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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 or MCA 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://www.torque.net/scsi/scsi_mid_low_api.txt.gz .
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 The Linux kernel source Documentation/DocBook/scsidrivers.tmpl file
59 refers to this file. With the appropriate DocBook tool-set, this permits
60 users to generate html, ps and pdf renderings of information within this
61 file (e.g. the interface functions).
63 Driver structure
64 ================
65 Traditionally an LLD for the SCSI subsystem has been at least two files in
66 the drivers/scsi directory. For example, a driver called "xyz" has a header
67 file "xyz.h" and a source file "xyz.c". [Actually there is no good reason
68 why this couldn't all be in one file; the header file is superfluous.] Some
69 drivers that have been ported to several operating systems have more than
70 two files. For example the aic7xxx driver has separate files for generic
71 and OS-specific code (e.g. FreeBSD and Linux). Such drivers tend to have
72 their own directory under the drivers/scsi directory.
74 When a new LLD is being added to Linux, the following files (found in the
75 drivers/scsi directory) will need some attention: Makefile and Kconfig .
76 It is probably best to study how existing LLDs are organized.
78 As the 2.5 series development kernels evolve into the 2.6 series
79 production series, changes are being introduced into this interface. An
80 example of this is driver initialization code where there are now 2 models
81 available. The older one, similar to what was found in the lk 2.4 series,
82 is based on hosts that are detected at HBA driver load time. This will be
83 referred to the "passive" initialization model. The newer model allows HBAs
84 to be hot plugged (and unplugged) during the lifetime of the LLD and will
85 be referred to as the "hotplug" initialization model. The newer model is
86 preferred as it can handle both traditional SCSI equipment that is
87 permanently connected as well as modern "SCSI" devices (e.g. USB or
88 IEEE 1394 connected digital cameras) that are hotplugged. Both
89 initialization models are discussed in the following sections.
91 An LLD interfaces to the SCSI subsystem several ways:
92 a) directly invoking functions supplied by the mid level
93 b) passing a set of function pointers to a registration function
94 supplied by the mid level. The mid level will then invoke these
95 functions at some point in the future. The LLD will supply
96 implementations of these functions.
97 c) direct access to instances of well known data structures maintained
98 by the mid level
100 Those functions in group a) are listed in a section entitled "Mid level
101 supplied functions" below.
103 Those functions in group b) are listed in a section entitled "Interface
104 functions" below. Their function pointers are placed in the members of
105 "struct scsi_host_template", an instance of which is passed to
106 scsi_host_alloc() ** . Those interface functions that the LLD does not
107 wish to supply should have NULL placed in the corresponding member of
108 struct scsi_host_template. Defining an instance of struct
109 scsi_host_template at file scope will cause NULL to be placed in function
110 pointer members not explicitly initialized.
112 Those usages in group c) should be handled with care, especially in a
113 "hotplug" environment. LLDs should be aware of the lifetime of instances
114 that are shared with the mid level and other layers.
116 All functions defined within an LLD and all data defined at file scope
117 should be static. For example the slave_alloc() function in an LLD
118 called "xxx" could be defined as
119 "static int xxx_slave_alloc(struct scsi_device * sdev) { /* code */ }"
121 ** the scsi_host_alloc() function is a replacement for the rather vaguely
122 named scsi_register() function in most situations. The scsi_register()
123 and scsi_unregister() functions remain to support legacy LLDs that use
124 the passive initialization model.
127 Hotplug initialization model
128 ============================
129 In this model an LLD controls when SCSI hosts are introduced and removed
130 from the SCSI subsystem. Hosts can be introduced as early as driver
131 initialization and removed as late as driver shutdown. Typically a driver
132 will respond to a sysfs probe() callback that indicates an HBA has been
133 detected. After confirming that the new device is one that the LLD wants
134 to control, the LLD will initialize the HBA and then register a new host
135 with the SCSI mid level.
137 During LLD initialization the driver should register itself with the
138 appropriate IO bus on which it expects to find HBA(s) (e.g. the PCI bus).
139 This can probably be done via sysfs. Any driver parameters (especially
140 those that are writable after the driver is loaded) could also be
141 registered with sysfs at this point. The SCSI mid level first becomes
142 aware of an LLD when that LLD registers its first HBA.
144 At some later time, the LLD becomes aware of an HBA and what follows
145 is a typical sequence of calls between the LLD and the mid level.
146 This example shows the mid level scanning the newly introduced HBA for 3
147 scsi devices of which only the first 2 respond:
149 HBA PROBE: assume 2 SCSI devices found in scan
150 LLD mid level LLD
151 ===-------------------=========--------------------===------
152 scsi_host_alloc() -->
153 scsi_add_host() --------+
154 |
155 slave_alloc()
156 slave_configure() --> scsi_adjust_queue_depth()
157 |
158 slave_alloc()
159 slave_configure()
160 |
161 slave_alloc() ***
162 slave_destroy() ***
163 ------------------------------------------------------------
165 If the LLD wants to adjust the default queue settings, it can invoke
166 scsi_adjust_queue_depth() in its slave_configure() routine.
168 *** For scsi devices that the mid level tries to scan but do not
169 respond, a slave_alloc(), slave_destroy() pair is called.
171 When an HBA is being removed it could be as part of an orderly shutdown
172 associated with the LLD module being unloaded (e.g. with the "rmmod"
173 command) or in response to a "hot unplug" indicated by sysfs()'s
174 remove() callback being invoked. In either case, the sequence is the
175 same:
177 HBA REMOVE: assume 2 SCSI devices attached
178 LLD mid level LLD
179 ===----------------------=========-----------------===------
180 scsi_remove_host() ---------+
181 |
182 slave_destroy()
183 slave_destroy()
184 scsi_host_put()
185 ------------------------------------------------------------
187 It may be useful for a LLD to keep track of struct Scsi_Host instances
188 (a pointer is returned by scsi_host_alloc()). Such instances are "owned"
189 by the mid-level. struct Scsi_Host instances are freed from
190 scsi_host_put() when the reference count hits zero.
192 Hot unplugging an HBA that controls a disk which is processing SCSI
193 commands on a mounted file system is an interesting situation. Reference
194 counting logic is being introduced into the mid level to cope with many
195 of the issues involved. See the section on reference counting below.
198 The hotplug concept may be extended to SCSI devices. Currently, when an
199 HBA is added, the scsi_add_host() function causes a scan for SCSI devices
200 attached to the HBA's SCSI transport. On newer SCSI transports the HBA
201 may become aware of a new SCSI device _after_ the scan has completed.
202 An LLD can use this sequence to make the mid level aware of a SCSI device:
204 SCSI DEVICE hotplug
205 LLD mid level LLD
206 ===-------------------=========--------------------===------
207 scsi_add_device() ------+
208 |
209 slave_alloc()
210 slave_configure() [--> scsi_adjust_queue_depth()]
211 ------------------------------------------------------------
213 In a similar fashion, an LLD may become aware that a SCSI device has been
214 removed (unplugged) or the connection to it has been interrupted. Some
215 existing SCSI transports (e.g. SPI) may not become aware that a SCSI
216 device has been removed until a subsequent SCSI command fails which will
217 probably cause that device to be set offline by the mid level. An LLD that
218 detects the removal of a SCSI device can instigate its removal from
219 upper layers with this sequence:
221 SCSI DEVICE hot unplug
222 LLD mid level LLD
223 ===----------------------=========-----------------===------
224 scsi_remove_device() -------+
225 |
226 slave_destroy()
227 ------------------------------------------------------------
229 It may be useful for an LLD to keep track of struct scsi_device instances
230 (a pointer is passed as the parameter to slave_alloc() and
231 slave_configure() callbacks). Such instances are "owned" by the mid-level.
