bus on which it expects to find HBA(s) (e.g. the PCI bus).
This can probably be done via sysfs. Any driver parameters (especially
those that are writable after the driver is loaded) could also be
registered with sysfs at this point. The SCSI mid level first becomes
aware of an LLD when that LLD registers its first HBA.
At some later time, the LLD becomes aware of an HBA and what follows
is a typical sequence of calls between the LLD and the mid level.
This example shows the mid level scanning the newly introduced HBA for 3
scsi devices of which only the first 2 respond:
HBA PROBE: assume 2 SCSI devices found in scan
LLD mid level LLD
===-------------------=========--------------------===------
scsi_host_alloc() -->
scsi_add_host() ---->
scsi_scan_host() -------+
|
slave_alloc()
slave_configure() --> scsi_change_queue_depth()
|
slave_alloc()
slave_configure()
|
slave_alloc() ***
slave_destroy() ***
------------------------------------------------------------
If the LLD wants to adjust the default queue settings, it can invoke
scsi_change_queue_depth() in its slave_configure() routine.
*** For scsi devices that the mid level tries to scan but do not
respond, a slave_alloc(), slave_destroy() pair is called.
When an HBA is being removed it could be as part of an orderly shutdown
associated with the LLD module being unloaded (e.g. with the "rmmod"
command) or in response to a "hot unplug" indicated by sysfs()'s
remove() callback being invoked. In either case, the sequence is the
same:
HBA REMOVE: assume 2 SCSI devices attached
LLD mid level LLD
===----------------------=========-----------------===------
scsi_remove_host() ---------+
|
slave_destroy()
slave_destroy()
scsi_host_put()
------------------------------------------------------------
It may be useful for a LLD to keep track of struct Scsi_Host instances
(a pointer is returned by scsi_host_alloc()). Such instances are "owned"
by the mid-level. struct Scsi_Host instances are freed from
scsi_host_put() when the reference count hits zero.
Hot unplugging an HBA that controls a disk which is processing SCSI
commands on a mounted file system is an interesting situation. Reference
counting logic is being introduced into the mid level to cope with many
of the issues involved. See the section on reference counting below.
The hotplug concept may be extended to SCSI devices. Currently, when an
HBA is added, the scsi_scan_host() function causes a scan for SCSI devices
attached to the HBA's SCSI transport. On newer SCSI transports the HBA
may become aware of a new SCSI device _after_ the scan has completed.
An LLD can use this sequence to make the mid level aware of a SCSI device:
SCSI DEVICE hotplug
LLD mid level LLD
===-------------------=========--------------------===------
scsi_add_device() ------+
|
slave_alloc()
slave_configure() [--> scsi_change_queue_depth()]
------------------------------------------------------------
In a similar fashion, an LLD may become aware that a SCSI device has been
removed (unplugged) or the connection to it has been interrupted. Some
existing SCSI transports (e.g. SPI) may not become aware that a SCSI
device has been removed until a subsequent SCSI command fails which will
probably cause that device to be set offline by the mid level. An LLD that
detects the removal of a SCSI device can instigate its removal from
upper layers with this sequence:
SCSI DEVICE hot unplug
LLD mid level LLD
===----------------------=========-----------------===------
scsi_remove_device() -------+
|
slave_destroy()
------------------------------------------------------------
It may be useful for an LLD to keep track of struct scsi_device instances
(a pointer is passed as the parameter to slave_alloc() and
slave_configure() callbacks). Such instances are "owned" by the mid-level.
struct scsi_device instances are freed after slave_destroy().
Reference Counting
==================
The Scsi_Host structure has had reference counting infrastructure added.
This effectively spreads the ownership of struct Scsi_Host instances
across the various SCSI layers which use them. Previously such instances
were exclusively owned by the mid level. LLDs would not usually need to
directly manipulate these reference counts but there may be some cases
where they do.
There are 3 reference counting functions of interest associated with
struct Scsi_Host:
- scsi_host_alloc(): returns a pointer to new instance of struct
Scsi_Host which has its reference count ^^ set to 1
- scsi_host_get(): adds 1 to the reference count of the given instance
- scsi_host_put(): decrements 1 from the reference count of the given
instance. If the reference count reaches 0 then the given instance
is freed
The scsi_device structure has had reference counting infrastructure added.
