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 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://web.archive.org/web/20070107183357rn_1/sg.torque.net/scsi/. 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 58Driver structure 59================ 60Traditionally an LLD for the SCSI subsystem has been at least two files in 61the drivers/scsi directory. For example, a driver called "xyz" has a header 62file "xyz.h" and a source file "xyz.c". [Actually there is no good reason 63why this couldn't all be in one file; the header file is superfluous.] Some 64drivers that have been ported to several operating systems have more than 65two files. For example the aic7xxx driver has separate files for generic 66and OS-specific code (e.g. FreeBSD and Linux). Such drivers tend to have 67their own directory under the drivers/scsi directory. 68 69When a new LLD is being added to Linux, the following files (found in the 70drivers/scsi directory) will need some attention: Makefile and Kconfig . 71It is probably best to study how existing LLDs are organized. 72 73As the 2.5 series development kernels evolve into the 2.6 series 74production series, changes are being introduced into this interface. An 75example of this is driver initialization code where there are now 2 models 76available. The older one, similar to what was found in the lk 2.4 series, 77is based on hosts that are detected at HBA driver load time. This will be 78referred to the "passive" initialization model. The newer model allows HBAs 79to be hot plugged (and unplugged) during the lifetime of the LLD and will 80be referred to as the "hotplug" initialization model. The newer model is 81preferred as it can handle both traditional SCSI equipment that is 82permanently connected as well as modern "SCSI" devices (e.g. USB or 83IEEE 1394 connected digital cameras) that are hotplugged. Both 84initialization models are discussed in the following sections. 85 86An LLD interfaces to the SCSI subsystem several ways: 87 a) directly invoking functions supplied by the mid level 88 b) passing a set of function pointers to a registration function 89 supplied by the mid level. The mid level will then invoke these 90 functions at some point in the future. The LLD will supply 91 implementations of these functions. 92 c) direct access to instances of well known data structures maintained 93 by the mid level 94 95Those functions in group a) are listed in a section entitled "Mid level 96supplied functions" below. 97 98Those functions in group b) are listed in a section entitled "Interface 99functions" below. Their function pointers are placed in the members of 100"struct scsi_host_template", an instance of which is passed to 101scsi_host_alloc() ** . Those interface functions that the LLD does not 102wish to supply should have NULL placed in the corresponding member of 103struct scsi_host_template. Defining an instance of struct 104scsi_host_template at file scope will cause NULL to be placed in function 105 pointer members not explicitly initialized. 106 107Those usages in group c) should be handled with care, especially in a 108"hotplug" environment. LLDs should be aware of the lifetime of instances 109that are shared with the mid level and other layers. 110 111All functions defined within an LLD and all data defined at file scope 112should be static. For example the slave_alloc() function in an LLD 113called "xxx" could be defined as 114"static int xxx_slave_alloc(struct scsi_device * sdev) { /* code */ }" 115 116** the scsi_host_alloc() function is a replacement for the rather vaguely 117named scsi_register() function in most situations. The scsi_register() 118and scsi_unregister() functions remain to support legacy LLDs that use 119the passive initialization model. 120 121 122Hotplug initialization model 123============================ 124In this model an LLD controls when SCSI hosts are introduced and removed 125from the SCSI subsystem. Hosts can be introduced as early as driver 126initialization and removed as late as driver shutdown. Typically a driver 127will respond to a sysfs probe() callback that indicates an HBA has been 128detected. After confirming that the new device is one that the LLD wants 129to control, the LLD will initialize the HBA and then register a new host 130with the SCSI mid level. 131 132During LLD initialization the driver should register itself with the 133appropriate IO bus on which it expects to find HBA(s) (e.g. the PCI bus). 134This can probably be done via sysfs. Any driver parameters (especially 135those that are writable after the driver is loaded) could also be 136registered with sysfs at this point. The SCSI mid level first becomes 137aware of an LLD when that LLD registers its first HBA. 138 139At some later time, the LLD becomes aware of an HBA and what follows 140is a typical sequence of calls between the LLD and the mid level. 141This example shows the mid level scanning the newly introduced HBA for 3 142scsi devices of which only the first 2 respond: 143 144 HBA PROBE: assume 2 SCSI devices found in scan 145LLD mid level LLD 146===-------------------=========--------------------===------ 147scsi_host_alloc() --> 148scsi_add_host() ----> 149scsi_scan_host() -------+ 150 | 151 slave_alloc() 152 slave_configure() --> scsi_change_queue_depth() 153 | 154 slave_alloc() 155 slave_configure() 156 | 157 slave_alloc() *** 158 slave_destroy() *** 159------------------------------------------------------------ 160 161If the LLD wants to adjust the default queue settings, it can invoke 162scsi_change_queue_depth() in its slave_configure() routine. 163 164*** For scsi devices that the mid level tries to scan but do not 165 respond, a slave_alloc(), slave_destroy() pair is called. 166 167When an HBA is being removed it could be as part of an orderly shutdown 168associated with the LLD module being unloaded (e.g. with the "rmmod" 169command) or in response to a "hot unplug" indicated by sysfs()'s 170remove() callback being invoked. In either case, the sequence is the 171same: 172 173 HBA REMOVE: assume 2 SCSI devices attached 174LLD mid level LLD 175===----------------------=========-----------------===------ 176scsi_remove_host() ---------+ 177 | 178 slave_destroy() 179 slave_destroy() 180scsi_host_put() 181------------------------------------------------------------ 182 183It may be useful for a LLD to keep track of struct Scsi_Host instances 184(a pointer is returned by scsi_host_alloc()). Such instances are "owned" 185by the mid-level. struct Scsi_Host instances are freed from 186scsi_host_put() when the reference count hits zero. 187 188Hot unplugging an HBA that controls a disk which is processing SCSI 189commands on a mounted file system is an interesting situation. Reference 190counting logic is being introduced into the mid level to cope with many 191of the issues involved. See the section on reference counting below. 