blob: 1f24129a3099071dd253d5a341b07ab4c944cc96 [file] [log] [blame]
Linus Torvalds1da177e2005-04-16 15:20:36 -07001 Linux Kernel 2.6 series
2 SCSI mid_level - lower_level driver interface
3 =============================================
4
5Introduction
6============
7This document outlines the interface between the Linux SCSI mid level and
8SCSI lower level drivers. Lower level drivers (LLDs) are variously called
9host bus adapter (HBA) drivers and host drivers (HD). A "host" in this
10context is a bridge between a computer IO bus (e.g. PCI or ISA) and a
11single SCSI initiator port on a SCSI transport. An "initiator" port
12(SCSI terminology, see SAM-3 at http://www.t10.org) sends SCSI commands
13to "target" SCSI ports (e.g. disks). There can be many LLDs in a running
14system, but only one per hardware type. Most LLDs can control one or more
15SCSI HBAs. Some HBAs contain multiple hosts.
16
17In some cases the SCSI transport is an external bus that already has
18its own subsystem in Linux (e.g. USB and ieee1394). In such cases the
19SCSI subsystem LLD is a software bridge to the other driver subsystem.
20Examples are the usb-storage driver (found in the drivers/usb/storage
21directory) and the ieee1394/sbp2 driver (found in the drivers/ieee1394
22directory).
23
24For example, the aic7xxx LLD controls Adaptec SCSI parallel interface
25(SPI) controllers based on that company's 7xxx chip series. The aic7xxx
26LLD can be built into the kernel or loaded as a module. There can only be
27one aic7xxx LLD running in a Linux system but it may be controlling many
28HBAs. These HBAs might be either on PCI daughter-boards or built into
29the motherboard (or both). Some aic7xxx based HBAs are dual controllers
30and thus represent two hosts. Like most modern HBAs, each aic7xxx host
31has its own PCI device address. [The one-to-one correspondence between
32a SCSI host and a PCI device is common but not required (e.g. with
33ISA or MCA adapters).]
34
35The SCSI mid level isolates an LLD from other layers such as the SCSI
36upper layer drivers and the block layer.
37
38This version of the document roughly matches linux kernel version 2.6.8 .
39
40Documentation
41=============
42There is a SCSI documentation directory within the kernel source tree,
43typically Documentation/scsi . Most documents are in plain
44(i.e. ASCII) text. This file is named scsi_mid_low_api.txt and can be
45found in that directory. A more recent copy of this document may be found
46at http://www.torque.net/scsi/scsi_mid_low_api.txt.gz .
47Many LLDs are documented there (e.g. aic7xxx.txt). The SCSI mid-level is
48briefly described in scsi.txt which contains a url to a document
49describing the SCSI subsystem in the lk 2.4 series. Two upper level
50drivers have documents in that directory: st.txt (SCSI tape driver) and
51scsi-generic.txt (for the sg driver).
52
53Some documentation (or urls) for LLDs may be found in the C source code
54or in the same directory as the C source code. For example to find a url
55about the USB mass storage driver see the
56/usr/src/linux/drivers/usb/storage directory.
57
58The Linux kernel source Documentation/DocBook/scsidrivers.tmpl file
59refers to this file. With the appropriate DocBook tool-set, this permits
60users to generate html, ps and pdf renderings of information within this
61file (e.g. the interface functions).
62
63Driver structure
64================
65Traditionally an LLD for the SCSI subsystem has been at least two files in
66the drivers/scsi directory. For example, a driver called "xyz" has a header
67file "xyz.h" and a source file "xyz.c". [Actually there is no good reason
68why this couldn't all be in one file; the header file is superfluous.] Some
69drivers that have been ported to several operating systems have more than
70two files. For example the aic7xxx driver has separate files for generic
71and OS-specific code (e.g. FreeBSD and Linux). Such drivers tend to have
72their own directory under the drivers/scsi directory.
73
74When a new LLD is being added to Linux, the following files (found in the
75drivers/scsi directory) will need some attention: Makefile and Kconfig .
76It is probably best to study how existing LLDs are organized.
77
78As the 2.5 series development kernels evolve into the 2.6 series
79production series, changes are being introduced into this interface. An
80example of this is driver initialization code where there are now 2 models
81available. The older one, similar to what was found in the lk 2.4 series,
82is based on hosts that are detected at HBA driver load time. This will be
83referred to the "passive" initialization model. The newer model allows HBAs
84to be hot plugged (and unplugged) during the lifetime of the LLD and will
85be referred to as the "hotplug" initialization model. The newer model is
86preferred as it can handle both traditional SCSI equipment that is
87permanently connected as well as modern "SCSI" devices (e.g. USB or
88IEEE 1394 connected digital cameras) that are hotplugged. Both
89initialization models are discussed in the following sections.
90
91An 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
99
100Those functions in group a) are listed in a section entitled "Mid level
101supplied functions" below.
102
103Those functions in group b) are listed in a section entitled "Interface
104functions" below. Their function pointers are placed in the members of
105"struct scsi_host_template", an instance of which is passed to
106scsi_host_alloc() ** . Those interface functions that the LLD does not
107wish to supply should have NULL placed in the corresponding member of
108struct scsi_host_template. Defining an instance of struct
109scsi_host_template at file scope will cause NULL to be placed in function
110 pointer members not explicitly initialized.
111
112Those usages in group c) should be handled with care, especially in a
113"hotplug" environment. LLDs should be aware of the lifetime of instances
114that are shared with the mid level and other layers.
115
116All functions defined within an LLD and all data defined at file scope
117should be static. For example the slave_alloc() function in an LLD
118called "xxx" could be defined as
119"static int xxx_slave_alloc(struct scsi_device * sdev) { /* code */ }"
120
121** the scsi_host_alloc() function is a replacement for the rather vaguely
122named scsi_register() function in most situations. The scsi_register()
123and scsi_unregister() functions remain to support legacy LLDs that use
124the passive initialization model.
125
126
127Hotplug initialization model
128============================
129In this model an LLD controls when SCSI hosts are introduced and removed
130from the SCSI subsystem. Hosts can be introduced as early as driver
131initialization and removed as late as driver shutdown. Typically a driver
132will respond to a sysfs probe() callback that indicates an HBA has been
133detected. After confirming that the new device is one that the LLD wants
134to control, the LLD will initialize the HBA and then register a new host
135with the SCSI mid level.
136
137During LLD initialization the driver should register itself with the
138appropriate IO bus on which it expects to find HBA(s) (e.g. the PCI bus).
139This can probably be done via sysfs. Any driver parameters (especially
140those that are writable after the driver is loaded) could also be
141registered with sysfs at this point. The SCSI mid level first becomes
142aware of an LLD when that LLD registers its first HBA.
143
144At some later time, the LLD becomes aware of an HBA and what follows
145is a typical sequence of calls between the LLD and the mid level.
146This example shows the mid level scanning the newly introduced HBA for 3
147scsi devices of which only the first 2 respond:
148
149 HBA PROBE: assume 2 SCSI devices found in scan
150LLD mid level LLD
151===-------------------=========--------------------===------
152scsi_host_alloc() -->
153scsi_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------------------------------------------------------------
164
165If the LLD wants to adjust the default queue settings, it can invoke
166scsi_adjust_queue_depth() in its slave_configure() routine.
167
168*** For scsi devices that the mid level tries to scan but do not
169 respond, a slave_alloc(), slave_destroy() pair is called.
