1 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() ----> 154scsi_scan_host() -------+ 155 | 156 slave_alloc() 157 slave_configure() --> scsi_adjust_queue_depth() 158 | 159 slave_alloc() 160 slave_configure() 161 | 162 slave_alloc() *** 163 slave_destroy() *** 164------------------------------------------------------------ 165 166If the LLD wants to adjust the default queue settings, it can invoke 167scsi_adjust_queue_depth() in its slave_configure() routine. 168 169*** For scsi devices that the mid level tries to scan but do not 170 respond, a slave_alloc(), slave_destroy() pair is called. 171 172When an HBA is being removed it could be as part of an orderly shutdown 173associated with the LLD module being unloaded (e.g. with the "rmmod" 174command) or in response to a "hot unplug" indicated by sysfs()'s 175remove() callback being invoked. In either case, the sequence is the 176same: 177 178 HBA REMOVE: assume 2 SCSI devices attached 179LLD mid level LLD 180===----------------------=========-----------------===------ 181scsi_remove_host() ---------+ 182 | 183 slave_destroy() 184 slave_destroy() 185scsi_host_put() 186------------------------------------------------------------ 187 188It may be useful for a LLD to keep track of struct Scsi_Host instances 189(a pointer is returned by scsi_host_alloc()). Such instances are "owned" 190by the mid-level. struct Scsi_Host instances are freed from 191scsi_host_put() when the reference count hits zero. 192 193Hot unplugging an HBA that controls a disk which is processing SCSI 194commands on a mounted file system is an interesting situation. Reference 195counting logic is being introduced into the mid level to cope with many 196of the issues involved. See the section on reference counting below. 197 198 199The hotplug concept may be extended to SCSI devices. Currently, when an 200HBA is added, the scsi_scan_host() function causes a scan for SCSI devices 201attached to the HBA's SCSI transport. On newer SCSI transports the HBA 202may become aware of a new SCSI device _after_ the scan has completed. 203An LLD can use this sequence to make the mid level aware of a SCSI device: 204 205 SCSI DEVICE hotplug 206LLD mid level LLD 207===-------------------=========--------------------===------ 208scsi_add_device() ------+ 209 | 210 slave_alloc() 211 slave_configure() [--> scsi_adjust_queue_depth()] 212------------------------------------------------------------ 213 214In a similar fashion, an LLD may become aware that a SCSI device has been 215removed (unplugged) or the connection to it has been interrupted. Some 216existing SCSI transports (e.g. SPI) may not become aware that a SCSI 217device has been removed until a subsequent SCSI command fails which will 218probably cause that device to be set offline by the mid level. An LLD that 219detects the removal of a SCSI device can instigate its removal from 220upper layers with this sequence: 221 222 SCSI DEVICE hot unplug 223LLD mid level LLD 224===----------------------=========-----------------===------ 225scsi_remove_device() -------+ 226 | 227 slave_destroy() 228------------------------------------------------------------ 229 230It may be useful for an LLD to keep track of struct scsi_device instances 231(a pointer is passed as the parameter to slave_alloc() and 232slave_configure() callbacks). Such instances are "owned" by the mid-level. 233struct scsi_device instances are freed after slave_destroy(). 234 235 236Passive initialization model 237============================ 238These older LLDs include a file called "scsi_module.c" [yes the ".c" is a 239little surprising] in their source code. For that file to work an 240instance of struct scsi_host_template with the name "driver_template" 241needs to be defined. Here is a typical code sequence used in this model: 242 static struct scsi_host_template driver_template = { 243 ... 244 }; 245 #include "scsi_module.c" 246 247The scsi_module.c file contains two functions: 248 - init_this_scsi_driver() which is executed when the LLD is 249 initialized (i.e. boot time or module load time) 250 - exit_this_scsi_driver() which is executed when the LLD is shut 251 down (i.e. module unload time) 252Note: since these functions are tagged with __init and __exit qualifiers 253an LLD should not call them explicitly (since the kernel does that). 254 255Here is an example of an initialization sequence when two hosts are 256detected (so detect() returns 2) and the SCSI bus scan on each host 257finds 1 SCSI device (and a second device does not respond). 258 259LLD mid level LLD 260===----------------------=========-----------------===------ 261init_this_scsi_driver() ----+ 262 | 263 detect() -----------------+ 264 | | 265 | scsi_register() 266 | scsi_register() 267 | 268 slave_alloc() 269 slave_configure() --> scsi_adjust_queue_depth() 270 slave_alloc() *** 271 slave_destroy() *** 272 | 273 slave_alloc() 274 slave_configure() 275 slave_alloc() *** 276 slave_destroy() *** 277------------------------------------------------------------ 278 279The mid level invokes scsi_adjust_queue_depth() with tagged queuing off and 280"cmd_per_lun" for that host as the queue length. These settings can be 281overridden by a slave_configure() supplied by the LLD. 282 283*** For scsi devices that the mid level tries to scan but do not 284 respond, a slave_alloc(), slave_destroy() pair is called. 285 286Here is an LLD shutdown sequence: 287 288LLD mid level LLD 289===----------------------=========-----------------===------ 290exit_this_scsi_driver() ----+ 291 | 292 slave_destroy() 293 release() --> scsi_unregister() 294 | 295 slave_destroy() 296 release() --> scsi_unregister() 297------------------------------------------------------------ 298 299An LLD need not define slave_destroy() (i.e. it is optional). 300 301The shortcoming of the "passive initialization model" is that host 302registration and de-registration are (typically) tied to LLD initialization 303and shutdown. Once the LLD is initialized then a new host that appears 304(e.g. via hotplugging) cannot easily be added without a redundant 305driver shutdown and re-initialization. It may be possible to write an LLD 306that uses both initialization models. 