192 193 194The hotplug concept may be extended to SCSI devices. Currently, when an 195HBA is added, the scsi_scan_host() function causes a scan for SCSI devices 196attached to the HBA's SCSI transport. On newer SCSI transports the HBA 197may become aware of a new SCSI device _after_ the scan has completed. 198An LLD can use this sequence to make the mid level aware of a SCSI device: 199 200 SCSI DEVICE hotplug 201LLD mid level LLD 202===-------------------=========--------------------===------ 203scsi_add_device() ------+ 204 | 205 slave_alloc() 206 slave_configure() [--> scsi_change_queue_depth()] 207------------------------------------------------------------ 208 209In a similar fashion, an LLD may become aware that a SCSI device has been 210removed (unplugged) or the connection to it has been interrupted. Some 211existing SCSI transports (e.g. SPI) may not become aware that a SCSI 212device has been removed until a subsequent SCSI command fails which will 213probably cause that device to be set offline by the mid level. An LLD that 214detects the removal of a SCSI device can instigate its removal from 215upper layers with this sequence: 216 217 SCSI DEVICE hot unplug 218LLD mid level LLD 219===----------------------=========-----------------===------ 220scsi_remove_device() -------+ 221 | 222 slave_destroy() 223------------------------------------------------------------ 224 225It may be useful for an LLD to keep track of struct scsi_device instances 226(a pointer is passed as the parameter to slave_alloc() and 227slave_configure() callbacks). Such instances are "owned" by the mid-level. 228struct scsi_device instances are freed after slave_destroy(). 229 230 231Passive initialization model 232============================ 233These older LLDs include a file called "scsi_module.c" [yes the ".c" is a 234little surprising] in their source code. For that file to work an 235instance of struct scsi_host_template with the name "driver_template" 236needs to be defined. Here is a typical code sequence used in this model: 237 static struct scsi_host_template driver_template = { 238 ... 239 }; 240 #include "scsi_module.c" 241 242The scsi_module.c file contains two functions: 243 - init_this_scsi_driver() which is executed when the LLD is 244 initialized (i.e. boot time or module load time) 245 - exit_this_scsi_driver() which is executed when the LLD is shut 246 down (i.e. module unload time) 247Note: since these functions are tagged with __init and __exit qualifiers 248an LLD should not call them explicitly (since the kernel does that). 249 250Here is an example of an initialization sequence when two hosts are 251detected (so detect() returns 2) and the SCSI bus scan on each host 252finds 1 SCSI device (and a second device does not respond). 253 254LLD mid level LLD 255===----------------------=========-----------------===------ 256init_this_scsi_driver() ----+ 257 | 258 detect() -----------------+ 259 | | 260 | scsi_register() 261 | scsi_register() 262 | 263 slave_alloc() 264 slave_configure() --> scsi_change_queue_depth() 265 slave_alloc() *** 266 slave_destroy() *** 267 | 268 slave_alloc() 269 slave_configure() 270 slave_alloc() *** 271 slave_destroy() *** 272------------------------------------------------------------ 273 274The mid level invokes scsi_change_queue_depth() with "cmd_per_lun" for that 275host as the queue length. These settings can be overridden by a 276slave_configure() supplied by the LLD. 277 278*** For scsi devices that the mid level tries to scan but do not 279 respond, a slave_alloc(), slave_destroy() pair is called. 280 281Here is an LLD shutdown sequence: 282 283LLD mid level LLD 284===----------------------=========-----------------===------ 285exit_this_scsi_driver() ----+ 286 | 287 slave_destroy() 288 release() --> scsi_unregister() 289 | 290 slave_destroy() 291 release() --> scsi_unregister() 292------------------------------------------------------------ 293 294An LLD need not define slave_destroy() (i.e. it is optional). 295 296The shortcoming of the "passive initialization model" is that host 297registration and de-registration are (typically) tied to LLD initialization 298and shutdown. Once the LLD is initialized then a new host that appears 299(e.g. via hotplugging) cannot easily be added without a redundant 300driver shutdown and re-initialization. It may be possible to write an LLD 301that uses both initialization models. 302 303 304Reference Counting 305================== 306The Scsi_Host structure has had reference counting infrastructure added. 307This effectively spreads the ownership of struct Scsi_Host instances 308across the various SCSI layers which use them. Previously such instances 309were exclusively owned by the mid level. LLDs would not usually need to 310directly manipulate these reference counts but there may be some cases 311where they do. 312 313There are 3 reference counting functions of interest associated with 314struct Scsi_Host: 315 - scsi_host_alloc(): returns a pointer to new instance of struct 316 Scsi_Host which has its reference count ^^ set to 1 317 - scsi_host_get(): adds 1 to the reference count of the given instance 318 - scsi_host_put(): decrements 1 from the reference count of the given 319 instance. If the reference count reaches 0 then the given instance 320 is freed 321 322The Scsi_device structure has had reference counting infrastructure added. 323This effectively spreads the ownership of struct Scsi_device instances 324across the various SCSI layers which use them. Previously such instances 325were exclusively owned by the mid level. See the access functions declared 326towards the end of include/scsi/scsi_device.h . If an LLD wants to keep 327a copy of a pointer to a Scsi_device instance it should use scsi_device_get() 328to bump its reference count. When it is finished with the pointer it can 329use scsi_device_put() to decrement its reference count (and potentially 330delete it). 331 332^^ struct Scsi_Host actually has 2 reference counts which are manipulated 333in parallel by these functions. 334 335 336Conventions 337=========== 338First, Linus Torvalds's thoughts on C coding style can be found in the 339Documentation/CodingStyle file. 340 341Next, there is a movement to "outlaw" typedefs introducing synonyms for 342struct tags. Both can be still found in the SCSI subsystem, but 343the typedefs have been moved to a single file, scsi_typedefs.h to 344make their future removal easier, for example: 345"typedef struct scsi_cmnd Scsi_Cmnd;" 346 347Also, most C99 enhancements are encouraged to the extent they are supported 348by the relevant gcc compilers. So C99 style structure and array 349initializers are encouraged where appropriate. Don't go too far, 350VLAs are not properly supported yet. An exception to this is the use of 351"//" style comments; /*...*/ comments are still preferred in Linux. 