1 .. SPDX-License-Identifier: GPL-2.0
2
3 =============================================
4 SCSI mid_level - lower_level driver interface
5 =============================================
6
7 Introduction
8 ============
9 This document outlines the interface between the Linux SCSI mid level and
10 SCSI lower level drivers. Lower level drivers (LLDs) are variously called
11 host bus adapter (HBA) drivers and host drivers (HD). A "host" in this
12 context is a bridge between a computer IO bus (e.g. PCI or ISA) and a
13 single SCSI initiator port on a SCSI transport. An "initiator" port
14 (SCSI terminology, see SAM-3 at http://www.t10.org) sends SCSI commands
15 to "target" SCSI ports (e.g. disks). There can be many LLDs in a running
16 system, but only one per hardware type. Most LLDs can control one or more
17 SCSI HBAs. Some HBAs contain multiple hosts.
18
19 In some cases the SCSI transport is an external bus that already has
20 its own subsystem in Linux (e.g. USB and ieee1394). In such cases the
21 SCSI subsystem LLD is a software bridge to the other driver subsystem.
22 Examples are the usb-storage driver (found in the drivers/usb/storage
23 directory) and the ieee1394/sbp2 driver (found in the drivers/ieee1394
24 directory).
25
26 For example, the aic7xxx LLD controls Adaptec SCSI parallel interface
27 (SPI) controllers based on that company's 7xxx chip series. The aic7xxx
28 LLD can be built into the kernel or loaded as a module. There can only be
29 one aic7xxx LLD running in a Linux system but it may be controlling many
30 HBAs. These HBAs might be either on PCI daughter-boards or built into
31 the motherboard (or both). Some aic7xxx based HBAs are dual controllers
32 and thus represent two hosts. Like most modern HBAs, each aic7xxx host
33 has its own PCI device address. [The one-to-one correspondence between
34 a SCSI host and a PCI device is common but not required (e.g. with
35 ISA adapters).]
36
37 The SCSI mid level isolates an LLD from other layers such as the SCSI
38 upper layer drivers and the block layer.
39
40 This version of the document roughly matches linux kernel version 2.6.8 .
41
42 Documentation
43 =============
44 There is a SCSI documentation directory within the kernel source tree,
45 typically Documentation/scsi . Most documents are in reStructuredText
46 format. This file is named scsi_mid_low_api.rst and can be
47 found in that directory. A more recent copy of this document may be found
48 at https://docs.kernel.org/scsi/scsi_mid_low_api.html. Many LLDs are
49 documented in Documentation/scsi (e.g. aic7xxx.rst). The SCSI mid-level is
50 briefly described in scsi.rst which contains a URL to a document describing
51 the SCSI subsystem in the Linux Kernel 2.4 series. Two upper level
52 drivers have documents in that directory: st.rst (SCSI tape driver) and
53 scsi-generic.rst (for the sg driver).
54
55 Some documentation (or URLs) for LLDs may be found in the C source code
56 or in the same directory as the C source code. For example to find a URL
57 about the USB mass storage driver see the
58 /usr/src/linux/drivers/usb/storage directory.
59
60 Driver structure
61 ================
62 Traditionally an LLD for the SCSI subsystem has been at least two files in
63 the drivers/scsi directory. For example, a driver called "xyz" has a header
64 file "xyz.h" and a source file "xyz.c". [Actually there is no good reason
65 why this couldn't all be in one file; the header file is superfluous.] Some
66 drivers that have been ported to several operating systems have more than
67 two files. For example the aic7xxx driver has separate files for generic
68 and OS-specific code (e.g. FreeBSD and Linux). Such drivers tend to have
69 their own directory under the drivers/scsi directory.
70
71 When a new LLD is being added to Linux, the following files (found in the
72 drivers/scsi directory) will need some attention: Makefile and Kconfig .
73 It is probably best to study how existing LLDs are organized.
74
75 As the 2.5 series development kernels evolve into the 2.6 series
76 production series, changes are being introduced into this interface. An
77 example of this is driver initialization code where there are now 2 models
78 available. The older one, similar to what was found in the lk 2.4 series,
79 is based on hosts that are detected at HBA driver load time. This will be
80 referred to the "passive" initialization model. The newer model allows HBAs
81 to be hot plugged (and unplugged) during the lifetime of the LLD and will
82 be referred to as the "hotplug" initialization model. The newer model is
83 preferred as it can handle both traditional SCSI equipment that is
84 permanently connected as well as modern "SCSI" devices (e.g. USB or
85 IEEE 1394 connected digital cameras) that are hotplugged. Both
86 initialization models are discussed in the following sections.
87
88 An LLD interfaces to the SCSI subsystem several ways:
89
90 a) directly invoking functions supplied by the mid level
91 b) passing a set of function pointers to a registration function
92 supplied by the mid level. The mid level will then invoke these
93 functions at some point in the future. The LLD will supply
94 implementations of these functions.
95 c) direct access to instances of well known data structures maintained
96 by the mid level
97
98 Those functions in group a) are listed in a section entitled "Mid level
99 supplied functions" below.
100
101 Those functions in group b) are listed in a section entitled "Interface
102 functions" below. Their function pointers are placed in the members of
103 "struct scsi_host_template", an instance of which is passed to
104 scsi_host_alloc() [#]_. Those interface functions that the LLD does not
105 wish to supply should have NULL placed in the corresponding member of
106 struct scsi_host_template. Defining an instance of struct
107 scsi_host_template at file scope will cause NULL to be placed in function
108 pointer members not explicitly initialized.
109
110 Those usages in group c) should be handled with care, especially in a
111 "hotplug" environment. LLDs should be aware of the lifetime of instances
112 that are shared with the mid level and other layers.
113
114 All functions defined within an LLD and all data defined at file scope
115 should be static. For example the slave_alloc() function in an LLD
116 called "xxx" could be defined as
117 ``static int xxx_slave_alloc(struct scsi_device * sdev) { /* code */ }``
118
119 .. [#] the scsi_host_alloc() function is a replacement for the rather vaguely
120 named scsi_register() function in most situations.
121
122
123 Hotplug initialization model
124 ============================
125 In this model an LLD controls when SCSI hosts are introduced and removed
126 from the SCSI subsystem. Hosts can be introduced as early as driver
127 initialization and removed as late as driver shutdown. Typically a driver
128 will respond to a sysfs probe() callback that indicates an HBA has been
129 detected. After confirming that the new device is one that the LLD wants
130 to control, the LLD will initialize the HBA and then register a new host
131 with the SCSI mid level.
