1.. SPDX-License-Identifier: GPL-2.0 2 3============================================= 4SCSI mid_level - lower_level driver interface 5============================================= 6 7Introduction 8============ 9This document outlines the interface between the Linux SCSI mid level and 10SCSI lower level drivers. Lower level drivers (LLDs) are variously called 11host bus adapter (HBA) drivers and host drivers (HD). A "host" in this 12context is a bridge between a computer IO bus (e.g. PCI or ISA) and a 13single SCSI initiator port on a SCSI transport. An "initiator" port 14(SCSI terminology, see SAM-3 at http://www.t10.org) sends SCSI commands 15to "target" SCSI ports (e.g. disks). There can be many LLDs in a running 16system, but only one per hardware type. Most LLDs can control one or more 17SCSI HBAs. Some HBAs contain multiple hosts. 18 19In some cases the SCSI transport is an external bus that already has 20its own subsystem in Linux (e.g. USB and ieee1394). In such cases the 21SCSI subsystem LLD is a software bridge to the other driver subsystem. 22Examples are the usb-storage driver (found in the drivers/usb/storage 23directory) and the ieee1394/sbp2 driver (found in the drivers/ieee1394 24directory). 25 26For example, the aic7xxx LLD controls Adaptec SCSI parallel interface 27(SPI) controllers based on that company's 7xxx chip series. The aic7xxx 28LLD can be built into the kernel or loaded as a module. There can only be 29one aic7xxx LLD running in a Linux system but it may be controlling many 30HBAs. These HBAs might be either on PCI daughter-boards or built into 31the motherboard (or both). Some aic7xxx based HBAs are dual controllers 32and thus represent two hosts. Like most modern HBAs, each aic7xxx host 33has its own PCI device address. [The one-to-one correspondence between 34a SCSI host and a PCI device is common but not required (e.g. with 35ISA adapters).] 36 37The SCSI mid level isolates an LLD from other layers such as the SCSI 38upper layer drivers and the block layer. 39 40This version of the document roughly matches linux kernel version 2.6.8 . 41 42Documentation 43============= 44There is a SCSI documentation directory within the kernel source tree, 45typically Documentation/scsi . Most documents are in plain 46(i.e. ASCII) text. This file is named scsi_mid_low_api.txt and can be 47found in that directory. A more recent copy of this document may be found 48at http://web.archive.org/web/20070107183357rn_1/sg.torque.net/scsi/. 49Many LLDs are documented there (e.g. aic7xxx.txt). The SCSI mid-level is 50briefly described in scsi.txt which contains a url to a document 51describing the SCSI subsystem in the lk 2.4 series. Two upper level 52drivers have documents in that directory: st.txt (SCSI tape driver) and 53scsi-generic.txt (for the sg driver). 54 55Some documentation (or urls) for LLDs may be found in the C source code 56or in the same directory as the C source code. For example to find a url 57about the USB mass storage driver see the 58/usr/src/linux/drivers/usb/storage directory. 59 60Driver structure 61================ 62Traditionally an LLD for the SCSI subsystem has been at least two files in 63the drivers/scsi directory. For example, a driver called "xyz" has a header 64file "xyz.h" and a source file "xyz.c". [Actually there is no good reason 65why this couldn't all be in one file; the header file is superfluous.] Some 66drivers that have been ported to several operating systems have more than 67two files. For example the aic7xxx driver has separate files for generic 68and OS-specific code (e.g. FreeBSD and Linux). Such drivers tend to have 69their own directory under the drivers/scsi directory. 70 71When a new LLD is being added to Linux, the following files (found in the 72drivers/scsi directory) will need some attention: Makefile and Kconfig . 73It is probably best to study how existing LLDs are organized. 74 75As the 2.5 series development kernels evolve into the 2.6 series 76production series, changes are being introduced into this interface. An 77example of this is driver initialization code where there are now 2 models 78available. The older one, similar to what was found in the lk 2.4 series, 79is based on hosts that are detected at HBA driver load time. This will be 80referred to the "passive" initialization model. The newer model allows HBAs 81to be hot plugged (and unplugged) during the lifetime of the LLD and will 82be referred to as the "hotplug" initialization model. The newer model is 83preferred as it can handle both traditional SCSI equipment that is 84permanently connected as well as modern "SCSI" devices (e.g. USB or 85IEEE 1394 connected digital cameras) that are hotplugged. Both 86initialization models are discussed in the following sections. 