232 struct scsi_device instances are freed after slave_destroy().
235 Passive initialization model
236 ============================
237 These older LLDs include a file called "scsi_module.c" [yes the ".c" is a
238 little surprising] in their source code. For that file to work an
239 instance of struct scsi_host_template with the name "driver_template"
240 needs to be defined. Here is a typical code sequence used in this model:
241 static struct scsi_host_template driver_template = {
242 ...
243 };
244 #include "scsi_module.c"
246 The scsi_module.c file contains two functions:
247 - init_this_scsi_driver() which is executed when the LLD is
248 initialized (i.e. boot time or module load time)
249 - exit_this_scsi_driver() which is executed when the LLD is shut
250 down (i.e. module unload time)
251 Note: since these functions are tagged with __init and __exit qualifiers
252 an LLD should not call them explicitly (since the kernel does that).
254 Here is an example of an initialization sequence when two hosts are
255 detected (so detect() returns 2) and the SCSI bus scan on each host
256 finds 1 SCSI device (and a second device does not respond).
258 LLD mid level LLD
259 ===----------------------=========-----------------===------
260 init_this_scsi_driver() ----+
261 |
262 detect() -----------------+
263 | |
264 | scsi_register()
265 | scsi_register()
266 |
267 slave_alloc()
268 slave_configure() --> scsi_adjust_queue_depth()
269 slave_alloc() ***
270 slave_destroy() ***
271 |
272 slave_alloc()
273 slave_configure()
274 slave_alloc() ***
275 slave_destroy() ***
276 ------------------------------------------------------------
278 The mid level invokes scsi_adjust_queue_depth() with tagged queuing off and
279 "cmd_per_lun" for that host as the queue length. These settings can be
280 overridden by a slave_configure() supplied by the LLD.
282 *** For scsi devices that the mid level tries to scan but do not
283 respond, a slave_alloc(), slave_destroy() pair is called.
285 Here is an LLD shutdown sequence:
287 LLD mid level LLD
288 ===----------------------=========-----------------===------
289 exit_this_scsi_driver() ----+
290 |
291 slave_destroy()
292 release() --> scsi_unregister()
293 |
294 slave_destroy()
295 release() --> scsi_unregister()
296 ------------------------------------------------------------
298 An LLD need not define slave_destroy() (i.e. it is optional).
300 The shortcoming of the "passive initialization model" is that host
301 registration and de-registration are (typically) tied to LLD initialization
302 and shutdown. Once the LLD is initialized then a new host that appears
303 (e.g. via hotplugging) cannot easily be added without a redundant
304 driver shutdown and re-initialization. It may be possible to write an LLD
305 that uses both initialization models.
308 Reference Counting
309 ==================
310 The Scsi_Host structure has had reference counting infrastructure added.
311 This effectively spreads the ownership of struct Scsi_Host instances
312 across the various SCSI layers which use them. Previously such instances
313 were exclusively owned by the mid level. LLDs would not usually need to
314 directly manipulate these reference counts but there may be some cases
315 where they do.
317 There are 3 reference counting functions of interest associated with
318 struct Scsi_Host:
319 - scsi_host_alloc(): returns a pointer to new instance of struct
320 Scsi_Host which has its reference count ^^ set to 1
321 - scsi_host_get(): adds 1 to the reference count of the given instance
322 - scsi_host_put(): decrements 1 from the reference count of the given
323 instance. If the reference count reaches 0 then the given instance
324 is freed
326 The Scsi_device structure has had reference counting infrastructure added.
327 This effectively spreads the ownership of struct Scsi_device instances
328 across the various SCSI layers which use them. Previously such instances
329 were exclusively owned by the mid level. See the access functions declared
330 towards the end of include/scsi/scsi_device.h . If an LLD wants to keep
331 a copy of a pointer to a Scsi_device instance it should use scsi_device_get()
332 to bump its reference count. When it is finished with the pointer it can
333 use scsi_device_put() to decrement its reference count (and potentially
334 delete it).
336 ^^ struct Scsi_Host actually has 2 reference counts which are manipulated
337 in parallel by these functions.
340 Conventions
341 ===========
342 First, Linus Torvalds's thoughts on C coding style can be found in the
343 Documentation/CodingStyle file.
345 Next, there is a movement to "outlaw" typedefs introducing synonyms for
346 struct tags. Both can be still found in the SCSI subsystem, but
347 the typedefs have been moved to a single file, scsi_typedefs.h to
348 make their future removal easier, for example:
349 "typedef struct scsi_host_template Scsi_Host_Template;"
351 Also, most C99 enhancements are encouraged to the extent they are supported
352 by the relevant gcc compilers. So C99 style structure and array
353 initializers are encouraged where appropriate. Don't go too far,
354 VLAs are not properly supported yet. An exception to this is the use of
355 "//" style comments; /*...*/ comments are still preferred in Linux.
357 Well written, tested and documented code, need not be re-formatted to
358 comply with the above conventions. For example, the aic7xxx driver
359 comes to Linux from FreeBSD and Adaptec's own labs. No doubt FreeBSD
360 and Adaptec have their own coding conventions.
363 Mid level supplied functions
364 ============================
365 These functions are supplied by the SCSI mid level for use by LLDs.
366 The names (i.e. entry points) of these functions are exported
367 so an LLD that is a module can access them. The kernel will
368 arrange for the SCSI mid level to be loaded and initialized before any LLD
369 is initialized. The functions below are listed alphabetically and their
370 names all start with "scsi_".
372 Summary:
373 scsi_activate_tcq - turn on tag command queueing
374 scsi_add_device - creates new scsi device (lu) instance
375 scsi_add_host - perform sysfs registration and SCSI bus scan.
376 scsi_add_timer - (re-)start timer on a SCSI command.
377 scsi_adjust_queue_depth - change the queue depth on a SCSI device
378 scsi_assign_lock - replace default host_lock with given lock
379 scsi_bios_ptable - return copy of block device's partition table
380 scsi_block_requests - prevent further commands being queued to given host
381 scsi_deactivate_tcq - turn off tag command queueing
382 scsi_delete_timer - cancel timer on a SCSI command.
383 scsi_host_alloc - return a new scsi_host instance whose refcount==1
384 scsi_host_get - increments Scsi_Host instance's refcount
385 scsi_host_put - decrements Scsi_Host instance's refcount (free if 0)
386 scsi_partsize - parse partition table into cylinders, heads + sectors
387 scsi_register - create and register a scsi host adapter instance.