This effectively spreads the ownership of struct scsi_device instances
across the various SCSI layers which use them. Previously such instances
were exclusively owned by the mid level. See the access functions declared
towards the end of include/scsi/scsi_device.h . If an LLD wants to keep
a copy of a pointer to a scsi_device instance it should use scsi_device_get()
to bump its reference count. When it is finished with the pointer it can
use scsi_device_put() to decrement its reference count (and potentially
delete it).
^^ struct Scsi_Host actually has 2 reference counts which are manipulated
in parallel by these functions.
Conventions
===========
First, Linus Torvalds's thoughts on C coding style can be found in the
Documentation/process/coding-style.rst file.
Next, there is a movement to "outlaw" typedefs introducing synonyms for
struct tags. Both can be still found in the SCSI subsystem, but
the typedefs have been moved to a single file, scsi_typedefs.h to
make their future removal easier, for example:
"typedef struct scsi_cmnd Scsi_Cmnd;"
Also, most C99 enhancements are encouraged to the extent they are supported
by the relevant gcc compilers. So C99 style structure and array
initializers are encouraged where appropriate. Don't go too far,
VLAs are not properly supported yet. An exception to this is the use of
"//" style comments; /*...*/ comments are still preferred in Linux.
Well written, tested and documented code, need not be re-formatted to
comply with the above conventions. For example, the aic7xxx driver
comes to Linux from FreeBSD and Adaptec's own labs. No doubt FreeBSD
and Adaptec have their own coding conventions.
Mid level supplied functions
============================
These functions are supplied by the SCSI mid level for use by LLDs.
The names (i.e. entry points) of these functions are exported
so an LLD that is a module can access them. The kernel will
arrange for the SCSI mid level to be loaded and initialized before any LLD
is initialized. The functions below are listed alphabetically and their
names all start with "scsi_".
Summary:
scsi_add_device - creates new scsi device (lu) instance
scsi_add_host - perform sysfs registration and set up transport class
scsi_change_queue_depth - change the queue depth on a SCSI device
scsi_bios_ptable - return copy of block device's partition table
scsi_block_requests - prevent further commands being queued to given host
scsi_host_alloc - return a new scsi_host instance whose refcount==1
scsi_host_get - increments Scsi_Host instance's refcount
scsi_host_put - decrements Scsi_Host instance's refcount (free if 0)
scsi_partsize - parse partition table into cylinders, heads + sectors
scsi_register - create and register a scsi host adapter instance.
scsi_remove_device - detach and remove a SCSI device
scsi_remove_host - detach and remove all SCSI devices owned by host
scsi_report_bus_reset - report scsi _bus_ reset observed
scsi_scan_host - scan SCSI bus
scsi_track_queue_full - track successive QUEUE_FULL events
scsi_unblock_requests - allow further commands to be queued to given host
scsi_unregister - [calls scsi_host_put()]
Details:
/**
* scsi_add_device - creates new scsi device (lu) instance
* @shost: pointer to scsi host instance
* @channel: channel number (rarely other than 0)
* @id: target id number
* @lun: logical unit number
*
* Returns pointer to new struct scsi_device instance or
* ERR_PTR(-ENODEV) (or some other bent pointer) if something is
* wrong (e.g. no lu responds at given address)
*
* Might block: yes
*
* Notes: This call is usually performed internally during a scsi
* bus scan when an HBA is added (i.e. scsi_scan_host()). So it
* should only be called if the HBA becomes aware of a new scsi
* device (lu) after scsi_scan_host() has completed. If successful
* this call can lead to slave_alloc() and slave_configure() callbacks
* into the LLD.
*
* Defined in: drivers/scsi/scsi_scan.c
**/
struct scsi_device * scsi_add_device(struct Scsi_Host *shost,
unsigned int channel,
unsigned int id, unsigned int lun)
/**
* scsi_add_host - perform sysfs registration and set up transport class
* @shost: pointer to scsi host instance
* @dev: pointer to struct device of type scsi class
*
* Returns 0 on success, negative errno of failure (e.g. -ENOMEM)
*
* Might block: no
*
* Notes: Only required in "hotplug initialization model" after a
* successful call to scsi_host_alloc(). This function does not
* scan the bus; this can be done by calling scsi_scan_host() or
* in some other transport-specific way. The LLD must set up
* the transport template before calling this function and may only
* access the transport class data after this function has been called.