132
133 During LLD initialization the driver should register itself with the
134 appropriate IO bus on which it expects to find HBA(s) (e.g. the PCI bus).
135 This can probably be done via sysfs. Any driver parameters (especially
136 those that are writable after the driver is loaded) could also be
137 registered with sysfs at this point. The SCSI mid level first becomes
138 aware of an LLD when that LLD registers its first HBA.
139
140 At some later time, the LLD becomes aware of an HBA and what follows
141 is a typical sequence of calls between the LLD and the mid level.
142 This example shows the mid level scanning the newly introduced HBA for 3
143 scsi devices of which only the first 2 respond::
144
145 HBA PROBE: assume 2 SCSI devices found in scan
146 LLD mid level LLD
147 ===-------------------=========--------------------===------
148 scsi_host_alloc() -->
149 scsi_add_host() ---->
150 scsi_scan_host() -------+
151 |
152 slave_alloc()
153 slave_configure() --> scsi_change_queue_depth()
154 |
155 slave_alloc()
156 slave_configure()
157 |
158 slave_alloc() ***
159 slave_destroy() ***
160
161
162 *** For scsi devices that the mid level tries to scan but do not
163 respond, a slave_alloc(), slave_destroy() pair is called.
164
165 If the LLD wants to adjust the default queue settings, it can invoke
166 scsi_change_queue_depth() in its slave_configure() routine.
167
168 When an HBA is being removed it could be as part of an orderly shutdown
169 associated with the LLD module being unloaded (e.g. with the "rmmod"
170 command) or in response to a "hot unplug" indicated by sysfs()'s
171 remove() callback being invoked. In either case, the sequence is the
172 same::
173
174 HBA REMOVE: assume 2 SCSI devices attached
175 LLD mid level LLD
176 ===----------------------=========-----------------===------
177 scsi_remove_host() ---------+
178 |
179 slave_destroy()
180 slave_destroy()
181 scsi_host_put()
182
183 It may be useful for a LLD to keep track of struct Scsi_Host instances
184 (a pointer is returned by scsi_host_alloc()). Such instances are "owned"
185 by the mid-level. struct Scsi_Host instances are freed from
186 scsi_host_put() when the reference count hits zero.
187
188 Hot unplugging an HBA that controls a disk which is processing SCSI
189 commands on a mounted file system is an interesting situation. Reference
190 counting logic is being introduced into the mid level to cope with many
191 of the issues involved. See the section on reference counting below.
192
193
194 The hotplug concept may be extended to SCSI devices. Currently, when an
195 HBA is added, the scsi_scan_host() function causes a scan for SCSI devices
196 attached to the HBA's SCSI transport. On newer SCSI transports the HBA
197 may become aware of a new SCSI device _after_ the scan has completed.
198 An LLD can use this sequence to make the mid level aware of a SCSI device::
199
200 SCSI DEVICE hotplug
201 LLD mid level LLD
202 ===-------------------=========--------------------===------
203 scsi_add_device() ------+
204 |
205 slave_alloc()
206 slave_configure() [--> scsi_change_queue_depth()]
207
208 In a similar fashion, an LLD may become aware that a SCSI device has been
209 removed (unplugged) or the connection to it has been interrupted. Some
210 existing SCSI transports (e.g. SPI) may not become aware that a SCSI
211 device has been removed until a subsequent SCSI command fails which will
212 probably cause that device to be set offline by the mid level. An LLD that
213 detects the removal of a SCSI device can instigate its removal from
214 upper layers with this sequence::
215
216 SCSI DEVICE hot unplug
217 LLD mid level LLD
218 ===----------------------=========-----------------===------
219 scsi_remove_device() -------+
220 |
221 slave_destroy()
222
223 It may be useful for an LLD to keep track of struct scsi_device instances
224 (a pointer is passed as the parameter to slave_alloc() and
225 slave_configure() callbacks). Such instances are "owned" by the mid-level.
226 struct scsi_device instances are freed after slave_destroy().
227
228
229 Reference Counting
230 ==================
231 The Scsi_Host structure has had reference counting infrastructure added.
232 This effectively spreads the ownership of struct Scsi_Host instances
233 across the various SCSI layers which use them. Previously such instances
234 were exclusively owned by the mid level. LLDs would not usually need to
235 directly manipulate these reference counts but there may be some cases
236 where they do.
237
238 There are 3 reference counting functions of interest associated with
239 struct Scsi_Host:
240
241 - scsi_host_alloc():
242 returns a pointer to new instance of struct
243 Scsi_Host which has its reference count ^^ set to 1
244
245 - scsi_host_get():
246 adds 1 to the reference count of the given instance
247
248 - scsi_host_put():
249 decrements 1 from the reference count of the given
250 instance. If the reference count reaches 0 then the given instance
251 is freed
252
253 The scsi_device structure has had reference counting infrastructure added.
254 This effectively spreads the ownership of struct scsi_device instances
255 across the various SCSI layers which use them. Previously such instances
256 were exclusively owned by the mid level. See the access functions declared
257 towards the end of include/scsi/scsi_device.h . If an LLD wants to keep
258 a copy of a pointer to a scsi_device instance it should use scsi_device_get()
259 to bump its reference count. When it is finished with the pointer it can
260 use scsi_device_put() to decrement its reference count (and potentially
261 delete it).
262
263 .. Note::
264
265 struct Scsi_Host actually has 2 reference counts which are manipulated
266 in parallel by these functions.
267
268
269 Conventions
270 ===========
271 First, Linus Torvalds's thoughts on C coding style can be found in the
272 Documentation/process/coding-style.rst file.
273
274 Also, most C99 enhancements are encouraged to the extent they are supported
275 by the relevant gcc compilers. So C99 style structure and array
276 initializers are encouraged where appropriate. Don't go too far,
277 VLAs are not properly supported yet. An exception to this is the use of
278 ``//`` style comments; ``/*...*/`` comments are still preferred in Linux.
279
280 Well written, tested and documented code, need not be re-formatted to
281 comply with the above conventions. For example, the aic7xxx driver
282 comes to Linux from FreeBSD and Adaptec's own labs. No doubt FreeBSD
283 and Adaptec have their own coding conventions.
284
285
286 Mid level supplied functions
287 ============================
288 These functions are supplied by the SCSI mid level for use by LLDs.
289 The names (i.e. entry points) of these functions are exported
290 so an LLD that is a module can access them. The kernel will
291 arrange for the SCSI mid level to be loaded and initialized before any LLD
292 is initialized. The functions below are listed alphabetically and their
293 names all start with ``scsi_``.