170
171When an HBA is being removed it could be as part of an orderly shutdown
172associated with the LLD module being unloaded (e.g. with the "rmmod"
173command) or in response to a "hot unplug" indicated by sysfs()'s
174remove() callback being invoked. In either case, the sequence is the
175same:
176
177 HBA REMOVE: assume 2 SCSI devices attached
178LLD mid level LLD
179===----------------------=========-----------------===------
180scsi_remove_host() ---------+
181 |
182 slave_destroy()
183 slave_destroy()
184scsi_host_put()
185------------------------------------------------------------
186
187It 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"
189by the mid-level. struct Scsi_Host instances are freed from
190scsi_host_put() when the reference count hits zero.
191
192Hot unplugging an HBA that controls a disk which is processing SCSI
193commands on a mounted file system is an interesting situation. Reference
194counting logic is being introduced into the mid level to cope with many
195of the issues involved. See the section on reference counting below.
196
197
198The hotplug concept may be extended to SCSI devices. Currently, when an
199HBA is added, the scsi_add_host() function causes a scan for SCSI devices
200attached to the HBA's SCSI transport. On newer SCSI transports the HBA
201may become aware of a new SCSI device _after_ the scan has completed.
202An LLD can use this sequence to make the mid level aware of a SCSI device:
203
204 SCSI DEVICE hotplug
205LLD mid level LLD
206===-------------------=========--------------------===------
207scsi_add_device() ------+
208 |
209 slave_alloc()
210 slave_configure() [--> scsi_adjust_queue_depth()]
211------------------------------------------------------------
212
213In a similar fashion, an LLD may become aware that a SCSI device has been
214removed (unplugged) or the connection to it has been interrupted. Some
215existing SCSI transports (e.g. SPI) may not become aware that a SCSI
216device has been removed until a subsequent SCSI command fails which will
217probably cause that device to be set offline by the mid level. An LLD that
218detects the removal of a SCSI device can instigate its removal from
219upper layers with this sequence:
220
221 SCSI DEVICE hot unplug
222LLD mid level LLD
223===----------------------=========-----------------===------
224scsi_remove_device() -------+
225 |
226 slave_destroy()
227------------------------------------------------------------
228
229It 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
231slave_configure() callbacks). Such instances are "owned" by the mid-level.
232struct scsi_device instances are freed after slave_destroy().
233
234
235Passive initialization model
236============================
237These older LLDs include a file called "scsi_module.c" [yes the ".c" is a
238little surprising] in their source code. For that file to work an
239instance of struct scsi_host_template with the name "driver_template"
240needs 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"
245
246The 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)
251Note: since these functions are tagged with __init and __exit qualifiers
252an LLD should not call them explicitly (since the kernel does that).
253
254Here is an example of an initialization sequence when two hosts are
255detected (so detect() returns 2) and the SCSI bus scan on each host
256finds 1 SCSI device (and a second device does not respond).
257
258LLD mid level LLD
259===----------------------=========-----------------===------
260init_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------------------------------------------------------------
277
278The 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
280overridden by a slave_configure() supplied by the LLD.
281
282*** For scsi devices that the mid level tries to scan but do not
283 respond, a slave_alloc(), slave_destroy() pair is called.
284
285Here is an LLD shutdown sequence:
286
287LLD mid level LLD
288===----------------------=========-----------------===------
289exit_this_scsi_driver() ----+
290 |
291 slave_destroy()
292 release() --> scsi_unregister()
293 |
294 slave_destroy()
295 release() --> scsi_unregister()
296------------------------------------------------------------
297
298An LLD need not define slave_destroy() (i.e. it is optional).
299
300The shortcoming of the "passive initialization model" is that host
301registration and de-registration are (typically) tied to LLD initialization
302and shutdown. Once the LLD is initialized then a new host that appears
303(e.g. via hotplugging) cannot easily be added without a redundant
304driver shutdown and re-initialization. It may be possible to write an LLD
305that uses both initialization models.
306
307
308Reference Counting
309==================
310The Scsi_Host structure has had reference counting infrastructure added.
311This effectively spreads the ownership of struct Scsi_Host instances
312across the various SCSI layers which use them. Previously such instances
313were exclusively owned by the mid level. LLDs would not usually need to
314directly manipulate these reference counts but there may be some cases
315where they do.
316
317There are 3 reference counting functions of interest associated with
318struct 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
325
326The Scsi_device structure has had reference counting infrastructure added.
327This effectively spreads the ownership of struct Scsi_device instances
328across the various SCSI layers which use them. Previously such instances
329were exclusively owned by the mid level. See the access functions declared
330towards the end of include/scsi/scsi_device.h . If an LLD wants to keep
331a copy of a pointer to a Scsi_device instance it should use scsi_device_get()
332to bump its reference count. When it is finished with the pointer it can
333use scsi_device_put() to decrement its reference count (and potentially
334delete it).
335
336^^ struct Scsi_Host actually has 2 reference counts which are manipulated
337in parallel by these functions.
338
339
340Conventions
341===========
342First, Linus Torvalds's thoughts on C coding style can be found in the
343Documentation/CodingStyle file.
344
345Next, there is a movement to "outlaw" typedefs introducing synonyms for
346struct tags. Both can be still found in the SCSI subsystem, but
347the typedefs have been moved to a single file, scsi_typedefs.h to
348make their future removal easier, for example:
349"typedef struct scsi_host_template Scsi_Host_Template;"
350
351Also, most C99 enhancements are encouraged to the extent they are supported
352by the relevant gcc compilers. So C99 style structure and array
353initializers are encouraged where appropriate. Don't go too far,
354VLAs are not properly supported yet. An exception to this is the use of
355"//" style comments; /*...*/ comments are still preferred in Linux.
356
357Well written, tested and documented code, need not be re-formatted to
358comply with the above conventions. For example, the aic7xxx driver
359comes to Linux from FreeBSD and Adaptec's own labs. No doubt FreeBSD
360and Adaptec have their own coding conventions.
361
362
363Mid level supplied functions
364============================
365These functions are supplied by the SCSI mid level for use by LLDs.
366The names (i.e. entry points) of these functions are exported
367so an LLD that is a module can access them. The kernel will
368arrange for the SCSI mid level to be loaded and initialized before any LLD
369is initialized. The functions below are listed alphabetically and their
370names all start with "scsi_".
371
372Summary:
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_to_pci_dma_dir - convert SCSI subsystem direction flag to PCI
393 scsi_to_sbus_dma_dir - convert SCSI subsystem direction flag to SBUS
394 scsi_track_queue_full - track successive QUEUE_FULL events
395 scsi_unblock_requests - allow further commands to be queued to given host
396 scsi_unregister - [calls scsi_host_put()]
397
398
399Details:
400
401/**
402 * scsi_activate_tcq - turn on tag command queueing ("ordered" task attribute)
403 * @sdev: device to turn on TCQ for
404 * @depth: queue depth
405 *
406 * Returns nothing
407 *
408 * Might block: no
409 *
410 * Notes: Eventually, it is hoped depth would be the maximum depth
411 * the device could cope with and the real queue depth
412 * would be adjustable from 0 to depth.