87 88An LLD interfaces to the SCSI subsystem several ways: 89 90 a) directly invoking functions supplied by the mid level 91 b) passing a set of function pointers to a registration function 92 supplied by the mid level. The mid level will then invoke these 93 functions at some point in the future. The LLD will supply 94 implementations of these functions. 95 c) direct access to instances of well known data structures maintained 96 by the mid level 97 98Those functions in group a) are listed in a section entitled "Mid level 99supplied functions" below. 100 101Those functions in group b) are listed in a section entitled "Interface 102functions" below. Their function pointers are placed in the members of 103"struct scsi_host_template", an instance of which is passed to 104scsi_host_alloc() [#]_. Those interface functions that the LLD does not 105wish to supply should have NULL placed in the corresponding member of 106struct scsi_host_template. Defining an instance of struct 107scsi_host_template at file scope will cause NULL to be placed in function 108pointer members not explicitly initialized. 109 110Those usages in group c) should be handled with care, especially in a 111"hotplug" environment. LLDs should be aware of the lifetime of instances 112that are shared with the mid level and other layers. 113 114All functions defined within an LLD and all data defined at file scope 115should be static. For example the slave_alloc() function in an LLD 116called "xxx" could be defined as 117``static int xxx_slave_alloc(struct scsi_device * sdev) { /* code */ }`` 118 119.. [#] the scsi_host_alloc() function is a replacement for the rather vaguely 120 named scsi_register() function in most situations. 121 122 123Hotplug initialization model 124============================ 125In this model an LLD controls when SCSI hosts are introduced and removed 126from the SCSI subsystem. Hosts can be introduced as early as driver 127initialization and removed as late as driver shutdown. Typically a driver 128will respond to a sysfs probe() callback that indicates an HBA has been 129detected. After confirming that the new device is one that the LLD wants 130to control, the LLD will initialize the HBA and then register a new host 131with the SCSI mid level. 132 133During LLD initialization the driver should register itself with the 134appropriate IO bus on which it expects to find HBA(s) (e.g. the PCI bus). 135This can probably be done via sysfs. Any driver parameters (especially 136those that are writable after the driver is loaded) could also be 137registered with sysfs at this point. The SCSI mid level first becomes 138aware of an LLD when that LLD registers its first HBA. 139 140At some later time, the LLD becomes aware of an HBA and what follows 141is a typical sequence of calls between the LLD and the mid level. 142This example shows the mid level scanning the newly introduced HBA for 3 143scsi devices of which only the first 2 respond:: 144 145 HBA PROBE: assume 2 SCSI devices found in scan 146 LLD mid level LLD 147 ===-------------------=========--------------------===------ 148 scsi_host_alloc() --> 149 scsi_add_host() ----> 150 scsi_scan_host() -------+ 151 | 152 slave_alloc() 153 slave_configure() --> scsi_change_queue_depth() 154 | 155 slave_alloc() 156 slave_configure() 157 | 158 slave_alloc() *** 159 slave_destroy() *** 160 161 162 *** For scsi devices that the mid level tries to scan but do not 163 respond, a slave_alloc(), slave_destroy() pair is called. 164 165If the LLD wants to adjust the default queue settings, it can invoke 166scsi_change_queue_depth() in its slave_configure() routine. 