*
* Defined in: drivers/scsi/hosts.c
**/
int scsi_add_host(struct Scsi_Host *shost, struct device * dev)
/**
* scsi_change_queue_depth - allow LLD to change queue depth on a SCSI device
* @sdev: pointer to SCSI device to change queue depth on
* @tags Number of tags allowed if tagged queuing enabled,
* or number of commands the LLD can queue up
* in non-tagged mode (as per cmd_per_lun).
*
* Returns nothing
*
* Might block: no
*
* Notes: Can be invoked any time on a SCSI device controlled by this
* LLD. [Specifically during and after slave_configure() and prior to
* slave_destroy().] Can safely be invoked from interrupt code.
*
* Defined in: drivers/scsi/scsi.c [see source code for more notes]
*
**/
int scsi_change_queue_depth(struct scsi_device *sdev, int tags)
/**
* scsi_bios_ptable - return copy of block device's partition table
* @dev: pointer to block device
*
* Returns pointer to partition table, or NULL for failure
*
* Might block: yes
*
* Notes: Caller owns memory returned (free with kfree() )
*
* Defined in: drivers/scsi/scsicam.c
**/
unsigned char *scsi_bios_ptable(struct block_device *dev)
/**
* scsi_block_requests - prevent further commands being queued to given host
*
* @shost: pointer to host to block commands on
*
* Returns nothing
*
* Might block: no
*
* Notes: There is no timer nor any other means by which the requests
* get unblocked other than the LLD calling scsi_unblock_requests().
*
* Defined in: drivers/scsi/scsi_lib.c
**/
void scsi_block_requests(struct Scsi_Host * shost)
/**
* scsi_host_alloc - create a scsi host adapter instance and perform basic
* initialization.
* @sht: pointer to scsi host template
* @privsize: extra bytes to allocate in hostdata array (which is the
* last member of the returned Scsi_Host instance)
*
* Returns pointer to new Scsi_Host instance or NULL on failure
*
* Might block: yes
*
* Notes: When this call returns to the LLD, the SCSI bus scan on
* this host has _not_ yet been done.
* The hostdata array (by default zero length) is a per host scratch
* area for the LLD's exclusive use.
* Both associated refcounting objects have their refcount set to 1.
* Full registration (in sysfs) and a bus scan are performed later when
* scsi_add_host() and scsi_scan_host() are called.
*
* Defined in: drivers/scsi/hosts.c .
**/
struct Scsi_Host * scsi_host_alloc(struct scsi_host_template * sht,
int privsize)
/**
* scsi_host_get - increment Scsi_Host instance refcount
* @shost: pointer to struct Scsi_Host instance
*
* Returns nothing
*
* Might block: currently may block but may be changed to not block
*
* Notes: Actually increments the counts in two sub-objects
*
* Defined in: drivers/scsi/hosts.c
**/
void scsi_host_get(struct Scsi_Host *shost)
/**
* scsi_host_put - decrement Scsi_Host instance refcount, free if 0
* @shost: pointer to struct Scsi_Host instance
*
* Returns nothing
*
* Might block: currently may block but may be changed to not block
*
* Notes: Actually decrements the counts in two sub-objects. If the
* latter refcount reaches 0, the Scsi_Host instance is freed.
* The LLD need not worry exactly when the Scsi_Host instance is
* freed, it just shouldn't access the instance after it has balanced
* out its refcount usage.