413 *
414 * Defined (inline) in: include/scsi/scsi_tcq.h
415 **/
416void scsi_activate_tcq(struct scsi_device *sdev, int depth)
417
418
419/**
420 * scsi_add_device - creates new scsi device (lu) instance
421 * @shost: pointer to scsi host instance
422 * @channel: channel number (rarely other than 0)
423 * @id: target id number
424 * @lun: logical unit number
425 *
426 * Returns pointer to new struct scsi_device instance or
427 * ERR_PTR(-ENODEV) (or some other bent pointer) if something is
428 * wrong (e.g. no lu responds at given address)
429 *
430 * Might block: yes
431 *
432 * Notes: This call is usually performed internally during a scsi
433 * bus scan when an HBA is added (i.e. scsi_add_host()). So it
434 * should only be called if the HBA becomes aware of a new scsi
435 * device (lu) after scsi_add_host() has completed. If successful
436 * this call we lead to slave_alloc() and slave_configure() callbacks
437 * into the LLD.
438 *
439 * Defined in: drivers/scsi/scsi_scan.c
440 **/
441struct scsi_device * scsi_add_device(struct Scsi_Host *shost,
442 unsigned int channel,
443 unsigned int id, unsigned int lun)
444
445
446/**
447 * scsi_add_host - perform sysfs registration and SCSI bus scan.
448 * @shost: pointer to scsi host instance
449 * @dev: pointer to struct device of type scsi class
450 *
451 * Returns 0 on success, negative errno of failure (e.g. -ENOMEM)
452 *
453 * Might block: no
454 *
455 * Notes: Only required in "hotplug initialization model" after a
456 * successful call to scsi_host_alloc().
457 *
458 * Defined in: drivers/scsi/hosts.c
459 **/
460int scsi_add_host(struct Scsi_Host *shost, struct device * dev)
461
462
463/**
464 * scsi_add_timer - (re-)start timer on a SCSI command.
465 * @scmd: pointer to scsi command instance
466 * @timeout: duration of timeout in "jiffies"
467 * @complete: pointer to function to call if timeout expires
468 *
469 * Returns nothing
470 *
471 * Might block: no
472 *
473 * Notes: Each scsi command has its own timer, and as it is added
474 * to the queue, we set up the timer. When the command completes,
475 * we cancel the timer. An LLD can use this function to change
476 * the existing timeout value.
477 *
478 * Defined in: drivers/scsi/scsi_error.c
479 **/
480void scsi_add_timer(struct scsi_cmnd *scmd, int timeout,
481 void (*complete)(struct scsi_cmnd *))
482
483
484/**
485 * scsi_adjust_queue_depth - allow LLD to change queue depth on a SCSI device
486 * @sdev: pointer to SCSI device to change queue depth on
487 * @tagged: 0 - no tagged queuing
488 * MSG_SIMPLE_TAG - simple tagged queuing
489 * MSG_ORDERED_TAG - ordered tagged queuing
490 * @tags Number of tags allowed if tagged queuing enabled,
491 * or number of commands the LLD can queue up
492 * in non-tagged mode (as per cmd_per_lun).
493 *
494 * Returns nothing
495 *
496 * Might block: no
497 *
498 * Notes: Can be invoked any time on a SCSI device controlled by this
499 * LLD. [Specifically during and after slave_configure() and prior to
500 * slave_destroy().] Can safely be invoked from interrupt code. Actual
501 * queue depth change may be delayed until the next command is being
502 * processed. See also scsi_activate_tcq() and scsi_deactivate_tcq().
503 *
504 * Defined in: drivers/scsi/scsi.c [see source code for more notes]
505 *
506 **/
507void scsi_adjust_queue_depth(struct scsi_device * sdev, int tagged,
508 int tags)
509
510
511/**
512 * scsi_assign_lock - replace default host_lock with given lock
513 * @shost: a pointer to a scsi host instance
514 * @lock: pointer to lock to replace host_lock for this host
515 *
516 * Returns nothing
517 *
518 * Might block: no
519 *
520 * Defined in: include/scsi/scsi_host.h .
521 **/
522void scsi_assign_lock(struct Scsi_Host *shost, spinlock_t *lock)
523
524
525/**
526 * scsi_bios_ptable - return copy of block device's partition table
527 * @dev: pointer to block device
528 *
529 * Returns pointer to partition table, or NULL for failure
530 *
531 * Might block: yes
532 *
533 * Notes: Caller owns memory returned (free with kfree() )
534 *
535 * Defined in: drivers/scsi/scsicam.c
536 **/
537unsigned char *scsi_bios_ptable(struct block_device *dev)
538
539
540/**
541 * scsi_block_requests - prevent further commands being queued to given host
542 *
543 * @shost: pointer to host to block commands on
544 *
545 * Returns nothing
546 *
547 * Might block: no
548 *
549 * Notes: There is no timer nor any other means by which the requests
550 * get unblocked other than the LLD calling scsi_unblock_requests().
551 *
552 * Defined in: drivers/scsi/scsi_lib.c
553**/
554void scsi_block_requests(struct Scsi_Host * shost)
555
556
557/**
558 * scsi_deactivate_tcq - turn off tag command queueing
559 * @sdev: device to turn off TCQ for
560 * @depth: queue depth (stored in sdev)
561 *
562 * Returns nothing
563 *
564 * Might block: no
565 *
566 * Defined (inline) in: include/scsi/scsi_tcq.h
567 **/
568void scsi_deactivate_tcq(struct scsi_device *sdev, int depth)
569
570
571/**
572 * scsi_delete_timer - cancel timer on a SCSI command.
573 * @scmd: pointer to scsi command instance
574 *
575 * Returns 1 if able to cancel timer else 0 (i.e. too late or already
576 * cancelled).
577 *
578 * Might block: no [may in the future if it invokes del_timer_sync()]
579 *
580 * Notes: All commands issued by upper levels already have a timeout
581 * associated with them. An LLD can use this function to cancel the
582 * timer.
583 *
584 * Defined in: drivers/scsi/scsi_error.c
585 **/
586int scsi_delete_timer(struct scsi_cmnd *scmd)
587
588
589/**
590 * scsi_host_alloc - create a scsi host adapter instance and perform basic
591 * initialization.
592 * @sht: pointer to scsi host template
593 * @privsize: extra bytes to allocate in hostdata array (which is the
594 * last member of the returned Scsi_Host instance)
595 *
596 * Returns pointer to new Scsi_Host instance or NULL on failure
597 *
598 * Might block: yes
599 *
600 * Notes: When this call returns to the LLD, the SCSI bus scan on
601 * this host has _not_ yet been done.
602 * The hostdata array (by default zero length) is a per host scratch
603 * area for the LLD's exclusive use.
604 * Both associated refcounting objects have their refcount set to 1.
605 * Full registration (in sysfs) and a bus scan are performed later when
606 * scsi_add_host() is called.
607 *
608 * Defined in: drivers/scsi/hosts.c .
609 **/
610struct Scsi_Host * scsi_host_alloc(struct scsi_host_template * sht,
611 int privsize)
612
613
614/**
615 * scsi_host_get - increment Scsi_Host instance refcount
616 * @shost: pointer to struct Scsi_Host instance
617 *
618 * Returns nothing
619 *
620 * Might block: currently may block but may be changed to not block
621 *
622 * Notes: Actually increments the counts in two sub-objects
623 *
624 * Defined in: drivers/scsi/hosts.c
625 **/
626void scsi_host_get(struct Scsi_Host *shost)
627
628
629/**
630 * scsi_host_put - decrement Scsi_Host instance refcount, free if 0
631 * @shost: pointer to struct Scsi_Host instance
632 *
633 * Returns nothing
634 *
635 * Might block: currently may block but may be changed to not block
636 *
637 * Notes: Actually decrements the counts in two sub-objects. If the
638 * latter refcount reaches 0, the Scsi_Host instance is freed.