388 scsi_remove_device - detach and remove a SCSI device
389 scsi_remove_host - detach and remove all SCSI devices owned by host
390 scsi_report_bus_reset - report scsi _bus_ reset observed
391 scsi_set_device - place device reference in host structure
392 scsi_track_queue_full - track successive QUEUE_FULL events
393 scsi_unblock_requests - allow further commands to be queued to given host
394 scsi_unregister - [calls scsi_host_put()]
397 Details:
399 /**
400 * scsi_activate_tcq - turn on tag command queueing ("ordered" task attribute)
401 * @sdev: device to turn on TCQ for
402 * @depth: queue depth
403 *
404 * Returns nothing
405 *
406 * Might block: no
407 *
408 * Notes: Eventually, it is hoped depth would be the maximum depth
409 * the device could cope with and the real queue depth
410 * would be adjustable from 0 to depth.
411 *
412 * Defined (inline) in: include/scsi/scsi_tcq.h
413 **/
414 void scsi_activate_tcq(struct scsi_device *sdev, int depth)
417 /**
418 * scsi_add_device - creates new scsi device (lu) instance
419 * @shost: pointer to scsi host instance
420 * @channel: channel number (rarely other than 0)
421 * @id: target id number
422 * @lun: logical unit number
423 *
424 * Returns pointer to new struct scsi_device instance or
425 * ERR_PTR(-ENODEV) (or some other bent pointer) if something is
426 * wrong (e.g. no lu responds at given address)
427 *
428 * Might block: yes
429 *
430 * Notes: This call is usually performed internally during a scsi
431 * bus scan when an HBA is added (i.e. scsi_add_host()). So it
432 * should only be called if the HBA becomes aware of a new scsi
433 * device (lu) after scsi_add_host() has completed. If successful
434 * this call we lead to slave_alloc() and slave_configure() callbacks
435 * into the LLD.
436 *
437 * Defined in: drivers/scsi/scsi_scan.c
438 **/
439 struct scsi_device * scsi_add_device(struct Scsi_Host *shost,
440 unsigned int channel,
441 unsigned int id, unsigned int lun)
444 /**
445 * scsi_add_host - perform sysfs registration and SCSI bus scan.
446 * @shost: pointer to scsi host instance
447 * @dev: pointer to struct device of type scsi class
448 *
449 * Returns 0 on success, negative errno of failure (e.g. -ENOMEM)
450 *
451 * Might block: no
452 *
453 * Notes: Only required in "hotplug initialization model" after a
454 * successful call to scsi_host_alloc().
455 *
456 * Defined in: drivers/scsi/hosts.c
457 **/
458 int scsi_add_host(struct Scsi_Host *shost, struct device * dev)
461 /**
462 * scsi_add_timer - (re-)start timer on a SCSI command.
463 * @scmd: pointer to scsi command instance
464 * @timeout: duration of timeout in "jiffies"
465 * @complete: pointer to function to call if timeout expires
466 *
467 * Returns nothing
468 *
469 * Might block: no
470 *
471 * Notes: Each scsi command has its own timer, and as it is added
472 * to the queue, we set up the timer. When the command completes,
473 * we cancel the timer. An LLD can use this function to change
474 * the existing timeout value.
475 *
476 * Defined in: drivers/scsi/scsi_error.c
477 **/
478 void scsi_add_timer(struct scsi_cmnd *scmd, int timeout,
479 void (*complete)(struct scsi_cmnd *))
482 /**
483 * scsi_adjust_queue_depth - allow LLD to change queue depth on a SCSI device
484 * @sdev: pointer to SCSI device to change queue depth on
485 * @tagged: 0 - no tagged queuing
486 * MSG_SIMPLE_TAG - simple tagged queuing
487 * MSG_ORDERED_TAG - ordered tagged queuing
488 * @tags Number of tags allowed if tagged queuing enabled,
489 * or number of commands the LLD can queue up
490 * in non-tagged mode (as per cmd_per_lun).
491 *
492 * Returns nothing
493 *
494 * Might block: no
495 *
496 * Notes: Can be invoked any time on a SCSI device controlled by this
497 * LLD. [Specifically during and after slave_configure() and prior to
498 * slave_destroy().] Can safely be invoked from interrupt code. Actual
499 * queue depth change may be delayed until the next command is being
500 * processed. See also scsi_activate_tcq() and scsi_deactivate_tcq().
501 *
502 * Defined in: drivers/scsi/scsi.c [see source code for more notes]
503 *
504 **/
505 void scsi_adjust_queue_depth(struct scsi_device * sdev, int tagged,
506 int tags)
509 /**
510 * scsi_assign_lock - replace default host_lock with given lock
511 * @shost: a pointer to a scsi host instance
512 * @lock: pointer to lock to replace host_lock for this host
513 *
514 * Returns nothing
515 *
516 * Might block: no
517 *
518 * Defined in: include/scsi/scsi_host.h .
519 **/
520 void scsi_assign_lock(struct Scsi_Host *shost, spinlock_t *lock)
523 /**
524 * scsi_bios_ptable - return copy of block device's partition table
525 * @dev: pointer to block device
526 *
527 * Returns pointer to partition table, or NULL for failure
528 *
529 * Might block: yes
530 *
531 * Notes: Caller owns memory returned (free with kfree() )
532 *
533 * Defined in: drivers/scsi/scsicam.c
534 **/
535 unsigned char *scsi_bios_ptable(struct block_device *dev)
538 /**
539 * scsi_block_requests - prevent further commands being queued to given host
540 *
541 * @shost: pointer to host to block commands on
542 *
543 * Returns nothing
544 *
545 * Might block: no
546 *
547 * Notes: There is no timer nor any other means by which the requests
548 * get unblocked other than the LLD calling scsi_unblock_requests().
549 *
550 * Defined in: drivers/scsi/scsi_lib.c
551 **/
552 void scsi_block_requests(struct Scsi_Host * shost)
555 /**
556 * scsi_deactivate_tcq - turn off tag command queueing
557 * @sdev: device to turn off TCQ for
558 * @depth: queue depth (stored in sdev)
559 *
560 * Returns nothing
561 *
562 * Might block: no
563 *
564 * Defined (inline) in: include/scsi/scsi_tcq.h
565 **/
566 void scsi_deactivate_tcq(struct scsi_device *sdev, int depth)
569 /**
570 * scsi_delete_timer - cancel timer on a SCSI command.
571 * @scmd: pointer to scsi command instance
572 *
573 * Returns 1 if able to cancel timer else 0 (i.e. too late or already
574 * cancelled).
575 *
576 * Might block: no [may in the future if it invokes del_timer_sync()]
577 *
578 * Notes: All commands issued by upper levels already have a timeout
579 * associated with them. An LLD can use this function to cancel the
580 * timer.
581 *
582 * Defined in: drivers/scsi/scsi_error.c
583 **/
584 int scsi_delete_timer(struct scsi_cmnd *scmd)
587 /**
588 * scsi_host_alloc - create a scsi host adapter instance and perform basic
589 * initialization.
590 * @sht: pointer to scsi host template
591 * @privsize: extra bytes to allocate in hostdata array (which is the
592 * last member of the returned Scsi_Host instance)
593 *
594 * Returns pointer to new Scsi_Host instance or NULL on failure
595 *
596 * Might block: yes
597 *
598 * Notes: When this call returns to the LLD, the SCSI bus scan on
599 * this host has _not_ yet been done.