307 308 309Reference Counting 310================== 311The Scsi_Host structure has had reference counting infrastructure added. 312This effectively spreads the ownership of struct Scsi_Host instances 313across the various SCSI layers which use them. Previously such instances 314were exclusively owned by the mid level. LLDs would not usually need to 315directly manipulate these reference counts but there may be some cases 316where they do. 317 318There are 3 reference counting functions of interest associated with 319struct Scsi_Host: 320 - scsi_host_alloc(): returns a pointer to new instance of struct 321 Scsi_Host which has its reference count ^^ set to 1 322 - scsi_host_get(): adds 1 to the reference count of the given instance 323 - scsi_host_put(): decrements 1 from the reference count of the given 324 instance. If the reference count reaches 0 then the given instance 325 is freed 326 327The Scsi_device structure has had reference counting infrastructure added. 328This effectively spreads the ownership of struct Scsi_device instances 329across the various SCSI layers which use them. Previously such instances 330were exclusively owned by the mid level. See the access functions declared 331towards the end of include/scsi/scsi_device.h . If an LLD wants to keep 332a copy of a pointer to a Scsi_device instance it should use scsi_device_get() 333to bump its reference count. When it is finished with the pointer it can 334use scsi_device_put() to decrement its reference count (and potentially 335delete it). 336 337^^ struct Scsi_Host actually has 2 reference counts which are manipulated 338in parallel by these functions. 339 340 341Conventions 342=========== 343First, Linus Torvalds's thoughts on C coding style can be found in the 344Documentation/CodingStyle file. 345 346Next, there is a movement to "outlaw" typedefs introducing synonyms for 347struct tags. Both can be still found in the SCSI subsystem, but 348the typedefs have been moved to a single file, scsi_typedefs.h to 349make their future removal easier, for example: 350"typedef struct scsi_cmnd Scsi_Cmnd;" 351 352Also, most C99 enhancements are encouraged to the extent they are supported 353by the relevant gcc compilers. So C99 style structure and array 354initializers are encouraged where appropriate. Don't go too far, 355VLAs are not properly supported yet. An exception to this is the use of 356"//" style comments; /*...*/ comments are still preferred in Linux. 357 358Well written, tested and documented code, need not be re-formatted to 359comply with the above conventions. For example, the aic7xxx driver 360comes to Linux from FreeBSD and Adaptec's own labs. No doubt FreeBSD 361and Adaptec have their own coding conventions. 362 363 364Mid level supplied functions 365============================ 366These functions are supplied by the SCSI mid level for use by LLDs. 367The names (i.e. entry points) of these functions are exported 368so an LLD that is a module can access them. The kernel will 369arrange for the SCSI mid level to be loaded and initialized before any LLD 370is initialized. The functions below are listed alphabetically and their 371names all start with "scsi_". 372 373Summary: 374 scsi_activate_tcq - turn on tag command queueing 375 scsi_add_device - creates new scsi device (lu) instance 376 scsi_add_host - perform sysfs registration and set up transport class 377 scsi_adjust_queue_depth - change the queue depth on a SCSI device 378 scsi_bios_ptable - return copy of block device's partition table 379 scsi_block_requests - prevent further commands being queued to given host 380 scsi_deactivate_tcq - turn off tag command queueing 381 scsi_host_alloc - return a new scsi_host instance whose refcount==1 382 scsi_host_get - increments Scsi_Host instance's refcount 383 scsi_host_put - decrements Scsi_Host instance's refcount (free if 0) 384 scsi_partsize - parse partition table into cylinders, heads + sectors 385 scsi_register - create and register a scsi host adapter instance. 386 scsi_remove_device - detach and remove a SCSI device 387 scsi_remove_host - detach and remove all SCSI devices owned by host 388 scsi_report_bus_reset - report scsi _bus_ reset observed 389 scsi_scan_host - scan SCSI bus 390 scsi_track_queue_full - track successive QUEUE_FULL events 391 scsi_unblock_requests - allow further commands to be queued to given host 392 scsi_unregister - [calls scsi_host_put()] 393 394 395Details: 396 397/** 398 * scsi_activate_tcq - turn on tag command queueing ("ordered" task attribute) 399 * @sdev: device to turn on TCQ for 400 * @depth: queue depth 401 * 402 * Returns nothing 403 * 404 * Might block: no 405 * 406 * Notes: Eventually, it is hoped depth would be the maximum depth 407 * the device could cope with and the real queue depth 408 * would be adjustable from 0 to depth. 409 * 410 * Defined (inline) in: include/scsi/scsi_tcq.h 411 **/ 412void scsi_activate_tcq(struct scsi_device *sdev, int depth) 413 414 415/** 416 * scsi_add_device - creates new scsi device (lu) instance 417 * @shost: pointer to scsi host instance 418 * @channel: channel number (rarely other than 0) 419 * @id: target id number 420 * @lun: logical unit number 421 * 422 * Returns pointer to new struct scsi_device instance or 423 * ERR_PTR(-ENODEV) (or some other bent pointer) if something is 424 * wrong (e.g. no lu responds at given address) 425 * 426 * Might block: yes 427 * 428 * Notes: This call is usually performed internally during a scsi 429 * bus scan when an HBA is added (i.e. scsi_scan_host()). So it 430 * should only be called if the HBA becomes aware of a new scsi 431 * device (lu) after scsi_scan_host() has completed. If successful 432 * this call can lead to slave_alloc() and slave_configure() callbacks 433 * into the LLD. 434 * 435 * Defined in: drivers/scsi/scsi_scan.c 436 **/ 437struct scsi_device * scsi_add_device(struct Scsi_Host *shost, 438 unsigned int channel, 439 unsigned int id, unsigned int lun) 440 441 442/** 443 * scsi_add_host - perform sysfs registration and set up transport class 444 * @shost: pointer to scsi host instance 445 * @dev: pointer to struct device of type scsi class 446 * 447 * Returns 0 on success, negative errno of failure (e.g. -ENOMEM) 448 * 449 * Might block: no 450 * 451 * Notes: Only required in "hotplug initialization model" after a 452 * successful call to scsi_host_alloc(). This function does not 453 * scan the bus; this can be done by calling scsi_scan_host() or 454 * in some other transport-specific way. The LLD must set up 455 * the transport template before calling this function and may only 456 * access the transport class data after this function has been called. 