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1 Linux Kernel 2.6 series
2 SCSI mid_level - lower_level driver interface
3 =============================================
5 Introduction
6 ============
7 This document outlines the interface between the Linux SCSI mid level and
8 SCSI lower level drivers. Lower level drivers (LLDs) are variously called
9 host bus adapter (HBA) drivers and host drivers (HD). A "host" in this
10 context is a bridge between a computer IO bus (e.g. PCI or ISA) and a
11 single SCSI initiator port on a SCSI transport. An "initiator" port
12 (SCSI terminology, see SAM-3 at http://www.t10.org) sends SCSI commands
13 to "target" SCSI ports (e.g. disks). There can be many LLDs in a running
14 system, but only one per hardware type. Most LLDs can control one or more
15 SCSI HBAs. Some HBAs contain multiple hosts.
17 In some cases the SCSI transport is an external bus that already has
18 its own subsystem in Linux (e.g. USB and ieee1394). In such cases the
19 SCSI subsystem LLD is a software bridge to the other driver subsystem.
20 Examples are the usb-storage driver (found in the drivers/usb/storage
21 directory) and the ieee1394/sbp2 driver (found in the drivers/ieee1394
22 directory).
24 For example, the aic7xxx LLD controls Adaptec SCSI parallel interface
25 (SPI) controllers based on that company's 7xxx chip series. The aic7xxx
26 LLD can be built into the kernel or loaded as a module. There can only be
27 one aic7xxx LLD running in a Linux system but it may be controlling many
28 HBAs. These HBAs might be either on PCI daughter-boards or built into
29 the motherboard (or both). Some aic7xxx based HBAs are dual controllers
30 and thus represent two hosts. Like most modern HBAs, each aic7xxx host
31 has its own PCI device address. [The one-to-one correspondence between
32 a SCSI host and a PCI device is common but not required (e.g. with
33 ISA adapters).]
35 The SCSI mid level isolates an LLD from other layers such as the SCSI
36 upper layer drivers and the block layer.
38 This version of the document roughly matches linux kernel version 2.6.8 .
40 Documentation
41 =============
42 There is a SCSI documentation directory within the kernel source tree,
43 typically Documentation/scsi . Most documents are in plain
44 (i.e. ASCII) text. This file is named scsi_mid_low_api.txt and can be
45 found in that directory. A more recent copy of this document may be found
46 at http://web.archive.org/web/20070107183357rn_1/sg.torque.net/scsi/.
47 Many LLDs are documented there (e.g. aic7xxx.txt). The SCSI mid-level is
48 briefly described in scsi.txt which contains a url to a document
49 describing the SCSI subsystem in the lk 2.4 series. Two upper level
50 drivers have documents in that directory: st.txt (SCSI tape driver) and
51 scsi-generic.txt (for the sg driver).
53 Some documentation (or urls) for LLDs may be found in the C source code
54 or in the same directory as the C source code. For example to find a url
55 about the USB mass storage driver see the
56 /usr/src/linux/drivers/usb/storage directory.
58 Driver structure
59 ================
60 Traditionally an LLD for the SCSI subsystem has been at least two files in
61 the drivers/scsi directory. For example, a driver called "xyz" has a header
62 file "xyz.h" and a source file "xyz.c". [Actually there is no good reason
63 why this couldn't all be in one file; the header file is superfluous.] Some
64 drivers that have been ported to several operating systems have more than
65 two files. For example the aic7xxx driver has separate files for generic
66 and OS-specific code (e.g. FreeBSD and Linux). Such drivers tend to have
67 their own directory under the drivers/scsi directory.
69 When a new LLD is being added to Linux, the following files (found in the
70 drivers/scsi directory) will need some attention: Makefile and Kconfig .
71 It is probably best to study how existing LLDs are organized.
73 As the 2.5 series development kernels evolve into the 2.6 series
74 production series, changes are being introduced into this interface. An
75 example of this is driver initialization code where there are now 2 models
76 available. The older one, similar to what was found in the lk 2.4 series,
77 is based on hosts that are detected at HBA driver load time. This will be
78 referred to the "passive" initialization model. The newer model allows HBAs
79 to be hot plugged (and unplugged) during the lifetime of the LLD and will
80 be referred to as the "hotplug" initialization model. The newer model is
81 preferred as it can handle both traditional SCSI equipment that is
82 permanently connected as well as modern "SCSI" devices (e.g. USB or
83 IEEE 1394 connected digital cameras) that are hotplugged. Both
84 initialization models are discussed in the following sections.
86 An LLD interfaces to the SCSI subsystem several ways:
87 a) directly invoking functions supplied by the mid level
88 b) passing a set of function pointers to a registration function
89 supplied by the mid level. The mid level will then invoke these
90 functions at some point in the future. The LLD will supply
91 implementations of these functions.
92 c) direct access to instances of well known data structures maintained
93 by the mid level
95 Those functions in group a) are listed in a section entitled "Mid level
96 supplied functions" below.
98 Those functions in group b) are listed in a section entitled "Interface
99 functions" below. Their function pointers are placed in the members of
100 "struct scsi_host_template", an instance of which is passed to
101 scsi_host_alloc() ** . Those interface functions that the LLD does not
102 wish to supply should have NULL placed in the corresponding member of
103 struct scsi_host_template. Defining an instance of struct
104 scsi_host_template at file scope will cause NULL to be placed in function
105 pointer members not explicitly initialized.
107 Those usages in group c) should be handled with care, especially in a
108 "hotplug" environment. LLDs should be aware of the lifetime of instances
109 that are shared with the mid level and other layers.
111 All functions defined within an LLD and all data defined at file scope
112 should be static. For example the slave_alloc() function in an LLD
113 called "xxx" could be defined as
114 "static int xxx_slave_alloc(struct scsi_device * sdev) { /* code */ }"
116 ** the scsi_host_alloc() function is a replacement for the rather vaguely
117 named scsi_register() function in most situations.
120 Hotplug initialization model
121 ============================
122 In this model an LLD controls when SCSI hosts are introduced and removed
123 from the SCSI subsystem. Hosts can be introduced as early as driver
124 initialization and removed as late as driver shutdown. Typically a driver
125 will respond to a sysfs probe() callback that indicates an HBA has been
126 detected. After confirming that the new device is one that the LLD wants
127 to control, the LLD will initialize the HBA and then register a new host
128 with the SCSI mid level.
130 During LLD initialization the driver should register itself with the
131 appropriate IO bus on which it expects to find HBA(s) (e.g. the PCI bus).