167 168When an HBA is being removed it could be as part of an orderly shutdown 169associated with the LLD module being unloaded (e.g. with the "rmmod" 170command) or in response to a "hot unplug" indicated by sysfs()'s 171remove() callback being invoked. In either case, the sequence is the 172same:: 173 174 HBA REMOVE: assume 2 SCSI devices attached 175 LLD mid level LLD 176 ===----------------------=========-----------------===------ 177 scsi_remove_host() ---------+ 178 | 179 slave_destroy() 180 slave_destroy() 181 scsi_host_put() 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 201 LLD mid level LLD 202 ===-------------------=========--------------------===------ 203 scsi_add_device() ------+ 204 | 205 slave_alloc() 206 slave_configure() [--> scsi_change_queue_depth()] 207 208In a similar fashion, an LLD may become aware that a SCSI device has been 209removed (unplugged) or the connection to it has been interrupted. Some 210existing SCSI transports (e.g. SPI) may not become aware that a SCSI 211device has been removed until a subsequent SCSI command fails which will 212probably cause that device to be set offline by the mid level. An LLD that 213detects the removal of a SCSI device can instigate its removal from 214upper layers with this sequence:: 215 216 SCSI DEVICE hot unplug 217 LLD mid level LLD 218 ===----------------------=========-----------------===------ 219 scsi_remove_device() -------+ 220 | 221 slave_destroy() 222 223It may be useful for an LLD to keep track of struct scsi_device instances 224(a pointer is passed as the parameter to slave_alloc() and 225slave_configure() callbacks). Such instances are "owned" by the mid-level. 226struct scsi_device instances are freed after slave_destroy(). 227 228 229Reference Counting 230================== 231The Scsi_Host structure has had reference counting infrastructure added. 232This effectively spreads the ownership of struct Scsi_Host instances 233across the various SCSI layers which use them. Previously such instances 234were exclusively owned by the mid level. LLDs would not usually need to 235directly manipulate these reference counts but there may be some cases 236where they do. 237 238There are 3 reference counting functions of interest associated with 239struct Scsi_Host: 240 241 - scsi_host_alloc(): 242 returns a pointer to new instance of struct 243 Scsi_Host which has its reference count ^^ set to 1 244 245 - scsi_host_get(): 246 adds 1 to the reference count of the given instance 247 248 - scsi_host_put(): 249 decrements 1 from the reference count of the given 250 instance. If the reference count reaches 0 then the given instance 251 is freed 252 253The scsi_device structure has had reference counting infrastructure added. 254This effectively spreads the ownership of struct scsi_device instances 255across the various SCSI layers which use them. Previously such instances 256were exclusively owned by the mid level. See the access functions declared 257towards the end of include/scsi/scsi_device.h . If an LLD wants to keep 258a copy of a pointer to a scsi_device instance it should use scsi_device_get() 259to bump its reference count. When it is finished with the pointer it can 260use scsi_device_put() to decrement its reference count (and potentially 261delete it). 262 263.. Note:: 264 265 struct Scsi_Host actually has 2 reference counts which are manipulated 266 in parallel by these functions. 267 268 269Conventions 270=========== 271First, Linus Torvalds's thoughts on C coding style can be found in the 272Documentation/process/coding-style.rst file. 273 274Next, there is a movement to "outlaw" typedefs introducing synonyms for 275struct tags. Both can be still found in the SCSI subsystem, but 276the typedefs have been moved to a single file, scsi_typedefs.h to 277make their future removal easier, for example: 278"typedef struct scsi_cmnd Scsi_Cmnd;" 279 280Also, most C99 enhancements are encouraged to the extent they are supported 281by the relevant gcc compilers. So C99 style structure and array 282initializers are encouraged where appropriate. Don't go too far, 283VLAs are not properly supported yet. An exception to this is the use of 284``//`` style comments; ``/*...*/`` comments are still preferred in Linux. 285 286Well written, tested and documented code, need not be re-formatted to 287comply with the above conventions. For example, the aic7xxx driver 288comes to Linux from FreeBSD and Adaptec's own labs. No doubt FreeBSD 289and Adaptec have their own coding conventions. 290 291 292Mid level supplied functions 293============================ 294These functions are supplied by the SCSI mid level for use by LLDs. 295The names (i.e. entry points) of these functions are exported 296so an LLD that is a module can access them. The kernel will 297arrange for the SCSI mid level to be loaded and initialized before any LLD 298is initialized. The functions below are listed alphabetically and their 299names all start with ``scsi_``. 