352 353Well written, tested and documented code, need not be re-formatted to 354comply with the above conventions. For example, the aic7xxx driver 355comes to Linux from FreeBSD and Adaptec's own labs. No doubt FreeBSD 356and Adaptec have their own coding conventions. 357 358 359Mid level supplied functions 360============================ 361These functions are supplied by the SCSI mid level for use by LLDs. 362The names (i.e. entry points) of these functions are exported 363so an LLD that is a module can access them. The kernel will 364arrange for the SCSI mid level to be loaded and initialized before any LLD 365is initialized. The functions below are listed alphabetically and their 366names all start with "scsi_". 367 368Summary: 369 scsi_add_device - creates new scsi device (lu) instance 370 scsi_add_host - perform sysfs registration and set up transport class 371 scsi_change_queue_depth - change the queue depth on a SCSI device 372 scsi_bios_ptable - return copy of block device's partition table 373 scsi_block_requests - prevent further commands being queued to given host 374 scsi_host_alloc - return a new scsi_host instance whose refcount==1 375 scsi_host_get - increments Scsi_Host instance's refcount 376 scsi_host_put - decrements Scsi_Host instance's refcount (free if 0) 377 scsi_partsize - parse partition table into cylinders, heads + sectors 378 scsi_register - create and register a scsi host adapter instance. 379 scsi_remove_device - detach and remove a SCSI device 380 scsi_remove_host - detach and remove all SCSI devices owned by host 381 scsi_report_bus_reset - report scsi _bus_ reset observed 382 scsi_scan_host - scan SCSI bus 383 scsi_track_queue_full - track successive QUEUE_FULL events 384 scsi_unblock_requests - allow further commands to be queued to given host 385 scsi_unregister - [calls scsi_host_put()] 386 387 388Details: 389 390/** 391 * scsi_add_device - creates new scsi device (lu) instance 392 * @shost: pointer to scsi host instance 393 * @channel: channel number (rarely other than 0) 394 * @id: target id number 395 * @lun: logical unit number 396 * 397 * Returns pointer to new struct scsi_device instance or 398 * ERR_PTR(-ENODEV) (or some other bent pointer) if something is 399 * wrong (e.g. no lu responds at given address) 400 * 401 * Might block: yes 402 * 403 * Notes: This call is usually performed internally during a scsi 404 * bus scan when an HBA is added (i.e. scsi_scan_host()). So it 405 * should only be called if the HBA becomes aware of a new scsi 406 * device (lu) after scsi_scan_host() has completed. If successful 407 * this call can lead to slave_alloc() and slave_configure() callbacks 408 * into the LLD. 409 * 410 * Defined in: drivers/scsi/scsi_scan.c 411 **/ 412struct scsi_device * scsi_add_device(struct Scsi_Host *shost, 413 unsigned int channel, 414 unsigned int id, unsigned int lun) 415 416 417/** 418 * scsi_add_host - perform sysfs registration and set up transport class 419 * @shost: pointer to scsi host instance 420 * @dev: pointer to struct device of type scsi class 421 * 422 * Returns 0 on success, negative errno of failure (e.g. -ENOMEM) 423 * 424 * Might block: no 425 * 426 * Notes: Only required in "hotplug initialization model" after a 427 * successful call to scsi_host_alloc(). This function does not 428 * scan the bus; this can be done by calling scsi_scan_host() or 429 * in some other transport-specific way. The LLD must set up 430 * the transport template before calling this function and may only 431 * access the transport class data after this function has been called. 432 * 433 * Defined in: drivers/scsi/hosts.c 434 **/ 435int scsi_add_host(struct Scsi_Host *shost, struct device * dev) 436 437 438/** 439 * scsi_change_queue_depth - allow LLD to change queue depth on a SCSI device 440 * @sdev: pointer to SCSI device to change queue depth on 441 * @tags Number of tags allowed if tagged queuing enabled, 442 * or number of commands the LLD can queue up 443 * in non-tagged mode (as per cmd_per_lun). 444 * 445 * Returns nothing 446 * 447 * Might block: no 448 * 449 * Notes: Can be invoked any time on a SCSI device controlled by this 450 * LLD. [Specifically during and after slave_configure() and prior to 451 * slave_destroy().] Can safely be invoked from interrupt code. 452 * 453 * Defined in: drivers/scsi/scsi.c [see source code for more notes] 454 * 455 **/ 456int scsi_change_queue_depth(struct scsi_device *sdev, int tags) 457 458 459/** 460 * scsi_bios_ptable - return copy of block device's partition table 461 * @dev: pointer to block device 462 * 463 * Returns pointer to partition table, or NULL for failure 464 * 465 * Might block: yes 466 * 467 * Notes: Caller owns memory returned (free with kfree() ) 468 * 469 * Defined in: drivers/scsi/scsicam.c 470 **/ 471unsigned char *scsi_bios_ptable(struct block_device *dev) 472 473 474/** 475 * scsi_block_requests - prevent further commands being queued to given host 476 * 477 * @shost: pointer to host to block commands on 478 * 479 * Returns nothing 480 * 481 * Might block: no 482 * 483 * Notes: There is no timer nor any other means by which the requests 484 * get unblocked other than the LLD calling scsi_unblock_requests(). 485 * 486 * Defined in: drivers/scsi/scsi_lib.c 487**/ 488void scsi_block_requests(struct Scsi_Host * shost) 489 490 491/** 492 * scsi_host_alloc - create a scsi host adapter instance and perform basic 493 * initialization. 494 * @sht: pointer to scsi host template 495 * @privsize: extra bytes to allocate in hostdata array (which is the 496 * last member of the returned Scsi_Host instance) 497 * 498 * Returns pointer to new Scsi_Host instance or NULL on failure 499 * 500 * Might block: yes 501 * 502 * Notes: When this call returns to the LLD, the SCSI bus scan on 503 * this host has _not_ yet been done. 504 * The hostdata array (by default zero length) is a per host scratch 505 * area for the LLD's exclusive use. 506 * Both associated refcounting objects have their refcount set to 1. 507 * Full registration (in sysfs) and a bus scan are performed later when 508 * scsi_add_host() and scsi_scan_host() are called. 509 * 510 * Defined in: drivers/scsi/hosts.c . 511 **/ 512struct Scsi_Host * scsi_host_alloc(struct scsi_host_template * sht, 513 int privsize) 514 515 516/** 517 * scsi_host_get - increment Scsi_Host instance refcount 518 * @shost: pointer to struct Scsi_Host instance 519 * 520 * Returns nothing 521 * 522 * Might block: currently may block but may be changed to not block 523 * 524 * Notes: Actually increments the counts in two sub-objects 525 * 526 * Defined in: drivers/scsi/hosts.c 527 **/ 528void scsi_host_get(struct Scsi_Host *shost) 529 530 531/** 532 * scsi_host_put - decrement Scsi_Host instance refcount, free if 0 533 * @shost: pointer to struct Scsi_Host instance 534 * 535 * Returns nothing 536 * 537 * Might block: currently may block but may be changed to not block 538 * 539 * Notes: Actually decrements the counts in two sub-objects. If the 540 * latter refcount reaches 0, the Scsi_Host instance is freed. 