132 This can probably be done via sysfs. Any driver parameters (especially
133 those that are writable after the driver is loaded) could also be
134 registered with sysfs at this point. The SCSI mid level first becomes
135 aware of an LLD when that LLD registers its first HBA.
137 At some later time, the LLD becomes aware of an HBA and what follows
138 is a typical sequence of calls between the LLD and the mid level.
139 This example shows the mid level scanning the newly introduced HBA for 3
140 scsi devices of which only the first 2 respond:
142 HBA PROBE: assume 2 SCSI devices found in scan
143 LLD mid level LLD
144 ===-------------------=========--------------------===------
145 scsi_host_alloc() -->
146 scsi_add_host() ---->
147 scsi_scan_host() -------+
148 |
149 slave_alloc()
150 slave_configure() --> scsi_change_queue_depth()
151 |
152 slave_alloc()
153 slave_configure()
154 |
155 slave_alloc() ***
156 slave_destroy() ***
157 ------------------------------------------------------------
159 If the LLD wants to adjust the default queue settings, it can invoke
160 scsi_change_queue_depth() in its slave_configure() routine.
162 *** For scsi devices that the mid level tries to scan but do not
163 respond, a slave_alloc(), slave_destroy() pair is called.
165 When an HBA is being removed it could be as part of an orderly shutdown
166 associated with the LLD module being unloaded (e.g. with the "rmmod"
167 command) or in response to a "hot unplug" indicated by sysfs()'s
168 remove() callback being invoked. In either case, the sequence is the
169 same:
171 HBA REMOVE: assume 2 SCSI devices attached
172 LLD mid level LLD
173 ===----------------------=========-----------------===------
174 scsi_remove_host() ---------+
175 |
176 slave_destroy()
177 slave_destroy()
178 scsi_host_put()
179 ------------------------------------------------------------
181 It may be useful for a LLD to keep track of struct Scsi_Host instances
182 (a pointer is returned by scsi_host_alloc()). Such instances are "owned"
183 by the mid-level. struct Scsi_Host instances are freed from
184 scsi_host_put() when the reference count hits zero.
186 Hot unplugging an HBA that controls a disk which is processing SCSI
187 commands on a mounted file system is an interesting situation. Reference
188 counting logic is being introduced into the mid level to cope with many
189 of the issues involved. See the section on reference counting below.
192 The hotplug concept may be extended to SCSI devices. Currently, when an
193 HBA is added, the scsi_scan_host() function causes a scan for SCSI devices
194 attached to the HBA's SCSI transport. On newer SCSI transports the HBA
195 may become aware of a new SCSI device _after_ the scan has completed.
196 An LLD can use this sequence to make the mid level aware of a SCSI device:
198 SCSI DEVICE hotplug
199 LLD mid level LLD
200 ===-------------------=========--------------------===------
201 scsi_add_device() ------+
202 |
203 slave_alloc()
204 slave_configure() [--> scsi_change_queue_depth()]
205 ------------------------------------------------------------
207 In a similar fashion, an LLD may become aware that a SCSI device has been
208 removed (unplugged) or the connection to it has been interrupted. Some
209 existing SCSI transports (e.g. SPI) may not become aware that a SCSI
210 device has been removed until a subsequent SCSI command fails which will
211 probably cause that device to be set offline by the mid level. An LLD that
212 detects the removal of a SCSI device can instigate its removal from
213 upper layers with this sequence:
215 SCSI DEVICE hot unplug
216 LLD mid level LLD
217 ===----------------------=========-----------------===------
218 scsi_remove_device() -------+
219 |
220 slave_destroy()
221 ------------------------------------------------------------
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().
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.
238 There are 3 reference counting functions of interest associated with
239 struct Scsi_Host:
240 - scsi_host_alloc(): returns a pointer to new instance of struct
241 Scsi_Host which has its reference count ^^ set to 1
242 - scsi_host_get(): adds 1 to the reference count of the given instance
243 - scsi_host_put(): decrements 1 from the reference count of the given
244 instance. If the reference count reaches 0 then the given instance
245 is freed
247 The scsi_device structure has had reference counting infrastructure added.
248 This effectively spreads the ownership of struct scsi_device instances
249 across the various SCSI layers which use them. Previously such instances
250 were exclusively owned by the mid level. See the access functions declared
251 towards the end of include/scsi/scsi_device.h . If an LLD wants to keep
252 a copy of a pointer to a scsi_device instance it should use scsi_device_get()
253 to bump its reference count. When it is finished with the pointer it can
254 use scsi_device_put() to decrement its reference count (and potentially
255 delete it).
257 ^^ struct Scsi_Host actually has 2 reference counts which are manipulated
258 in parallel by these functions.
261 Conventions
262 ===========
263 First, Linus Torvalds's thoughts on C coding style can be found in the
264 Documentation/process/coding-style.rst file.
266 Next, there is a movement to "outlaw" typedefs introducing synonyms for
267 struct tags. Both can be still found in the SCSI subsystem, but
268 the typedefs have been moved to a single file, scsi_typedefs.h to
269 make their future removal easier, for example:
270 "typedef struct scsi_cmnd Scsi_Cmnd;"
272 Also, most C99 enhancements are encouraged to the extent they are supported
273 by the relevant gcc compilers. So C99 style structure and array
274 initializers are encouraged where appropriate. Don't go too far,
275 VLAs are not properly supported yet. An exception to this is the use of
276 "//" style comments; /*...*/ comments are still preferred in Linux.
278 Well written, tested and documented code, need not be re-formatted to
279 comply with the above conventions. For example, the aic7xxx driver
280 comes to Linux from FreeBSD and Adaptec's own labs. No doubt FreeBSD
281 and Adaptec have their own coding conventions.
284 Mid level supplied functions
285 ============================
286 These functions are supplied by the SCSI mid level for use by LLDs.
287 The names (i.e. entry points) of these functions are exported
288 so an LLD that is a module can access them. The kernel will
289 arrange for the SCSI mid level to be loaded and initialized before any LLD
290 is initialized. The functions below are listed alphabetically and their
291 names all start with "scsi_".
293 Summary:
294 scsi_add_device - creates new scsi device (lu) instance
295 scsi_add_host - perform sysfs registration and set up transport class
296 scsi_change_queue_depth - change the queue depth on a SCSI device
297 scsi_bios_ptable - return copy of block device's partition table
298 scsi_block_requests - prevent further commands being queued to given host
299 scsi_host_alloc - return a new scsi_host instance whose refcount==1
300 scsi_host_get - increments Scsi_Host instance's refcount
301 scsi_host_put - decrements Scsi_Host instance's refcount (free if 0)
302 scsi_partsize - parse partition table into cylinders, heads + sectors
303 scsi_register - create and register a scsi host adapter instance.