300 301Summary: 302 303 - scsi_add_device - creates new scsi device (lu) instance 304 - scsi_add_host - perform sysfs registration and set up transport class 305 - scsi_change_queue_depth - change the queue depth on a SCSI device 306 - scsi_bios_ptable - return copy of block device's partition table 307 - scsi_block_requests - prevent further commands being queued to given host 308 - scsi_host_alloc - return a new scsi_host instance whose refcount==1 309 - scsi_host_get - increments Scsi_Host instance's refcount 310 - scsi_host_put - decrements Scsi_Host instance's refcount (free if 0) 311 - scsi_register - create and register a scsi host adapter instance. 312 - scsi_remove_device - detach and remove a SCSI device 313 - scsi_remove_host - detach and remove all SCSI devices owned by host 314 - scsi_report_bus_reset - report scsi _bus_ reset observed 315 - scsi_scan_host - scan SCSI bus 316 - scsi_track_queue_full - track successive QUEUE_FULL events 317 - scsi_unblock_requests - allow further commands to be queued to given host 318 - scsi_unregister - [calls scsi_host_put()] 319 320 321Details:: 322 323 /** 324 * scsi_add_device - creates new scsi device (lu) instance 325 * @shost: pointer to scsi host instance 326 * @channel: channel number (rarely other than 0) 327 * @id: target id number 328 * @lun: logical unit number 329 * 330 * Returns pointer to new struct scsi_device instance or 331 * ERR_PTR(-ENODEV) (or some other bent pointer) if something is 332 * wrong (e.g. no lu responds at given address) 333 * 334 * Might block: yes 335 * 336 * Notes: This call is usually performed internally during a scsi 337 * bus scan when an HBA is added (i.e. scsi_scan_host()). So it 338 * should only be called if the HBA becomes aware of a new scsi 339 * device (lu) after scsi_scan_host() has completed. If successful 340 * this call can lead to slave_alloc() and slave_configure() callbacks 341 * into the LLD. 342 * 343 * Defined in: drivers/scsi/scsi_scan.c 344 **/ 345 struct scsi_device * scsi_add_device(struct Scsi_Host *shost, 346 unsigned int channel, 347 unsigned int id, unsigned int lun) 348 349 350 /** 351 * scsi_add_host - perform sysfs registration and set up transport class 352 * @shost: pointer to scsi host instance 353 * @dev: pointer to struct device of type scsi class 354 * 355 * Returns 0 on success, negative errno of failure (e.g. -ENOMEM) 356 * 357 * Might block: no 358 * 359 * Notes: Only required in "hotplug initialization model" after a 360 * successful call to scsi_host_alloc(). This function does not 361 * scan the bus; this can be done by calling scsi_scan_host() or 362 * in some other transport-specific way. The LLD must set up 363 * the transport template before calling this function and may only 364 * access the transport class data after this function has been called. 365 * 366 * Defined in: drivers/scsi/hosts.c 367 **/ 368 int scsi_add_host(struct Scsi_Host *shost, struct device * dev) 369 370 371 /** 372 * scsi_change_queue_depth - allow LLD to change queue depth on a SCSI device 373 * @sdev: pointer to SCSI device to change queue depth on 374 * @tags Number of tags allowed if tagged queuing enabled, 375 * or number of commands the LLD can queue up 376 * in non-tagged mode (as per cmd_per_lun). 377 * 378 * Returns nothing 379 * 380 * Might block: no 381 * 382 * Notes: Can be invoked any time on a SCSI device controlled by this 383 * LLD. [Specifically during and after slave_configure() and prior to 384 * slave_destroy().] Can safely be invoked from interrupt code. 385 * 386 * Defined in: drivers/scsi/scsi.c [see source code for more notes] 387 * 388 **/ 389 int scsi_change_queue_depth(struct scsi_device *sdev, int tags) 390 391 392 /** 393 * scsi_bios_ptable - return copy of block device's partition table 394 * @dev: pointer to block device 395 * 396 * Returns pointer to partition table, or NULL for failure 397 * 398 * Might block: yes 399 * 400 * Notes: Caller owns memory returned (free with kfree() ) 401 * 402 * Defined in: drivers/scsi/scsicam.c 403 **/ 404 unsigned char *scsi_bios_ptable(struct block_device *dev) 405 406 407 /** 408 * scsi_block_requests - prevent further commands being queued to given host 409 * 410 * @shost: pointer to host to block commands on 411 * 412 * Returns nothing 413 * 414 * Might block: no 415 * 416 * Notes: There is no timer nor any other means by which the requests 417 * get unblocked other than the LLD calling scsi_unblock_requests(). 