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_adjust_queue_depth - allow LLD to change queue depth on a SCSI device 465 * @sdev: pointer to SCSI device to change queue depth on 466 * @tagged: 0 - no tagged queuing 467 * MSG_SIMPLE_TAG - simple tagged queuing 468 * MSG_ORDERED_TAG - ordered tagged queuing 469 * @tags Number of tags allowed if tagged queuing enabled, 470 * or number of commands the LLD can queue up 471 * in non-tagged mode (as per cmd_per_lun). 472 * 473 * Returns nothing 474 * 475 * Might block: no 476 * 477 * Notes: Can be invoked any time on a SCSI device controlled by this 478 * LLD. [Specifically during and after slave_configure() and prior to 479 * slave_destroy().] Can safely be invoked from interrupt code. Actual 480 * queue depth change may be delayed until the next command is being 481 * processed. See also scsi_activate_tcq() and scsi_deactivate_tcq(). 482 * 483 * Defined in: drivers/scsi/scsi.c [see source code for more notes] 484 * 485 **/ 486void scsi_adjust_queue_depth(struct scsi_device * sdev, int tagged, 487 int tags) 488 489 490/** 491 * scsi_bios_ptable - return copy of block device's partition table 492 * @dev: pointer to block device 493 * 494 * Returns pointer to partition table, or NULL for failure 495 * 496 * Might block: yes 497 * 498 * Notes: Caller owns memory returned (free with kfree() ) 499 * 500 * Defined in: drivers/scsi/scsicam.c 501 **/ 502unsigned char *scsi_bios_ptable(struct block_device *dev) 503 504 505/** 506 * scsi_block_requests - prevent further commands being queued to given host 507 * 508 * @shost: pointer to host to block commands on 509 * 510 * Returns nothing 511 * 512 * Might block: no 513 * 514 * Notes: There is no timer nor any other means by which the requests 515 * get unblocked other than the LLD calling scsi_unblock_requests(). 516 * 517 * Defined in: drivers/scsi/scsi_lib.c 518**/ 519void scsi_block_requests(struct Scsi_Host * shost) 520 521 522/** 523 * scsi_deactivate_tcq - turn off tag command queueing 524 * @sdev: device to turn off TCQ for 525 * @depth: queue depth (stored in sdev) 526 * 527 * Returns nothing 528 * 529 * Might block: no 530 * 531 * Defined (inline) in: include/scsi/scsi_tcq.h 532 **/ 533void scsi_deactivate_tcq(struct scsi_device *sdev, int depth) 534 535 536/** 537 * scsi_host_alloc - create a scsi host adapter instance and perform basic 538 * initialization. 539 * @sht: pointer to scsi host template 540 * @privsize: extra bytes to allocate in hostdata array (which is the 541 * last member of the returned Scsi_Host instance) 542 * 543 * Returns pointer to new Scsi_Host instance or NULL on failure 544 * 545 * Might block: yes 546 * 547 * Notes: When this call returns to the LLD, the SCSI bus scan on 548 * this host has _not_ yet been done. 549 * The hostdata array (by default zero length) is a per host scratch 550 * area for the LLD's exclusive use. 551 * Both associated refcounting objects have their refcount set to 1. 552 * Full registration (in sysfs) and a bus scan are performed later when 553 * scsi_add_host() and scsi_scan_host() are called. 554 * 555 * Defined in: drivers/scsi/hosts.c . 556 **/ 557struct Scsi_Host * scsi_host_alloc(struct scsi_host_template * sht, 558 int privsize) 559 560 561/** 562 * scsi_host_get - increment Scsi_Host instance refcount 563 * @shost: pointer to struct Scsi_Host instance 564 * 565 * Returns nothing 566 * 567 * Might block: currently may block but may be changed to not block 568 * 569 * Notes: Actually increments the counts in two sub-objects 570 * 571 * Defined in: drivers/scsi/hosts.c 572 **/ 573void scsi_host_get(struct Scsi_Host *shost) 574 575 576/** 577 * scsi_host_put - decrement Scsi_Host instance refcount, free if 0 578 * @shost: pointer to struct Scsi_Host instance 579 * 580 * Returns nothing 581 * 582 * Might block: currently may block but may be changed to not block 583 * 584 * Notes: Actually decrements the counts in two sub-objects. If the 585 * latter refcount reaches 0, the Scsi_Host instance is freed. 586 * The LLD need not worry exactly when the Scsi_Host instance is 587 * freed, it just shouldn't access the instance after it has balanced 588 * out its refcount usage. 589 * 590 * Defined in: drivers/scsi/hosts.c 591 **/ 592void scsi_host_put(struct Scsi_Host *shost) 593 594 595/** 596 * scsi_partsize - parse partition table into cylinders, heads + sectors 597 * @buf: pointer to partition table 598 * @capacity: size of (total) disk in 512 byte sectors 599 * @cyls: outputs number of cylinders calculated via this pointer 600 * @hds: outputs number of heads calculated via this pointer 601 * @secs: outputs number of sectors calculated via this pointer 602 * 603 * Returns 0 on success, -1 on failure 604 * 605 * Might block: no 606 * 607 * Notes: Caller owns memory returned (free with kfree() ) 608 * 609 * Defined in: drivers/scsi/scsicam.c 610 **/ 611int scsi_partsize(unsigned char *buf, unsigned long capacity, 612 unsigned int *cyls, unsigned int *hds, unsigned int *secs) 613 614 615/** 616 * scsi_register - create and register a scsi host adapter instance. 617 * @sht: pointer to scsi host template 618 * @privsize: extra bytes to allocate in hostdata array (which is the 619 * last member of the returned Scsi_Host instance) 620 * 621 * Returns pointer to new Scsi_Host instance or NULL on failure 622 * 623 * Might block: yes 624 * 625 * Notes: When this call returns to the LLD, the SCSI bus scan on 626 * this host has _not_ yet been done. 627 * The hostdata array (by default zero length) is a per host scratch 628 * area for the LLD. 629 * 630 * Defined in: drivers/scsi/hosts.c . 