639 * The LLD need not worry exactly when the Scsi_Host instance is
640 * freed, it just shouldn't access the instance after it has balanced
641 * out its refcount usage.
642 *
643 * Defined in: drivers/scsi/hosts.c
644 **/
645void scsi_host_put(struct Scsi_Host *shost)
646
647
648/**
649 * scsi_partsize - parse partition table into cylinders, heads + sectors
650 * @buf: pointer to partition table
651 * @capacity: size of (total) disk in 512 byte sectors
652 * @cyls: outputs number of cylinders calculated via this pointer
653 * @hds: outputs number of heads calculated via this pointer
654 * @secs: outputs number of sectors calculated via this pointer
655 *
656 * Returns 0 on success, -1 on failure
657 *
658 * Might block: no
659 *
660 * Notes: Caller owns memory returned (free with kfree() )
661 *
662 * Defined in: drivers/scsi/scsicam.c
663 **/
664int scsi_partsize(unsigned char *buf, unsigned long capacity,
665 unsigned int *cyls, unsigned int *hds, unsigned int *secs)
666
667
668/**
669 * scsi_register - create and register a scsi host adapter instance.
670 * @sht: pointer to scsi host template
671 * @privsize: extra bytes to allocate in hostdata array (which is the
672 * last member of the returned Scsi_Host instance)
673 *
674 * Returns pointer to new Scsi_Host instance or NULL on failure
675 *
676 * Might block: yes
677 *
678 * Notes: When this call returns to the LLD, the SCSI bus scan on
679 * this host has _not_ yet been done.
680 * The hostdata array (by default zero length) is a per host scratch
681 * area for the LLD.
682 *
683 * Defined in: drivers/scsi/hosts.c .
684 **/
685struct Scsi_Host * scsi_register(struct scsi_host_template * sht,
686 int privsize)
687
688
689/**
690 * scsi_remove_device - detach and remove a SCSI device
691 * @sdev: a pointer to a scsi device instance
692 *
693 * Returns value: 0 on success, -EINVAL if device not attached
694 *
695 * Might block: yes
696 *
697 * Notes: If an LLD becomes aware that a scsi device (lu) has
698 * been removed but its host is still present then it can request
699 * the removal of that scsi device. If successful this call will
700 * lead to the slave_destroy() callback being invoked. sdev is an
701 * invalid pointer after this call.
702 *
703 * Defined in: drivers/scsi/scsi_sysfs.c .
704 **/
705int scsi_remove_device(struct scsi_device *sdev)
706
707
708/**
709 * scsi_remove_host - detach and remove all SCSI devices owned by host
710 * @shost: a pointer to a scsi host instance
711 *
712 * Returns value: 0 on success, 1 on failure (e.g. LLD busy ??)
713 *
714 * Might block: yes
715 *
716 * Notes: Should only be invoked if the "hotplug initialization
717 * model" is being used. It should be called _prior_ to
718 * scsi_unregister().
719 *
720 * Defined in: drivers/scsi/hosts.c .
721 **/
722int scsi_remove_host(struct Scsi_Host *shost)
723
724
725/**
726 * scsi_report_bus_reset - report scsi _bus_ reset observed
727 * @shost: a pointer to a scsi host involved
728 * @channel: channel (within) host on which scsi bus reset occurred
729 *
730 * Returns nothing
731 *
732 * Might block: no
733 *
734 * Notes: This only needs to be called if the reset is one which
735 * originates from an unknown location. Resets originated by the
736 * mid level itself don't need to call this, but there should be
737 * no harm. The main purpose of this is to make sure that a
738 * CHECK_CONDITION is properly treated.
739 *
740 * Defined in: drivers/scsi/scsi_error.c .
741 **/
742void scsi_report_bus_reset(struct Scsi_Host * shost, int channel)
743
744
745/**
746 * scsi_set_device - place device reference in host structure
747 * @shost: a pointer to a scsi host instance
748 * @pdev: pointer to device instance to assign
749 *
750 * Returns nothing
751 *
752 * Might block: no
753 *
754 * Defined in: include/scsi/scsi_host.h .
755 **/
756void scsi_set_device(struct Scsi_Host * shost, struct device * dev)
757
758
759/**
760 * scsi_to_pci_dma_dir - convert SCSI subsystem direction flag to PCI
761 * @scsi_data_direction: SCSI subsystem direction flag
762 *
763 * Returns DMA_TO_DEVICE given SCSI_DATA_WRITE,
764 * DMA_FROM_DEVICE given SCSI_DATA_READ
765 * DMA_BIDIRECTIONAL given SCSI_DATA_UNKNOWN
766 * else returns DMA_NONE
767 *
768 * Might block: no
769 *
770 * Notes: The SCSI subsystem now uses the same values for these
771 * constants as the PCI subsystem so this function is a nop.
772 * The recommendation is not to use this conversion function anymore
773 * (in the 2.6 kernel series) as it is not needed.
774 *
775 * Defined in: drivers/scsi/scsi.h .
776 **/
777int scsi_to_pci_dma_dir(unsigned char scsi_data_direction)
778
779
780/**
781 * scsi_to_sbus_dma_dir - convert SCSI subsystem direction flag to SBUS
782 * @scsi_data_direction: SCSI subsystem direction flag
783 *
784 * Returns DMA_TO_DEVICE given SCSI_DATA_WRITE,
785 * FROM_DEVICE given SCSI_DATA_READ
786 * DMA_BIDIRECTIONAL given SCSI_DATA_UNKNOWN
787 * else returns DMA_NONE
788 *
789 * Notes: The SCSI subsystem now uses the same values for these
790 * constants as the SBUS subsystem so this function is a nop.
791 * The recommendation is not to use this conversion function anymore
792 * (in the 2.6 kernel series) as it is not needed.
793 *
794 * Might block: no
795 *
796 * Defined in: drivers/scsi/scsi.h .
797 **/
798int scsi_to_sbus_dma_dir(unsigned char scsi_data_direction)
799
800
801/**
802 * scsi_track_queue_full - track successive QUEUE_FULL events on given
803 * device to determine if and when there is a need
804 * to adjust the queue depth on the device.
805 * @sdev: pointer to SCSI device instance
806 * @depth: Current number of outstanding SCSI commands on this device,
807 * not counting the one returned as QUEUE_FULL.
808 *
809 * Returns 0 - no change needed
810 * >0 - adjust queue depth to this new depth
811 * -1 - drop back to untagged operation using host->cmd_per_lun
812 * as the untagged command depth
813 *
814 * Might block: no
815 *
816 * Notes: LLDs may call this at any time and we will do "The Right
817 * Thing"; interrupt context safe.
818 *
819 * Defined in: drivers/scsi/scsi.c .
820 **/
821int scsi_track_queue_full(Scsi_Device *sdev, int depth)
822
823
824/**
825 * scsi_unblock_requests - allow further commands to be queued to given host
826 *
827 * @shost: pointer to host to unblock commands on
828 *
829 * Returns nothing
830 *
831 * Might block: no
832 *
833 * Defined in: drivers/scsi/scsi_lib.c .