541 * The LLD need not worry exactly when the Scsi_Host instance is 542 * freed, it just shouldn't access the instance after it has balanced 543 * out its refcount usage. 544 * 545 * Defined in: drivers/scsi/hosts.c 546 **/ 547void scsi_host_put(struct Scsi_Host *shost) 548 549 550/** 551 * scsi_partsize - parse partition table into cylinders, heads + sectors 552 * @buf: pointer to partition table 553 * @capacity: size of (total) disk in 512 byte sectors 554 * @cyls: outputs number of cylinders calculated via this pointer 555 * @hds: outputs number of heads calculated via this pointer 556 * @secs: outputs number of sectors calculated via this pointer 557 * 558 * Returns 0 on success, -1 on failure 559 * 560 * Might block: no 561 * 562 * Notes: Caller owns memory returned (free with kfree() ) 563 * 564 * Defined in: drivers/scsi/scsicam.c 565 **/ 566int scsi_partsize(unsigned char *buf, unsigned long capacity, 567 unsigned int *cyls, unsigned int *hds, unsigned int *secs) 568 569 570/** 571 * scsi_register - create and register a scsi host adapter instance. 572 * @sht: pointer to scsi host template 573 * @privsize: extra bytes to allocate in hostdata array (which is the 574 * last member of the returned Scsi_Host instance) 575 * 576 * Returns pointer to new Scsi_Host instance or NULL on failure 577 * 578 * Might block: yes 579 * 580 * Notes: When this call returns to the LLD, the SCSI bus scan on 581 * this host has _not_ yet been done. 582 * The hostdata array (by default zero length) is a per host scratch 583 * area for the LLD. 584 * 585 * Defined in: drivers/scsi/hosts.c . 586 **/ 587struct Scsi_Host * scsi_register(struct scsi_host_template * sht, 588 int privsize) 589 590 591/** 592 * scsi_remove_device - detach and remove a SCSI device 593 * @sdev: a pointer to a scsi device instance 594 * 595 * Returns value: 0 on success, -EINVAL if device not attached 596 * 597 * Might block: yes 598 * 599 * Notes: If an LLD becomes aware that a scsi device (lu) has 600 * been removed but its host is still present then it can request 601 * the removal of that scsi device. If successful this call will 602 * lead to the slave_destroy() callback being invoked. sdev is an 603 * invalid pointer after this call. 604 * 605 * Defined in: drivers/scsi/scsi_sysfs.c . 606 **/ 607int scsi_remove_device(struct scsi_device *sdev) 608 609 610/** 611 * scsi_remove_host - detach and remove all SCSI devices owned by host 612 * @shost: a pointer to a scsi host instance 613 * 614 * Returns value: 0 on success, 1 on failure (e.g. LLD busy ??) 615 * 616 * Might block: yes 617 * 618 * Notes: Should only be invoked if the "hotplug initialization 619 * model" is being used. It should be called _prior_ to 620 * scsi_unregister(). 621 * 622 * Defined in: drivers/scsi/hosts.c . 623 **/ 624int scsi_remove_host(struct Scsi_Host *shost) 625 626 627/** 628 * scsi_report_bus_reset - report scsi _bus_ reset observed 629 * @shost: a pointer to a scsi host involved 630 * @channel: channel (within) host on which scsi bus reset occurred 631 * 632 * Returns nothing 633 * 634 * Might block: no 635 * 636 * Notes: This only needs to be called if the reset is one which 637 * originates from an unknown location. Resets originated by the 638 * mid level itself don't need to call this, but there should be 639 * no harm. The main purpose of this is to make sure that a 640 * CHECK_CONDITION is properly treated. 641 * 642 * Defined in: drivers/scsi/scsi_error.c . 643 **/ 644void scsi_report_bus_reset(struct Scsi_Host * shost, int channel) 645 646 647/** 648 * scsi_scan_host - scan SCSI bus 649 * @shost: a pointer to a scsi host instance 650 * 651 * Might block: yes 652 * 653 * Notes: Should be called after scsi_add_host() 654 * 655 * Defined in: drivers/scsi/scsi_scan.c 656 **/ 657void scsi_scan_host(struct Scsi_Host *shost) 658 659 660/** 661 * scsi_track_queue_full - track successive QUEUE_FULL events on given 662 * device to determine if and when there is a need 663 * to adjust the queue depth on the device. 664 * @sdev: pointer to SCSI device instance 665 * @depth: Current number of outstanding SCSI commands on this device, 666 * not counting the one returned as QUEUE_FULL. 667 * 668 * Returns 0 - no change needed 669 * >0 - adjust queue depth to this new depth 670 * -1 - drop back to untagged operation using host->cmd_per_lun 671 * as the untagged command depth 672 * 673 * Might block: no 674 * 675 * Notes: LLDs may call this at any time and we will do "The Right 676 * Thing"; interrupt context safe. 677 * 678 * Defined in: drivers/scsi/scsi.c . 679 **/ 680int scsi_track_queue_full(struct scsi_device *sdev, int depth) 681 682 683/** 684 * scsi_unblock_requests - allow further commands to be queued to given host 685 * 686 * @shost: pointer to host to unblock commands on 687 * 688 * Returns nothing 689 * 690 * Might block: no 691 * 692 * Defined in: drivers/scsi/scsi_lib.c . 693**/ 694void scsi_unblock_requests(struct Scsi_Host * shost) 695 696 697/** 698 * scsi_unregister - unregister and free memory used by host instance 699 * @shp: pointer to scsi host instance to unregister. 700 * 701 * Returns nothing 702 * 703 * Might block: no 704 * 705 * Notes: Should not be invoked if the "hotplug initialization 706 * model" is being used. Called internally by exit_this_scsi_driver() 707 * in the "passive initialization model". Hence a LLD has no need to 708 * call this function directly. 709 * 710 * Defined in: drivers/scsi/hosts.c . 711 **/ 712void scsi_unregister(struct Scsi_Host * shp) 713 714 715 716 717Interface Functions 718=================== 719Interface functions are supplied (defined) by LLDs and their function 720pointers are placed in an instance of struct scsi_host_template which 721is passed to scsi_host_alloc() [or scsi_register() / init_this_scsi_driver()]. 722Some are mandatory. Interface functions should be declared static. The 723accepted convention is that driver "xyz" will declare its slave_configure() 724function as: 725 static int xyz_slave_configure(struct scsi_device * sdev); 726and so forth for all interface functions listed below. 727 728A pointer to this function should be placed in the 'slave_configure' member 729of a "struct scsi_host_template" instance. A pointer to such an instance 730should be passed to the mid level's scsi_host_alloc() [or scsi_register() / 731init_this_scsi_driver()]. 732 733The interface functions are also described in the include/scsi/scsi_host.h 734file immediately above their definition point in "struct scsi_host_template". 735In some cases more detail is given in scsi_host.h than below. 736 737The interface functions are listed below in alphabetical order. 