*
* Defined in: drivers/scsi/hosts.c
**/
void scsi_host_put(struct Scsi_Host *shost)
/**
* scsi_partsize - parse partition table into cylinders, heads + sectors
* @buf: pointer to partition table
* @capacity: size of (total) disk in 512 byte sectors
* @cyls: outputs number of cylinders calculated via this pointer
* @hds: outputs number of heads calculated via this pointer
* @secs: outputs number of sectors calculated via this pointer
*
* Returns 0 on success, -1 on failure
*
* Might block: no
*
* Notes: Caller owns memory returned (free with kfree() )
*
* Defined in: drivers/scsi/scsicam.c
**/
int scsi_partsize(unsigned char *buf, unsigned long capacity,
unsigned int *cyls, unsigned int *hds, unsigned int *secs)
/**
* scsi_register - create and register a scsi host adapter instance.
* @sht: pointer to scsi host template
* @privsize: extra bytes to allocate in hostdata array (which is the
* last member of the returned Scsi_Host instance)
*
* Returns pointer to new Scsi_Host instance or NULL on failure
*
* Might block: yes
*
* Notes: When this call returns to the LLD, the SCSI bus scan on
* this host has _not_ yet been done.
* The hostdata array (by default zero length) is a per host scratch
* area for the LLD.
*
* Defined in: drivers/scsi/hosts.c .
**/
struct Scsi_Host * scsi_register(struct scsi_host_template * sht,
int privsize)
/**
* scsi_remove_device - detach and remove a SCSI device
* @sdev: a pointer to a scsi device instance
*
* Returns value: 0 on success, -EINVAL if device not attached
*
* Might block: yes
*
* Notes: If an LLD becomes aware that a scsi device (lu) has
* been removed but its host is still present then it can request
* the removal of that scsi device. If successful this call will
* lead to the slave_destroy() callback being invoked. sdev is an
* invalid pointer after this call.
*
* Defined in: drivers/scsi/scsi_sysfs.c .
**/
int scsi_remove_device(struct scsi_device *sdev)
/**
* scsi_remove_host - detach and remove all SCSI devices owned by host
* @shost: a pointer to a scsi host instance
*
* Returns value: 0 on success, 1 on failure (e.g. LLD busy ??)
*
* Might block: yes
*
* Notes: Should only be invoked if the "hotplug initialization
* model" is being used. It should be called _prior_ to
* scsi_unregister().
*
* Defined in: drivers/scsi/hosts.c .
**/
int scsi_remove_host(struct Scsi_Host *shost)
/**
* scsi_report_bus_reset - report scsi _bus_ reset observed
* @shost: a pointer to a scsi host involved
* @channel: channel (within) host on which scsi bus reset occurred
*
* Returns nothing
*
* Might block: no
*
* Notes: This only needs to be called if the reset is one which
* originates from an unknown location. Resets originated by the
* mid level itself don't need to call this, but there should be
* no harm. The main purpose of this is to make sure that a
* CHECK_CONDITION is properly treated.
*
* Defined in: drivers/scsi/scsi_error.c .
**/
void scsi_report_bus_reset(struct Scsi_Host * shost, int channel)
/**
* scsi_scan_host - scan SCSI bus
* @shost: a pointer to a scsi host instance
*
* Might block: yes
*
* Notes: Should be called after scsi_add_host()
*
* Defined in: drivers/scsi/scsi_scan.c
**/
void scsi_scan_host(struct Scsi_Host *shost)
/**
* scsi_track_queue_full - track successive QUEUE_FULL events on given
* device to determine if and when there is a need
* to adjust the queue depth on the device.
* @sdev: pointer to SCSI device instance
* @depth: Current number of outstanding SCSI commands on this device,
* not counting the one returned as QUEUE_FULL.
*
* Returns 0 - no change needed
* >0 - adjust queue depth to this new depth
* -1 - drop back to untagged operation using host->cmd_per_lun
* as the untagged command depth
*
* Might block: no
*
* Notes: LLDs may call this at any time and we will do "The Right
* Thing"; interrupt context safe.
*
* Defined in: drivers/scsi/scsi.c .
**/
int scsi_track_queue_full(struct scsi_device *sdev, int depth)
/**
* scsi_unblock_requests - allow further commands to be queued to given host
*
* @shost: pointer to host to unblock commands on
*
* Returns nothing
*
* Might block: no
*
* Defined in: drivers/scsi/scsi_lib.c .
**/
void scsi_unblock_requests(struct Scsi_Host * shost)
/**
* scsi_unregister - unregister and free memory used by host instance
* @shp: pointer to scsi host instance to unregister.