294
295 Summary:
296
297 - scsi_add_device - creates new scsi device (lu) instance
298 - scsi_add_host - perform sysfs registration and set up transport class
299 - scsi_change_queue_depth - change the queue depth on a SCSI device
300 - scsi_bios_ptable - return copy of block device's partition table
301 - scsi_block_requests - prevent further commands being queued to given host
302 - scsi_host_alloc - return a new scsi_host instance whose refcount==1
303 - scsi_host_get - increments Scsi_Host instance's refcount
304 - scsi_host_put - decrements Scsi_Host instance's refcount (free if 0)
305 - scsi_register - create and register a scsi host adapter instance.
306 - scsi_remove_device - detach and remove a SCSI device
307 - scsi_remove_host - detach and remove all SCSI devices owned by host
308 - scsi_report_bus_reset - report scsi _bus_ reset observed
309 - scsi_scan_host - scan SCSI bus
310 - scsi_track_queue_full - track successive QUEUE_FULL events
311 - scsi_unblock_requests - allow further commands to be queued to given host
312 - scsi_unregister - [calls scsi_host_put()]
313
314
315 Details::
316
317 /**
318 * scsi_add_device - creates new scsi device (lu) instance
319 * @shost: pointer to scsi host instance
320 * @channel: channel number (rarely other than 0)
321 * @id: target id number
322 * @lun: logical unit number
323 *
324 * Returns pointer to new struct scsi_device instance or
325 * ERR_PTR(-ENODEV) (or some other bent pointer) if something is
326 * wrong (e.g. no lu responds at given address)
327 *
328 * Might block: yes
329 *
330 * Notes: This call is usually performed internally during a scsi
331 * bus scan when an HBA is added (i.e. scsi_scan_host()). So it
332 * should only be called if the HBA becomes aware of a new scsi
333 * device (lu) after scsi_scan_host() has completed. If successful
334 * this call can lead to slave_alloc() and slave_configure() callbacks
335 * into the LLD.
336 *
337 * Defined in: drivers/scsi/scsi_scan.c
338 **/
339 struct scsi_device * scsi_add_device(struct Scsi_Host *shost,
340 unsigned int channel,
341 unsigned int id, unsigned int lun)
342
343
344 /**
345 * scsi_add_host - perform sysfs registration and set up transport class
346 * @shost: pointer to scsi host instance
347 * @dev: pointer to struct device of type scsi class
348 *
349 * Returns 0 on success, negative errno of failure (e.g. -ENOMEM)
350 *
351 * Might block: no
352 *
353 * Notes: Only required in "hotplug initialization model" after a
354 * successful call to scsi_host_alloc(). This function does not
355 * scan the bus; this can be done by calling scsi_scan_host() or
356 * in some other transport-specific way. The LLD must set up
357 * the transport template before calling this function and may only
358 * access the transport class data after this function has been called.
359 *
360 * Defined in: drivers/scsi/hosts.c
361 **/
362 int scsi_add_host(struct Scsi_Host *shost, struct device * dev)
363
364
365 /**
366 * scsi_change_queue_depth - allow LLD to change queue depth on a SCSI device
367 * @sdev: pointer to SCSI device to change queue depth on
368 * @tags Number of tags allowed if tagged queuing enabled,
369 * or number of commands the LLD can queue up
370 * in non-tagged mode (as per cmd_per_lun).
371 *
372 * Returns nothing
373 *
374 * Might block: no
375 *
376 * Notes: Can be invoked any time on a SCSI device controlled by this
377 * LLD. [Specifically during and after slave_configure() and prior to
378 * slave_destroy().] Can safely be invoked from interrupt code.
379 *
380 * Defined in: drivers/scsi/scsi.c [see source code for more notes]
381 *
382 **/
383 int scsi_change_queue_depth(struct scsi_device *sdev, int tags)
384
385
386 /**
387 * scsi_bios_ptable - return copy of block device's partition table
388 * @dev: pointer to block device
389 *
390 * Returns pointer to partition table, or NULL for failure
391 *
392 * Might block: yes
393 *
394 * Notes: Caller owns memory returned (free with kfree() )
395 *
396 * Defined in: drivers/scsi/scsicam.c
397 **/
398 unsigned char *scsi_bios_ptable(struct block_device *dev)
399
400
401 /**
402 * scsi_block_requests - prevent further commands being queued to given host
403 *
404 * @shost: pointer to host to block commands on
405 *
406 * Returns nothing
407 *
408 * Might block: no
409 *
410 * Notes: There is no timer nor any other means by which the requests
411 * get unblocked other than the LLD calling scsi_unblock_requests().
412 *
413 * Defined in: drivers/scsi/scsi_lib.c
414 **/
415 void scsi_block_requests(struct Scsi_Host * shost)
416
417
418 /**
419 * scsi_host_alloc - create a scsi host adapter instance and perform basic
420 * initialization.
421 * @sht: pointer to scsi host template
422 * @privsize: extra bytes to allocate in hostdata array (which is the
423 * last member of the returned Scsi_Host instance)
424 *
425 * Returns pointer to new Scsi_Host instance or NULL on failure
426 *
427 * Might block: yes
428 *
429 * Notes: When this call returns to the LLD, the SCSI bus scan on
430 * this host has _not_ yet been done.
431 * The hostdata array (by default zero length) is a per host scratch
432 * area for the LLD's exclusive use.
433 * Both associated refcounting objects have their refcount set to 1.
434 * Full registration (in sysfs) and a bus scan are performed later when
435 * scsi_add_host() and scsi_scan_host() are called.
436 *
437 * Defined in: drivers/scsi/hosts.c .
438 **/
439 struct Scsi_Host * scsi_host_alloc(const struct scsi_host_template * sht,
440 int privsize)
441
442
443 /**
444 * scsi_host_get - increment Scsi_Host instance refcount
445 * @shost: pointer to struct Scsi_Host instance
446 *
447 * Returns nothing
448 *
449 * Might block: currently may block but may be changed to not block
450 *
451 * Notes: Actually increments the counts in two sub-objects
452 *
453 * Defined in: drivers/scsi/hosts.c
454 **/
455 void scsi_host_get(struct Scsi_Host *shost)
456
457
458 /**
459 * scsi_host_put - decrement Scsi_Host instance refcount, free if 0
460 * @shost: pointer to struct Scsi_Host instance
461 *
462 * Returns nothing
463 *
464 * Might block: currently may block but may be changed to not block
465 *
466 * Notes: Actually decrements the counts in two sub-objects. If the
467 * latter refcount reaches 0, the Scsi_Host instance is freed.