304 scsi_remove_device - detach and remove a SCSI device
305 scsi_remove_host - detach and remove all SCSI devices owned by host
306 scsi_report_bus_reset - report scsi _bus_ reset observed
307 scsi_scan_host - scan SCSI bus
308 scsi_track_queue_full - track successive QUEUE_FULL events
309 scsi_unblock_requests - allow further commands to be queued to given host
310 scsi_unregister - [calls scsi_host_put()]
313 Details:
315 /**
316 * scsi_add_device - creates new scsi device (lu) instance
317 * @shost: pointer to scsi host instance
318 * @channel: channel number (rarely other than 0)
319 * @id: target id number
320 * @lun: logical unit number
321 *
322 * Returns pointer to new struct scsi_device instance or
323 * ERR_PTR(-ENODEV) (or some other bent pointer) if something is
324 * wrong (e.g. no lu responds at given address)
325 *
326 * Might block: yes
327 *
328 * Notes: This call is usually performed internally during a scsi
329 * bus scan when an HBA is added (i.e. scsi_scan_host()). So it
330 * should only be called if the HBA becomes aware of a new scsi
331 * device (lu) after scsi_scan_host() has completed. If successful
332 * this call can lead to slave_alloc() and slave_configure() callbacks
333 * into the LLD.
334 *
335 * Defined in: drivers/scsi/scsi_scan.c
336 **/
337 struct scsi_device * scsi_add_device(struct Scsi_Host *shost,
338 unsigned int channel,
339 unsigned int id, unsigned int lun)
342 /**
343 * scsi_add_host - perform sysfs registration and set up transport class
344 * @shost: pointer to scsi host instance
345 * @dev: pointer to struct device of type scsi class
346 *
347 * Returns 0 on success, negative errno of failure (e.g. -ENOMEM)
348 *
349 * Might block: no
350 *
351 * Notes: Only required in "hotplug initialization model" after a
352 * successful call to scsi_host_alloc(). This function does not
353 * scan the bus; this can be done by calling scsi_scan_host() or
354 * in some other transport-specific way. The LLD must set up
355 * the transport template before calling this function and may only
356 * access the transport class data after this function has been called.
357 *
358 * Defined in: drivers/scsi/hosts.c
359 **/
360 int scsi_add_host(struct Scsi_Host *shost, struct device * dev)
363 /**
364 * scsi_change_queue_depth - allow LLD to change queue depth on a SCSI device
365 * @sdev: pointer to SCSI device to change queue depth on
366 * @tags Number of tags allowed if tagged queuing enabled,
367 * or number of commands the LLD can queue up
368 * in non-tagged mode (as per cmd_per_lun).
369 *
370 * Returns nothing
371 *
372 * Might block: no
373 *
374 * Notes: Can be invoked any time on a SCSI device controlled by this
375 * LLD. [Specifically during and after slave_configure() and prior to
376 * slave_destroy().] Can safely be invoked from interrupt code.
377 *
378 * Defined in: drivers/scsi/scsi.c [see source code for more notes]
379 *
380 **/
381 int scsi_change_queue_depth(struct scsi_device *sdev, int tags)
384 /**
385 * scsi_bios_ptable - return copy of block device's partition table
386 * @dev: pointer to block device
387 *
388 * Returns pointer to partition table, or NULL for failure
389 *
390 * Might block: yes
391 *
392 * Notes: Caller owns memory returned (free with kfree() )
393 *
394 * Defined in: drivers/scsi/scsicam.c
395 **/
396 unsigned char *scsi_bios_ptable(struct block_device *dev)
399 /**
400 * scsi_block_requests - prevent further commands being queued to given host
401 *
402 * @shost: pointer to host to block commands on
403 *
404 * Returns nothing
405 *
406 * Might block: no
407 *
408 * Notes: There is no timer nor any other means by which the requests
409 * get unblocked other than the LLD calling scsi_unblock_requests().
410 *
411 * Defined in: drivers/scsi/scsi_lib.c
412 **/
413 void scsi_block_requests(struct Scsi_Host * shost)
416 /**
417 * scsi_host_alloc - create a scsi host adapter instance and perform basic
418 * initialization.
419 * @sht: pointer to scsi host template
420 * @privsize: extra bytes to allocate in hostdata array (which is the
421 * last member of the returned Scsi_Host instance)
422 *
423 * Returns pointer to new Scsi_Host instance or NULL on failure
424 *
425 * Might block: yes
426 *
427 * Notes: When this call returns to the LLD, the SCSI bus scan on
428 * this host has _not_ yet been done.
429 * The hostdata array (by default zero length) is a per host scratch
430 * area for the LLD's exclusive use.
431 * Both associated refcounting objects have their refcount set to 1.
432 * Full registration (in sysfs) and a bus scan are performed later when
433 * scsi_add_host() and scsi_scan_host() are called.
434 *
435 * Defined in: drivers/scsi/hosts.c .
436 **/
437 struct Scsi_Host * scsi_host_alloc(struct scsi_host_template * sht,
438 int privsize)
441 /**
442 * scsi_host_get - increment Scsi_Host instance refcount
443 * @shost: pointer to struct Scsi_Host instance
444 *
445 * Returns nothing
446 *
447 * Might block: currently may block but may be changed to not block
448 *
449 * Notes: Actually increments the counts in two sub-objects
450 *
451 * Defined in: drivers/scsi/hosts.c
452 **/
453 void scsi_host_get(struct Scsi_Host *shost)
456 /**
457 * scsi_host_put - decrement Scsi_Host instance refcount, free if 0
458 * @shost: pointer to struct Scsi_Host instance
459 *
460 * Returns nothing
461 *
462 * Might block: currently may block but may be changed to not block
463 *
464 * Notes: Actually decrements the counts in two sub-objects. If the
465 * latter refcount reaches 0, the Scsi_Host instance is freed.
466 * The LLD need not worry exactly when the Scsi_Host instance is
467 * freed, it just shouldn't access the instance after it has balanced
468 * out its refcount usage.