631 **/ 632struct Scsi_Host * scsi_register(struct scsi_host_template * sht, 633 int privsize) 634 635 636/** 637 * scsi_remove_device - detach and remove a SCSI device 638 * @sdev: a pointer to a scsi device instance 639 * 640 * Returns value: 0 on success, -EINVAL if device not attached 641 * 642 * Might block: yes 643 * 644 * Notes: If an LLD becomes aware that a scsi device (lu) has 645 * been removed but its host is still present then it can request 646 * the removal of that scsi device. If successful this call will 647 * lead to the slave_destroy() callback being invoked. sdev is an 648 * invalid pointer after this call. 649 * 650 * Defined in: drivers/scsi/scsi_sysfs.c . 651 **/ 652int scsi_remove_device(struct scsi_device *sdev) 653 654 655/** 656 * scsi_remove_host - detach and remove all SCSI devices owned by host 657 * @shost: a pointer to a scsi host instance 658 * 659 * Returns value: 0 on success, 1 on failure (e.g. LLD busy ??) 660 * 661 * Might block: yes 662 * 663 * Notes: Should only be invoked if the "hotplug initialization 664 * model" is being used. It should be called _prior_ to 665 * scsi_unregister(). 666 * 667 * Defined in: drivers/scsi/hosts.c . 668 **/ 669int scsi_remove_host(struct Scsi_Host *shost) 670 671 672/** 673 * scsi_report_bus_reset - report scsi _bus_ reset observed 674 * @shost: a pointer to a scsi host involved 675 * @channel: channel (within) host on which scsi bus reset occurred 676 * 677 * Returns nothing 678 * 679 * Might block: no 680 * 681 * Notes: This only needs to be called if the reset is one which 682 * originates from an unknown location. Resets originated by the 683 * mid level itself don't need to call this, but there should be 684 * no harm. The main purpose of this is to make sure that a 685 * CHECK_CONDITION is properly treated. 686 * 687 * Defined in: drivers/scsi/scsi_error.c . 688 **/ 689void scsi_report_bus_reset(struct Scsi_Host * shost, int channel) 690 691 692/** 693 * scsi_scan_host - scan SCSI bus 694 * @shost: a pointer to a scsi host instance 695 * 696 * Might block: yes 697 * 698 * Notes: Should be called after scsi_add_host() 699 * 700 * Defined in: drivers/scsi/scsi_scan.c 701 **/ 702void scsi_scan_host(struct Scsi_Host *shost) 703 704 705/** 706 * scsi_track_queue_full - track successive QUEUE_FULL events on given 707 * device to determine if and when there is a need 708 * to adjust the queue depth on the device. 709 * @sdev: pointer to SCSI device instance 710 * @depth: Current number of outstanding SCSI commands on this device, 711 * not counting the one returned as QUEUE_FULL. 712 * 713 * Returns 0 - no change needed 714 * >0 - adjust queue depth to this new depth 715 * -1 - drop back to untagged operation using host->cmd_per_lun 716 * as the untagged command depth 717 * 718 * Might block: no 719 * 720 * Notes: LLDs may call this at any time and we will do "The Right 721 * Thing"; interrupt context safe. 722 * 723 * Defined in: drivers/scsi/scsi.c . 724 **/ 725int scsi_track_queue_full(struct scsi_device *sdev, int depth) 726 727 728/** 729 * scsi_unblock_requests - allow further commands to be queued to given host 730 * 731 * @shost: pointer to host to unblock commands on 732 * 733 * Returns nothing 734 * 735 * Might block: no 736 * 737 * Defined in: drivers/scsi/scsi_lib.c . 738**/ 739void scsi_unblock_requests(struct Scsi_Host * shost) 740 741 742/** 743 * scsi_unregister - unregister and free memory used by host instance 744 * @shp: pointer to scsi host instance to unregister. 745 * 746 * Returns nothing 747 * 748 * Might block: no 749 * 750 * Notes: Should not be invoked if the "hotplug initialization 751 * model" is being used. Called internally by exit_this_scsi_driver() 752 * in the "passive initialization model". Hence a LLD has no need to 753 * call this function directly. 754 * 755 * Defined in: drivers/scsi/hosts.c . 756 **/ 757void scsi_unregister(struct Scsi_Host * shp) 758 759 760 761 762Interface Functions 763=================== 764Interface functions are supplied (defined) by LLDs and their function 765pointers are placed in an instance of struct scsi_host_template which 766is passed to scsi_host_alloc() [or scsi_register() / init_this_scsi_driver()]. 767Some are mandatory. Interface functions should be declared static. The 768accepted convention is that driver "xyz" will declare its slave_configure() 769function as: 770 static int xyz_slave_configure(struct scsi_device * sdev); 771and so forth for all interface functions listed below. 772 773A pointer to this function should be placed in the 'slave_configure' member 774of a "struct scsi_host_template" instance. A pointer to such an instance 775should be passed to the mid level's scsi_host_alloc() [or scsi_register() / 776init_this_scsi_driver()]. 777 778The interface functions are also described in the include/scsi/scsi_host.h 779file immediately above their definition point in "struct scsi_host_template". 780In some cases more detail is given in scsi_host.h than below. 781 782The interface functions are listed below in alphabetical order. 783 784Summary: 785 bios_param - fetch head, sector, cylinder info for a disk 786 detect - detects HBAs this driver wants to control 787 eh_timed_out - notify the host that a command timer expired 788 eh_abort_handler - abort given command 789 eh_bus_reset_handler - issue SCSI bus reset 790 eh_device_reset_handler - issue SCSI device reset 791 eh_host_reset_handler - reset host (host bus adapter) 792 info - supply information about given host 793 ioctl - driver can respond to ioctls 794 proc_info - supports /proc/scsi/{driver_name}/{host_no} 795 queuecommand - queue scsi command, invoke 'done' on completion 796 release - release all resources associated with given host 797 slave_alloc - prior to any commands being sent to a new device 798 slave_configure - driver fine tuning for given device after attach 799 slave_destroy - given device is about to be shut down 800 801 802Details: 803 804/** 805 * bios_param - fetch head, sector, cylinder info for a disk 806 * @sdev: pointer to scsi device context (defined in 807 * include/scsi/scsi_device.h) 808 * @bdev: pointer to block device context (defined in fs.h) 809 * @capacity: device size (in 512 byte sectors) 810 * @params: three element array to place output: 811 * params[0] number of heads (max 255) 812 * params[1] number of sectors (max 63) 813 * params[2] number of cylinders 814 * 815 * Return value is ignored 816 * 817 * Locks: none 818 * 819 * Calling context: process (sd) 820 * 821 * Notes: an arbitrary geometry (based on READ CAPACITY) is used 822 * if this function is not provided. The params array is 823 * pre-initialized with made up values just in case this function 824 * doesn't output anything. 