600 * The hostdata array (by default zero length) is a per host scratch
601 * area for the LLD's exclusive use.
602 * Both associated refcounting objects have their refcount set to 1.
603 * Full registration (in sysfs) and a bus scan are performed later when
604 * scsi_add_host() is called.
605 *
606 * Defined in: drivers/scsi/hosts.c .
607 **/
608 struct Scsi_Host * scsi_host_alloc(struct scsi_host_template * sht,
609 int privsize)
612 /**
613 * scsi_host_get - increment Scsi_Host instance refcount
614 * @shost: pointer to struct Scsi_Host instance
615 *
616 * Returns nothing
617 *
618 * Might block: currently may block but may be changed to not block
619 *
620 * Notes: Actually increments the counts in two sub-objects
621 *
622 * Defined in: drivers/scsi/hosts.c
623 **/
624 void scsi_host_get(struct Scsi_Host *shost)
627 /**
628 * scsi_host_put - decrement Scsi_Host instance refcount, free if 0
629 * @shost: pointer to struct Scsi_Host instance
630 *
631 * Returns nothing
632 *
633 * Might block: currently may block but may be changed to not block
634 *
635 * Notes: Actually decrements the counts in two sub-objects. If the
636 * latter refcount reaches 0, the Scsi_Host instance is freed.
637 * The LLD need not worry exactly when the Scsi_Host instance is
638 * freed, it just shouldn't access the instance after it has balanced
639 * out its refcount usage.
640 *
641 * Defined in: drivers/scsi/hosts.c
642 **/
643 void scsi_host_put(struct Scsi_Host *shost)
646 /**
647 * scsi_partsize - parse partition table into cylinders, heads + sectors
648 * @buf: pointer to partition table
649 * @capacity: size of (total) disk in 512 byte sectors
650 * @cyls: outputs number of cylinders calculated via this pointer
651 * @hds: outputs number of heads calculated via this pointer
652 * @secs: outputs number of sectors calculated via this pointer
653 *
654 * Returns 0 on success, -1 on failure
655 *
656 * Might block: no
657 *
658 * Notes: Caller owns memory returned (free with kfree() )
659 *
660 * Defined in: drivers/scsi/scsicam.c
661 **/
662 int scsi_partsize(unsigned char *buf, unsigned long capacity,
663 unsigned int *cyls, unsigned int *hds, unsigned int *secs)
666 /**
667 * scsi_register - create and register a scsi host adapter instance.
668 * @sht: pointer to scsi host template
669 * @privsize: extra bytes to allocate in hostdata array (which is the
670 * last member of the returned Scsi_Host instance)
671 *
672 * Returns pointer to new Scsi_Host instance or NULL on failure
673 *
674 * Might block: yes
675 *
676 * Notes: When this call returns to the LLD, the SCSI bus scan on
677 * this host has _not_ yet been done.
678 * The hostdata array (by default zero length) is a per host scratch
679 * area for the LLD.
680 *
681 * Defined in: drivers/scsi/hosts.c .
682 **/
683 struct Scsi_Host * scsi_register(struct scsi_host_template * sht,
684 int privsize)
687 /**
688 * scsi_remove_device - detach and remove a SCSI device
689 * @sdev: a pointer to a scsi device instance
690 *
691 * Returns value: 0 on success, -EINVAL if device not attached
692 *
693 * Might block: yes
694 *
695 * Notes: If an LLD becomes aware that a scsi device (lu) has
696 * been removed but its host is still present then it can request
697 * the removal of that scsi device. If successful this call will
698 * lead to the slave_destroy() callback being invoked. sdev is an
699 * invalid pointer after this call.
700 *
701 * Defined in: drivers/scsi/scsi_sysfs.c .
702 **/
703 int scsi_remove_device(struct scsi_device *sdev)
706 /**
707 * scsi_remove_host - detach and remove all SCSI devices owned by host
708 * @shost: a pointer to a scsi host instance
709 *
710 * Returns value: 0 on success, 1 on failure (e.g. LLD busy ??)
711 *
712 * Might block: yes
713 *
714 * Notes: Should only be invoked if the "hotplug initialization
715 * model" is being used. It should be called _prior_ to
716 * scsi_unregister().
717 *
718 * Defined in: drivers/scsi/hosts.c .
719 **/
720 int scsi_remove_host(struct Scsi_Host *shost)
723 /**
724 * scsi_report_bus_reset - report scsi _bus_ reset observed
725 * @shost: a pointer to a scsi host involved
726 * @channel: channel (within) host on which scsi bus reset occurred
727 *
728 * Returns nothing
729 *
730 * Might block: no
731 *
732 * Notes: This only needs to be called if the reset is one which
733 * originates from an unknown location. Resets originated by the
734 * mid level itself don't need to call this, but there should be
735 * no harm. The main purpose of this is to make sure that a
736 * CHECK_CONDITION is properly treated.
737 *
738 * Defined in: drivers/scsi/scsi_error.c .
739 **/
740 void scsi_report_bus_reset(struct Scsi_Host * shost, int channel)
743 /**
744 * scsi_set_device - place device reference in host structure
745 * @shost: a pointer to a scsi host instance
746 * @pdev: pointer to device instance to assign
747 *
748 * Returns nothing
749 *
750 * Might block: no
751 *
752 * Defined in: include/scsi/scsi_host.h .
753 **/
754 void scsi_set_device(struct Scsi_Host * shost, struct device * dev)
757 /**
758 * scsi_track_queue_full - track successive QUEUE_FULL events on given
759 * device to determine if and when there is a need
760 * to adjust the queue depth on the device.
761 * @sdev: pointer to SCSI device instance
762 * @depth: Current number of outstanding SCSI commands on this device,
763 * not counting the one returned as QUEUE_FULL.
764 *
765 * Returns 0 - no change needed
766 * >0 - adjust queue depth to this new depth
767 * -1 - drop back to untagged operation using host->cmd_per_lun
768 * as the untagged command depth
769 *
770 * Might block: no
771 *
772 * Notes: LLDs may call this at any time and we will do "The Right
773 * Thing"; interrupt context safe.
774 *
775 * Defined in: drivers/scsi/scsi.c .
776 **/
777 int scsi_track_queue_full(Scsi_Device *sdev, int depth)
780 /**
781 * scsi_unblock_requests - allow further commands to be queued to given host
782 *
783 * @shost: pointer to host to unblock commands on
784 *
785 * Returns nothing
786 *
787 * Might block: no
788 *
789 * Defined in: drivers/scsi/scsi_lib.c .
790 **/
791 void scsi_unblock_requests(struct Scsi_Host * shost)
794 /**
795 * scsi_unregister - unregister and free memory used by host instance
796 * @shp: pointer to scsi host instance to unregister.
797 *
798 * Returns nothing
799 *
800 * Might block: no
801 *
802 * Notes: Should not be invoked if the "hotplug initialization
803 * model" is being used. Called internally by exit_this_scsi_driver()
804 * in the "passive initialization model". Hence a LLD has no need to
805 * call this function directly.
806 *
807 * Defined in: drivers/scsi/hosts.c .