469 *
470 * Defined in: drivers/scsi/hosts.c
471 **/
472 void scsi_host_put(struct Scsi_Host *shost)
475 /**
476 * scsi_partsize - parse partition table into cylinders, heads + sectors
477 * @buf: pointer to partition table
478 * @capacity: size of (total) disk in 512 byte sectors
479 * @cyls: outputs number of cylinders calculated via this pointer
480 * @hds: outputs number of heads calculated via this pointer
481 * @secs: outputs number of sectors calculated via this pointer
482 *
483 * Returns 0 on success, -1 on failure
484 *
485 * Might block: no
486 *
487 * Notes: Caller owns memory returned (free with kfree() )
488 *
489 * Defined in: drivers/scsi/scsicam.c
490 **/
491 int scsi_partsize(unsigned char *buf, unsigned long capacity,
492 unsigned int *cyls, unsigned int *hds, unsigned int *secs)
495 /**
496 * scsi_register - create and register a scsi host adapter instance.
497 * @sht: pointer to scsi host template
498 * @privsize: extra bytes to allocate in hostdata array (which is the
499 * last member of the returned Scsi_Host instance)
500 *
501 * Returns pointer to new Scsi_Host instance or NULL on failure
502 *
503 * Might block: yes
504 *
505 * Notes: When this call returns to the LLD, the SCSI bus scan on
506 * this host has _not_ yet been done.
507 * The hostdata array (by default zero length) is a per host scratch
508 * area for the LLD.
509 *
510 * Defined in: drivers/scsi/hosts.c .
511 **/
512 struct Scsi_Host * scsi_register(struct scsi_host_template * sht,
513 int privsize)
516 /**
517 * scsi_remove_device - detach and remove a SCSI device
518 * @sdev: a pointer to a scsi device instance
519 *
520 * Returns value: 0 on success, -EINVAL if device not attached
521 *
522 * Might block: yes
523 *
524 * Notes: If an LLD becomes aware that a scsi device (lu) has
525 * been removed but its host is still present then it can request
526 * the removal of that scsi device. If successful this call will
527 * lead to the slave_destroy() callback being invoked. sdev is an
528 * invalid pointer after this call.
529 *
530 * Defined in: drivers/scsi/scsi_sysfs.c .
531 **/
532 int scsi_remove_device(struct scsi_device *sdev)
535 /**
536 * scsi_remove_host - detach and remove all SCSI devices owned by host
537 * @shost: a pointer to a scsi host instance
538 *
539 * Returns value: 0 on success, 1 on failure (e.g. LLD busy ??)
540 *
541 * Might block: yes
542 *
543 * Notes: Should only be invoked if the "hotplug initialization
544 * model" is being used. It should be called _prior_ to
545 * scsi_unregister().
546 *
547 * Defined in: drivers/scsi/hosts.c .
548 **/
549 int scsi_remove_host(struct Scsi_Host *shost)
552 /**
553 * scsi_report_bus_reset - report scsi _bus_ reset observed
554 * @shost: a pointer to a scsi host involved
555 * @channel: channel (within) host on which scsi bus reset occurred
556 *
557 * Returns nothing
558 *
559 * Might block: no
560 *
561 * Notes: This only needs to be called if the reset is one which
562 * originates from an unknown location. Resets originated by the
563 * mid level itself don't need to call this, but there should be
564 * no harm. The main purpose of this is to make sure that a
565 * CHECK_CONDITION is properly treated.
566 *
567 * Defined in: drivers/scsi/scsi_error.c .
568 **/
569 void scsi_report_bus_reset(struct Scsi_Host * shost, int channel)
572 /**
573 * scsi_scan_host - scan SCSI bus
574 * @shost: a pointer to a scsi host instance
575 *
576 * Might block: yes
577 *
578 * Notes: Should be called after scsi_add_host()
579 *
580 * Defined in: drivers/scsi/scsi_scan.c
581 **/
582 void scsi_scan_host(struct Scsi_Host *shost)
585 /**
586 * scsi_track_queue_full - track successive QUEUE_FULL events on given
587 * device to determine if and when there is a need
588 * to adjust the queue depth on the device.
589 * @sdev: pointer to SCSI device instance
590 * @depth: Current number of outstanding SCSI commands on this device,
591 * not counting the one returned as QUEUE_FULL.
592 *
593 * Returns 0 - no change needed
594 * >0 - adjust queue depth to this new depth
595 * -1 - drop back to untagged operation using host->cmd_per_lun
596 * as the untagged command depth
597 *
598 * Might block: no
599 *
600 * Notes: LLDs may call this at any time and we will do "The Right
601 * Thing"; interrupt context safe.
602 *
603 * Defined in: drivers/scsi/scsi.c .
604 **/
605 int scsi_track_queue_full(struct scsi_device *sdev, int depth)
608 /**
609 * scsi_unblock_requests - allow further commands to be queued to given host
610 *
611 * @shost: pointer to host to unblock commands on
612 *
613 * Returns nothing
614 *
615 * Might block: no
616 *
617 * Defined in: drivers/scsi/scsi_lib.c .
618 **/
619 void scsi_unblock_requests(struct Scsi_Host * shost)
622 /**
623 * scsi_unregister - unregister and free memory used by host instance
624 * @shp: pointer to scsi host instance to unregister.
625 *
626 * Returns nothing
627 *
628 * Might block: no
629 *
630 * Notes: Should not be invoked if the "hotplug initialization
631 * model" is being used. Called internally by exit_this_scsi_driver()
632 * in the "passive initialization model". Hence a LLD has no need to
633 * call this function directly.
634 *
635 * Defined in: drivers/scsi/hosts.c .
636 **/
637 void scsi_unregister(struct Scsi_Host * shp)
642 Interface Functions
643 ===================
644 Interface functions are supplied (defined) by LLDs and their function
645 pointers are placed in an instance of struct scsi_host_template which
646 is passed to scsi_host_alloc() [or scsi_register() / init_this_scsi_driver()].
647 Some are mandatory. Interface functions should be declared static. The
648 accepted convention is that driver "xyz" will declare its slave_configure()
649 function as:
650 static int xyz_slave_configure(struct scsi_device * sdev);
651 and so forth for all interface functions listed below.
653 A pointer to this function should be placed in the 'slave_configure' member
654 of a "struct scsi_host_template" instance. A pointer to such an instance
655 should be passed to the mid level's scsi_host_alloc() [or scsi_register() /
656 init_this_scsi_driver()].
658 The interface functions are also described in the include/scsi/scsi_host.h
659 file immediately above their definition point in "struct scsi_host_template".