*
* Returns nothing
*
* Might block: no
*
* Notes: Should not be invoked if the "hotplug initialization
* model" is being used. Called internally by exit_this_scsi_driver()
* in the "passive initialization model". Hence a LLD has no need to
* call this function directly.
*
* Defined in: drivers/scsi/hosts.c .
**/
void scsi_unregister(struct Scsi_Host * shp)
Interface Functions
===================
Interface functions are supplied (defined) by LLDs and their function
pointers are placed in an instance of struct scsi_host_template which
is passed to scsi_host_alloc() [or scsi_register() / init_this_scsi_driver()].
Some are mandatory. Interface functions should be declared static. The
accepted convention is that driver "xyz" will declare its slave_configure()
function as:
static int xyz_slave_configure(struct scsi_device * sdev);
and so forth for all interface functions listed below.
A pointer to this function should be placed in the 'slave_configure' member
of a "struct scsi_host_template" instance. A pointer to such an instance
should be passed to the mid level's scsi_host_alloc() [or scsi_register() /
init_this_scsi_driver()].
The interface functions are also described in the include/scsi/scsi_host.h
file immediately above their definition point in "struct scsi_host_template".
In some cases more detail is given in scsi_host.h than below.
The interface functions are listed below in alphabetical order.
Summary:
bios_param - fetch head, sector, cylinder info for a disk
eh_timed_out - notify the host that a command timer expired
eh_abort_handler - abort given command
eh_bus_reset_handler - issue SCSI bus reset
eh_device_reset_handler - issue SCSI device reset
eh_host_reset_handler - reset host (host bus adapter)
info - supply information about given host
ioctl - driver can respond to ioctls
proc_info - supports /proc/scsi/{driver_name}/{host_no}
queuecommand - queue scsi command, invoke 'done' on completion
slave_alloc - prior to any commands being sent to a new device
slave_configure - driver fine tuning for given device after attach
slave_destroy - given device is about to be shut down
Details:
/**
* bios_param - fetch head, sector, cylinder info for a disk
* @sdev: pointer to scsi device context (defined in
* include/scsi/scsi_device.h)
* @bdev: pointer to block device context (defined in fs.h)
* @capacity: device size (in 512 byte sectors)
* @params: three element array to place output:
* params[0] number of heads (max 255)
* params[1] number of sectors (max 63)
* params[2] number of cylinders
*
* Return value is ignored
*
* Locks: none
*
* Calling context: process (sd)
*
* Notes: an arbitrary geometry (based on READ CAPACITY) is used
* if this function is not provided. The params array is
* pre-initialized with made up values just in case this function
* doesn't output anything.
*
* Optionally defined in: LLD
**/
int bios_param(struct scsi_device * sdev, struct block_device *bdev,
sector_t capacity, int params[3])
/**
* eh_timed_out - The timer for the command has just fired
* @scp: identifies command timing out
*
* Returns:
*
* EH_HANDLED: I fixed the error, please complete the command
* EH_RESET_TIMER: I need more time, reset the timer and
* begin counting again
* EH_NOT_HANDLED Begin normal error recovery
*
*
* Locks: None held
*
* Calling context: interrupt
*
* Notes: This is to give the LLD an opportunity to do local recovery.
* This recovery is limited to determining if the outstanding command
* will ever complete. You may not abort and restart the command from
* this callback.
*
* Optionally defined in: LLD
**/
int eh_timed_out(struct scsi_cmnd * scp)
/**
* eh_abort_handler - abort command associated with scp
* @scp: identifies command to be aborted
*
* Returns SUCCESS if command aborted else FAILED
*
* Locks: None held
*
* Calling context: kernel thread
*
* Notes: If 'no_async_abort' is defined this callback
* will be invoked from scsi_eh thread. No other commands
* will then be queued on current host during eh.
* Otherwise it will be called whenever scsi_times_out()
* is called due to a command timeout.
*
* Optionally defined in: LLD
**/
int eh_abort_handler(struct scsi_cmnd * scp)
/**
* eh_bus_reset_handler - issue SCSI bus reset
* @scp: SCSI bus that contains this device should be reset
*
* Returns SUCCESS if command aborted else FAILED
*
* Locks: None held
*
* Calling context: kernel thread
*
* Notes: Invoked from scsi_eh thread. No other commands will be
* queued on current host during eh.