468 * The LLD need not worry exactly when the Scsi_Host instance is
469 * freed, it just shouldn't access the instance after it has balanced
470 * out its refcount usage.
471 *
472 * Defined in: drivers/scsi/hosts.c
473 **/
474 void scsi_host_put(struct Scsi_Host *shost)
475
476
477 /**
478 * scsi_register - create and register a scsi host adapter instance.
479 * @sht: pointer to scsi host template
480 * @privsize: extra bytes to allocate in hostdata array (which is the
481 * last member of the returned Scsi_Host instance)
482 *
483 * Returns pointer to new Scsi_Host instance or NULL on failure
484 *
485 * Might block: yes
486 *
487 * Notes: When this call returns to the LLD, the SCSI bus scan on
488 * this host has _not_ yet been done.
489 * The hostdata array (by default zero length) is a per host scratch
490 * area for the LLD.
491 *
492 * Defined in: drivers/scsi/hosts.c .
493 **/
494 struct Scsi_Host * scsi_register(struct scsi_host_template * sht,
495 int privsize)
496
497
498 /**
499 * scsi_remove_device - detach and remove a SCSI device
500 * @sdev: a pointer to a scsi device instance
501 *
502 * Returns value: 0 on success, -EINVAL if device not attached
503 *
504 * Might block: yes
505 *
506 * Notes: If an LLD becomes aware that a scsi device (lu) has
507 * been removed but its host is still present then it can request
508 * the removal of that scsi device. If successful this call will
509 * lead to the slave_destroy() callback being invoked. sdev is an
510 * invalid pointer after this call.
511 *
512 * Defined in: drivers/scsi/scsi_sysfs.c .
513 **/
514 int scsi_remove_device(struct scsi_device *sdev)
515
516
517 /**
518 * scsi_remove_host - detach and remove all SCSI devices owned by host
519 * @shost: a pointer to a scsi host instance
520 *
521 * Returns value: 0 on success, 1 on failure (e.g. LLD busy ??)
522 *
523 * Might block: yes
524 *
525 * Notes: Should only be invoked if the "hotplug initialization
526 * model" is being used. It should be called _prior_ to
527 * scsi_unregister().
528 *
529 * Defined in: drivers/scsi/hosts.c .
530 **/
531 int scsi_remove_host(struct Scsi_Host *shost)
532
533
534 /**
535 * scsi_report_bus_reset - report scsi _bus_ reset observed
536 * @shost: a pointer to a scsi host involved
537 * @channel: channel (within) host on which scsi bus reset occurred
538 *
539 * Returns nothing
540 *
541 * Might block: no
542 *
543 * Notes: This only needs to be called if the reset is one which
544 * originates from an unknown location. Resets originated by the
545 * mid level itself don't need to call this, but there should be
546 * no harm. The main purpose of this is to make sure that a
547 * CHECK_CONDITION is properly treated.
548 *
549 * Defined in: drivers/scsi/scsi_error.c .
550 **/
551 void scsi_report_bus_reset(struct Scsi_Host * shost, int channel)
552
553
554 /**
555 * scsi_scan_host - scan SCSI bus
556 * @shost: a pointer to a scsi host instance
557 *
558 * Might block: yes
559 *
560 * Notes: Should be called after scsi_add_host()
561 *
562 * Defined in: drivers/scsi/scsi_scan.c
563 **/
564 void scsi_scan_host(struct Scsi_Host *shost)
565
566
567 /**
568 * scsi_track_queue_full - track successive QUEUE_FULL events on given
569 * device to determine if and when there is a need
570 * to adjust the queue depth on the device.
571 * @sdev: pointer to SCSI device instance
572 * @depth: Current number of outstanding SCSI commands on this device,
573 * not counting the one returned as QUEUE_FULL.
574 *
575 * Returns 0 - no change needed
576 * >0 - adjust queue depth to this new depth
577 * -1 - drop back to untagged operation using host->cmd_per_lun
578 * as the untagged command depth
579 *
580 * Might block: no
581 *
582 * Notes: LLDs may call this at any time and we will do "The Right
583 * Thing"; interrupt context safe.
584 *
585 * Defined in: drivers/scsi/scsi.c .
586 **/
587 int scsi_track_queue_full(struct scsi_device *sdev, int depth)
588
589
590 /**
591 * scsi_unblock_requests - allow further commands to be queued to given host
592 *
593 * @shost: pointer to host to unblock commands on
594 *
595 * Returns nothing
596 *
597 * Might block: no
598 *
599 * Defined in: drivers/scsi/scsi_lib.c .
600 **/
601 void scsi_unblock_requests(struct Scsi_Host * shost)
602
603
604 /**
605 * scsi_unregister - unregister and free memory used by host instance
606 * @shp: pointer to scsi host instance to unregister.
607 *
608 * Returns nothing
609 *
610 * Might block: no
611 *
612 * Notes: Should not be invoked if the "hotplug initialization
613 * model" is being used. Called internally by exit_this_scsi_driver()
614 * in the "passive initialization model". Hence a LLD has no need to
615 * call this function directly.
616 *
617 * Defined in: drivers/scsi/hosts.c .
618 **/
619 void scsi_unregister(struct Scsi_Host * shp)
620
621
622
623
624 Interface Functions
625 ===================
626 Interface functions are supplied (defined) by LLDs and their function
627 pointers are placed in an instance of struct scsi_host_template which
628 is passed to scsi_host_alloc() [or scsi_register() / init_this_scsi_driver()].
629 Some are mandatory. Interface functions should be declared static. The
630 accepted convention is that driver "xyz" will declare its slave_configure()
631 function as::
632
633 static int xyz_slave_configure(struct scsi_device * sdev);
634
635 and so forth for all interface functions listed below.
636
637 A pointer to this function should be placed in the 'slave_configure' member
638 of a "struct scsi_host_template" instance. A pointer to such an instance
639 should be passed to the mid level's scsi_host_alloc() [or scsi_register() /
640 init_this_scsi_driver()].
641
642 The interface functions are also described in the include/scsi/scsi_host.h
643 file immediately above their definition point in "struct scsi_host_template".