418 * 419 * Defined in: drivers/scsi/scsi_lib.c 420 **/ 421 void scsi_block_requests(struct Scsi_Host * shost) 422 423 424 /** 425 * scsi_host_alloc - create a scsi host adapter instance and perform basic 426 * initialization. 427 * @sht: pointer to scsi host template 428 * @privsize: extra bytes to allocate in hostdata array (which is the 429 * last member of the returned Scsi_Host instance) 430 * 431 * Returns pointer to new Scsi_Host instance or NULL on failure 432 * 433 * Might block: yes 434 * 435 * Notes: When this call returns to the LLD, the SCSI bus scan on 436 * this host has _not_ yet been done. 437 * The hostdata array (by default zero length) is a per host scratch 438 * area for the LLD's exclusive use. 439 * Both associated refcounting objects have their refcount set to 1. 440 * Full registration (in sysfs) and a bus scan are performed later when 441 * scsi_add_host() and scsi_scan_host() are called. 442 * 443 * Defined in: drivers/scsi/hosts.c . 444 **/ 445 struct Scsi_Host * scsi_host_alloc(struct scsi_host_template * sht, 446 int privsize) 447 448 449 /** 450 * scsi_host_get - increment Scsi_Host instance refcount 451 * @shost: pointer to struct Scsi_Host instance 452 * 453 * Returns nothing 454 * 455 * Might block: currently may block but may be changed to not block 456 * 457 * Notes: Actually increments the counts in two sub-objects 458 * 459 * Defined in: drivers/scsi/hosts.c 460 **/ 461 void scsi_host_get(struct Scsi_Host *shost) 462 463 464 /** 465 * scsi_host_put - decrement Scsi_Host instance refcount, free if 0 466 * @shost: pointer to struct Scsi_Host instance 467 * 468 * Returns nothing 469 * 470 * Might block: currently may block but may be changed to not block 471 * 472 * Notes: Actually decrements the counts in two sub-objects. If the 473 * latter refcount reaches 0, the Scsi_Host instance is freed. 474 * The LLD need not worry exactly when the Scsi_Host instance is 475 * freed, it just shouldn't access the instance after it has balanced 476 * out its refcount usage. 477 * 478 * Defined in: drivers/scsi/hosts.c 479 **/ 480 void scsi_host_put(struct Scsi_Host *shost) 481 482 483 /** 484 * scsi_register - create and register a scsi host adapter instance. 485 * @sht: pointer to scsi host template 486 * @privsize: extra bytes to allocate in hostdata array (which is the 487 * last member of the returned Scsi_Host instance) 488 * 489 * Returns pointer to new Scsi_Host instance or NULL on failure 490 * 491 * Might block: yes 492 * 493 * Notes: When this call returns to the LLD, the SCSI bus scan on 494 * this host has _not_ yet been done. 495 * The hostdata array (by default zero length) is a per host scratch 496 * area for the LLD. 497 * 498 * Defined in: drivers/scsi/hosts.c . 499 **/ 500 struct Scsi_Host * scsi_register(struct scsi_host_template * sht, 501 int privsize) 502 503 504 /** 505 * scsi_remove_device - detach and remove a SCSI device 506 * @sdev: a pointer to a scsi device instance 507 * 508 * Returns value: 0 on success, -EINVAL if device not attached 509 * 510 * Might block: yes 511 * 512 * Notes: If an LLD becomes aware that a scsi device (lu) has 513 * been removed but its host is still present then it can request 514 * the removal of that scsi device. If successful this call will 515 * lead to the slave_destroy() callback being invoked. sdev is an 516 * invalid pointer after this call. 517 * 518 * Defined in: drivers/scsi/scsi_sysfs.c . 519 **/ 520 int scsi_remove_device(struct scsi_device *sdev) 521 522 523 /** 524 * scsi_remove_host - detach and remove all SCSI devices owned by host 525 * @shost: a pointer to a scsi host instance 526 * 527 * Returns value: 0 on success, 1 on failure (e.g. LLD busy ??) 528 * 529 * Might block: yes 530 * 531 * Notes: Should only be invoked if the "hotplug initialization 532 * model" is being used. It should be called _prior_ to 533 * scsi_unregister(). 534 * 535 * Defined in: drivers/scsi/hosts.c . 536 **/ 537 int scsi_remove_host(struct Scsi_Host *shost) 538 539 540 /** 541 * scsi_report_bus_reset - report scsi _bus_ reset observed 542 * @shost: a pointer to a scsi host involved 543 * @channel: channel (within) host on which scsi bus reset occurred 544 * 545 * Returns nothing 546 * 547 * Might block: no 548 * 549 * Notes: This only needs to be called if the reset is one which 550 * originates from an unknown location. Resets originated by the 551 * mid level itself don't need to call this, but there should be 552 * no harm. The main purpose of this is to make sure that a 553 * CHECK_CONDITION is properly treated. 