808 **/
809 void scsi_unregister(struct Scsi_Host * shp)
814 Interface Functions
815 ===================
816 Interface functions are supplied (defined) by LLDs and their function
817 pointers are placed in an instance of struct scsi_host_template which
818 is passed to scsi_host_alloc() [or scsi_register() / init_this_scsi_driver()].
819 Some are mandatory. Interface functions should be declared static. The
820 accepted convention is that driver "xyz" will declare its slave_configure()
821 function as:
822 static int xyz_slave_configure(struct scsi_device * sdev);
823 and so forth for all interface functions listed below.
825 A pointer to this function should be placed in the 'slave_configure' member
826 of a "struct scsi_host_template" instance. A pointer to such an instance
827 should be passed to the mid level's scsi_host_alloc() [or scsi_register() /
828 init_this_scsi_driver()].
830 The interface functions are also described in the include/scsi/scsi_host.h
831 file immediately above their definition point in "struct scsi_host_template".
832 In some cases more detail is given in scsi_host.h than below.
834 The interface functions are listed below in alphabetical order.
836 Summary:
837 bios_param - fetch head, sector, cylinder info for a disk
838 detect - detects HBAs this driver wants to control
839 eh_timed_out - notify the host that a command timer expired
840 eh_abort_handler - abort given command
841 eh_bus_reset_handler - issue SCSI bus reset
842 eh_device_reset_handler - issue SCSI device reset
843 eh_host_reset_handler - reset host (host bus adapter)
844 eh_strategy_handler - driver supplied alternate to scsi_unjam_host()
845 info - supply information about given host
846 ioctl - driver can respond to ioctls
847 proc_info - supports /proc/scsi/{driver_name}/{host_no}
848 queuecommand - queue scsi command, invoke 'done' on completion
849 release - release all resources associated with given host
850 slave_alloc - prior to any commands being sent to a new device
851 slave_configure - driver fine tuning for given device after attach
852 slave_destroy - given device is about to be shut down
855 Details:
857 /**
858 * bios_param - fetch head, sector, cylinder info for a disk
859 * @sdev: pointer to scsi device context (defined in
860 * include/scsi/scsi_device.h)
861 * @bdev: pointer to block device context (defined in fs.h)
862 * @capacity: device size (in 512 byte sectors)
863 * @params: three element array to place output:
864 * params[0] number of heads (max 255)
865 * params[1] number of sectors (max 63)
866 * params[2] number of cylinders
867 *
868 * Return value is ignored
869 *
870 * Locks: none
871 *
872 * Calling context: process (sd)
873 *
874 * Notes: an arbitrary geometry (based on READ CAPACITY) is used
875 * if this function is not provided. The params array is
876 * pre-initialized with made up values just in case this function
877 * doesn't output anything.
878 *
879 * Optionally defined in: LLD
880 **/
881 int bios_param(struct scsi_device * sdev, struct block_device *bdev,
882 sector_t capacity, int params[3])
885 /**
886 * detect - detects HBAs this driver wants to control
887 * @shtp: host template for this driver.
888 *
889 * Returns number of hosts this driver wants to control. 0 means no
890 * suitable hosts found.
891 *
892 * Locks: none held
893 *
894 * Calling context: process [invoked from init_this_scsi_driver()]
895 *
896 * Notes: First function called from the SCSI mid level on this
897 * driver. Upper level drivers (e.g. sd) may not (yet) be present.
898 * For each host found, this method should call scsi_register()
899 * [see hosts.c].
900 *
901 * Defined in: LLD (required if "passive initialization mode" is used,
902 * not invoked in "hotplug initialization mode")
903 **/
904 int detect(struct scsi_host_template * shtp)
907 /**
908 * eh_timed_out - The timer for the command has just fired
909 * @scp: identifies command timing out
910 *
911 * Returns:
912 *
913 * EH_HANDLED: I fixed the error, please complete the command
914 * EH_RESET_TIMER: I need more time, reset the timer and
915 * begin counting again
916 * EH_NOT_HANDLED Begin normal error recovery
917 *
918 *
919 * Locks: None held
920 *
921 * Calling context: interrupt
922 *
923 * Notes: This is to give the LLD an opportunity to do local recovery.
924 * This recovery is limited to determining if the outstanding command
925 * will ever complete. You may not abort and restart the command from
926 * this callback.
927 *
928 * Optionally defined in: LLD
929 **/
930 int eh_timed_out(struct scsi_cmnd * scp)
933 /**
934 * eh_abort_handler - abort command associated with scp
935 * @scp: identifies command to be aborted
936 *
937 * Returns SUCCESS if command aborted else FAILED
938 *
939 * Locks: struct Scsi_Host::host_lock held (with irqsave) on entry
940 * and assumed to be held on return.
941 *
942 * Calling context: kernel thread
943 *
944 * Notes: Invoked from scsi_eh thread. No other commands will be
945 * queued on current host during eh.
946 *
947 * Optionally defined in: LLD
948 **/
949 int eh_abort_handler(struct scsi_cmnd * scp)
952 /**
953 * eh_bus_reset_handler - issue SCSI bus reset
954 * @scp: SCSI bus that contains this device should be reset
955 *
956 * Returns SUCCESS if command aborted else FAILED
957 *
958 * Locks: struct Scsi_Host::host_lock held (with irqsave) on entry
959 * and assumed to be held on return.
960 *
961 * Calling context: kernel thread
962 *
963 * Notes: Invoked from scsi_eh thread. No other commands will be
964 * queued on current host during eh.
965 *
966 * Optionally defined in: LLD
967 **/
968 int eh_bus_reset_handler(struct scsi_cmnd * scp)
971 /**
972 * eh_device_reset_handler - issue SCSI device reset
973 * @scp: identifies SCSI device to be reset
974 *
975 * Returns SUCCESS if command aborted else FAILED
976 *
977 * Locks: struct Scsi_Host::host_lock held (with irqsave) on entry
978 * and assumed to be held on return.
979 *
980 * Calling context: kernel thread
981 *
982 * Notes: Invoked from scsi_eh thread. No other commands will be
983 * queued on current host during eh.
984 *
985 * Optionally defined in: LLD
986 **/
987 int eh_device_reset_handler(struct scsi_cmnd * scp)
990 /**
991 * eh_host_reset_handler - reset host (host bus adapter)
992 * @scp: SCSI host that contains this device should be reset
993 *
994 * Returns SUCCESS if command aborted else FAILED
995 *
996 * Locks: struct Scsi_Host::host_lock held (with irqsave) on entry
997 * and assumed to be held on return.
998 *
999 * Calling context: kernel thread
1000 *
1001 * Notes: Invoked from scsi_eh thread. No other commands will be
1002 * queued on current host during eh.
1003 * With the default eh_strategy in place, if none of the _abort_,
1004 * _device_reset_, _bus_reset_ or this eh handler function are
1005 * defined (or they all return FAILED) then the device in question
1006 * will be set offline whenever eh is invoked.
1007 *
1008 * Optionally defined in: LLD
1009 **/
1010 int eh_host_reset_handler(struct scsi_cmnd * scp)
1013 /**
1014 * eh_strategy_handler - driver supplied alternate to scsi_unjam_host()
1015 * @shp: host on which error has occurred
1016 *
1017 * Returns TRUE if host unjammed, else FALSE.