644 In some cases more detail is given in scsi_host.h than below.
645
646 The interface functions are listed below in alphabetical order.
647
648 Summary:
649
650 - bios_param - fetch head, sector, cylinder info for a disk
651 - eh_timed_out - notify the host that a command timer expired
652 - eh_abort_handler - abort given command
653 - eh_bus_reset_handler - issue SCSI bus reset
654 - eh_device_reset_handler - issue SCSI device reset
655 - eh_host_reset_handler - reset host (host bus adapter)
656 - info - supply information about given host
657 - ioctl - driver can respond to ioctls
658 - proc_info - supports /proc/scsi/{driver_name}/{host_no}
659 - queuecommand - queue scsi command, invoke 'done' on completion
660 - slave_alloc - prior to any commands being sent to a new device
661 - slave_configure - driver fine tuning for given device after attach
662 - slave_destroy - given device is about to be shut down
663
664
665 Details::
666
667 /**
668 * bios_param - fetch head, sector, cylinder info for a disk
669 * @sdev: pointer to scsi device context (defined in
670 * include/scsi/scsi_device.h)
671 * @bdev: pointer to block device context (defined in fs.h)
672 * @capacity: device size (in 512 byte sectors)
673 * @params: three element array to place output:
674 * params[0] number of heads (max 255)
675 * params[1] number of sectors (max 63)
676 * params[2] number of cylinders
677 *
678 * Return value is ignored
679 *
680 * Locks: none
681 *
682 * Calling context: process (sd)
683 *
684 * Notes: an arbitrary geometry (based on READ CAPACITY) is used
685 * if this function is not provided. The params array is
686 * pre-initialized with made up values just in case this function
687 * doesn't output anything.
688 *
689 * Optionally defined in: LLD
690 **/
691 int bios_param(struct scsi_device * sdev, struct block_device *bdev,
692 sector_t capacity, int params[3])
693
694
695 /**
696 * eh_timed_out - The timer for the command has just fired
697 * @scp: identifies command timing out
698 *
699 * Returns:
700 *
701 * EH_HANDLED: I fixed the error, please complete the command
702 * EH_RESET_TIMER: I need more time, reset the timer and
703 * begin counting again
704 * EH_NOT_HANDLED Begin normal error recovery
705 *
706 *
707 * Locks: None held
708 *
709 * Calling context: interrupt
710 *
711 * Notes: This is to give the LLD an opportunity to do local recovery.
712 * This recovery is limited to determining if the outstanding command
713 * will ever complete. You may not abort and restart the command from
714 * this callback.
715 *
716 * Optionally defined in: LLD
717 **/
718 int eh_timed_out(struct scsi_cmnd * scp)
719
720
721 /**
722 * eh_abort_handler - abort command associated with scp
723 * @scp: identifies command to be aborted
724 *
725 * Returns SUCCESS if command aborted else FAILED
726 *
727 * Locks: None held
728 *
729 * Calling context: kernel thread
730 *
731 * Notes: If 'no_async_abort' is defined this callback
732 * will be invoked from scsi_eh thread. No other commands
733 * will then be queued on current host during eh.
734 * Otherwise it will be called whenever scsi_timeout()
735 * is called due to a command timeout.
736 *
737 * Optionally defined in: LLD
738 **/
739 int eh_abort_handler(struct scsi_cmnd * scp)
740
741
742 /**
743 * eh_bus_reset_handler - issue SCSI bus reset
744 * @scp: SCSI bus that contains this device should be reset
745 *
746 * Returns SUCCESS if command aborted else FAILED
747 *
748 * Locks: None held
749 *
750 * Calling context: kernel thread
751 *
752 * Notes: Invoked from scsi_eh thread. No other commands will be
753 * queued on current host during eh.
754 *
755 * Optionally defined in: LLD
756 **/
757 int eh_bus_reset_handler(struct scsi_cmnd * scp)
758
759
760 /**
761 * eh_device_reset_handler - issue SCSI device reset
762 * @scp: identifies SCSI device to be reset
763 *
764 * Returns SUCCESS if command aborted else FAILED
765 *
766 * Locks: None held
767 *
768 * Calling context: kernel thread
769 *
770 * Notes: Invoked from scsi_eh thread. No other commands will be
771 * queued on current host during eh.
772 *
773 * Optionally defined in: LLD
774 **/
775 int eh_device_reset_handler(struct scsi_cmnd * scp)
776
777
778 /**
779 * eh_host_reset_handler - reset host (host bus adapter)
780 * @scp: SCSI host that contains this device should be reset
781 *
782 * Returns SUCCESS if command aborted else FAILED
783 *
784 * Locks: None held
785 *
786 * Calling context: kernel thread
787 *
788 * Notes: Invoked from scsi_eh thread. No other commands will be
789 * queued on current host during eh.
790 * With the default eh_strategy in place, if none of the _abort_,
791 * _device_reset_, _bus_reset_ or this eh handler function are
792 * defined (or they all return FAILED) then the device in question
793 * will be set offline whenever eh is invoked.
794 *
795 * Optionally defined in: LLD
796 **/
797 int eh_host_reset_handler(struct scsi_cmnd * scp)
798
799
800 /**
801 * info - supply information about given host: driver name plus data
802 * to distinguish given host
803 * @shp: host to supply information about
804 *
805 * Return ASCII null terminated string. [This driver is assumed to
806 * manage the memory pointed to and maintain it, typically for the
807 * lifetime of this host.]
808 *
809 * Locks: none
810 *
811 * Calling context: process
812 *
813 * Notes: Often supplies PCI or ISA information such as IO addresses
814 * and interrupt numbers. If not supplied struct Scsi_Host::name used
815 * instead. It is assumed the returned information fits on one line
816 * (i.e. does not included embedded newlines).
817 * The SCSI_IOCTL_PROBE_HOST ioctl yields the string returned by this
818 * function (or struct Scsi_Host::name if this function is not
819 * available).
820 * In a similar manner, init_this_scsi_driver() outputs to the console
821 * each host's "info" (or name) for the driver it is registering.
822 * Also if proc_info() is not supplied, the output of this function
823 * is used instead.
824 *
825 * Optionally defined in: LLD
826 **/
827 const char * info(struct Scsi_Host * shp)
828
829
830 /**
831 * ioctl - driver can respond to ioctls
832 * @sdp: device that ioctl was issued for
833 * @cmd: ioctl number
834 * @arg: pointer to read or write data from. Since it points to
835 * user space, should use appropriate kernel functions
836 * (e.g. copy_from_user() ). In the Unix style this argument
837 * can also be viewed as an unsigned long.
838 *
839 * Returns negative "errno" value when there is a problem. 0 or a
840 * positive value indicates success and is returned to the user space.
841 *
842 * Locks: none
843 *
844 * Calling context: process
845 *
846 * Notes: The SCSI subsystem uses a "trickle down" ioctl model.