660 In some cases more detail is given in scsi_host.h than below.
662 The interface functions are listed below in alphabetical order.
664 Summary:
665 bios_param - fetch head, sector, cylinder info for a disk
666 eh_timed_out - notify the host that a command timer expired
667 eh_abort_handler - abort given command
668 eh_bus_reset_handler - issue SCSI bus reset
669 eh_device_reset_handler - issue SCSI device reset
670 eh_host_reset_handler - reset host (host bus adapter)
671 info - supply information about given host
672 ioctl - driver can respond to ioctls
673 proc_info - supports /proc/scsi/{driver_name}/{host_no}
674 queuecommand - queue scsi command, invoke 'done' on completion
675 slave_alloc - prior to any commands being sent to a new device
676 slave_configure - driver fine tuning for given device after attach
677 slave_destroy - given device is about to be shut down
680 Details:
682 /**
683 * bios_param - fetch head, sector, cylinder info for a disk
684 * @sdev: pointer to scsi device context (defined in
685 * include/scsi/scsi_device.h)
686 * @bdev: pointer to block device context (defined in fs.h)
687 * @capacity: device size (in 512 byte sectors)
688 * @params: three element array to place output:
689 * params[0] number of heads (max 255)
690 * params[1] number of sectors (max 63)
691 * params[2] number of cylinders
692 *
693 * Return value is ignored
694 *
695 * Locks: none
696 *
697 * Calling context: process (sd)
698 *
699 * Notes: an arbitrary geometry (based on READ CAPACITY) is used
700 * if this function is not provided. The params array is
701 * pre-initialized with made up values just in case this function
702 * doesn't output anything.
703 *
704 * Optionally defined in: LLD
705 **/
706 int bios_param(struct scsi_device * sdev, struct block_device *bdev,
707 sector_t capacity, int params[3])
710 /**
711 * eh_timed_out - The timer for the command has just fired
712 * @scp: identifies command timing out
713 *
714 * Returns:
715 *
716 * EH_HANDLED: I fixed the error, please complete the command
717 * EH_RESET_TIMER: I need more time, reset the timer and
718 * begin counting again
719 * EH_NOT_HANDLED Begin normal error recovery
720 *
721 *
722 * Locks: None held
723 *
724 * Calling context: interrupt
725 *
726 * Notes: This is to give the LLD an opportunity to do local recovery.
727 * This recovery is limited to determining if the outstanding command
728 * will ever complete. You may not abort and restart the command from
729 * this callback.
730 *
731 * Optionally defined in: LLD
732 **/
733 int eh_timed_out(struct scsi_cmnd * scp)
736 /**
737 * eh_abort_handler - abort command associated with scp
738 * @scp: identifies command to be aborted
739 *
740 * Returns SUCCESS if command aborted else FAILED
741 *
742 * Locks: None held
743 *
744 * Calling context: kernel thread
745 *
746 * Notes: If 'no_async_abort' is defined this callback
747 * will be invoked from scsi_eh thread. No other commands
748 * will then be queued on current host during eh.
749 * Otherwise it will be called whenever scsi_times_out()
750 * is called due to a command timeout.
751 *
752 * Optionally defined in: LLD
753 **/
754 int eh_abort_handler(struct scsi_cmnd * scp)
757 /**
758 * eh_bus_reset_handler - issue SCSI bus reset
759 * @scp: SCSI bus that contains this device should be reset
760 *
761 * Returns SUCCESS if command aborted else FAILED
762 *
763 * Locks: None held
764 *
765 * Calling context: kernel thread
766 *
767 * Notes: Invoked from scsi_eh thread. No other commands will be
768 * queued on current host during eh.
769 *
770 * Optionally defined in: LLD
771 **/
772 int eh_bus_reset_handler(struct scsi_cmnd * scp)
775 /**
776 * eh_device_reset_handler - issue SCSI device reset
777 * @scp: identifies SCSI device to be reset
778 *
779 * Returns SUCCESS if command aborted else FAILED
780 *
781 * Locks: None held
782 *
783 * Calling context: kernel thread
784 *
785 * Notes: Invoked from scsi_eh thread. No other commands will be
786 * queued on current host during eh.
787 *
788 * Optionally defined in: LLD
789 **/
790 int eh_device_reset_handler(struct scsi_cmnd * scp)
793 /**
794 * eh_host_reset_handler - reset host (host bus adapter)
795 * @scp: SCSI host that contains this device should be reset
796 *
797 * Returns SUCCESS if command aborted else FAILED
798 *
799 * Locks: None held
800 *
801 * Calling context: kernel thread
802 *
803 * Notes: Invoked from scsi_eh thread. No other commands will be
804 * queued on current host during eh.
805 * With the default eh_strategy in place, if none of the _abort_,
806 * _device_reset_, _bus_reset_ or this eh handler function are
807 * defined (or they all return FAILED) then the device in question
808 * will be set offline whenever eh is invoked.
809 *
810 * Optionally defined in: LLD
811 **/
812 int eh_host_reset_handler(struct scsi_cmnd * scp)
815 /**
816 * info - supply information about given host: driver name plus data
817 * to distinguish given host
818 * @shp: host to supply information about
819 *
820 * Return ASCII null terminated string. [This driver is assumed to
821 * manage the memory pointed to and maintain it, typically for the
822 * lifetime of this host.]
823 *
824 * Locks: none
825 *
826 * Calling context: process
827 *
828 * Notes: Often supplies PCI or ISA information such as IO addresses
829 * and interrupt numbers. If not supplied struct Scsi_Host::name used
830 * instead. It is assumed the returned information fits on one line
831 * (i.e. does not included embedded newlines).
832 * The SCSI_IOCTL_PROBE_HOST ioctl yields the string returned by this
833 * function (or struct Scsi_Host::name if this function is not
834 * available).
835 * In a similar manner, init_this_scsi_driver() outputs to the console
836 * each host's "info" (or name) for the driver it is registering.
837 * Also if proc_info() is not supplied, the output of this function
838 * is used instead.
839 *
840 * Optionally defined in: LLD
841 **/
842 const char * info(struct Scsi_Host * shp)
845 /**
846 * ioctl - driver can respond to ioctls
847 * @sdp: device that ioctl was issued for
848 * @cmd: ioctl number
849 * @arg: pointer to read or write data from. Since it points to
850 * user space, should use appropriate kernel functions
851 * (e.g. copy_from_user() ). In the Unix style this argument
852 * can also be viewed as an unsigned long.
853 *
854 * Returns negative "errno" value when there is a problem. 0 or a
855 * positive value indicates success and is returned to the user space.