834**/
835void scsi_unblock_requests(struct Scsi_Host * shost)
836
837
838/**
839 * scsi_unregister - unregister and free memory used by host instance
840 * @shp: pointer to scsi host instance to unregister.
841 *
842 * Returns nothing
843 *
844 * Might block: no
845 *
846 * Notes: Should not be invoked if the "hotplug initialization
847 * model" is being used. Called internally by exit_this_scsi_driver()
848 * in the "passive initialization model". Hence a LLD has no need to
849 * call this function directly.
850 *
851 * Defined in: drivers/scsi/hosts.c .
852 **/
853void scsi_unregister(struct Scsi_Host * shp)
854
855
856
857
858Interface Functions
859===================
860Interface functions are supplied (defined) by LLDs and their function
861pointers are placed in an instance of struct scsi_host_template which
862is passed to scsi_host_alloc() [or scsi_register() / init_this_scsi_driver()].
863Some are mandatory. Interface functions should be declared static. The
864accepted convention is that driver "xyz" will declare its slave_configure()
865function as:
866 static int xyz_slave_configure(struct scsi_device * sdev);
867and so forth for all interface functions listed below.
868
869A pointer to this function should be placed in the 'slave_configure' member
870of a "struct scsi_host_template" instance. A pointer to such an instance
871should be passed to the mid level's scsi_host_alloc() [or scsi_register() /
872init_this_scsi_driver()].
873
874The interface functions are also described in the include/scsi/scsi_host.h
875file immediately above their definition point in "struct scsi_host_template".
876In some cases more detail is given in scsi_host.h than below.
877
878The interface functions are listed below in alphabetical order.
879
880Summary:
881 bios_param - fetch head, sector, cylinder info for a disk
882 detect - detects HBAs this driver wants to control
883 eh_timed_out - notify the host that a command timer expired
884 eh_abort_handler - abort given command
885 eh_bus_reset_handler - issue SCSI bus reset
886 eh_device_reset_handler - issue SCSI device reset
887 eh_host_reset_handler - reset host (host bus adapter)
888 eh_strategy_handler - driver supplied alternate to scsi_unjam_host()
889 info - supply information about given host
890 ioctl - driver can respond to ioctls
891 proc_info - supports /proc/scsi/{driver_name}/{host_no}
892 queuecommand - queue scsi command, invoke 'done' on completion
893 release - release all resources associated with given host
894 slave_alloc - prior to any commands being sent to a new device
895 slave_configure - driver fine tuning for given device after attach
896 slave_destroy - given device is about to be shut down
897
898
899Details:
900
901/**
902 * bios_param - fetch head, sector, cylinder info for a disk
903 * @sdev: pointer to scsi device context (defined in
904 * include/scsi/scsi_device.h)
905 * @bdev: pointer to block device context (defined in fs.h)
906 * @capacity: device size (in 512 byte sectors)
907 * @params: three element array to place output:
908 * params[0] number of heads (max 255)
909 * params[1] number of sectors (max 63)
910 * params[2] number of cylinders
911 *
912 * Return value is ignored
913 *
914 * Locks: none
915 *
916 * Calling context: process (sd)
917 *
918 * Notes: an arbitrary geometry (based on READ CAPACITY) is used
919 * if this function is not provided. The params array is
920 * pre-initialized with made up values just in case this function
921 * doesn't output anything.
922 *
923 * Optionally defined in: LLD
924 **/
925 int bios_param(struct scsi_device * sdev, struct block_device *bdev,
926 sector_t capacity, int params[3])
927
928
929/**
930 * detect - detects HBAs this driver wants to control
931 * @shtp: host template for this driver.
932 *
933 * Returns number of hosts this driver wants to control. 0 means no
934 * suitable hosts found.
935 *
936 * Locks: none held
937 *
938 * Calling context: process [invoked from init_this_scsi_driver()]
939 *
940 * Notes: First function called from the SCSI mid level on this
941 * driver. Upper level drivers (e.g. sd) may not (yet) be present.
942 * For each host found, this method should call scsi_register()
943 * [see hosts.c].
944 *
945 * Defined in: LLD (required if "passive initialization mode" is used,
946 * not invoked in "hotplug initialization mode")
947 **/
948 int detect(struct scsi_host_template * shtp)
949
950
951/**
952 * eh_timed_out - The timer for the command has just fired
953 * @scp: identifies command timing out
954 *
955 * Returns:
956 *
957 * EH_HANDLED: I fixed the error, please complete the command
958 * EH_RESET_TIMER: I need more time, reset the timer and
959 * begin counting again
960 * EH_NOT_HANDLED Begin normal error recovery
961 *
962 *
963 * Locks: None held
964 *
965 * Calling context: interrupt
966 *
967 * Notes: This is to give the LLD an opportunity to do local recovery.
968 * This recovery is limited to determining if the outstanding command
969 * will ever complete. You may not abort and restart the command from
970 * this callback.
971 *
972 * Optionally defined in: LLD
973 **/
974 int eh_timed_out(struct scsi_cmnd * scp)
975
976
977/**
978 * eh_abort_handler - abort command associated with scp
979 * @scp: identifies command to be aborted
980 *
981 * Returns SUCCESS if command aborted else FAILED
982 *
983 * Locks: struct Scsi_Host::host_lock held (with irqsave) on entry
984 * and assumed to be held on return.
985 *
986 * Calling context: kernel thread
987 *
988 * Notes: Invoked from scsi_eh thread. No other commands will be
989 * queued on current host during eh.
990 *
991 * Optionally defined in: LLD
992 **/
993 int eh_abort_handler(struct scsi_cmnd * scp)
994
995
996/**
997 * eh_bus_reset_handler - issue SCSI bus reset
998 * @scp: SCSI bus that contains this device should be reset
999 *
1000 * Returns SUCCESS if command aborted else FAILED
1001 *
1002 * Locks: struct Scsi_Host::host_lock held (with irqsave) on entry
1003 * and assumed to be held on return.
1004 *
1005 * Calling context: kernel thread
1006 *
1007 * Notes: Invoked from scsi_eh thread. No other commands will be
1008 * queued on current host during eh.
1009 *
1010 * Optionally defined in: LLD
1011 **/
1012 int eh_bus_reset_handler(struct scsi_cmnd * scp)
1013
1014
1015/**
1016 * eh_device_reset_handler - issue SCSI device reset
1017 * @scp: identifies SCSI device to be reset
1018 *
1019 * Returns SUCCESS if command aborted else FAILED
1020 *
1021 * Locks: struct Scsi_Host::host_lock held (with irqsave) on entry
1022 * and assumed to be held on return.
1023 *
1024 * Calling context: kernel thread
1025 *
1026 * Notes: Invoked from scsi_eh thread. No other commands will be
1027 * queued on current host during eh.
1028 *
1029 * Optionally defined in: LLD
1030 **/
1031 int eh_device_reset_handler(struct scsi_cmnd * scp)
1032
1033
1034/**
1035 * eh_host_reset_handler - reset host (host bus adapter)
1036 * @scp: SCSI host that contains this device should be reset
1037 *
1038 * Returns SUCCESS if command aborted else FAILED
1039 *
1040 * Locks: struct Scsi_Host::host_lock held (with irqsave) on entry
1041 * and assumed to be held on return.
1042 *
1043 * Calling context: kernel thread
1044 *
1045 * Notes: Invoked from scsi_eh thread. No other commands will be
1046 * queued on current host during eh.