847 * The user issues an ioctl() against an upper level driver
848 * (e.g. /dev/sdc) and if the upper level driver doesn't recognize
849 * the 'cmd' then it is passed to the SCSI mid level. If the SCSI
850 * mid level does not recognize it, then the LLD that controls
851 * the device receives the ioctl. According to recent Unix standards
852 * unsupported ioctl() 'cmd' numbers should return -ENOTTY.
853 *
854 * Optionally defined in: LLD
855 **/
856 int ioctl(struct scsi_device *sdp, int cmd, void *arg)
857
858
859 /**
860 * proc_info - supports /proc/scsi/{driver_name}/{host_no}
861 * @buffer: anchor point to output to (0==writeto1_read0) or fetch from
862 * (1==writeto1_read0).
863 * @start: where "interesting" data is written to. Ignored when
864 * 1==writeto1_read0.
865 * @offset: offset within buffer 0==writeto1_read0 is actually
866 * interested in. Ignored when 1==writeto1_read0 .
867 * @length: maximum (or actual) extent of buffer
868 * @host_no: host number of interest (struct Scsi_Host::host_no)
869 * @writeto1_read0: 1 -> data coming from user space towards driver
870 * (e.g. "echo some_string > /proc/scsi/xyz/2")
871 * 0 -> user what data from this driver
872 * (e.g. "cat /proc/scsi/xyz/2")
873 *
874 * Returns length when 1==writeto1_read0. Otherwise number of chars
875 * output to buffer past offset.
876 *
877 * Locks: none held
878 *
879 * Calling context: process
880 *
881 * Notes: Driven from scsi_proc.c which interfaces to proc_fs. proc_fs
882 * support can now be configured out of the scsi subsystem.
883 *
884 * Optionally defined in: LLD
885 **/
886 int proc_info(char * buffer, char ** start, off_t offset,
887 int length, int host_no, int writeto1_read0)
888
889
890 /**
891 * queuecommand - queue scsi command, invoke scp->scsi_done on completion
892 * @shost: pointer to the scsi host object
893 * @scp: pointer to scsi command object
894 *
895 * Returns 0 on success.
896 *
897 * If there's a failure, return either:
898 *
899 * SCSI_MLQUEUE_DEVICE_BUSY if the device queue is full, or
900 * SCSI_MLQUEUE_HOST_BUSY if the entire host queue is full
901 *
902 * On both of these returns, the mid-layer will requeue the I/O
903 *
904 * - if the return is SCSI_MLQUEUE_DEVICE_BUSY, only that particular
905 * device will be paused, and it will be unpaused when a command to
906 * the device returns (or after a brief delay if there are no more
907 * outstanding commands to it). Commands to other devices continue
908 * to be processed normally.
909 *
910 * - if the return is SCSI_MLQUEUE_HOST_BUSY, all I/O to the host
911 * is paused and will be unpaused when any command returns from
912 * the host (or after a brief delay if there are no outstanding
913 * commands to the host).
914 *
915 * For compatibility with earlier versions of queuecommand, any
916 * other return value is treated the same as
917 * SCSI_MLQUEUE_HOST_BUSY.
918 *
919 * Other types of errors that are detected immediately may be
920 * flagged by setting scp->result to an appropriate value,
921 * invoking the scp->scsi_done callback, and then returning 0
922 * from this function. If the command is not performed
923 * immediately (and the LLD is starting (or will start) the given
924 * command) then this function should place 0 in scp->result and
925 * return 0.
926 *
927 * Command ownership. If the driver returns zero, it owns the
928 * command and must take responsibility for ensuring the
929 * scp->scsi_done callback is executed. Note: the driver may
930 * call scp->scsi_done before returning zero, but after it has
931 * called scp->scsi_done, it may not return any value other than
932 * zero. If the driver makes a non-zero return, it must not
933 * execute the command's scsi_done callback at any time.
934 *
935 * Locks: up to and including 2.6.36, struct Scsi_Host::host_lock
936 * held on entry (with "irqsave") and is expected to be
937 * held on return. From 2.6.37 onwards, queuecommand is
938 * called without any locks held.
939 *
940 * Calling context: in interrupt (soft irq) or process context
941 *
942 * Notes: This function should be relatively fast. Normally it
943 * will not wait for IO to complete. Hence the scp->scsi_done
944 * callback is invoked (often directly from an interrupt service
945 * routine) some time after this function has returned. In some
946 * cases (e.g. pseudo adapter drivers that manufacture the
947 * response to a SCSI INQUIRY) the scp->scsi_done callback may be
948 * invoked before this function returns. If the scp->scsi_done
949 * callback is not invoked within a certain period the SCSI mid
950 * level will commence error processing. If a status of CHECK
951 * CONDITION is placed in "result" when the scp->scsi_done
952 * callback is invoked, then the LLD driver should perform
953 * autosense and fill in the struct scsi_cmnd::sense_buffer
954 * array. The scsi_cmnd::sense_buffer array is zeroed prior to
955 * the mid level queuing a command to an LLD.
956 *
957 * Defined in: LLD
958 **/
959 int queuecommand(struct Scsi_Host *shost, struct scsi_cmnd * scp)
960
961
962 /**
963 * slave_alloc - prior to any commands being sent to a new device
964 * (i.e. just prior to scan) this call is made
965 * @sdp: pointer to new device (about to be scanned)
966 *
967 * Returns 0 if ok. Any other return is assumed to be an error and
968 * the device is ignored.
969 *
970 * Locks: none
971 *
972 * Calling context: process
973 *
974 * Notes: Allows the driver to allocate any resources for a device
975 * prior to its initial scan. The corresponding scsi device may not
976 * exist but the mid level is just about to scan for it (i.e. send
977 * and INQUIRY command plus ...). If a device is found then
978 * slave_configure() will be called while if a device is not found
979 * slave_destroy() is called.
980 * For more details see the include/scsi/scsi_host.h file.
981 *
982 * Optionally defined in: LLD
983 **/
984 int slave_alloc(struct scsi_device *sdp)
985
986
987 /**
988 * slave_configure - driver fine tuning for given device just after it
989 * has been first scanned (i.e. it responded to an
990 * INQUIRY)
991 * @sdp: device that has just been attached
992 *
993 * Returns 0 if ok. Any other return is assumed to be an error and
994 * the device is taken offline. [offline devices will _not_ have
995 * slave_destroy() called on them so clean up resources.]
996 *
997 * Locks: none
998 *
999 * Calling context: process
1000 *
1001 * Notes: Allows the driver to inspect the response to the initial
1002 * INQUIRY done by the scanning code and take appropriate action.
1003 * For more details see the include/scsi/scsi_host.h file.