1018 *
1019 * Locks: none
1020 *
1021 * Calling context: kernel thread
1022 *
1023 * Notes: Invoked from scsi_eh thread. LLD supplied alternate to
1024 * scsi_unjam_host() found in scsi_error.c
1025 *
1026 * Optionally defined in: LLD
1027 **/
1028 int eh_strategy_handler(struct Scsi_Host * shp)
1031 /**
1032 * info - supply information about given host: driver name plus data
1033 * to distinguish given host
1034 * @shp: host to supply information about
1035 *
1036 * Return ASCII null terminated string. [This driver is assumed to
1037 * manage the memory pointed to and maintain it, typically for the
1038 * lifetime of this host.]
1039 *
1040 * Locks: none
1041 *
1042 * Calling context: process
1043 *
1044 * Notes: Often supplies PCI or ISA information such as IO addresses
1045 * and interrupt numbers. If not supplied struct Scsi_Host::name used
1046 * instead. It is assumed the returned information fits on one line
1047 * (i.e. does not included embedded newlines).
1048 * The SCSI_IOCTL_PROBE_HOST ioctl yields the string returned by this
1049 * function (or struct Scsi_Host::name if this function is not
1050 * available).
1051 * In a similar manner, init_this_scsi_driver() outputs to the console
1052 * each host's "info" (or name) for the driver it is registering.
1053 * Also if proc_info() is not supplied, the output of this function
1054 * is used instead.
1055 *
1056 * Optionally defined in: LLD
1057 **/
1058 const char * info(struct Scsi_Host * shp)
1061 /**
1062 * ioctl - driver can respond to ioctls
1063 * @sdp: device that ioctl was issued for
1064 * @cmd: ioctl number
1065 * @arg: pointer to read or write data from. Since it points to
1066 * user space, should use appropriate kernel functions
1067 * (e.g. copy_from_user() ). In the Unix style this argument
1068 * can also be viewed as an unsigned long.
1069 *
1070 * Returns negative "errno" value when there is a problem. 0 or a
1071 * positive value indicates success and is returned to the user space.
1072 *
1073 * Locks: none
1074 *
1075 * Calling context: process
1076 *
1077 * Notes: The SCSI subsystem uses a "trickle down" ioctl model.
1078 * The user issues an ioctl() against an upper level driver
1079 * (e.g. /dev/sdc) and if the upper level driver doesn't recognize
1080 * the 'cmd' then it is passed to the SCSI mid level. If the SCSI
1081 * mid level does not recognize it, then the LLD that controls
1082 * the device receives the ioctl. According to recent Unix standards
1083 * unsupported ioctl() 'cmd' numbers should return -ENOTTY.
1084 *
1085 * Optionally defined in: LLD
1086 **/
1087 int ioctl(struct scsi_device *sdp, int cmd, void *arg)
1090 /**
1091 * proc_info - supports /proc/scsi/{driver_name}/{host_no}
1092 * @buffer: anchor point to output to (0==writeto1_read0) or fetch from
1093 * (1==writeto1_read0).
1094 * @start: where "interesting" data is written to. Ignored when
1095 * 1==writeto1_read0.
1096 * @offset: offset within buffer 0==writeto1_read0 is actually
1097 * interested in. Ignored when 1==writeto1_read0 .
1098 * @length: maximum (or actual) extent of buffer
1099 * @host_no: host number of interest (struct Scsi_Host::host_no)
1100 * @writeto1_read0: 1 -> data coming from user space towards driver
1101 * (e.g. "echo some_string > /proc/scsi/xyz/2")
1102 * 0 -> user what data from this driver
1103 * (e.g. "cat /proc/scsi/xyz/2")
1104 *
1105 * Returns length when 1==writeto1_read0. Otherwise number of chars
1106 * output to buffer past offset.
1107 *
1108 * Locks: none held
1109 *
1110 * Calling context: process
1111 *
1112 * Notes: Driven from scsi_proc.c which interfaces to proc_fs. proc_fs
1113 * support can now be configured out of the scsi subsystem.
1114 *
1115 * Optionally defined in: LLD
1116 **/
1117 int proc_info(char * buffer, char ** start, off_t offset,
1118 int length, int host_no, int writeto1_read0)
1121 /**
1122 * queuecommand - queue scsi command, invoke 'done' on completion
1123 * @scp: pointer to scsi command object
1124 * @done: function pointer to be invoked on completion
1125 *
1126 * Returns 0 on success.
1127 *
1128 * If there's a failure, return either:
1129 *
1130 * SCSI_MLQUEUE_DEVICE_BUSY if the device queue is full, or
1131 * SCSI_MLQUEUE_HOST_BUSY if the entire host queue is full
1132 *
1133 * On both of these returns, the mid-layer will requeue the I/O
1134 *
1135 * - if the return is SCSI_MLQUEUE_DEVICE_BUSY, only that particular
1136 * device will be paused, and it will be unpaused when a command to
1137 * the device returns (or after a brief delay if there are no more
1138 * outstanding commands to it). Commands to other devices continue
1139 * to be processed normally.
1140 *
1141 * - if the return is SCSI_MLQUEUE_HOST_BUSY, all I/O to the host
1142 * is paused and will be unpaused when any command returns from
1143 * the host (or after a brief delay if there are no outstanding
1144 * commands to the host).
1145 *
1146 * For compatibility with earlier versions of queuecommand, any
1147 * other return value is treated the same as
1148 * SCSI_MLQUEUE_HOST_BUSY.
1149 *
1150 * Other types of errors that are detected immediately may be
1151 * flagged by setting scp->result to an appropriate value,
1152 * invoking the 'done' callback, and then returning 0 from this
1153 * function. If the command is not performed immediately (and the
1154 * LLD is starting (or will start) the given command) then this
1155 * function should place 0 in scp->result and return 0.
1156 *
1157 * Command ownership. If the driver returns zero, it owns the
1158 * command and must take responsibility for ensuring the 'done'
1159 * callback is executed. Note: the driver may call done before
1160 * returning zero, but after it has called done, it may not
1161 * return any value other than zero. If the driver makes a
1162 * non-zero return, it must not execute the command's done
1163 * callback at any time.
1164 *
1165 * Locks: struct Scsi_Host::host_lock held on entry (with "irqsave")
1166 * and is expected to be held on return.
1167 *
1168 * Calling context: in interrupt (soft irq) or process context
1169 *
1170 * Notes: This function should be relatively fast. Normally it will
1171 * not wait for IO to complete. Hence the 'done' callback is invoked
1172 * (often directly from an interrupt service routine) some time after
1173 * this function has returned. In some cases (e.g. pseudo adapter
1174 * drivers that manufacture the response to a SCSI INQUIRY)
1175 * the 'done' callback may be invoked before this function returns.
1176 * If the 'done' callback is not invoked within a certain period
1177 * the SCSI mid level will commence error processing.
1178 * If a status of CHECK CONDITION is placed in "result" when the
1179 * 'done' callback is invoked, then the LLD driver should
1180 * perform autosense and fill in the struct scsi_cmnd::sense_buffer
1181 * array. The scsi_cmnd::sense_buffer array is zeroed prior to
1182 * the mid level queuing a command to an LLD.