*
* Optionally defined in: LLD
**/
int eh_bus_reset_handler(struct scsi_cmnd * scp)
/**
* eh_device_reset_handler - issue SCSI device reset
* @scp: identifies SCSI device to be reset
*
* Returns SUCCESS if command aborted else FAILED
*
* Locks: None held
*
* Calling context: kernel thread
*
* Notes: Invoked from scsi_eh thread. No other commands will be
* queued on current host during eh.
*
* Optionally defined in: LLD
**/
int eh_device_reset_handler(struct scsi_cmnd * scp)
/**
* eh_host_reset_handler - reset host (host bus adapter)
* @scp: SCSI host that contains this device should be reset
*
* Returns SUCCESS if command aborted else FAILED
*
* Locks: None held
*
* Calling context: kernel thread
*
* Notes: Invoked from scsi_eh thread. No other commands will be
* queued on current host during eh.
* With the default eh_strategy in place, if none of the _abort_,
* _device_reset_, _bus_reset_ or this eh handler function are
* defined (or they all return FAILED) then the device in question
* will be set offline whenever eh is invoked.
*
* Optionally defined in: LLD
**/
int eh_host_reset_handler(struct scsi_cmnd * scp)
/**
* info - supply information about given host: driver name plus data
* to distinguish given host
* @shp: host to supply information about
*
* Return ASCII null terminated string. [This driver is assumed to
* manage the memory pointed to and maintain it, typically for the
* lifetime of this host.]
*
* Locks: none
*
* Calling context: process
*
* Notes: Often supplies PCI or ISA information such as IO addresses
* and interrupt numbers. If not supplied struct Scsi_Host::name used
* instead. It is assumed the returned information fits on one line
* (i.e. does not included embedded newlines).
* The SCSI_IOCTL_PROBE_HOST ioctl yields the string returned by this
* function (or struct Scsi_Host::name if this function is not
* available).
* In a similar manner, init_this_scsi_driver() outputs to the console
* each host's "info" (or name) for the driver it is registering.
* Also if proc_info() is not supplied, the output of this function
* is used instead.
*
* Optionally defined in: LLD
**/
const char * info(struct Scsi_Host * shp)
/**
* ioctl - driver can respond to ioctls
* @sdp: device that ioctl was issued for
* @cmd: ioctl number
* @arg: pointer to read or write data from. Since it points to
* user space, should use appropriate kernel functions
* (e.g. copy_from_user() ). In the Unix style this argument
* can also be viewed as an unsigned long.
*
* Returns negative "errno" value when there is a problem. 0 or a
* positive value indicates success and is returned to the user space.
*
* Locks: none
*
* Calling context: process
*
* Notes: The SCSI subsystem uses a "trickle down" ioctl model.
* The user issues an ioctl() against an upper level driver
* (e.g. /dev/sdc) and if the upper level driver doesn't recognize
* the 'cmd' then it is passed to the SCSI mid level. If the SCSI
* mid level does not recognize it, then the LLD that controls
* the device receives the ioctl. According to recent Unix standards
* unsupported ioctl() 'cmd' numbers should return -ENOTTY.
*
* Optionally defined in: LLD
**/
int ioctl(struct scsi_device *sdp, int cmd, void *arg)
/**
* proc_info - supports /proc/scsi/{driver_name}/{host_no}
* @buffer: anchor point to output to (0==writeto1_read0) or fetch from
* (1==writeto1_read0).
* @start: where "interesting" data is written to. Ignored when
* 1==writeto1_read0.
* @offset: offset within buffer 0==writeto1_read0 is actually
* interested in. Ignored when 1==writeto1_read0 .
* @length: maximum (or actual) extent of buffer
* @host_no: host number of interest (struct Scsi_Host::host_no)
* @writeto1_read0: 1 -> data coming from user space towards driver
* (e.g. "echo some_string > /proc/scsi/xyz/2")
* 0 -> user what data from this driver
* (e.g. "cat /proc/scsi/xyz/2")
*
* Returns length when 1==writeto1_read0. Otherwise number of chars
* output to buffer past offset.