738 739Summary: 740 bios_param - fetch head, sector, cylinder info for a disk 741 detect - detects HBAs this driver wants to control 742 eh_timed_out - notify the host that a command timer expired 743 eh_abort_handler - abort given command 744 eh_bus_reset_handler - issue SCSI bus reset 745 eh_device_reset_handler - issue SCSI device reset 746 eh_host_reset_handler - reset host (host bus adapter) 747 info - supply information about given host 748 ioctl - driver can respond to ioctls 749 proc_info - supports /proc/scsi/{driver_name}/{host_no} 750 queuecommand - queue scsi command, invoke 'done' on completion 751 release - release all resources associated with given host 752 slave_alloc - prior to any commands being sent to a new device 753 slave_configure - driver fine tuning for given device after attach 754 slave_destroy - given device is about to be shut down 755 756 757Details: 758 759/** 760 * bios_param - fetch head, sector, cylinder info for a disk 761 * @sdev: pointer to scsi device context (defined in 762 * include/scsi/scsi_device.h) 763 * @bdev: pointer to block device context (defined in fs.h) 764 * @capacity: device size (in 512 byte sectors) 765 * @params: three element array to place output: 766 * params[0] number of heads (max 255) 767 * params[1] number of sectors (max 63) 768 * params[2] number of cylinders 769 * 770 * Return value is ignored 771 * 772 * Locks: none 773 * 774 * Calling context: process (sd) 775 * 776 * Notes: an arbitrary geometry (based on READ CAPACITY) is used 777 * if this function is not provided. The params array is 778 * pre-initialized with made up values just in case this function 779 * doesn't output anything. 780 * 781 * Optionally defined in: LLD 782 **/ 783 int bios_param(struct scsi_device * sdev, struct block_device *bdev, 784 sector_t capacity, int params[3]) 785 786 787/** 788 * detect - detects HBAs this driver wants to control 789 * @shtp: host template for this driver. 790 * 791 * Returns number of hosts this driver wants to control. 0 means no 792 * suitable hosts found. 793 * 794 * Locks: none held 795 * 796 * Calling context: process [invoked from init_this_scsi_driver()] 797 * 798 * Notes: First function called from the SCSI mid level on this 799 * driver. Upper level drivers (e.g. sd) may not (yet) be present. 800 * For each host found, this method should call scsi_register() 801 * [see hosts.c]. 802 * 803 * Defined in: LLD (required if "passive initialization mode" is used, 804 * not invoked in "hotplug initialization mode") 805 **/ 806 int detect(struct scsi_host_template * shtp) 807 808 809/** 810 * eh_timed_out - The timer for the command has just fired 811 * @scp: identifies command timing out 812 * 813 * Returns: 814 * 815 * EH_HANDLED: I fixed the error, please complete the command 816 * EH_RESET_TIMER: I need more time, reset the timer and 817 * begin counting again 818 * EH_NOT_HANDLED Begin normal error recovery 819 * 820 * 821 * Locks: None held 822 * 823 * Calling context: interrupt 824 * 825 * Notes: This is to give the LLD an opportunity to do local recovery. 826 * This recovery is limited to determining if the outstanding command 827 * will ever complete. You may not abort and restart the command from 828 * this callback. 829 * 830 * Optionally defined in: LLD 831 **/ 832 int eh_timed_out(struct scsi_cmnd * scp) 833 834 835/** 836 * eh_abort_handler - abort command associated with scp 837 * @scp: identifies command to be aborted 838 * 839 * Returns SUCCESS if command aborted else FAILED 840 * 841 * Locks: None held 842 * 843 * Calling context: kernel thread 844 * 845 * Notes: If 'no_async_abort' is defined this callback 846 * will be invoked from scsi_eh thread. No other commands 847 * will then be queued on current host during eh. 848 * Otherwise it will be called whenever scsi_times_out() 849 * is called due to a command timeout. 850 * 851 * Optionally defined in: LLD 852 **/ 853 int eh_abort_handler(struct scsi_cmnd * scp) 854 855 856/** 857 * eh_bus_reset_handler - issue SCSI bus reset 858 * @scp: SCSI bus that contains this device should be reset 859 * 860 * Returns SUCCESS if command aborted else FAILED 861 * 862 * Locks: None held 863 * 864 * Calling context: kernel thread 865 * 866 * Notes: Invoked from scsi_eh thread. No other commands will be 867 * queued on current host during eh. 868 * 869 * Optionally defined in: LLD 870 **/ 871 int eh_bus_reset_handler(struct scsi_cmnd * scp) 872 873 874/** 875 * eh_device_reset_handler - issue SCSI device reset 876 * @scp: identifies SCSI device to be reset 877 * 878 * Returns SUCCESS if command aborted else FAILED 879 * 880 * Locks: None held 881 * 882 * Calling context: kernel thread 883 * 884 * Notes: Invoked from scsi_eh thread. No other commands will be 885 * queued on current host during eh. 886 * 887 * Optionally defined in: LLD 888 **/ 889 int eh_device_reset_handler(struct scsi_cmnd * scp) 890 891 892/** 893 * eh_host_reset_handler - reset host (host bus adapter) 894 * @scp: SCSI host that contains this device should be reset 895 * 896 * Returns SUCCESS if command aborted else FAILED 897 * 898 * Locks: None held 899 * 900 * Calling context: kernel thread 901 * 902 * Notes: Invoked from scsi_eh thread. No other commands will be 903 * queued on current host during eh. 904 * With the default eh_strategy in place, if none of the _abort_, 905 * _device_reset_, _bus_reset_ or this eh handler function are 906 * defined (or they all return FAILED) then the device in question 907 * will be set offline whenever eh is invoked. 908 * 909 * Optionally defined in: LLD 910 **/ 911 int eh_host_reset_handler(struct scsi_cmnd * scp) 912 913 914/** 915 * info - supply information about given host: driver name plus data 916 * to distinguish given host 917 * @shp: host to supply information about 918 * 919 * Return ASCII null terminated string. [This driver is assumed to 920 * manage the memory pointed to and maintain it, typically for the 921 * lifetime of this host.] 922 * 923 * Locks: none 924 * 925 * Calling context: process 926 * 927 * Notes: Often supplies PCI or ISA information such as IO addresses 928 * and interrupt numbers. If not supplied struct Scsi_Host::name used 929 * instead. It is assumed the returned information fits on one line 930 * (i.e. does not included embedded newlines). 931 * The SCSI_IOCTL_PROBE_HOST ioctl yields the string returned by this 932 * function (or struct Scsi_Host::name if this function is not 933 * available). 934 * In a similar manner, init_this_scsi_driver() outputs to the console 935 * each host's "info" (or name) for the driver it is registering. 936 * Also if proc_info() is not supplied, the output of this function 937 * is used instead. 938 * 939 * Optionally defined in: LLD 940 **/ 941 const char * info(struct Scsi_Host * shp) 942 943 944/** 945 * ioctl - driver can respond to ioctls 946 * @sdp: device that ioctl was issued for 947 * @cmd: ioctl number 948 * @arg: pointer to read or write data from. Since it points to 949 * user space, should use appropriate kernel functions 950 * (e.g. copy_from_user() ). In the Unix style this argument 951 * can also be viewed as an unsigned long. 952 * 953 * Returns negative "errno" value when there is a problem. 