1183 *
1184 * Defined in: LLD
1185 **/
1186 int queuecommand(struct scsi_cmnd * scp,
1187 void (*done)(struct scsi_cmnd *))
1190 /**
1191 * release - release all resources associated with given host
1192 * @shp: host to be released.
1193 *
1194 * Return value ignored (could soon be a function returning void).
1195 *
1196 * Locks: none held
1197 *
1198 * Calling context: process
1199 *
1200 * Notes: Invoked from scsi_module.c's exit_this_scsi_driver().
1201 * LLD's implementation of this function should call
1202 * scsi_unregister(shp) prior to returning.
1203 * Only needed for old-style host templates.
1204 *
1205 * Defined in: LLD (required in "passive initialization model",
1206 * should not be defined in hotplug model)
1207 **/
1208 int release(struct Scsi_Host * shp)
1211 /**
1212 * slave_alloc - prior to any commands being sent to a new device
1213 * (i.e. just prior to scan) this call is made
1214 * @sdp: pointer to new device (about to be scanned)
1215 *
1216 * Returns 0 if ok. Any other return is assumed to be an error and
1217 * the device is ignored.
1218 *
1219 * Locks: none
1220 *
1221 * Calling context: process
1222 *
1223 * Notes: Allows the driver to allocate any resources for a device
1224 * prior to its initial scan. The corresponding scsi device may not
1225 * exist but the mid level is just about to scan for it (i.e. send
1226 * and INQUIRY command plus ...). If a device is found then
1227 * slave_configure() will be called while if a device is not found
1228 * slave_destroy() is called.
1229 * For more details see the include/scsi/scsi_host.h file.
1230 *
1231 * Optionally defined in: LLD
1232 **/
1233 int slave_alloc(struct scsi_device *sdp)
1236 /**
1237 * slave_configure - driver fine tuning for given device just after it
1238 * has been first scanned (i.e. it responded to an
1239 * INQUIRY)
1240 * @sdp: device that has just been attached
1241 *
1242 * Returns 0 if ok. Any other return is assumed to be an error and
1243 * the device is taken offline. [offline devices will _not_ have
1244 * slave_destroy() called on them so clean up resources.]
1245 *
1246 * Locks: none
1247 *
1248 * Calling context: process
1249 *
1250 * Notes: Allows the driver to inspect the response to the initial
1251 * INQUIRY done by the scanning code and take appropriate action.
1252 * For more details see the include/scsi/scsi_host.h file.
1253 *
1254 * Optionally defined in: LLD
1255 **/
1256 int slave_configure(struct scsi_device *sdp)
1259 /**
1260 * slave_destroy - given device is about to be shut down. All
1261 * activity has ceased on this device.
1262 * @sdp: device that is about to be shut down
1263 *
1264 * Returns nothing
1265 *
1266 * Locks: none
1267 *
1268 * Calling context: process
1269 *
1270 * Notes: Mid level structures for given device are still in place
1271 * but are about to be torn down. Any per device resources allocated
1272 * by this driver for given device should be freed now. No further
1273 * commands will be sent for this sdp instance. [However the device
1274 * could be re-attached in the future in which case a new instance
1275 * of struct scsi_device would be supplied by future slave_alloc()
1276 * and slave_configure() calls.]
1277 *
1278 * Optionally defined in: LLD
1279 **/
1280 void slave_destroy(struct scsi_device *sdp)
1284 Data Structures
1285 ===============
1286 struct scsi_host_template
1287 -------------------------
1288 There is one "struct scsi_host_template" instance per LLD ***. It is
1289 typically initialized as a file scope static in a driver's header file. That
1290 way members that are not explicitly initialized will be set to 0 or NULL.
1291 Member of interest:
1292 name - name of driver (may contain spaces, please limit to
1293 less than 80 characters)
1294 proc_name - name used in "/proc/scsi/<proc_name>/<host_no>" and
1295 by sysfs in one of its "drivers" directories. Hence
1296 "proc_name" should only contain characters acceptable
1297 to a Unix file name.
1298 (*queuecommand)() - primary callback that the mid level uses to inject
1299 SCSI commands into an LLD.
1300 The structure is defined and commented in include/scsi/scsi_host.h
1302 *** In extreme situations a single driver may have several instances
1303 if it controls several different classes of hardware (e.g. an LLD
1304 that handles both ISA and PCI cards and has a separate instance of
1305 struct scsi_host_template for each class).
1307 struct Scsi_Host
1308 ----------------
1309 There is one struct Scsi_Host instance per host (HBA) that an LLD
1310 controls. The struct Scsi_Host structure has many members in common
1311 with "struct scsi_host_template". When a new struct Scsi_Host instance
1312 is created (in scsi_host_alloc() in hosts.c) those common members are
1313 initialized from the driver's struct scsi_host_template instance. Members
1314 of interest:
1315 host_no - system wide unique number that is used for identifying
1316 this host. Issued in ascending order from 0.
1317 can_queue - must be greater than 0; do not send more than can_queue
1318 commands to the adapter.
1319 this_id - scsi id of host (scsi initiator) or -1 if not known
1320 sg_tablesize - maximum scatter gather elements allowed by host.
1321 0 implies scatter gather not supported by host
1322 max_sectors - maximum number of sectors (usually 512 bytes) allowed
1323 in a single SCSI command. The default value of 0 leads
1324 to a setting of SCSI_DEFAULT_MAX_SECTORS (defined in
1325 scsi_host.h) which is currently set to 1024. So for a
1326 disk the maximum transfer size is 512 KB when max_sectors
1327 is not defined. Note that this size may not be sufficient
1328 for disk firmware uploads.
1329 cmd_per_lun - maximum number of commands that can be queued on devices
1330 controlled by the host. Overridden by LLD calls to
1331 scsi_adjust_queue_depth().
1332 unchecked_isa_dma - 1=>only use bottom 16 MB of ram (ISA DMA addressing
1333 restriction), 0=>can use full 32 bit (or better) DMA
1334 address space
1335 use_clustering - 1=>SCSI commands in mid level's queue can be merged,
1336 0=>disallow SCSI command merging
1337 hostt - pointer to driver's struct scsi_host_template from which
1338 this struct Scsi_Host instance was spawned
1339 hostt->proc_name - name of LLD. This is the driver name that sysfs uses
1340 transportt - pointer to driver's struct scsi_transport_template instance
1341 (if any). FC and SPI transports currently supported.
1342 sh_list - a double linked list of pointers to all struct Scsi_Host
1343 instances (currently ordered by ascending host_no)
1344 my_devices - a double linked list of pointers to struct scsi_device
1345 instances that belong to this host.
1346 hostdata[0] - area reserved for LLD at end of struct Scsi_Host. Size
1347 is set by the second argument (named 'xtr_bytes') to
1348 scsi_host_alloc() or scsi_register().
1350 The scsi_host structure is defined in include/scsi/scsi_host.h
1352 struct scsi_device
1353 ------------------
1354 Generally, there is one instance of this structure for each SCSI logical unit
1355 on a host. Scsi devices connected to a host are uniquely identified by a
1356 channel number, target id and logical unit number (lun).