825 * 826 * Optionally defined in: LLD 827 **/ 828 int bios_param(struct scsi_device * sdev, struct block_device *bdev, 829 sector_t capacity, int params[3]) 830 831 832/** 833 * detect - detects HBAs this driver wants to control 834 * @shtp: host template for this driver. 835 * 836 * Returns number of hosts this driver wants to control. 0 means no 837 * suitable hosts found. 838 * 839 * Locks: none held 840 * 841 * Calling context: process [invoked from init_this_scsi_driver()] 842 * 843 * Notes: First function called from the SCSI mid level on this 844 * driver. Upper level drivers (e.g. sd) may not (yet) be present. 845 * For each host found, this method should call scsi_register() 846 * [see hosts.c]. 847 * 848 * Defined in: LLD (required if "passive initialization mode" is used, 849 * not invoked in "hotplug initialization mode") 850 **/ 851 int detect(struct scsi_host_template * shtp) 852 853 854/** 855 * eh_timed_out - The timer for the command has just fired 856 * @scp: identifies command timing out 857 * 858 * Returns: 859 * 860 * EH_HANDLED: I fixed the error, please complete the command 861 * EH_RESET_TIMER: I need more time, reset the timer and 862 * begin counting again 863 * EH_NOT_HANDLED Begin normal error recovery 864 * 865 * 866 * Locks: None held 867 * 868 * Calling context: interrupt 869 * 870 * Notes: This is to give the LLD an opportunity to do local recovery. 871 * This recovery is limited to determining if the outstanding command 872 * will ever complete. You may not abort and restart the command from 873 * this callback. 874 * 875 * Optionally defined in: LLD 876 **/ 877 int eh_timed_out(struct scsi_cmnd * scp) 878 879 880/** 881 * eh_abort_handler - abort command associated with scp 882 * @scp: identifies command to be aborted 883 * 884 * Returns SUCCESS if command aborted else FAILED 885 * 886 * Locks: None held 887 * 888 * Calling context: kernel thread 889 * 890 * Notes: Invoked from scsi_eh thread. No other commands will be 891 * queued on current host during eh. 892 * 893 * Optionally defined in: LLD 894 **/ 895 int eh_abort_handler(struct scsi_cmnd * scp) 896 897 898/** 899 * eh_bus_reset_handler - issue SCSI bus reset 900 * @scp: SCSI bus that contains this device should be reset 901 * 902 * Returns SUCCESS if command aborted else FAILED 903 * 904 * Locks: None held 905 * 906 * Calling context: kernel thread 907 * 908 * Notes: Invoked from scsi_eh thread. No other commands will be 909 * queued on current host during eh. 910 * 911 * Optionally defined in: LLD 912 **/ 913 int eh_bus_reset_handler(struct scsi_cmnd * scp) 914 915 916/** 917 * eh_device_reset_handler - issue SCSI device reset 918 * @scp: identifies SCSI device to be reset 919 * 920 * Returns SUCCESS if command aborted else FAILED 921 * 922 * Locks: None held 923 * 924 * Calling context: kernel thread 925 * 926 * Notes: Invoked from scsi_eh thread. No other commands will be 927 * queued on current host during eh. 928 * 929 * Optionally defined in: LLD 930 **/ 931 int eh_device_reset_handler(struct scsi_cmnd * scp) 932 933 934/** 935 * eh_host_reset_handler - reset host (host bus adapter) 936 * @scp: SCSI host that contains this device should be reset 937 * 938 * Returns SUCCESS if command aborted else FAILED 939 * 940 * Locks: None held 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 * With the default eh_strategy in place, if none of the _abort_, 947 * _device_reset_, _bus_reset_ or this eh handler function are 948 * defined (or they all return FAILED) then the device in question 949 * will be set offline whenever eh is invoked. 950 * 951 * Optionally defined in: LLD 952 **/ 953 int eh_host_reset_handler(struct scsi_cmnd * scp) 954 955 956/** 957 * info - supply information about given host: driver name plus data 958 * to distinguish given host 959 * @shp: host to supply information about 960 * 961 * Return ASCII null terminated string. [This driver is assumed to 962 * manage the memory pointed to and maintain it, typically for the 963 * lifetime of this host.] 964 * 965 * Locks: none 966 * 967 * Calling context: process 968 * 969 * Notes: Often supplies PCI or ISA information such as IO addresses 970 * and interrupt numbers. If not supplied struct Scsi_Host::name used 971 * instead. It is assumed the returned information fits on one line 972 * (i.e. does not included embedded newlines). 973 * The SCSI_IOCTL_PROBE_HOST ioctl yields the string returned by this 974 * function (or struct Scsi_Host::name if this function is not 975 * available). 976 * In a similar manner, init_this_scsi_driver() outputs to the console 977 * each host's "info" (or name) for the driver it is registering. 978 * Also if proc_info() is not supplied, the output of this function 979 * is used instead. 980 * 981 * Optionally defined in: LLD 982 **/ 983 const char * info(struct Scsi_Host * shp) 984 985 986/** 987 * ioctl - driver can respond to ioctls 988 * @sdp: device that ioctl was issued for 989 * @cmd: ioctl number 990 * @arg: pointer to read or write data from. Since it points to 991 * user space, should use appropriate kernel functions 992 * (e.g. copy_from_user() ). In the Unix style this argument 993 * can also be viewed as an unsigned long. 994 * 995 * Returns negative "errno" value when there is a problem. 0 or a 996 * positive value indicates success and is returned to the user space. 997 * 998 * Locks: none 999 * 1000 * Calling context: process 1001 * 1002 * Notes: The SCSI subsystem uses a "trickle down" ioctl model. 1003 * The user issues an ioctl() against an upper level driver 1004 * (e.g. /dev/sdc) and if the upper level driver doesn't recognize 1005 * the 'cmd' then it is passed to the SCSI mid level. If the SCSI 1006 * mid level does not recognize it, then the LLD that controls 1007 * the device receives the ioctl. According to recent Unix standards 1008 * unsupported ioctl() 'cmd' numbers should return -ENOTTY. 