1047 * With the default eh_strategy in place, if none of the _abort_,
1048 * _device_reset_, _bus_reset_ or this eh handler function are
1049 * defined (or they all return FAILED) then the device in question
1050 * will be set offline whenever eh is invoked.
1051 *
1052 * Optionally defined in: LLD
1053 **/
1054 int eh_host_reset_handler(struct scsi_cmnd * scp)
1055
1056
1057/**
1058 * eh_strategy_handler - driver supplied alternate to scsi_unjam_host()
1059 * @shp: host on which error has occurred
1060 *
1061 * Returns TRUE if host unjammed, else FALSE.
1062 *
1063 * Locks: none
1064 *
1065 * Calling context: kernel thread
1066 *
1067 * Notes: Invoked from scsi_eh thread. LLD supplied alternate to
1068 * scsi_unjam_host() found in scsi_error.c
1069 *
1070 * Optionally defined in: LLD
1071 **/
1072 int eh_strategy_handler(struct Scsi_Host * shp)
1073
1074
1075/**
1076 * info - supply information about given host: driver name plus data
1077 * to distinguish given host
1078 * @shp: host to supply information about
1079 *
1080 * Return ASCII null terminated string. [This driver is assumed to
1081 * manage the memory pointed to and maintain it, typically for the
1082 * lifetime of this host.]
1083 *
1084 * Locks: none
1085 *
1086 * Calling context: process
1087 *
1088 * Notes: Often supplies PCI or ISA information such as IO addresses
1089 * and interrupt numbers. If not supplied struct Scsi_Host::name used
1090 * instead. It is assumed the returned information fits on one line
1091 * (i.e. does not included embedded newlines).
1092 * The SCSI_IOCTL_PROBE_HOST ioctl yields the string returned by this
1093 * function (or struct Scsi_Host::name if this function is not
1094 * available).
1095 * In a similar manner, init_this_scsi_driver() outputs to the console
1096 * each host's "info" (or name) for the driver it is registering.
1097 * Also if proc_info() is not supplied, the output of this function
1098 * is used instead.
1099 *
1100 * Optionally defined in: LLD
1101 **/
1102 const char * info(struct Scsi_Host * shp)
1103
1104
1105/**
1106 * ioctl - driver can respond to ioctls
1107 * @sdp: device that ioctl was issued for
1108 * @cmd: ioctl number
1109 * @arg: pointer to read or write data from. Since it points to
1110 * user space, should use appropriate kernel functions
1111 * (e.g. copy_from_user() ). In the Unix style this argument
1112 * can also be viewed as an unsigned long.
1113 *
1114 * Returns negative "errno" value when there is a problem. 0 or a
1115 * positive value indicates success and is returned to the user space.
1116 *
1117 * Locks: none
1118 *
1119 * Calling context: process
1120 *
1121 * Notes: The SCSI subsystem uses a "trickle down" ioctl model.
1122 * The user issues an ioctl() against an upper level driver
1123 * (e.g. /dev/sdc) and if the upper level driver doesn't recognize
1124 * the 'cmd' then it is passed to the SCSI mid level. If the SCSI
1125 * mid level does not recognize it, then the LLD that controls
1126 * the device receives the ioctl. According to recent Unix standards
1127 * unsupported ioctl() 'cmd' numbers should return -ENOTTY.
1128 *
1129 * Optionally defined in: LLD
1130 **/
1131 int ioctl(struct scsi_device *sdp, int cmd, void *arg)
1132
1133
1134/**
1135 * proc_info - supports /proc/scsi/{driver_name}/{host_no}
1136 * @buffer: anchor point to output to (0==writeto1_read0) or fetch from
1137 * (1==writeto1_read0).
1138 * @start: where "interesting" data is written to. Ignored when
1139 * 1==writeto1_read0.
1140 * @offset: offset within buffer 0==writeto1_read0 is actually
1141 * interested in. Ignored when 1==writeto1_read0 .
1142 * @length: maximum (or actual) extent of buffer
1143 * @host_no: host number of interest (struct Scsi_Host::host_no)
1144 * @writeto1_read0: 1 -> data coming from user space towards driver
1145 * (e.g. "echo some_string > /proc/scsi/xyz/2")
1146 * 0 -> user what data from this driver
1147 * (e.g. "cat /proc/scsi/xyz/2")
1148 *
1149 * Returns length when 1==writeto1_read0. Otherwise number of chars
1150 * output to buffer past offset.
1151 *
1152 * Locks: none held
1153 *
1154 * Calling context: process
1155 *
1156 * Notes: Driven from scsi_proc.c which interfaces to proc_fs. proc_fs
1157 * support can now be configured out of the scsi subsystem.
1158 *
1159 * Optionally defined in: LLD
1160 **/
1161 int proc_info(char * buffer, char ** start, off_t offset,
1162 int length, int host_no, int writeto1_read0)
1163
1164
1165/**
1166 * queuecommand - queue scsi command, invoke 'done' on completion
1167 * @scp: pointer to scsi command object
1168 * @done: function pointer to be invoked on completion
1169 *
1170 * Returns 0 on success.
1171 *
1172 * If there's a failure, return either:
1173 *
1174 * SCSI_MLQUEUE_DEVICE_BUSY if the device queue is full, or
1175 * SCSI_MLQUEUE_HOST_BUSY if the entire host queue is full
1176 *
1177 * On both of these returns, the mid-layer will requeue the I/O
1178 *
1179 * - if the return is SCSI_MLQUEUE_DEVICE_BUSY, only that particular
1180 * device will be paused, and it will be unpaused when a command to
1181 * the device returns (or after a brief delay if there are no more
1182 * outstanding commands to it). Commands to other devices continue
1183 * to be processed normally.
1184 *
1185 * - if the return is SCSI_MLQUEUE_HOST_BUSY, all I/O to the host
1186 * is paused and will be unpaused when any command returns from
1187 * the host (or after a brief delay if there are no outstanding
1188 * commands to the host).
1189 *
1190 * For compatibility with earlier versions of queuecommand, any
1191 * other return value is treated the same as
1192 * SCSI_MLQUEUE_HOST_BUSY.
1193 *
1194 * Other types of errors that are detected immediately may be
1195 * flagged by setting scp->result to an appropriate value,
1196 * invoking the 'done' callback, and then returning 0 from this
1197 * function. If the command is not performed immediately (and the
1198 * LLD is starting (or will start) the given command) then this
1199 * function should place 0 in scp->result and return 0.
1200 *
1201 * Command ownership. If the driver returns zero, it owns the
1202 * command and must take responsibility for ensuring the 'done'
1203 * callback is executed. Note: the driver may call done before
1204 * returning zero, but after it has called done, it may not
1205 * return any value other than zero. If the driver makes a
1206 * non-zero return, it must not execute the command's done
1207 * callback at any time.
1208 *
1209 * Locks: struct Scsi_Host::host_lock held on entry (with "irqsave")
1210 * and is expected to be held on return.
1211 *
1212 * Calling context: in interrupt (soft irq) or process context
1213 *
1214 * Notes: This function should be relatively fast. Normally it will
1215 * not wait for IO to complete. Hence the 'done' callback is invoked
1216 * (often directly from an interrupt service routine) some time after
1217 * this function has returned. In some cases (e.g. pseudo adapter
1218 * drivers that manufacture the response to a SCSI INQUIRY)
1219 * the 'done' callback may be invoked before this function returns.