1004 *
1005 * Optionally defined in: LLD
1006 **/
1007 int slave_configure(struct scsi_device *sdp)
1008
1009
1010 /**
1011 * slave_destroy - given device is about to be shut down. All
1012 * activity has ceased on this device.
1013 * @sdp: device that is about to be shut down
1014 *
1015 * Returns nothing
1016 *
1017 * Locks: none
1018 *
1019 * Calling context: process
1020 *
1021 * Notes: Mid level structures for given device are still in place
1022 * but are about to be torn down. Any per device resources allocated
1023 * by this driver for given device should be freed now. No further
1024 * commands will be sent for this sdp instance. [However the device
1025 * could be re-attached in the future in which case a new instance
1026 * of struct scsi_device would be supplied by future slave_alloc()
1027 * and slave_configure() calls.]
1028 *
1029 * Optionally defined in: LLD
1030 **/
1031 void slave_destroy(struct scsi_device *sdp)
1032
1033
1034
1035 Data Structures
1036 ===============
1037 struct scsi_host_template
1038 -------------------------
1039 There is one "struct scsi_host_template" instance per LLD [#]_. It is
1040 typically initialized as a file scope static in a driver's header file. That
1041 way members that are not explicitly initialized will be set to 0 or NULL.
1042 Member of interest:
1043
1044 name
1045 - name of driver (may contain spaces, please limit to
1046 less than 80 characters)
1047
1048 proc_name
1049 - name used in "/proc/scsi/<proc_name>/<host_no>" and
1050 by sysfs in one of its "drivers" directories. Hence
1051 "proc_name" should only contain characters acceptable
1052 to a Unix file name.
1053
1054 ``(*queuecommand)()``
1055 - primary callback that the mid level uses to inject
1056 SCSI commands into an LLD.
1057
1058 The structure is defined and commented in include/scsi/scsi_host.h
1059
1060 .. [#] In extreme situations a single driver may have several instances
1061 if it controls several different classes of hardware (e.g. an LLD
1062 that handles both ISA and PCI cards and has a separate instance of
1063 struct scsi_host_template for each class).
1064
1065 struct Scsi_Host
1066 ----------------
1067 There is one struct Scsi_Host instance per host (HBA) that an LLD
1068 controls. The struct Scsi_Host structure has many members in common
1069 with "struct scsi_host_template". When a new struct Scsi_Host instance
1070 is created (in scsi_host_alloc() in hosts.c) those common members are
1071 initialized from the driver's struct scsi_host_template instance. Members
1072 of interest:
1073
1074 host_no
1075 - system wide unique number that is used for identifying
1076 this host. Issued in ascending order from 0.
1077 can_queue
1078 - must be greater than 0; do not send more than can_queue
1079 commands to the adapter.
1080 this_id
1081 - scsi id of host (scsi initiator) or -1 if not known
1082 sg_tablesize
1083 - maximum scatter gather elements allowed by host.
1084 Set this to SG_ALL or less to avoid chained SG lists.
1085 Must be at least 1.
1086 max_sectors
1087 - maximum number of sectors (usually 512 bytes) allowed
1088 in a single SCSI command. The default value of 0 leads
1089 to a setting of SCSI_DEFAULT_MAX_SECTORS (defined in
1090 scsi_host.h) which is currently set to 1024. So for a
1091 disk the maximum transfer size is 512 KB when max_sectors
1092 is not defined. Note that this size may not be sufficient
1093 for disk firmware uploads.
1094 cmd_per_lun
1095 - maximum number of commands that can be queued on devices
1096 controlled by the host. Overridden by LLD calls to
1097 scsi_change_queue_depth().
1098 no_async_abort
1099 - 1=>Asynchronous aborts are not supported
1100 - 0=>Timed-out commands will be aborted asynchronously
1101 hostt
1102 - pointer to driver's struct scsi_host_template from which
1103 this struct Scsi_Host instance was spawned
1104 hostt->proc_name
1105 - name of LLD. This is the driver name that sysfs uses
1106 transportt
1107 - pointer to driver's struct scsi_transport_template instance
1108 (if any). FC and SPI transports currently supported.
1109 sh_list
1110 - a double linked list of pointers to all struct Scsi_Host
1111 instances (currently ordered by ascending host_no)
1112 my_devices
1113 - a double linked list of pointers to struct scsi_device
1114 instances that belong to this host.
1115 hostdata[0]
1116 - area reserved for LLD at end of struct Scsi_Host. Size
1117 is set by the second argument (named 'xtr_bytes') to
1118 scsi_host_alloc() or scsi_register().
1119 vendor_id
1120 - a unique value that identifies the vendor supplying
1121 the LLD for the Scsi_Host. Used most often in validating
1122 vendor-specific message requests. Value consists of an
1123 identifier type and a vendor-specific value.
1124 See scsi_netlink.h for a description of valid formats.
1125
1126 The scsi_host structure is defined in include/scsi/scsi_host.h
1127
1128 struct scsi_device
1129 ------------------
1130 Generally, there is one instance of this structure for each SCSI logical unit
1131 on a host. Scsi devices connected to a host are uniquely identified by a
1132 channel number, target id and logical unit number (lun).
1133 The structure is defined in include/scsi/scsi_device.h
1134
1135 struct scsi_cmnd
1136 ----------------
1137 Instances of this structure convey SCSI commands to the LLD and responses
1138 back to the mid level. The SCSI mid level will ensure that no more SCSI
1139 commands become queued against the LLD than are indicated by
1140 scsi_change_queue_depth() (or struct Scsi_Host::cmd_per_lun). There will
1141 be at least one instance of struct scsi_cmnd available for each SCSI device.
1142 Members of interest:
1143
1144 cmnd
1145 - array containing SCSI command
1146 cmnd_len
1147 - length (in bytes) of SCSI command
1148 sc_data_direction
1149 - direction of data transfer in data phase. See
1150 "enum dma_data_direction" in include/linux/dma-mapping.h
1151 request_bufflen
1152 - number of data bytes to transfer (0 if no data phase)
1153 use_sg
1154 - ==0 -> no scatter gather list, hence transfer data
1155 to/from request_buffer
1156 - >0 -> scatter gather list (actually an array) in
1157 request_buffer with use_sg elements
1158 request_buffer
1159 - either contains data buffer or scatter gather list
1160 depending on the setting of use_sg. Scatter gather
1161 elements are defined by 'struct scatterlist' found
1162 in include/linux/scatterlist.h .