1009 * 1010 * Optionally defined in: LLD 1011 **/ 1012 int ioctl(struct scsi_device *sdp, int cmd, void *arg) 1013 1014 1015/** 1016 * proc_info - supports /proc/scsi/{driver_name}/{host_no} 1017 * @buffer: anchor point to output to (0==writeto1_read0) or fetch from 1018 * (1==writeto1_read0). 1019 * @start: where "interesting" data is written to. Ignored when 1020 * 1==writeto1_read0. 1021 * @offset: offset within buffer 0==writeto1_read0 is actually 1022 * interested in. Ignored when 1==writeto1_read0 . 1023 * @length: maximum (or actual) extent of buffer 1024 * @host_no: host number of interest (struct Scsi_Host::host_no) 1025 * @writeto1_read0: 1 -> data coming from user space towards driver 1026 * (e.g. "echo some_string > /proc/scsi/xyz/2") 1027 * 0 -> user what data from this driver 1028 * (e.g. "cat /proc/scsi/xyz/2") 1029 * 1030 * Returns length when 1==writeto1_read0. Otherwise number of chars 1031 * output to buffer past offset. 1032 * 1033 * Locks: none held 1034 * 1035 * Calling context: process 1036 * 1037 * Notes: Driven from scsi_proc.c which interfaces to proc_fs. proc_fs 1038 * support can now be configured out of the scsi subsystem. 1039 * 1040 * Optionally defined in: LLD 1041 **/ 1042 int proc_info(char * buffer, char ** start, off_t offset, 1043 int length, int host_no, int writeto1_read0) 1044 1045 1046/** 1047 * queuecommand - queue scsi command, invoke 'done' on completion 1048 * @scp: pointer to scsi command object 1049 * @done: function pointer to be invoked on completion 1050 * 1051 * Returns 0 on success. 1052 * 1053 * If there's a failure, return either: 1054 * 1055 * SCSI_MLQUEUE_DEVICE_BUSY if the device queue is full, or 1056 * SCSI_MLQUEUE_HOST_BUSY if the entire host queue is full 1057 * 1058 * On both of these returns, the mid-layer will requeue the I/O 1059 * 1060 * - if the return is SCSI_MLQUEUE_DEVICE_BUSY, only that particular 1061 * device will be paused, and it will be unpaused when a command to 1062 * the device returns (or after a brief delay if there are no more 1063 * outstanding commands to it). Commands to other devices continue 1064 * to be processed normally. 1065 * 1066 * - if the return is SCSI_MLQUEUE_HOST_BUSY, all I/O to the host 1067 * is paused and will be unpaused when any command returns from 1068 * the host (or after a brief delay if there are no outstanding 1069 * commands to the host). 1070 * 1071 * For compatibility with earlier versions of queuecommand, any 1072 * other return value is treated the same as 1073 * SCSI_MLQUEUE_HOST_BUSY. 1074 * 1075 * Other types of errors that are detected immediately may be 1076 * flagged by setting scp->result to an appropriate value, 1077 * invoking the 'done' callback, and then returning 0 from this 1078 * function. If the command is not performed immediately (and the 1079 * LLD is starting (or will start) the given command) then this 1080 * function should place 0 in scp->result and return 0. 1081 * 1082 * Command ownership. If the driver returns zero, it owns the 1083 * command and must take responsibility for ensuring the 'done' 1084 * callback is executed. Note: the driver may call done before 1085 * returning zero, but after it has called done, it may not 1086 * return any value other than zero. If the driver makes a 1087 * non-zero return, it must not execute the command's done 1088 * callback at any time. 1089 * 1090 * Locks: struct Scsi_Host::host_lock held on entry (with "irqsave") 1091 * and is expected to be held on return. 1092 * 1093 * Calling context: in interrupt (soft irq) or process context 1094 * 1095 * Notes: This function should be relatively fast. Normally it will 1096 * not wait for IO to complete. Hence the 'done' callback is invoked 1097 * (often directly from an interrupt service routine) some time after 1098 * this function has returned. In some cases (e.g. pseudo adapter 1099 * drivers that manufacture the response to a SCSI INQUIRY) 1100 * the 'done' callback may be invoked before this function returns. 1101 * If the 'done' callback is not invoked within a certain period 1102 * the SCSI mid level will commence error processing. 1103 * If a status of CHECK CONDITION is placed in "result" when the 1104 * 'done' callback is invoked, then the LLD driver should 1105 * perform autosense and fill in the struct scsi_cmnd::sense_buffer 1106 * array. The scsi_cmnd::sense_buffer array is zeroed prior to 1107 * the mid level queuing a command to an LLD. 1108 * 1109 * Defined in: LLD 1110 **/ 1111 int queuecommand(struct scsi_cmnd * scp, 1112 void (*done)(struct scsi_cmnd *)) 1113 1114 1115/** 1116 * release - release all resources associated with given host 1117 * @shp: host to be released. 1118 * 1119 * Return value ignored (could soon be a function returning void). 1120 * 1121 * Locks: none held 1122 * 1123 * Calling context: process 1124 * 1125 * Notes: Invoked from scsi_module.c's exit_this_scsi_driver(). 1126 * LLD's implementation of this function should call 1127 * scsi_unregister(shp) prior to returning. 1128 * Only needed for old-style host templates. 1129 * 1130 * Defined in: LLD (required in "passive initialization model", 1131 * should not be defined in hotplug model) 1132 **/ 1133 int release(struct Scsi_Host * shp) 1134 1135 1136/** 1137 * slave_alloc - prior to any commands being sent to a new device 1138 * (i.e. just prior to scan) this call is made 1139 * @sdp: pointer to new device (about to be scanned) 1140 * 1141 * Returns 0 if ok. Any other return is assumed to be an error and 1142 * the device is ignored. 1143 * 1144 * Locks: none 1145 * 1146 * Calling context: process 1147 * 1148 * Notes: Allows the driver to allocate any resources for a device 1149 * prior to its initial scan. The corresponding scsi device may not 1150 * exist but the mid level is just about to scan for it (i.e. send 1151 * and INQUIRY command plus ...). If a device is found then 1152 * slave_configure() will be called while if a device is not found 1153 * slave_destroy() is called. 