1357 The structure is defined in include/scsi/scsi_device.h
1359 struct scsi_cmnd
1360 ----------------
1361 Instances of this structure convey SCSI commands to the LLD and responses
1362 back to the mid level. The SCSI mid level will ensure that no more SCSI
1363 commands become queued against the LLD than are indicated by
1364 scsi_adjust_queue_depth() (or struct Scsi_Host::cmd_per_lun). There will
1365 be at least one instance of struct scsi_cmnd available for each SCSI device.
1366 Members of interest:
1367 cmnd - array containing SCSI command
1368 cmnd_len - length (in bytes) of SCSI command
1369 sc_data_direction - direction of data transfer in data phase. See
1370 "enum dma_data_direction" in include/linux/dma-mapping.h
1371 request_bufflen - number of data bytes to transfer (0 if no data phase)
1372 use_sg - ==0 -> no scatter gather list, hence transfer data
1373 to/from request_buffer
1374 - >0 -> scatter gather list (actually an array) in
1375 request_buffer with use_sg elements
1376 request_buffer - either contains data buffer or scatter gather list
1377 depending on the setting of use_sg. Scatter gather
1378 elements are defined by 'struct scatterlist' found
1379 in include/asm/scatterlist.h .
1380 done - function pointer that should be invoked by LLD when the
1381 SCSI command is completed (successfully or otherwise).
1382 Should only be called by an LLD if the LLD has accepted
1383 the command (i.e. queuecommand() returned or will return
1384 0). The LLD may invoke 'done' prior to queuecommand()
1385 finishing.
1386 result - should be set by LLD prior to calling 'done'. A value
1387 of 0 implies a successfully completed command (and all
1388 data (if any) has been transferred to or from the SCSI
1389 target device). 'result' is a 32 bit unsigned integer that
1390 can be viewed as 4 related bytes. The SCSI status value is
1391 in the LSB. See include/scsi/scsi.h status_byte(),
1392 msg_byte(), host_byte() and driver_byte() macros and
1393 related constants.
1394 sense_buffer - an array (maximum size: SCSI_SENSE_BUFFERSIZE bytes) that
1395 should be written when the SCSI status (LSB of 'result')
1396 is set to CHECK_CONDITION (2). When CHECK_CONDITION is
1397 set, if the top nibble of sense_buffer[0] has the value 7
1398 then the mid level will assume the sense_buffer array
1399 contains a valid SCSI sense buffer; otherwise the mid
1400 level will issue a REQUEST_SENSE SCSI command to
1401 retrieve the sense buffer. The latter strategy is error
1402 prone in the presence of command queuing so the LLD should
1403 always "auto-sense".
1404 device - pointer to scsi_device object that this command is
1405 associated with.
1406 resid - an LLD should set this signed integer to the requested
1407 transfer length (i.e. 'request_bufflen') less the number
1408 of bytes that are actually transferred. 'resid' is
1409 preset to 0 so an LLD can ignore it if it cannot detect
1410 underruns (overruns should be rare). If possible an LLD
1411 should set 'resid' prior to invoking 'done'. The most
1412 interesting case is data transfers from a SCSI target
1413 device device (i.e. READs) that underrun.
1414 underflow - LLD should place (DID_ERROR << 16) in 'result' if
1415 actual number of bytes transferred is less than this
1416 figure. Not many LLDs implement this check and some that
1417 do just output an error message to the log rather than
1418 report a DID_ERROR. Better for an LLD to implement
1419 'resid'.
1421 The scsi_cmnd structure is defined in include/scsi/scsi_cmnd.h
1424 Locks
1425 =====
1426 Each struct Scsi_Host instance has a spin_lock called struct
1427 Scsi_Host::default_lock which is initialized in scsi_host_alloc() [found in
1428 hosts.c]. Within the same function the struct Scsi_Host::host_lock pointer
1429 is initialized to point at default_lock with the scsi_assign_lock() function.
1430 Thereafter lock and unlock operations performed by the mid level use the
1431 struct Scsi_Host::host_lock pointer.
1433 LLDs can override the use of struct Scsi_Host::default_lock by
1434 using scsi_assign_lock(). The earliest opportunity to do this would
1435 be in the detect() function after it has invoked scsi_register(). It
1436 could be replaced by a coarser grain lock (e.g. per driver) or a
1437 lock of equal granularity (i.e. per host). Using finer grain locks
1438 (e.g. per SCSI device) may be possible by juggling locks in
1439 queuecommand().
1441 Autosense
1442 =========
1443 Autosense (or auto-sense) is defined in the SAM-2 document as "the
1444 automatic return of sense data to the application client coincident
1445 with the completion of a SCSI command" when a status of CHECK CONDITION
1446 occurs. LLDs should perform autosense. This should be done when the LLD
1447 detects a CHECK CONDITION status by either:
1448 a) instructing the SCSI protocol (e.g. SCSI Parallel Interface (SPI))
1449 to perform an extra data in phase on such responses
1450 b) or, the LLD issuing a REQUEST SENSE command itself
1452 Either way, when a status of CHECK CONDITION is detected, the mid level
1453 decides whether the LLD has performed autosense by checking struct
1454 scsi_cmnd::sense_buffer[0] . If this byte has an upper nibble of 7 (or 0xf)
1455 then autosense is assumed to have taken place. If it has another value (and
1456 this byte is initialized to 0 before each command) then the mid level will
1457 issue a REQUEST SENSE command.
1459 In the presence of queued commands the "nexus" that maintains sense
1460 buffer data from the command that failed until a following REQUEST SENSE
1461 may get out of synchronization. This is why it is best for the LLD
1462 to perform autosense.
1465 Changes since lk 2.4 series
1466 ===========================
1467 io_request_lock has been replaced by several finer grained locks. The lock
1468 relevant to LLDs is struct Scsi_Host::host_lock and there is
1469 one per SCSI host.
1471 The older error handling mechanism has been removed. This means the
1472 LLD interface functions abort() and reset() have been removed.
1473 The struct scsi_host_template::use_new_eh_code flag has been removed.
1475 In the 2.4 series the SCSI subsystem configuration descriptions were
1476 aggregated with the configuration descriptions from all other Linux
1477 subsystems in the Documentation/Configure.help file. In the 2.6 series,
1478 the SCSI subsystem now has its own (much smaller) drivers/scsi/Kconfig
1479 file that contains both configuration and help information.
1481 struct SHT has been renamed to struct scsi_host_template.
1483 Addition of the "hotplug initialization model" and many extra functions
1484 to support it.
1487 Credits
1488 =======
1489 The following people have contributed to this document:
1490 Mike Anderson <andmike at us dot ibm dot com>
1491 James Bottomley <James dot Bottomley at steeleye dot com>
1492 Patrick Mansfield <patmans at us dot ibm dot com>
1493 Christoph Hellwig <hch at infradead dot org>
1494 Doug Ledford <dledford at redhat dot com>
1495 Andries Brouwer <Andries dot Brouwer at cwi dot nl>
1496 Randy Dunlap <rddunlap at osdl dot org>
1497 Alan Stern <stern at rowland dot harvard dot edu>
1500 Douglas Gilbert
1501 dgilbert at interlog dot com
1502 21st September 2004