0 or a 954 * positive value indicates success and is returned to the user space. 955 * 956 * Locks: none 957 * 958 * Calling context: process 959 * 960 * Notes: The SCSI subsystem uses a "trickle down" ioctl model. 961 * The user issues an ioctl() against an upper level driver 962 * (e.g. /dev/sdc) and if the upper level driver doesn't recognize 963 * the 'cmd' then it is passed to the SCSI mid level. If the SCSI 964 * mid level does not recognize it, then the LLD that controls 965 * the device receives the ioctl. According to recent Unix standards 966 * unsupported ioctl() 'cmd' numbers should return -ENOTTY. 967 * 968 * Optionally defined in: LLD 969 **/ 970 int ioctl(struct scsi_device *sdp, int cmd, void *arg) 971 972 973/** 974 * proc_info - supports /proc/scsi/{driver_name}/{host_no} 975 * @buffer: anchor point to output to (0==writeto1_read0) or fetch from 976 * (1==writeto1_read0). 977 * @start: where "interesting" data is written to. Ignored when 978 * 1==writeto1_read0. 979 * @offset: offset within buffer 0==writeto1_read0 is actually 980 * interested in. Ignored when 1==writeto1_read0 . 981 * @length: maximum (or actual) extent of buffer 982 * @host_no: host number of interest (struct Scsi_Host::host_no) 983 * @writeto1_read0: 1 -> data coming from user space towards driver 984 * (e.g. "echo some_string > /proc/scsi/xyz/2") 985 * 0 -> user what data from this driver 986 * (e.g. "cat /proc/scsi/xyz/2") 987 * 988 * Returns length when 1==writeto1_read0. Otherwise number of chars 989 * output to buffer past offset. 990 * 991 * Locks: none held 992 * 993 * Calling context: process 994 * 995 * Notes: Driven from scsi_proc.c which interfaces to proc_fs. proc_fs 996 * support can now be configured out of the scsi subsystem. 997 * 998 * Optionally defined in: LLD 999 **/ 1000 int proc_info(char * buffer, char ** start, off_t offset, 1001 int length, int host_no, int writeto1_read0) 1002 1003 1004/** 1005 * queuecommand - queue scsi command, invoke scp->scsi_done on completion 1006 * @shost: pointer to the scsi host object 1007 * @scp: pointer to scsi command object 1008 * 1009 * Returns 0 on success. 1010 * 1011 * If there's a failure, return either: 1012 * 1013 * SCSI_MLQUEUE_DEVICE_BUSY if the device queue is full, or 1014 * SCSI_MLQUEUE_HOST_BUSY if the entire host queue is full 1015 * 1016 * On both of these returns, the mid-layer will requeue the I/O 1017 * 1018 * - if the return is SCSI_MLQUEUE_DEVICE_BUSY, only that particular 1019 * device will be paused, and it will be unpaused when a command to 1020 * the device returns (or after a brief delay if there are no more 1021 * outstanding commands to it). Commands to other devices continue 1022 * to be processed normally. 1023 * 1024 * - if the return is SCSI_MLQUEUE_HOST_BUSY, all I/O to the host 1025 * is paused and will be unpaused when any command returns from 1026 * the host (or after a brief delay if there are no outstanding 1027 * commands to the host). 1028 * 1029 * For compatibility with earlier versions of queuecommand, any 1030 * other return value is treated the same as 1031 * SCSI_MLQUEUE_HOST_BUSY. 1032 * 1033 * Other types of errors that are detected immediately may be 1034 * flagged by setting scp->result to an appropriate value, 1035 * invoking the scp->scsi_done callback, and then returning 0 1036 * from this function. If the command is not performed 1037 * immediately (and the LLD is starting (or will start) the given 1038 * command) then this function should place 0 in scp->result and 1039 * return 0. 1040 * 1041 * Command ownership. If the driver returns zero, it owns the 1042 * command and must take responsibility for ensuring the 1043 * scp->scsi_done callback is executed. Note: the driver may 1044 * call scp->scsi_done before returning zero, but after it has 1045 * called scp->scsi_done, it may not return any value other than 1046 * zero. If the driver makes a non-zero return, it must not 1047 * execute the command's scsi_done callback at any time. 1048 * 1049 * Locks: up to and including 2.6.36, struct Scsi_Host::host_lock 1050 * held on entry (with "irqsave") and is expected to be 1051 * held on return. From 2.6.37 onwards, queuecommand is 1052 * called without any locks held. 1053 * 1054 * Calling context: in interrupt (soft irq) or process context 1055 * 1056 * Notes: This function should be relatively fast. Normally it 1057 * will not wait for IO to complete. Hence the scp->scsi_done 1058 * callback is invoked (often directly from an interrupt service 1059 * routine) some time after this function has returned. In some 1060 * cases (e.g. pseudo adapter drivers that manufacture the 1061 * response to a SCSI INQUIRY) the scp->scsi_done callback may be 1062 * invoked before this function returns. If the scp->scsi_done 1063 * callback is not invoked within a certain period the SCSI mid 1064 * level will commence error processing. If a status of CHECK 1065 * CONDITION is placed in "result" when the scp->scsi_done 1066 * callback is invoked, then the LLD driver should perform 1067 * autosense and fill in the struct scsi_cmnd::sense_buffer 1068 * array. The scsi_cmnd::sense_buffer array is zeroed prior to 1069 * the mid level queuing a command to an LLD. 1070 * 1071 * Defined in: LLD 1072 **/ 1073 int queuecommand(struct Scsi_Host *shost, struct scsi_cmnd * scp) 1074 1075 1076/** 1077 * release - release all resources associated with given host 1078 * @shp: host to be released. 1079 * 1080 * Return value ignored (could soon be a function returning void). 1081 * 1082 * Locks: none held 1083 * 1084 * Calling context: process 1085 * 1086 * Notes: Invoked from scsi_module.c's exit_this_scsi_driver(). 1087 * LLD's implementation of this function should call 1088 * scsi_unregister(shp) prior to returning. 1089 * Only needed for old-style host templates. 1090 * 1091 * Defined in: LLD (required in "passive initialization model", 1092 * should not be defined in hotplug model) 1093 **/ 1094 int release(struct Scsi_Host * shp) 1095 1096 1097/** 1098 * slave_alloc - prior to any commands being sent to a new device 1099 * (i.e. just prior to scan) this call is made 1100 * @sdp: pointer to new device (about to be scanned) 1101 * 1102 * Returns 0 if ok. Any other return is assumed to be an error and 1103 * the device is ignored. 1104 * 1105 * Locks: none 1106 * 1107 * Calling context: process 1108 * 1109 * Notes: Allows the driver to allocate any resources for a device 1110 * prior to its initial scan. The corresponding scsi device may not 1111 * exist but the mid level is just about to scan for it (i.e. send 1112 * and INQUIRY command plus ...). If a device is found then 1113 * slave_configure() will be called while if a device is not found 1114 * slave_destroy() is called. 