554 * 555 * Defined in: drivers/scsi/scsi_error.c . 556 **/ 557 void scsi_report_bus_reset(struct Scsi_Host * shost, int channel) 558 559 560 /** 561 * scsi_scan_host - scan SCSI bus 562 * @shost: a pointer to a scsi host instance 563 * 564 * Might block: yes 565 * 566 * Notes: Should be called after scsi_add_host() 567 * 568 * Defined in: drivers/scsi/scsi_scan.c 569 **/ 570 void scsi_scan_host(struct Scsi_Host *shost) 571 572 573 /** 574 * scsi_track_queue_full - track successive QUEUE_FULL events on given 575 * device to determine if and when there is a need 576 * to adjust the queue depth on the device. 577 * @sdev: pointer to SCSI device instance 578 * @depth: Current number of outstanding SCSI commands on this device, 579 * not counting the one returned as QUEUE_FULL. 580 * 581 * Returns 0 - no change needed 582 * >0 - adjust queue depth to this new depth 583 * -1 - drop back to untagged operation using host->cmd_per_lun 584 * as the untagged command depth 585 * 586 * Might block: no 587 * 588 * Notes: LLDs may call this at any time and we will do "The Right 589 * Thing"; interrupt context safe. 590 * 591 * Defined in: drivers/scsi/scsi.c . 592 **/ 593 int scsi_track_queue_full(struct scsi_device *sdev, int depth) 594 595 596 /** 597 * scsi_unblock_requests - allow further commands to be queued to given host 598 * 599 * @shost: pointer to host to unblock commands on 600 * 601 * Returns nothing 602 * 603 * Might block: no 604 * 605 * Defined in: drivers/scsi/scsi_lib.c . 606 **/ 607 void scsi_unblock_requests(struct Scsi_Host * shost) 608 609 610 /** 611 * scsi_unregister - unregister and free memory used by host instance 612 * @shp: pointer to scsi host instance to unregister. 613 * 614 * Returns nothing 615 * 616 * Might block: no 617 * 618 * Notes: Should not be invoked if the "hotplug initialization 619 * model" is being used. Called internally by exit_this_scsi_driver() 620 * in the "passive initialization model". Hence a LLD has no need to 621 * call this function directly. 622 * 623 * Defined in: drivers/scsi/hosts.c . 624 **/ 625 void scsi_unregister(struct Scsi_Host * shp) 626 627 628 629 630Interface Functions 631=================== 632Interface functions are supplied (defined) by LLDs and their function 633pointers are placed in an instance of struct scsi_host_template which 634is passed to scsi_host_alloc() [or scsi_register() / init_this_scsi_driver()]. 635Some are mandatory. Interface functions should be declared static. The 636accepted convention is that driver "xyz" will declare its slave_configure() 637function as:: 638 639 static int xyz_slave_configure(struct scsi_device * sdev); 640 641and so forth for all interface functions listed below. 642 643A pointer to this function should be placed in the 'slave_configure' member 644of a "struct scsi_host_template" instance. A pointer to such an instance 645should be passed to the mid level's scsi_host_alloc() [or scsi_register() / 646init_this_scsi_driver()]. 647 648The interface functions are also described in the include/scsi/scsi_host.h 649file immediately above their definition point in "struct scsi_host_template". 650In some cases more detail is given in scsi_host.h than below. 651 652The interface functions are listed below in alphabetical order. 653 654Summary: 655 656 - bios_param - fetch head, sector, cylinder info for a disk 657 - eh_timed_out - notify the host that a command timer expired 658 - eh_abort_handler - abort given command 659 - eh_bus_reset_handler - issue SCSI bus reset 660 - eh_device_reset_handler - issue SCSI device reset 661 - eh_host_reset_handler - reset host (host bus adapter) 662 - info - supply information about given host 663 - ioctl - driver can respond to ioctls 664 - proc_info - supports /proc/scsi/{driver_name}/{host_no} 665 - queuecommand - queue scsi command, invoke 'done' on completion 666 - slave_alloc - prior to any commands being sent to a new device 667 - slave_configure - driver fine tuning for given device after attach 668 - slave_destroy - given device is about to be shut down 669 670 671Details:: 672 673 /** 674 * bios_param - fetch head, sector, cylinder info for a disk 675 * @sdev: pointer to scsi device context (defined in 676 * include/scsi/scsi_device.h) 677 * @bdev: pointer to block device context (defined in fs.h) 678 * @capacity: device size (in 512 byte sectors) 679 * @params: three element array to place output: 680 * params[0] number of heads (max 255) 681 * params[1] number of sectors (max 63) 682 * params[2] number of cylinders 683 * 684 * Return value is ignored 685 * 686 * Locks: none 687 * 688 * Calling context: process (sd) 689 * 690 * Notes: an arbitrary geometry (based on READ CAPACITY) is used 691 * if this function is not provided. The params array is 692 * pre-initialized with made up values just in case this function 693 * doesn't output anything. 