1154 * For more details see the include/scsi/scsi_host.h file. 1155 * 1156 * Optionally defined in: LLD 1157 **/ 1158 int slave_alloc(struct scsi_device *sdp) 1159 1160 1161/** 1162 * slave_configure - driver fine tuning for given device just after it 1163 * has been first scanned (i.e. it responded to an 1164 * INQUIRY) 1165 * @sdp: device that has just been attached 1166 * 1167 * Returns 0 if ok. Any other return is assumed to be an error and 1168 * the device is taken offline. [offline devices will _not_ have 1169 * slave_destroy() called on them so clean up resources.] 1170 * 1171 * Locks: none 1172 * 1173 * Calling context: process 1174 * 1175 * Notes: Allows the driver to inspect the response to the initial 1176 * INQUIRY done by the scanning code and take appropriate action. 1177 * For more details see the include/scsi/scsi_host.h file. 1178 * 1179 * Optionally defined in: LLD 1180 **/ 1181 int slave_configure(struct scsi_device *sdp) 1182 1183 1184/** 1185 * slave_destroy - given device is about to be shut down. All 1186 * activity has ceased on this device. 1187 * @sdp: device that is about to be shut down 1188 * 1189 * Returns nothing 1190 * 1191 * Locks: none 1192 * 1193 * Calling context: process 1194 * 1195 * Notes: Mid level structures for given device are still in place 1196 * but are about to be torn down. Any per device resources allocated 1197 * by this driver for given device should be freed now. No further 1198 * commands will be sent for this sdp instance. [However the device 1199 * could be re-attached in the future in which case a new instance 1200 * of struct scsi_device would be supplied by future slave_alloc() 1201 * and slave_configure() calls.] 1202 * 1203 * Optionally defined in: LLD 1204 **/ 1205 void slave_destroy(struct scsi_device *sdp) 1206 1207 1208 1209Data Structures 1210=============== 1211struct scsi_host_template 1212------------------------- 1213There is one "struct scsi_host_template" instance per LLD ***. It is 1214typically initialized as a file scope static in a driver's header file. That 1215way members that are not explicitly initialized will be set to 0 or NULL. 1216Member of interest: 1217 name - name of driver (may contain spaces, please limit to 1218 less than 80 characters) 1219 proc_name - name used in "/proc/scsi/<proc_name>/<host_no>" and 1220 by sysfs in one of its "drivers" directories. Hence 1221 "proc_name" should only contain characters acceptable 1222 to a Unix file name. 1223 (*queuecommand)() - primary callback that the mid level uses to inject 1224 SCSI commands into an LLD. 1225The structure is defined and commented in include/scsi/scsi_host.h 1226 1227*** In extreme situations a single driver may have several instances 1228 if it controls several different classes of hardware (e.g. an LLD 1229 that handles both ISA and PCI cards and has a separate instance of 1230 struct scsi_host_template for each class). 1231 1232struct Scsi_Host 1233---------------- 1234There is one struct Scsi_Host instance per host (HBA) that an LLD 1235controls. The struct Scsi_Host structure has many members in common 1236with "struct scsi_host_template". When a new struct Scsi_Host instance 1237is created (in scsi_host_alloc() in hosts.c) those common members are 1238initialized from the driver's struct scsi_host_template instance. Members 1239of interest: 1240 host_no - system wide unique number that is used for identifying 1241 this host. Issued in ascending order from 0. 1242 can_queue - must be greater than 0; do not send more than can_queue 1243 commands to the adapter. 1244 this_id - scsi id of host (scsi initiator) or -1 if not known 1245 sg_tablesize - maximum scatter gather elements allowed by host. 1246 0 implies scatter gather not supported by host 1247 max_sectors - maximum number of sectors (usually 512 bytes) allowed 1248 in a single SCSI command. The default value of 0 leads 1249 to a setting of SCSI_DEFAULT_MAX_SECTORS (defined in 1250 scsi_host.h) which is currently set to 1024. So for a 1251 disk the maximum transfer size is 512 KB when max_sectors 1252 is not defined. Note that this size may not be sufficient 1253 for disk firmware uploads. 1254 cmd_per_lun - maximum number of commands that can be queued on devices 1255 controlled by the host. Overridden by LLD calls to 1256 scsi_adjust_queue_depth(). 1257 unchecked_isa_dma - 1=>only use bottom 16 MB of ram (ISA DMA addressing 1258 restriction), 0=>can use full 32 bit (or better) DMA 1259 address space 1260 use_clustering - 1=>SCSI commands in mid level's queue can be merged, 1261 0=>disallow SCSI command merging 1262 hostt - pointer to driver's struct scsi_host_template from which 1263 this struct Scsi_Host instance was spawned 1264 hostt->proc_name - name of LLD. This is the driver name that sysfs uses 1265 transportt - pointer to driver's struct scsi_transport_template instance 1266 (if any). FC and SPI transports currently supported. 1267 sh_list - a double linked list of pointers to all struct Scsi_Host 1268 instances (currently ordered by ascending host_no) 1269 my_devices - a double linked list of pointers to struct scsi_device 1270 instances that belong to this host. 1271 hostdata[0] - area reserved for LLD at end of struct Scsi_Host. Size 1272 is set by the second argument (named 'xtr_bytes') to 1273 scsi_host_alloc() or scsi_register(). 1274 1275The scsi_host structure is defined in include/scsi/scsi_host.h 1276 1277struct scsi_device 1278------------------ 1279Generally, there is one instance of this structure for each SCSI logical unit 1280on a host. Scsi devices connected to a host are uniquely identified by a 1281channel number, target id and logical unit number (lun). 1282The structure is defined in include/scsi/scsi_device.h 1283 1284struct scsi_cmnd 1285---------------- 1286Instances of this structure convey SCSI commands to the LLD and responses 1287back to the mid level. The SCSI mid level will ensure that no more SCSI 1288commands become queued against the LLD than are indicated by 1289scsi_adjust_queue_depth() (or struct Scsi_Host::cmd_per_lun). There will 1290be at least one instance of struct scsi_cmnd available for each SCSI device. 