1115 * For more details see the include/scsi/scsi_host.h file. 1116 * 1117 * Optionally defined in: LLD 1118 **/ 1119 int slave_alloc(struct scsi_device *sdp) 1120 1121 1122/** 1123 * slave_configure - driver fine tuning for given device just after it 1124 * has been first scanned (i.e. it responded to an 1125 * INQUIRY) 1126 * @sdp: device that has just been attached 1127 * 1128 * Returns 0 if ok. Any other return is assumed to be an error and 1129 * the device is taken offline. [offline devices will _not_ have 1130 * slave_destroy() called on them so clean up resources.] 1131 * 1132 * Locks: none 1133 * 1134 * Calling context: process 1135 * 1136 * Notes: Allows the driver to inspect the response to the initial 1137 * INQUIRY done by the scanning code and take appropriate action. 1138 * For more details see the include/scsi/scsi_host.h file. 1139 * 1140 * Optionally defined in: LLD 1141 **/ 1142 int slave_configure(struct scsi_device *sdp) 1143 1144 1145/** 1146 * slave_destroy - given device is about to be shut down. All 1147 * activity has ceased on this device. 1148 * @sdp: device that is about to be shut down 1149 * 1150 * Returns nothing 1151 * 1152 * Locks: none 1153 * 1154 * Calling context: process 1155 * 1156 * Notes: Mid level structures for given device are still in place 1157 * but are about to be torn down. Any per device resources allocated 1158 * by this driver for given device should be freed now. No further 1159 * commands will be sent for this sdp instance. [However the device 1160 * could be re-attached in the future in which case a new instance 1161 * of struct scsi_device would be supplied by future slave_alloc() 1162 * and slave_configure() calls.] 1163 * 1164 * Optionally defined in: LLD 1165 **/ 1166 void slave_destroy(struct scsi_device *sdp) 1167 1168 1169 1170Data Structures 1171=============== 1172struct scsi_host_template 1173------------------------- 1174There is one "struct scsi_host_template" instance per LLD ***. It is 1175typically initialized as a file scope static in a driver's header file. That 1176way members that are not explicitly initialized will be set to 0 or NULL. 1177Member of interest: 1178 name - name of driver (may contain spaces, please limit to 1179 less than 80 characters) 1180 proc_name - name used in "/proc/scsi/<proc_name>/<host_no>" and 1181 by sysfs in one of its "drivers" directories. Hence 1182 "proc_name" should only contain characters acceptable 1183 to a Unix file name. 1184 (*queuecommand)() - primary callback that the mid level uses to inject 1185 SCSI commands into an LLD. 1186The structure is defined and commented in include/scsi/scsi_host.h 1187 1188*** In extreme situations a single driver may have several instances 1189 if it controls several different classes of hardware (e.g. an LLD 1190 that handles both ISA and PCI cards and has a separate instance of 1191 struct scsi_host_template for each class). 1192 1193struct Scsi_Host 1194---------------- 1195There is one struct Scsi_Host instance per host (HBA) that an LLD 1196controls. The struct Scsi_Host structure has many members in common 1197with "struct scsi_host_template". When a new struct Scsi_Host instance 1198is created (in scsi_host_alloc() in hosts.c) those common members are 1199initialized from the driver's struct scsi_host_template instance. Members 1200of interest: 1201 host_no - system wide unique number that is used for identifying 1202 this host. Issued in ascending order from 0. 1203 can_queue - must be greater than 0; do not send more than can_queue 1204 commands to the adapter. 1205 this_id - scsi id of host (scsi initiator) or -1 if not known 1206 sg_tablesize - maximum scatter gather elements allowed by host. 1207 0 implies scatter gather not supported by host 1208 max_sectors - maximum number of sectors (usually 512 bytes) allowed 1209 in a single SCSI command. The default value of 0 leads 1210 to a setting of SCSI_DEFAULT_MAX_SECTORS (defined in 1211 scsi_host.h) which is currently set to 1024. So for a 1212 disk the maximum transfer size is 512 KB when max_sectors 1213 is not defined. Note that this size may not be sufficient 1214 for disk firmware uploads. 1215 cmd_per_lun - maximum number of commands that can be queued on devices 1216 controlled by the host. Overridden by LLD calls to 1217 scsi_change_queue_depth(). 1218 unchecked_isa_dma - 1=>only use bottom 16 MB of ram (ISA DMA addressing 1219 restriction), 0=>can use full 32 bit (or better) DMA 1220 address space 1221 use_clustering - 1=>SCSI commands in mid level's queue can be merged, 1222 0=>disallow SCSI command merging 1223 no_async_abort - 1=>Asynchronous aborts are not supported 1224 0=>Timed-out commands will be aborted asynchronously 1225 hostt - pointer to driver's struct scsi_host_template from which 1226 this struct Scsi_Host instance was spawned 1227 hostt->proc_name - name of LLD. This is the driver name that sysfs uses 1228 transportt - pointer to driver's struct scsi_transport_template instance 1229 (if any). FC and SPI transports currently supported. 1230 sh_list - a double linked list of pointers to all struct Scsi_Host 1231 instances (currently ordered by ascending host_no) 1232 my_devices - a double linked list of pointers to struct scsi_device 1233 instances that belong to this host. 1234 hostdata[0] - area reserved for LLD at end of struct Scsi_Host. Size 1235 is set by the second argument (named 'xtr_bytes') to 1236 scsi_host_alloc() or scsi_register(). 1237 vendor_id - a unique value that identifies the vendor supplying 1238 the LLD for the Scsi_Host. Used most often in validating 1239 vendor-specific message requests. Value consists of an 1240 identifier type and a vendor-specific value. 1241 See scsi_netlink.h for a description of valid formats. 1242 1243The scsi_host structure is defined in include/scsi/scsi_host.h 1244 1245struct scsi_device 1246------------------ 1247Generally, there is one instance of this structure for each SCSI logical unit 1248on a host. Scsi devices connected to a host are uniquely identified by a 1249channel number, target id and logical unit number (lun). 1250The structure is defined in include/scsi/scsi_device.h 1251 1252struct scsi_cmnd 1253---------------- 1254Instances of this structure convey SCSI commands to the LLD and responses 1255back to the mid level. The SCSI mid level will ensure that no more SCSI 1256commands become queued against the LLD than are indicated by 1257scsi_change_queue_depth() (or struct Scsi_Host::cmd_per_lun). There will 1258be at least one instance of struct scsi_cmnd available for each SCSI device. 