1220 * If the 'done' callback is not invoked within a certain period
1221 * the SCSI mid level will commence error processing.
1222 * If a status of CHECK CONDITION is placed in "result" when the
1223 * 'done' callback is invoked, then the LLD driver should
1224 * perform autosense and fill in the struct scsi_cmnd::sense_buffer
1225 * array. The scsi_cmnd::sense_buffer array is zeroed prior to
1226 * the mid level queuing a command to an LLD.
1227 *
1228 * Defined in: LLD
1229 **/
1230 int queuecommand(struct scsi_cmnd * scp,
1231 void (*done)(struct scsi_cmnd *))
1232
1233
1234/**
1235 * release - release all resources associated with given host
1236 * @shp: host to be released.
1237 *
1238 * Return value ignored (could soon be a function returning void).
1239 *
1240 * Locks: none held
1241 *
1242 * Calling context: process
1243 *
1244 * Notes: Invoked from scsi_module.c's exit_this_scsi_driver().
1245 * LLD's implementation of this function should call
1246 * scsi_unregister(shp) prior to returning.
1247 * Only needed for old-style host templates.
1248 *
1249 * Defined in: LLD (required in "passive initialization model",
1250 * should not be defined in hotplug model)
1251 **/
1252 int release(struct Scsi_Host * shp)
1253
1254
1255/**
1256 * slave_alloc - prior to any commands being sent to a new device
1257 * (i.e. just prior to scan) this call is made
1258 * @sdp: pointer to new device (about to be scanned)
1259 *
1260 * Returns 0 if ok. Any other return is assumed to be an error and
1261 * the device is ignored.
1262 *
1263 * Locks: none
1264 *
1265 * Calling context: process
1266 *
1267 * Notes: Allows the driver to allocate any resources for a device
1268 * prior to its initial scan. The corresponding scsi device may not
1269 * exist but the mid level is just about to scan for it (i.e. send
1270 * and INQUIRY command plus ...). If a device is found then
1271 * slave_configure() will be called while if a device is not found
1272 * slave_destroy() is called.
1273 * For more details see the include/scsi/scsi_host.h file.
1274 *
1275 * Optionally defined in: LLD
1276 **/
1277 int slave_alloc(struct scsi_device *sdp)
1278
1279
1280/**
1281 * slave_configure - driver fine tuning for given device just after it
1282 * has been first scanned (i.e. it responded to an
1283 * INQUIRY)
1284 * @sdp: device that has just been attached
1285 *
1286 * Returns 0 if ok. Any other return is assumed to be an error and
1287 * the device is taken offline. [offline devices will _not_ have
1288 * slave_destroy() called on them so clean up resources.]
1289 *
1290 * Locks: none
1291 *
1292 * Calling context: process
1293 *
1294 * Notes: Allows the driver to inspect the response to the initial
1295 * INQUIRY done by the scanning code and take appropriate action.
1296 * For more details see the include/scsi/scsi_host.h file.
1297 *
1298 * Optionally defined in: LLD
1299 **/
1300 int slave_configure(struct scsi_device *sdp)
1301
1302
1303/**
1304 * slave_destroy - given device is about to be shut down. All
1305 * activity has ceased on this device.
1306 * @sdp: device that is about to be shut down
1307 *
1308 * Returns nothing
1309 *
1310 * Locks: none
1311 *
1312 * Calling context: process
1313 *
1314 * Notes: Mid level structures for given device are still in place
1315 * but are about to be torn down. Any per device resources allocated
1316 * by this driver for given device should be freed now. No further
1317 * commands will be sent for this sdp instance. [However the device
1318 * could be re-attached in the future in which case a new instance
1319 * of struct scsi_device would be supplied by future slave_alloc()
1320 * and slave_configure() calls.]
1321 *
1322 * Optionally defined in: LLD
1323 **/
1324 void slave_destroy(struct scsi_device *sdp)
1325
1326
1327
1328Data Structures
1329===============
1330struct scsi_host_template
1331-------------------------
1332There is one "struct scsi_host_template" instance per LLD ***. It is
1333typically initialized as a file scope static in a driver's header file. That
1334way members that are not explicitly initialized will be set to 0 or NULL.
1335Member of interest:
1336 name - name of driver (may contain spaces, please limit to
1337 less than 80 characters)
1338 proc_name - name used in "/proc/scsi/<proc_name>/<host_no>" and
1339 by sysfs in one of its "drivers" directories. Hence
1340 "proc_name" should only contain characters acceptable
1341 to a Unix file name.
1342 (*queuecommand)() - primary callback that the mid level uses to inject
1343 SCSI commands into an LLD.
1344The structure is defined and commented in include/scsi/scsi_host.h
1345
1346*** In extreme situations a single driver may have several instances
1347 if it controls several different classes of hardware (e.g. an LLD
1348 that handles both ISA and PCI cards and has a separate instance of
1349 struct scsi_host_template for each class).
1350
1351struct Scsi_Host
1352----------------
1353There is one struct Scsi_Host instance per host (HBA) that an LLD
1354controls. The struct Scsi_Host structure has many members in common
1355with "struct scsi_host_template". When a new struct Scsi_Host instance
1356is created (in scsi_host_alloc() in hosts.c) those common members are
1357initialized from the driver's struct scsi_host_template instance. Members
1358of interest:
1359 host_no - system wide unique number that is used for identifying
1360 this host. Issued in ascending order from 0.
1361 can_queue - must be greater than 0; do not send more than can_queue
1362 commands to the adapter.
1363 this_id - scsi id of host (scsi initiator) or -1 if not known
1364 sg_tablesize - maximum scatter gather elements allowed by host.
1365 0 implies scatter gather not supported by host
1366 max_sectors - maximum number of sectors (usually 512 bytes) allowed
1367 in a single SCSI command. The default value of 0 leads
1368 to a setting of SCSI_DEFAULT_MAX_SECTORS (defined in
1369 scsi_host.h) which is currently set to 1024. So for a
1370 disk the maximum transfer size is 512 KB when max_sectors
1371 is not defined. Note that this size may not be sufficient
1372 for disk firmware uploads.
1373 cmd_per_lun - maximum number of commands that can be queued on devices
1374 controlled by the host. Overridden by LLD calls to
1375 scsi_adjust_queue_depth().
1376 unchecked_isa_dma - 1=>only use bottom 16 MB of ram (ISA DMA addressing
1377 restriction), 0=>can use full 32 bit (or better) DMA
1378 address space
1379 use_clustering - 1=>SCSI commands in mid level's queue can be merged,
1380 0=>disallow SCSI command merging
1381 hostt - pointer to driver's struct scsi_host_template from which
1382 this struct Scsi_Host instance was spawned
1383 hostt->proc_name - name of LLD. This is the driver name that sysfs uses
1384 transportt - pointer to driver's struct scsi_transport_template instance
1385 (if any). FC and SPI transports currently supported.
1386 sh_list - a double linked list of pointers to all struct Scsi_Host
1387 instances (currently ordered by ascending host_no)
1388 my_devices - a double linked list of pointers to struct scsi_device
1389 instances that belong to this host.
1390 hostdata[0] - area reserved for LLD at end of struct Scsi_Host. Size
1391 is set by the second argument (named 'xtr_bytes') to
1392 scsi_host_alloc() or scsi_register().