1163 done
1164 - function pointer that should be invoked by LLD when the
1165 SCSI command is completed (successfully or otherwise).
1166 Should only be called by an LLD if the LLD has accepted
1167 the command (i.e. queuecommand() returned or will return
1168 0). The LLD may invoke 'done' prior to queuecommand()
1169 finishing.
1170 result
1171 - should be set by LLD prior to calling 'done'. A value
1172 of 0 implies a successfully completed command (and all
1173 data (if any) has been transferred to or from the SCSI
1174 target device). 'result' is a 32 bit unsigned integer that
1175 can be viewed as 2 related bytes. The SCSI status value is
1176 in the LSB. See include/scsi/scsi.h status_byte() and
1177 host_byte() macros and related constants.
1178 sense_buffer
1179 - an array (maximum size: SCSI_SENSE_BUFFERSIZE bytes) that
1180 should be written when the SCSI status (LSB of 'result')
1181 is set to CHECK_CONDITION (2). When CHECK_CONDITION is
1182 set, if the top nibble of sense_buffer[0] has the value 7
1183 then the mid level will assume the sense_buffer array
1184 contains a valid SCSI sense buffer; otherwise the mid
1185 level will issue a REQUEST_SENSE SCSI command to
1186 retrieve the sense buffer. The latter strategy is error
1187 prone in the presence of command queuing so the LLD should
1188 always "auto-sense".
1189 device
1190 - pointer to scsi_device object that this command is
1191 associated with.
1192 resid
1193 - an LLD should set this unsigned integer to the requested
1194 transfer length (i.e. 'request_bufflen') less the number
1195 of bytes that are actually transferred. 'resid' is
1196 preset to 0 so an LLD can ignore it if it cannot detect
1197 underruns (overruns should not be reported). An LLD
1198 should set 'resid' prior to invoking 'done'. The most
1199 interesting case is data transfers from a SCSI target
1200 device (e.g. READs) that underrun.
1201 underflow
1202 - LLD should place (DID_ERROR << 16) in 'result' if
1203 actual number of bytes transferred is less than this
1204 figure. Not many LLDs implement this check and some that
1205 do just output an error message to the log rather than
1206 report a DID_ERROR. Better for an LLD to implement
1207 'resid'.
1208
1209 It is recommended that a LLD set 'resid' on data transfers from a SCSI
1210 target device (e.g. READs). It is especially important that 'resid' is set
1211 when such data transfers have sense keys of MEDIUM ERROR and HARDWARE ERROR
1212 (and possibly RECOVERED ERROR). In these cases if a LLD is in doubt how much
1213 data has been received then the safest approach is to indicate no bytes have
1214 been received. For example: to indicate that no valid data has been received
1215 a LLD might use these helpers::
1216
1217 scsi_set_resid(SCpnt, scsi_bufflen(SCpnt));
1218
1219 where 'SCpnt' is a pointer to a scsi_cmnd object. To indicate only three 512
1220 bytes blocks has been received 'resid' could be set like this::
1221
1222 scsi_set_resid(SCpnt, scsi_bufflen(SCpnt) - (3 * 512));
1223
1224 The scsi_cmnd structure is defined in include/scsi/scsi_cmnd.h
1225
1226
1227 Locks
1228 =====
1229 Each struct Scsi_Host instance has a spin_lock called struct
1230 Scsi_Host::default_lock which is initialized in scsi_host_alloc() [found in
1231 hosts.c]. Within the same function the struct Scsi_Host::host_lock pointer
1232 is initialized to point at default_lock. Thereafter lock and unlock
1233 operations performed by the mid level use the struct Scsi_Host::host_lock
1234 pointer. Previously drivers could override the host_lock pointer but
1235 this is not allowed anymore.
1236
1237
1238 Autosense
1239 =========
1240 Autosense (or auto-sense) is defined in the SAM-2 document as "the
1241 automatic return of sense data to the application client coincident
1242 with the completion of a SCSI command" when a status of CHECK CONDITION
1243 occurs. LLDs should perform autosense. This should be done when the LLD
1244 detects a CHECK CONDITION status by either:
1245
1246 a) instructing the SCSI protocol (e.g. SCSI Parallel Interface (SPI))
1247 to perform an extra data in phase on such responses
1248 b) or, the LLD issuing a REQUEST SENSE command itself
1249
1250 Either way, when a status of CHECK CONDITION is detected, the mid level
1251 decides whether the LLD has performed autosense by checking struct
1252 scsi_cmnd::sense_buffer[0] . If this byte has an upper nibble of 7 (or 0xf)
1253 then autosense is assumed to have taken place. If it has another value (and
1254 this byte is initialized to 0 before each command) then the mid level will
1255 issue a REQUEST SENSE command.
1256
1257 In the presence of queued commands the "nexus" that maintains sense
1258 buffer data from the command that failed until a following REQUEST SENSE
1259 may get out of synchronization. This is why it is best for the LLD
1260 to perform autosense.
1261
1262
1263 Changes since lk 2.4 series
1264 ===========================
1265 io_request_lock has been replaced by several finer grained locks. The lock
1266 relevant to LLDs is struct Scsi_Host::host_lock and there is
1267 one per SCSI host.
1268
1269 The older error handling mechanism has been removed. This means the
1270 LLD interface functions abort() and reset() have been removed.
1271 The struct scsi_host_template::use_new_eh_code flag has been removed.
1272
1273 In the 2.4 series the SCSI subsystem configuration descriptions were
1274 aggregated with the configuration descriptions from all other Linux
1275 subsystems in the Documentation/Configure.help file. In the 2.6 series,
1276 the SCSI subsystem now has its own (much smaller) drivers/scsi/Kconfig
1277 file that contains both configuration and help information.
1278
1279 struct SHT has been renamed to struct scsi_host_template.
1280
1281 Addition of the "hotplug initialization model" and many extra functions
1282 to support it.
1283
1284
1285 Credits
1286 =======
1287 The following people have contributed to this document:
1288
1289 - Mike Anderson <andmike at us dot ibm dot com>
1290 - James Bottomley <James dot Bottomley at hansenpartnership dot com>
1291 - Patrick Mansfield <patmans at us dot ibm dot com>
1292 - Christoph Hellwig <hch at infradead dot org>
1293 - Doug Ledford <dledford at redhat dot com>
1294 - Andries Brouwer <Andries dot Brouwer at cwi dot nl>
1295 - Randy Dunlap <rdunlap at xenotime dot net>
1296 - Alan Stern <stern at rowland dot harvard dot edu>
1297
1298
1299 Douglas Gilbert
1300 dgilbert at interlog dot com
1301
1302 21st September 2004
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