856 *
857 * Locks: none
858 *
859 * Calling context: process
860 *
861 * Notes: The SCSI subsystem uses a "trickle down" ioctl model.
862 * The user issues an ioctl() against an upper level driver
863 * (e.g. /dev/sdc) and if the upper level driver doesn't recognize
864 * the 'cmd' then it is passed to the SCSI mid level. If the SCSI
865 * mid level does not recognize it, then the LLD that controls
866 * the device receives the ioctl. According to recent Unix standards
867 * unsupported ioctl() 'cmd' numbers should return -ENOTTY.
868 *
869 * Optionally defined in: LLD
870 **/
871 int ioctl(struct scsi_device *sdp, int cmd, void *arg)
874 /**
875 * proc_info - supports /proc/scsi/{driver_name}/{host_no}
876 * @buffer: anchor point to output to (0==writeto1_read0) or fetch from
877 * (1==writeto1_read0).
878 * @start: where "interesting" data is written to. Ignored when
879 * 1==writeto1_read0.
880 * @offset: offset within buffer 0==writeto1_read0 is actually
881 * interested in. Ignored when 1==writeto1_read0 .
882 * @length: maximum (or actual) extent of buffer
883 * @host_no: host number of interest (struct Scsi_Host::host_no)
884 * @writeto1_read0: 1 -> data coming from user space towards driver
885 * (e.g. "echo some_string > /proc/scsi/xyz/2")
886 * 0 -> user what data from this driver
887 * (e.g. "cat /proc/scsi/xyz/2")
888 *
889 * Returns length when 1==writeto1_read0. Otherwise number of chars
890 * output to buffer past offset.
891 *
892 * Locks: none held
893 *
894 * Calling context: process
895 *
896 * Notes: Driven from scsi_proc.c which interfaces to proc_fs. proc_fs
897 * support can now be configured out of the scsi subsystem.
898 *
899 * Optionally defined in: LLD
900 **/
901 int proc_info(char * buffer, char ** start, off_t offset,
902 int length, int host_no, int writeto1_read0)
905 /**
906 * queuecommand - queue scsi command, invoke scp->scsi_done on completion
907 * @shost: pointer to the scsi host object
908 * @scp: pointer to scsi command object
909 *
910 * Returns 0 on success.
911 *
912 * If there's a failure, return either:
913 *
914 * SCSI_MLQUEUE_DEVICE_BUSY if the device queue is full, or
915 * SCSI_MLQUEUE_HOST_BUSY if the entire host queue is full
916 *
917 * On both of these returns, the mid-layer will requeue the I/O
918 *
919 * - if the return is SCSI_MLQUEUE_DEVICE_BUSY, only that particular
920 * device will be paused, and it will be unpaused when a command to
921 * the device returns (or after a brief delay if there are no more
922 * outstanding commands to it). Commands to other devices continue
923 * to be processed normally.
924 *
925 * - if the return is SCSI_MLQUEUE_HOST_BUSY, all I/O to the host
926 * is paused and will be unpaused when any command returns from
927 * the host (or after a brief delay if there are no outstanding
928 * commands to the host).
929 *
930 * For compatibility with earlier versions of queuecommand, any
931 * other return value is treated the same as
932 * SCSI_MLQUEUE_HOST_BUSY.
933 *
934 * Other types of errors that are detected immediately may be
935 * flagged by setting scp->result to an appropriate value,
936 * invoking the scp->scsi_done callback, and then returning 0
937 * from this function. If the command is not performed
938 * immediately (and the LLD is starting (or will start) the given
939 * command) then this function should place 0 in scp->result and
940 * return 0.
941 *
942 * Command ownership. If the driver returns zero, it owns the
943 * command and must take responsibility for ensuring the
944 * scp->scsi_done callback is executed. Note: the driver may
945 * call scp->scsi_done before returning zero, but after it has
946 * called scp->scsi_done, it may not return any value other than
947 * zero. If the driver makes a non-zero return, it must not
948 * execute the command's scsi_done callback at any time.
949 *
950 * Locks: up to and including 2.6.36, struct Scsi_Host::host_lock
951 * held on entry (with "irqsave") and is expected to be
952 * held on return. From 2.6.37 onwards, queuecommand is
953 * called without any locks held.
954 *
955 * Calling context: in interrupt (soft irq) or process context
956 *
957 * Notes: This function should be relatively fast. Normally it
958 * will not wait for IO to complete. Hence the scp->scsi_done
959 * callback is invoked (often directly from an interrupt service
960 * routine) some time after this function has returned. In some
961 * cases (e.g. pseudo adapter drivers that manufacture the
962 * response to a SCSI INQUIRY) the scp->scsi_done callback may be
963 * invoked before this function returns. If the scp->scsi_done
964 * callback is not invoked within a certain period the SCSI mid
965 * level will commence error processing. If a status of CHECK
966 * CONDITION is placed in "result" when the scp->scsi_done
967 * callback is invoked, then the LLD driver should perform
968 * autosense and fill in the struct scsi_cmnd::sense_buffer
969 * array. The scsi_cmnd::sense_buffer array is zeroed prior to
970 * the mid level queuing a command to an LLD.
971 *
972 * Defined in: LLD
973 **/
974 int queuecommand(struct Scsi_Host *shost, struct scsi_cmnd * scp)
977 /**
978 * slave_alloc - prior to any commands being sent to a new device
979 * (i.e. just prior to scan) this call is made
980 * @sdp: pointer to new device (about to be scanned)
981 *
982 * Returns 0 if ok. Any other return is assumed to be an error and
983 * the device is ignored.
984 *
985 * Locks: none
986 *
987 * Calling context: process
988 *
989 * Notes: Allows the driver to allocate any resources for a device
990 * prior to its initial scan. The corresponding scsi device may not
991 * exist but the mid level is just about to scan for it (i.e. send
992 * and INQUIRY command plus ...). If a device is found then
993 * slave_configure() will be called while if a device is not found
994 * slave_destroy() is called.
995 * For more details see the include/scsi/scsi_host.h file.
996 *
997 * Optionally defined in: LLD
998 **/
999 int slave_alloc(struct scsi_device *sdp)
1002 /**
1003 * slave_configure - driver fine tuning for given device just after it
1004 * has been first scanned (i.e. it responded to an
1005 * INQUIRY)
1006 * @sdp: device that has just been attached
1007 *
1008 * Returns 0 if ok. Any other return is assumed to be an error and
1009 * the device is taken offline. [offline devices will _not_ have
1010 * slave_destroy() called on them so clean up resources.]