*
* Locks: none held
*
* Calling context: process
*
* Notes: Driven from scsi_proc.c which interfaces to proc_fs. proc_fs
* support can now be configured out of the scsi subsystem.
*
* Optionally defined in: LLD
**/
int proc_info(char * buffer, char ** start, off_t offset,
int length, int host_no, int writeto1_read0)
/**
* queuecommand - queue scsi command, invoke scp->scsi_done on completion
* @shost: pointer to the scsi host object
* @scp: pointer to scsi command object
*
* Returns 0 on success.
*
* If there's a failure, return either:
*
* SCSI_MLQUEUE_DEVICE_BUSY if the device queue is full, or
* SCSI_MLQUEUE_HOST_BUSY if the entire host queue is full
*
* On both of these returns, the mid-layer will requeue the I/O
*
* - if the return is SCSI_MLQUEUE_DEVICE_BUSY, only that particular
* device will be paused, and it will be unpaused when a command to
* the device returns (or after a brief delay if there are no more
* outstanding commands to it). Commands to other devices continue
* to be processed normally.
*
* - if the return is SCSI_MLQUEUE_HOST_BUSY, all I/O to the host
* is paused and will be unpaused when any command returns from
* the host (or after a brief delay if there are no outstanding
* commands to the host).
*
* For compatibility with earlier versions of queuecommand, any
* other return value is treated the same as
* SCSI_MLQUEUE_HOST_BUSY.
*
* Other types of errors that are detected immediately may be
* flagged by setting scp->result to an appropriate value,
* invoking the scp->scsi_done callback, and then returning 0
* from this function. If the command is not performed
* immediately (and the LLD is starting (or will start) the given
* command) then this function should place 0 in scp->result and
* return 0.
*
* Command ownership. If the driver returns zero, it owns the
* command and must take responsibility for ensuring the
* scp->scsi_done callback is executed. Note: the driver may
* call scp->scsi_done before returning zero, but after it has
* called scp->scsi_done, it may not return any value other than
* zero. If the driver makes a non-zero return, it must not
* execute the command's scsi_done callback at any time.
*
* Locks: up to and including 2.6.36, struct Scsi_Host::host_lock
* held on entry (with "irqsave") and is expected to be
* held on return. From 2.6.37 onwards, queuecommand is
* called without any locks held.
*
* Calling context: in interrupt (soft irq) or process context
*
* Notes: This function should be relatively fast. Normally it
* will not wait for IO to complete. Hence the scp->scsi_done
* callback is invoked (often directly from an interrupt service
* routine) some time after this function has returned. In some
* cases (e.g. pseudo adapter drivers that manufacture the
* response to a SCSI INQUIRY) the scp->scsi_done callback may be
* invoked before this function returns. If the scp->scsi_done
* callback is not invoked within a certain period the SCSI mid
* level will commence error processing. If a status of CHECK
* CONDITION is placed in "result" when the scp->scsi_done
* callback is invoked, then the LLD driver should perform
* autosense and fill in the struct scsi_cmnd::sense_buffer
* array. The scsi_cmnd::sense_buffer array is zeroed prior to
* the mid level queuing a command to an LLD.
*
* Defined in: LLD
**/
int queuecommand(struct Scsi_Host *shost, struct scsi_cmnd * scp)
/**
* slave_alloc - prior to any commands being sent to a new device
* (i.e. just prior to scan) this call is made
* @sdp: pointer to new device (about to be scanned)
*
* Returns 0 if ok. Any other return is assumed to be an error and
* the device is ignored.
*
* Locks: none
*
* Calling context: process
*
* Notes: Allows the driver to allocate any resources for a device
* prior to its initial scan. The corresponding scsi device may not
* exist but the mid level is just about to scan for it (i.e. send
* and INQUIRY command plus ...). If a device is found then
* slave_configure() will be called while if a device is not found
* slave_destroy() is called.
* For more details see the include/scsi/scsi_host.h file.
*
* Optionally defined in: LLD
**/
int slave_alloc(struct scsi_device *sdp)