1259Members of interest: 1260 cmnd - array containing SCSI command 1261 cmnd_len - length (in bytes) of SCSI command 1262 sc_data_direction - direction of data transfer in data phase. See 1263 "enum dma_data_direction" in include/linux/dma-mapping.h 1264 request_bufflen - number of data bytes to transfer (0 if no data phase) 1265 use_sg - ==0 -> no scatter gather list, hence transfer data 1266 to/from request_buffer 1267 - >0 -> scatter gather list (actually an array) in 1268 request_buffer with use_sg elements 1269 request_buffer - either contains data buffer or scatter gather list 1270 depending on the setting of use_sg. Scatter gather 1271 elements are defined by 'struct scatterlist' found 1272 in include/asm/scatterlist.h . 1273 done - function pointer that should be invoked by LLD when the 1274 SCSI command is completed (successfully or otherwise). 1275 Should only be called by an LLD if the LLD has accepted 1276 the command (i.e. queuecommand() returned or will return 1277 0). The LLD may invoke 'done' prior to queuecommand() 1278 finishing. 1279 result - should be set by LLD prior to calling 'done'. A value 1280 of 0 implies a successfully completed command (and all 1281 data (if any) has been transferred to or from the SCSI 1282 target device). 'result' is a 32 bit unsigned integer that 1283 can be viewed as 4 related bytes. The SCSI status value is 1284 in the LSB. See include/scsi/scsi.h status_byte(), 1285 msg_byte(), host_byte() and driver_byte() macros and 1286 related constants. 1287 sense_buffer - an array (maximum size: SCSI_SENSE_BUFFERSIZE bytes) that 1288 should be written when the SCSI status (LSB of 'result') 1289 is set to CHECK_CONDITION (2). When CHECK_CONDITION is 1290 set, if the top nibble of sense_buffer[0] has the value 7 1291 then the mid level will assume the sense_buffer array 1292 contains a valid SCSI sense buffer; otherwise the mid 1293 level will issue a REQUEST_SENSE SCSI command to 1294 retrieve the sense buffer. The latter strategy is error 1295 prone in the presence of command queuing so the LLD should 1296 always "auto-sense". 1297 device - pointer to scsi_device object that this command is 1298 associated with. 1299 resid - an LLD should set this signed integer to the requested 1300 transfer length (i.e. 'request_bufflen') less the number 1301 of bytes that are actually transferred. 'resid' is 1302 preset to 0 so an LLD can ignore it if it cannot detect 1303 underruns (overruns should be rare). If possible an LLD 1304 should set 'resid' prior to invoking 'done'. The most 1305 interesting case is data transfers from a SCSI target 1306 device (e.g. READs) that underrun. 1307 underflow - LLD should place (DID_ERROR << 16) in 'result' if 1308 actual number of bytes transferred is less than this 1309 figure. Not many LLDs implement this check and some that 1310 do just output an error message to the log rather than 1311 report a DID_ERROR. Better for an LLD to implement 1312 'resid'. 1313 1314It is recommended that a LLD set 'resid' on data transfers from a SCSI 1315target device (e.g. READs). It is especially important that 'resid' is set 1316when such data transfers have sense keys of MEDIUM ERROR and HARDWARE ERROR 1317(and possibly RECOVERED ERROR). In these cases if a LLD is in doubt how much 1318data has been received then the safest approach is to indicate no bytes have 1319been received. For example: to indicate that no valid data has been received 1320a LLD might use these helpers: 1321 scsi_set_resid(SCpnt, scsi_bufflen(SCpnt)); 1322where 'SCpnt' is a pointer to a scsi_cmnd object. To indicate only three 512 1323bytes blocks has been received 'resid' could be set like this: 1324 scsi_set_resid(SCpnt, scsi_bufflen(SCpnt) - (3 * 512)); 1325 1326The scsi_cmnd structure is defined in include/scsi/scsi_cmnd.h 1327 1328 1329Locks 1330===== 1331Each struct Scsi_Host instance has a spin_lock called struct 1332Scsi_Host::default_lock which is initialized in scsi_host_alloc() [found in 1333hosts.c]. Within the same function the struct Scsi_Host::host_lock pointer 1334is initialized to point at default_lock. Thereafter lock and unlock 1335operations performed by the mid level use the struct Scsi_Host::host_lock 1336pointer. Previously drivers could override the host_lock pointer but 1337this is not allowed anymore. 1338 1339 1340Autosense 1341========= 1342Autosense (or auto-sense) is defined in the SAM-2 document as "the 1343automatic return of sense data to the application client coincident 1344with the completion of a SCSI command" when a status of CHECK CONDITION 1345occurs. LLDs should perform autosense. This should be done when the LLD 1346detects a CHECK CONDITION status by either: 1347 a) instructing the SCSI protocol (e.g. SCSI Parallel Interface (SPI)) 1348 to perform an extra data in phase on such responses 1349 b) or, the LLD issuing a REQUEST SENSE command itself 1350 1351Either way, when a status of CHECK CONDITION is detected, the mid level 1352decides whether the LLD has performed autosense by checking struct 1353scsi_cmnd::sense_buffer[0] . If this byte has an upper nibble of 7 (or 0xf) 1354then autosense is assumed to have taken place. If it has another value (and 1355this byte is initialized to 0 before each command) then the mid level will 1356issue a REQUEST SENSE command. 1357 1358In the presence of queued commands the "nexus" that maintains sense 1359buffer data from the command that failed until a following REQUEST SENSE 1360may get out of synchronization. This is why it is best for the LLD 1361to perform autosense. 1362 1363 1364Changes since lk 2.4 series 1365=========================== 1366io_request_lock has been replaced by several finer grained locks. The lock 1367relevant to LLDs is struct Scsi_Host::host_lock and there is 1368one per SCSI host. 1369 1370The older error handling mechanism has been removed. This means the 1371LLD interface functions abort() and reset() have been removed. 1372The struct scsi_host_template::use_new_eh_code flag has been removed. 1373 1374In the 2.4 series the SCSI subsystem configuration descriptions were 1375aggregated with the configuration descriptions from all other Linux 1376subsystems in the Documentation/Configure.help file. In the 2.6 series, 1377the SCSI subsystem now has its own (much smaller) drivers/scsi/Kconfig 1378file that contains both configuration and help information. 1379 1380struct SHT has been renamed to struct scsi_host_template. 1381 1382Addition of the "hotplug initialization model" and many extra functions 1383to support it. 1384 1385 1386Credits 1387======= 1388The following people have contributed to this document: 1389 Mike Anderson <andmike at us dot ibm dot com> 1390 James Bottomley <James dot Bottomley at hansenpartnership dot com> 1391 Patrick Mansfield <patmans at us dot ibm dot com> 1392 Christoph Hellwig <hch at infradead dot org> 1393 Doug Ledford <dledford at redhat dot com> 1394 Andries Brouwer <Andries dot Brouwer at cwi dot nl> 1395 Randy Dunlap <rdunlap at xenotime dot net> 1396 Alan Stern <stern at rowland dot harvard dot edu> 1397 1398 1399Douglas Gilbert 1400dgilbert at interlog dot com 140121st September 2004 1402