694 * 695 * Optionally defined in: LLD 696 **/ 697 int bios_param(struct scsi_device * sdev, struct block_device *bdev, 698 sector_t capacity, int params[3]) 699 700 701 /** 702 * eh_timed_out - The timer for the command has just fired 703 * @scp: identifies command timing out 704 * 705 * Returns: 706 * 707 * EH_HANDLED: I fixed the error, please complete the command 708 * EH_RESET_TIMER: I need more time, reset the timer and 709 * begin counting again 710 * EH_NOT_HANDLED Begin normal error recovery 711 * 712 * 713 * Locks: None held 714 * 715 * Calling context: interrupt 716 * 717 * Notes: This is to give the LLD an opportunity to do local recovery. 718 * This recovery is limited to determining if the outstanding command 719 * will ever complete. You may not abort and restart the command from 720 * this callback. 721 * 722 * Optionally defined in: LLD 723 **/ 724 int eh_timed_out(struct scsi_cmnd * scp) 725 726 727 /** 728 * eh_abort_handler - abort command associated with scp 729 * @scp: identifies command to be aborted 730 * 731 * Returns SUCCESS if command aborted else FAILED 732 * 733 * Locks: None held 734 * 735 * Calling context: kernel thread 736 * 737 * Notes: If 'no_async_abort' is defined this callback 738 * will be invoked from scsi_eh thread. No other commands 739 * will then be queued on current host during eh. 740 * Otherwise it will be called whenever scsi_times_out() 741 * is called due to a command timeout. 742 * 743 * Optionally defined in: LLD 744 **/ 745 int eh_abort_handler(struct scsi_cmnd * scp) 746 747 748 /** 749 * eh_bus_reset_handler - issue SCSI bus reset 750 * @scp: SCSI bus that contains this device should be reset 751 * 752 * Returns SUCCESS if command aborted else FAILED 753 * 754 * Locks: None held 755 * 756 * Calling context: kernel thread 757 * 758 * Notes: Invoked from scsi_eh thread. No other commands will be 759 * queued on current host during eh. 760 * 761 * Optionally defined in: LLD 762 **/ 763 int eh_bus_reset_handler(struct scsi_cmnd * scp) 764 765 766 /** 767 * eh_device_reset_handler - issue SCSI device reset 768 * @scp: identifies SCSI device to be reset 769 * 770 * Returns SUCCESS if command aborted else FAILED 771 * 772 * Locks: None held 773 * 774 * Calling context: kernel thread 775 * 776 * Notes: Invoked from scsi_eh thread. No other commands will be 777 * queued on current host during eh. 778 * 779 * Optionally defined in: LLD 780 **/ 781 int eh_device_reset_handler(struct scsi_cmnd * scp) 782 783 784 /** 785 * eh_host_reset_handler - reset host (host bus adapter) 786 * @scp: SCSI host that contains this device should be reset 787 * 788 * Returns SUCCESS if command aborted else FAILED 789 * 790 * Locks: None held 791 * 792 * Calling context: kernel thread 793 * 794 * Notes: Invoked from scsi_eh thread. No other commands will be 795 * queued on current host during eh. 796 * With the default eh_strategy in place, if none of the _abort_, 797 * _device_reset_, _bus_reset_ or this eh handler function are 798 * defined (or they all return FAILED) then the device in question 799 * will be set offline whenever eh is invoked. 800 * 801 * Optionally defined in: LLD 802 **/ 803 int eh_host_reset_handler(struct scsi_cmnd * scp) 804 805 806 /** 807 * info - supply information about given host: driver name plus data 808 * to distinguish given host 809 * @shp: host to supply information about 810 * 811 * Return ASCII null terminated string. [This driver is assumed to 812 * manage the memory pointed to and maintain it, typically for the 813 * lifetime of this host.] 814 * 815 * Locks: none 816 * 817 * Calling context: process 818 * 819 * Notes: Often supplies PCI or ISA information such as IO addresses 820 * and interrupt numbers. If not supplied struct Scsi_Host::name used 821 * instead. It is assumed the returned information fits on one line 822 * (i.e. does not included embedded newlines). 823 * The SCSI_IOCTL_PROBE_HOST ioctl yields the string returned by this 824 * function (or struct Scsi_Host::name if this function is not 825 * available). 