1011 *
1012 * Locks: none
1013 *
1014 * Calling context: process
1015 *
1016 * Notes: Allows the driver to inspect the response to the initial
1017 * INQUIRY done by the scanning code and take appropriate action.
1018 * For more details see the include/scsi/scsi_host.h file.
1019 *
1020 * Optionally defined in: LLD
1021 **/
1022 int slave_configure(struct scsi_device *sdp)
1025 /**
1026 * slave_destroy - given device is about to be shut down. All
1027 * activity has ceased on this device.
1028 * @sdp: device that is about to be shut down
1029 *
1030 * Returns nothing
1031 *
1032 * Locks: none
1033 *
1034 * Calling context: process
1035 *
1036 * Notes: Mid level structures for given device are still in place
1037 * but are about to be torn down. Any per device resources allocated
1038 * by this driver for given device should be freed now. No further
1039 * commands will be sent for this sdp instance. [However the device
1040 * could be re-attached in the future in which case a new instance
1041 * of struct scsi_device would be supplied by future slave_alloc()
1042 * and slave_configure() calls.]
1043 *
1044 * Optionally defined in: LLD
1045 **/
1046 void slave_destroy(struct scsi_device *sdp)
1050 Data Structures
1051 ===============
1052 struct scsi_host_template
1053 -------------------------
1054 There is one "struct scsi_host_template" instance per LLD ***. It is
1055 typically initialized as a file scope static in a driver's header file. That
1056 way members that are not explicitly initialized will be set to 0 or NULL.
1057 Member of interest:
1058 name - name of driver (may contain spaces, please limit to
1059 less than 80 characters)
1060 proc_name - name used in "/proc/scsi/<proc_name>/<host_no>" and
1061 by sysfs in one of its "drivers" directories. Hence
1062 "proc_name" should only contain characters acceptable
1063 to a Unix file name.
1064 (*queuecommand)() - primary callback that the mid level uses to inject
1065 SCSI commands into an LLD.
1066 The structure is defined and commented in include/scsi/scsi_host.h
1068 *** In extreme situations a single driver may have several instances
1069 if it controls several different classes of hardware (e.g. an LLD
1070 that handles both ISA and PCI cards and has a separate instance of
1071 struct scsi_host_template for each class).
1073 struct Scsi_Host
1074 ----------------
1075 There is one struct Scsi_Host instance per host (HBA) that an LLD
1076 controls. The struct Scsi_Host structure has many members in common
1077 with "struct scsi_host_template". When a new struct Scsi_Host instance
1078 is created (in scsi_host_alloc() in hosts.c) those common members are
1079 initialized from the driver's struct scsi_host_template instance. Members
1080 of interest:
1081 host_no - system wide unique number that is used for identifying
1082 this host. Issued in ascending order from 0.
1083 can_queue - must be greater than 0; do not send more than can_queue
1084 commands to the adapter.
1085 this_id - scsi id of host (scsi initiator) or -1 if not known
1086 sg_tablesize - maximum scatter gather elements allowed by host.
1087 0 implies scatter gather not supported by host
1088 max_sectors - maximum number of sectors (usually 512 bytes) allowed
1089 in a single SCSI command. The default value of 0 leads
1090 to a setting of SCSI_DEFAULT_MAX_SECTORS (defined in
1091 scsi_host.h) which is currently set to 1024. So for a
1092 disk the maximum transfer size is 512 KB when max_sectors
1093 is not defined. Note that this size may not be sufficient
1094 for disk firmware uploads.
1095 cmd_per_lun - 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 unchecked_isa_dma - 1=>only use bottom 16 MB of ram (ISA DMA addressing
1099 restriction), 0=>can use full 32 bit (or better) DMA
1100 address space
1101 use_clustering - 1=>SCSI commands in mid level's queue can be merged,
1102 0=>disallow SCSI command merging
1103 no_async_abort - 1=>Asynchronous aborts are not supported
1104 0=>Timed-out commands will be aborted asynchronously
1105 hostt - pointer to driver's struct scsi_host_template from which
1106 this struct Scsi_Host instance was spawned
1107 hostt->proc_name - name of LLD. This is the driver name that sysfs uses
1108 transportt - pointer to driver's struct scsi_transport_template instance
1109 (if any). FC and SPI transports currently supported.
1110 sh_list - a double linked list of pointers to all struct Scsi_Host
1111 instances (currently ordered by ascending host_no)
1112 my_devices - a double linked list of pointers to struct scsi_device
1113 instances that belong to this host.
1114 hostdata[0] - area reserved for LLD at end of struct Scsi_Host. Size
1115 is set by the second argument (named 'xtr_bytes') to
1116 scsi_host_alloc() or scsi_register().
1117 vendor_id - a unique value that identifies the vendor supplying
1118 the LLD for the Scsi_Host. Used most often in validating
1119 vendor-specific message requests. Value consists of an
1120 identifier type and a vendor-specific value.
1121 See scsi_netlink.h for a description of valid formats.
1123 The scsi_host structure is defined in include/scsi/scsi_host.h
1125 struct scsi_device
1126 ------------------
1127 Generally, there is one instance of this structure for each SCSI logical unit
1128 on a host. Scsi devices connected to a host are uniquely identified by a
1129 channel number, target id and logical unit number (lun).
1130 The structure is defined in include/scsi/scsi_device.h
1132 struct scsi_cmnd
1133 ----------------
1134 Instances of this structure convey SCSI commands to the LLD and responses
1135 back to the mid level. The SCSI mid level will ensure that no more SCSI
1136 commands become queued against the LLD than are indicated by
1137 scsi_change_queue_depth() (or struct Scsi_Host::cmd_per_lun). There will
1138 be at least one instance of struct scsi_cmnd available for each SCSI device.
1139 Members of interest:
1140 cmnd - array containing SCSI command
1141 cmnd_len - length (in bytes) of SCSI command
1142 sc_data_direction - direction of data transfer in data phase. See
1143 "enum dma_data_direction" in include/linux/dma-mapping.h
1144 request_bufflen - number of data bytes to transfer (0 if no data phase)
1145 use_sg - ==0 -> no scatter gather list, hence transfer data
1146 to/from request_buffer
1147 - >0 -> scatter gather list (actually an array) in
1148 request_buffer with use_sg elements
1149 request_buffer - either contains data buffer or scatter gather list
1150 depending on the setting of use_sg. Scatter gather
1151 elements are defined by 'struct scatterlist' found
1152 in include/linux/scatterlist.h .