1291Members of interest: 1292 cmnd - array containing SCSI command 1293 cmnd_len - length (in bytes) of SCSI command 1294 sc_data_direction - direction of data transfer in data phase. See 1295 "enum dma_data_direction" in include/linux/dma-mapping.h 1296 request_bufflen - number of data bytes to transfer (0 if no data phase) 1297 use_sg - ==0 -> no scatter gather list, hence transfer data 1298 to/from request_buffer 1299 - >0 -> scatter gather list (actually an array) in 1300 request_buffer with use_sg elements 1301 request_buffer - either contains data buffer or scatter gather list 1302 depending on the setting of use_sg. Scatter gather 1303 elements are defined by 'struct scatterlist' found 1304 in include/asm/scatterlist.h . 1305 done - function pointer that should be invoked by LLD when the 1306 SCSI command is completed (successfully or otherwise). 1307 Should only be called by an LLD if the LLD has accepted 1308 the command (i.e. queuecommand() returned or will return 1309 0). The LLD may invoke 'done' prior to queuecommand() 1310 finishing. 1311 result - should be set by LLD prior to calling 'done'. A value 1312 of 0 implies a successfully completed command (and all 1313 data (if any) has been transferred to or from the SCSI 1314 target device). 'result' is a 32 bit unsigned integer that 1315 can be viewed as 4 related bytes. The SCSI status value is 1316 in the LSB. See include/scsi/scsi.h status_byte(), 1317 msg_byte(), host_byte() and driver_byte() macros and 1318 related constants. 1319 sense_buffer - an array (maximum size: SCSI_SENSE_BUFFERSIZE bytes) that 1320 should be written when the SCSI status (LSB of 'result') 1321 is set to CHECK_CONDITION (2). When CHECK_CONDITION is 1322 set, if the top nibble of sense_buffer[0] has the value 7 1323 then the mid level will assume the sense_buffer array 1324 contains a valid SCSI sense buffer; otherwise the mid 1325 level will issue a REQUEST_SENSE SCSI command to 1326 retrieve the sense buffer. The latter strategy is error 1327 prone in the presence of command queuing so the LLD should 1328 always "auto-sense". 1329 device - pointer to scsi_device object that this command is 1330 associated with. 1331 resid - an LLD should set this signed integer to the requested 1332 transfer length (i.e. 'request_bufflen') less the number 1333 of bytes that are actually transferred. 'resid' is 1334 preset to 0 so an LLD can ignore it if it cannot detect 1335 underruns (overruns should be rare). If possible an LLD 1336 should set 'resid' prior to invoking 'done'. The most 1337 interesting case is data transfers from a SCSI target 1338 device device (i.e. READs) that underrun. 1339 underflow - LLD should place (DID_ERROR << 16) in 'result' if 1340 actual number of bytes transferred is less than this 1341 figure. Not many LLDs implement this check and some that 1342 do just output an error message to the log rather than 1343 report a DID_ERROR. Better for an LLD to implement 1344 'resid'. 1345 1346The scsi_cmnd structure is defined in include/scsi/scsi_cmnd.h 1347 1348 1349Locks 1350===== 1351Each struct Scsi_Host instance has a spin_lock called struct 1352Scsi_Host::default_lock which is initialized in scsi_host_alloc() [found in 1353hosts.c]. Within the same function the struct Scsi_Host::host_lock pointer 1354is initialized to point at default_lock. Thereafter lock and unlock 1355operations performed by the mid level use the struct Scsi_Host::host_lock 1356pointer. Previously drivers could override the host_lock pointer but 1357this is not allowed anymore. 1358 1359 1360Autosense 1361========= 1362Autosense (or auto-sense) is defined in the SAM-2 document as "the 1363automatic return of sense data to the application client coincident 1364with the completion of a SCSI command" when a status of CHECK CONDITION 1365occurs. LLDs should perform autosense. This should be done when the LLD 1366detects a CHECK CONDITION status by either: 1367 a) instructing the SCSI protocol (e.g. SCSI Parallel Interface (SPI)) 1368 to perform an extra data in phase on such responses 1369 b) or, the LLD issuing a REQUEST SENSE command itself 1370 1371Either way, when a status of CHECK CONDITION is detected, the mid level 1372decides whether the LLD has performed autosense by checking struct 1373scsi_cmnd::sense_buffer[0] . If this byte has an upper nibble of 7 (or 0xf) 1374then autosense is assumed to have taken place. If it has another value (and 1375this byte is initialized to 0 before each command) then the mid level will 1376issue a REQUEST SENSE command. 1377 1378In the presence of queued commands the "nexus" that maintains sense 1379buffer data from the command that failed until a following REQUEST SENSE 1380may get out of synchronization. This is why it is best for the LLD 1381to perform autosense. 1382 1383 1384Changes since lk 2.4 series 1385=========================== 1386io_request_lock has been replaced by several finer grained locks. The lock 1387relevant to LLDs is struct Scsi_Host::host_lock and there is 1388one per SCSI host. 1389 1390The older error handling mechanism has been removed. This means the 1391LLD interface functions abort() and reset() have been removed. 1392The struct scsi_host_template::use_new_eh_code flag has been removed. 1393 1394In the 2.4 series the SCSI subsystem configuration descriptions were 1395aggregated with the configuration descriptions from all other Linux 1396subsystems in the Documentation/Configure.help file. In the 2.6 series, 1397the SCSI subsystem now has its own (much smaller) drivers/scsi/Kconfig 1398file that contains both configuration and help information. 1399 1400struct SHT has been renamed to struct scsi_host_template. 1401 1402Addition of the "hotplug initialization model" and many extra functions 1403to support it. 1404 1405 1406Credits 1407======= 1408The following people have contributed to this document: 1409 Mike Anderson <andmike at us dot ibm dot com> 1410 James Bottomley <James dot Bottomley at steeleye dot com> 1411 Patrick Mansfield <patmans at us dot ibm dot com> 1412 Christoph Hellwig <hch at infradead dot org> 1413 Doug Ledford <dledford at redhat dot com> 1414 Andries Brouwer <Andries dot Brouwer at cwi dot nl> 1415 Randy Dunlap <rdunlap at xenotime dot net> 1416 Alan Stern <stern at rowland dot harvard dot edu> 1417 1418 1419Douglas Gilbert 1420dgilbert at interlog dot com 142121st September 2004 1422