1393
1394The scsi_host structure is defined in include/scsi/scsi_host.h
1395
1396struct scsi_device
1397------------------
1398Generally, there is one instance of this structure for each SCSI logical unit
1399on a host. Scsi devices connected to a host are uniquely identified by a
1400channel number, target id and logical unit number (lun).
1401The structure is defined in include/scsi/scsi_device.h
1402
1403struct scsi_cmnd
1404----------------
1405Instances of this structure convey SCSI commands to the LLD and responses
1406back to the mid level. The SCSI mid level will ensure that no more SCSI
1407commands become queued against the LLD than are indicated by
1408scsi_adjust_queue_depth() (or struct Scsi_Host::cmd_per_lun). There will
1409be at least one instance of struct scsi_cmnd available for each SCSI device.
1410Members of interest:
1411 cmnd - array containing SCSI command
1412 cmnd_len - length (in bytes) of SCSI command
1413 sc_data_direction - direction of data transfer in data phase. See
1414 "enum dma_data_direction" in include/linux/dma-mapping.h
1415 request_bufflen - number of data bytes to transfer (0 if no data phase)
1416 use_sg - ==0 -> no scatter gather list, hence transfer data
1417 to/from request_buffer
1418 - >0 -> scatter gather list (actually an array) in
1419 request_buffer with use_sg elements
1420 request_buffer - either contains data buffer or scatter gather list
1421 depending on the setting of use_sg. Scatter gather
1422 elements are defined by 'struct scatterlist' found
1423 in include/asm/scatterlist.h .
1424 done - function pointer that should be invoked by LLD when the
1425 SCSI command is completed (successfully or otherwise).
1426 Should only be called by an LLD if the LLD has accepted
1427 the command (i.e. queuecommand() returned or will return
1428 0). The LLD may invoke 'done' prior to queuecommand()
1429 finishing.
1430 result - should be set by LLD prior to calling 'done'. A value
1431 of 0 implies a successfully completed command (and all
1432 data (if any) has been transferred to or from the SCSI
1433 target device). 'result' is a 32 bit unsigned integer that
1434 can be viewed as 4 related bytes. The SCSI status value is
1435 in the LSB. See include/scsi/scsi.h status_byte(),
1436 msg_byte(), host_byte() and driver_byte() macros and
1437 related constants.
1438 sense_buffer - an array (maximum size: SCSI_SENSE_BUFFERSIZE bytes) that
1439 should be written when the SCSI status (LSB of 'result')
1440 is set to CHECK_CONDITION (2). When CHECK_CONDITION is
1441 set, if the top nibble of sense_buffer[0] has the value 7
1442 then the mid level will assume the sense_buffer array
1443 contains a valid SCSI sense buffer; otherwise the mid
1444 level will issue a REQUEST_SENSE SCSI command to
1445 retrieve the sense buffer. The latter strategy is error
1446 prone in the presence of command queuing so the LLD should
1447 always "auto-sense".
1448 device - pointer to scsi_device object that this command is
1449 associated with.
1450 resid - an LLD should set this signed integer to the requested
1451 transfer length (i.e. 'request_bufflen') less the number
1452 of bytes that are actually transferred. 'resid' is
1453 preset to 0 so an LLD can ignore it if it cannot detect
1454 underruns (overruns should be rare). If possible an LLD
1455 should set 'resid' prior to invoking 'done'. The most
1456 interesting case is data transfers from a SCSI target
1457 device device (i.e. READs) that underrun.
1458 underflow - LLD should place (DID_ERROR << 16) in 'result' if
1459 actual number of bytes transferred is less than this
1460 figure. Not many LLDs implement this check and some that
1461 do just output an error message to the log rather than
1462 report a DID_ERROR. Better for an LLD to implement
1463 'resid'.
1464
1465The scsi_cmnd structure is defined in include/scsi/scsi_cmnd.h
1466
1467
1468Locks
1469=====
1470Each struct Scsi_Host instance has a spin_lock called struct
1471Scsi_Host::default_lock which is initialized in scsi_host_alloc() [found in
1472hosts.c]. Within the same function the struct Scsi_Host::host_lock pointer
1473is initialized to point at default_lock with the scsi_assign_lock() function.
1474Thereafter lock and unlock operations performed by the mid level use the
1475struct Scsi_Host::host_lock pointer.
1476
1477LLDs can override the use of struct Scsi_Host::default_lock by
1478using scsi_assign_lock(). The earliest opportunity to do this would
1479be in the detect() function after it has invoked scsi_register(). It
1480could be replaced by a coarser grain lock (e.g. per driver) or a
1481lock of equal granularity (i.e. per host). Using finer grain locks
1482(e.g. per SCSI device) may be possible by juggling locks in
1483queuecommand().
1484
1485Autosense
1486=========
1487Autosense (or auto-sense) is defined in the SAM-2 document as "the
1488automatic return of sense data to the application client coincident
1489with the completion of a SCSI command" when a status of CHECK CONDITION
1490occurs. LLDs should perform autosense. This should be done when the LLD
1491detects a CHECK CONDITION status by either:
1492 a) instructing the SCSI protocol (e.g. SCSI Parallel Interface (SPI))
1493 to perform an extra data in phase on such responses
1494 b) or, the LLD issuing a REQUEST SENSE command itself
1495
1496Either way, when a status of CHECK CONDITION is detected, the mid level
1497decides whether the LLD has performed autosense by checking struct
1498scsi_cmnd::sense_buffer[0] . If this byte has an upper nibble of 7 (or 0xf)
1499then autosense is assumed to have taken place. If it has another value (and
1500this byte is initialized to 0 before each command) then the mid level will
1501issue a REQUEST SENSE command.
1502
1503In the presence of queued commands the "nexus" that maintains sense
1504buffer data from the command that failed until a following REQUEST SENSE
1505may get out of synchronization. This is why it is best for the LLD
1506to perform autosense.
1507
1508
1509Changes since lk 2.4 series
1510===========================
1511io_request_lock has been replaced by several finer grained locks. The lock
1512relevant to LLDs is struct Scsi_Host::host_lock and there is
1513one per SCSI host.
1514
1515The older error handling mechanism has been removed. This means the
1516LLD interface functions abort() and reset() have been removed.
1517The struct scsi_host_template::use_new_eh_code flag has been removed.
1518
1519In the 2.4 series the SCSI subsystem configuration descriptions were
1520aggregated with the configuration descriptions from all other Linux
1521subsystems in the Documentation/Configure.help file. In the 2.6 series,
1522the SCSI subsystem now has its own (much smaller) drivers/scsi/Kconfig
1523file that contains both configuration and help information.
1524
1525struct SHT has been renamed to struct scsi_host_template.
1526
1527Addition of the "hotplug initialization model" and many extra functions
1528to support it.
1529
1530
1531Credits
1532=======
1533The following people have contributed to this document:
1534 Mike Anderson <andmike at us dot ibm dot com>
1535 James Bottomley <James dot Bottomley at steeleye dot com>
1536 Patrick Mansfield <patmans at us dot ibm dot com>
1537 Christoph Hellwig <hch at infradead dot org>
1538 Doug Ledford <dledford at redhat dot com>
1539 Andries Brouwer <Andries dot Brouwer at cwi dot nl>
1540 Randy Dunlap <rddunlap at osdl dot org>
1541 Alan Stern <stern at rowland dot harvard dot edu>
1542
1543
1544Douglas Gilbert
1545dgilbert at interlog dot com
154621st September 2004