1153 done - function pointer that should be invoked by LLD when the
1154 SCSI command is completed (successfully or otherwise).
1155 Should only be called by an LLD if the LLD has accepted
1156 the command (i.e. queuecommand() returned or will return
1157 0). The LLD may invoke 'done' prior to queuecommand()
1158 finishing.
1159 result - should be set by LLD prior to calling 'done'. A value
1160 of 0 implies a successfully completed command (and all
1161 data (if any) has been transferred to or from the SCSI
1162 target device). 'result' is a 32 bit unsigned integer that
1163 can be viewed as 4 related bytes. The SCSI status value is
1164 in the LSB. See include/scsi/scsi.h status_byte(),
1165 msg_byte(), host_byte() and driver_byte() macros and
1166 related constants.
1167 sense_buffer - an array (maximum size: SCSI_SENSE_BUFFERSIZE bytes) that
1168 should be written when the SCSI status (LSB of 'result')
1169 is set to CHECK_CONDITION (2). When CHECK_CONDITION is
1170 set, if the top nibble of sense_buffer[0] has the value 7
1171 then the mid level will assume the sense_buffer array
1172 contains a valid SCSI sense buffer; otherwise the mid
1173 level will issue a REQUEST_SENSE SCSI command to
1174 retrieve the sense buffer. The latter strategy is error
1175 prone in the presence of command queuing so the LLD should
1176 always "auto-sense".
1177 device - pointer to scsi_device object that this command is
1178 associated with.
1179 resid - an LLD should set this signed integer to the requested
1180 transfer length (i.e. 'request_bufflen') less the number
1181 of bytes that are actually transferred. 'resid' is
1182 preset to 0 so an LLD can ignore it if it cannot detect
1183 underruns (overruns should be rare). If possible an LLD
1184 should set 'resid' prior to invoking 'done'. The most
1185 interesting case is data transfers from a SCSI target
1186 device (e.g. READs) that underrun.
1187 underflow - LLD should place (DID_ERROR << 16) in 'result' if
1188 actual number of bytes transferred is less than this
1189 figure. Not many LLDs implement this check and some that
1190 do just output an error message to the log rather than
1191 report a DID_ERROR. Better for an LLD to implement
1192 'resid'.
1194 It is recommended that a LLD set 'resid' on data transfers from a SCSI
1195 target device (e.g. READs). It is especially important that 'resid' is set
1196 when such data transfers have sense keys of MEDIUM ERROR and HARDWARE ERROR
1197 (and possibly RECOVERED ERROR). In these cases if a LLD is in doubt how much
1198 data has been received then the safest approach is to indicate no bytes have
1199 been received. For example: to indicate that no valid data has been received
1200 a LLD might use these helpers:
1201 scsi_set_resid(SCpnt, scsi_bufflen(SCpnt));
1202 where 'SCpnt' is a pointer to a scsi_cmnd object. To indicate only three 512
1203 bytes blocks has been received 'resid' could be set like this:
1204 scsi_set_resid(SCpnt, scsi_bufflen(SCpnt) - (3 * 512));
1206 The scsi_cmnd structure is defined in include/scsi/scsi_cmnd.h
1209 Locks
1210 =====
1211 Each struct Scsi_Host instance has a spin_lock called struct
1212 Scsi_Host::default_lock which is initialized in scsi_host_alloc() [found in
1213 hosts.c]. Within the same function the struct Scsi_Host::host_lock pointer
1214 is initialized to point at default_lock. Thereafter lock and unlock
1215 operations performed by the mid level use the struct Scsi_Host::host_lock
1216 pointer. Previously drivers could override the host_lock pointer but
1217 this is not allowed anymore.
1220 Autosense
1221 =========
1222 Autosense (or auto-sense) is defined in the SAM-2 document as "the
1223 automatic return of sense data to the application client coincident
1224 with the completion of a SCSI command" when a status of CHECK CONDITION
1225 occurs. LLDs should perform autosense. This should be done when the LLD
1226 detects a CHECK CONDITION status by either:
1227 a) instructing the SCSI protocol (e.g. SCSI Parallel Interface (SPI))
1228 to perform an extra data in phase on such responses
1229 b) or, the LLD issuing a REQUEST SENSE command itself
1231 Either way, when a status of CHECK CONDITION is detected, the mid level
1232 decides whether the LLD has performed autosense by checking struct
1233 scsi_cmnd::sense_buffer[0] . If this byte has an upper nibble of 7 (or 0xf)
1234 then autosense is assumed to have taken place. If it has another value (and
1235 this byte is initialized to 0 before each command) then the mid level will
1236 issue a REQUEST SENSE command.
1238 In the presence of queued commands the "nexus" that maintains sense
1239 buffer data from the command that failed until a following REQUEST SENSE
1240 may get out of synchronization. This is why it is best for the LLD
1241 to perform autosense.
1244 Changes since lk 2.4 series
1245 ===========================
1246 io_request_lock has been replaced by several finer grained locks. The lock
1247 relevant to LLDs is struct Scsi_Host::host_lock and there is
1248 one per SCSI host.
1250 The older error handling mechanism has been removed. This means the
1251 LLD interface functions abort() and reset() have been removed.
1252 The struct scsi_host_template::use_new_eh_code flag has been removed.
1254 In the 2.4 series the SCSI subsystem configuration descriptions were
1255 aggregated with the configuration descriptions from all other Linux
1256 subsystems in the Documentation/Configure.help file. In the 2.6 series,
1257 the SCSI subsystem now has its own (much smaller) drivers/scsi/Kconfig
1258 file that contains both configuration and help information.
1260 struct SHT has been renamed to struct scsi_host_template.
1262 Addition of the "hotplug initialization model" and many extra functions
1263 to support it.
1266 Credits
1267 =======
1268 The following people have contributed to this document:
1269 Mike Anderson <andmike at us dot ibm dot com>
1270 James Bottomley <James dot Bottomley at hansenpartnership dot com>
1271 Patrick Mansfield <patmans at us dot ibm dot com>
1272 Christoph Hellwig <hch at infradead dot org>
1273 Doug Ledford <dledford at redhat dot com>
1274 Andries Brouwer <Andries dot Brouwer at cwi dot nl>
1275 Randy Dunlap <rdunlap at xenotime dot net>
1276 Alan Stern <stern at rowland dot harvard dot edu>
1279 Douglas Gilbert
1280 dgilbert at interlog dot com
1281 21st September 2004