826 * In a similar manner, init_this_scsi_driver() outputs to the console 827 * each host's "info" (or name) for the driver it is registering. 828 * Also if proc_info() is not supplied, the output of this function 829 * is used instead. 830 * 831 * Optionally defined in: LLD 832 **/ 833 const char * info(struct Scsi_Host * shp) 834 835 836 /** 837 * ioctl - driver can respond to ioctls 838 * @sdp: device that ioctl was issued for 839 * @cmd: ioctl number 840 * @arg: pointer to read or write data from. Since it points to 841 * user space, should use appropriate kernel functions 842 * (e.g. copy_from_user() ). In the Unix style this argument 843 * can also be viewed as an unsigned long. 844 * 845 * Returns negative "errno" value when there is a problem. 0 or a 846 * positive value indicates success and is returned to the user space. 847 * 848 * Locks: none 849 * 850 * Calling context: process 851 * 852 * Notes: The SCSI subsystem uses a "trickle down" ioctl model. 853 * The user issues an ioctl() against an upper level driver 854 * (e.g. /dev/sdc) and if the upper level driver doesn't recognize 855 * the 'cmd' then it is passed to the SCSI mid level. If the SCSI 856 * mid level does not recognize it, then the LLD that controls 857 * the device receives the ioctl. According to recent Unix standards 858 * unsupported ioctl() 'cmd' numbers should return -ENOTTY. 859 * 860 * Optionally defined in: LLD 861 **/ 862 int ioctl(struct scsi_device *sdp, int cmd, void *arg) 863 864 865 /** 866 * proc_info - supports /proc/scsi/{driver_name}/{host_no} 867 * @buffer: anchor point to output to (0==writeto1_read0) or fetch from 868 * (1==writeto1_read0). 869 * @start: where "interesting" data is written to. Ignored when 870 * 1==writeto1_read0. 871 * @offset: offset within buffer 0==writeto1_read0 is actually 872 * interested in. Ignored when 1==writeto1_read0 . 873 * @length: maximum (or actual) extent of buffer 874 * @host_no: host number of interest (struct Scsi_Host::host_no) 875 * @writeto1_read0: 1 -> data coming from user space towards driver 876 * (e.g. "echo some_string > /proc/scsi/xyz/2") 877 * 0 -> user what data from this driver 878 * (e.g. "cat /proc/scsi/xyz/2") 879 * 880 * Returns length when 1==writeto1_read0. Otherwise number of chars 881 * output to buffer past offset. 882 * 883 * Locks: none held 884 * 885 * Calling context: process 886 * 887 * Notes: Driven from scsi_proc.c which interfaces to proc_fs. proc_fs 888 * support can now be configured out of the scsi subsystem. 889 * 890 * Optionally defined in: LLD 891 **/ 892 int proc_info(char * buffer, char ** start, off_t offset, 893 int length, int host_no, int writeto1_read0) 894 895 896 /** 897 * queuecommand - queue scsi command, invoke scp->scsi_done on completion 898 * @shost: pointer to the scsi host object 899 * @scp: pointer to scsi command object 900 * 901 * Returns 0 on success. 902 * 903 * If there's a failure, return either: 904 * 905 * SCSI_MLQUEUE_DEVICE_BUSY if the device queue is full, or 906 * SCSI_MLQUEUE_HOST_BUSY if the entire host queue is full 907 * 908 * On both of these returns, the mid-layer will requeue the I/O 909 * 910 * - if the return is SCSI_MLQUEUE_DEVICE_BUSY, only that particular 911 * device will be paused, and it will be unpaused when a command to 912 * the device returns (or after a brief delay if there are no more 913 * outstanding commands to it). Commands to other devices continue 914 * to be processed normally. 915 * 916 * - if the return is SCSI_MLQUEUE_HOST_BUSY, all I/O to the host 917 * is paused and will be unpaused when any command returns from 918 * the host (or after a brief delay if there are no outstanding 919 * commands to the host). 920 * 921 * For compatibility with earlier versions of queuecommand, any 922 * other return value is treated the same as 923 * SCSI_MLQUEUE_HOST_BUSY. 924 * 925 * Other types of errors that are detected immediately may be 926 * flagged by setting scp->result to an appropriate value, 927 * invoking the scp->scsi_done callback, and then returning 0 928 * from this function. If the command is not performed 929 * immediately (and the LLD is starting (or will start) the given 930 * command) then this function should place 0 in scp->result and 931 * return 0. 932 * 933 * Command ownership. If the driver returns zero, it owns the 934 * command and must take responsibility for ensuring the 935 * scp->scsi_done callback is executed. Note: the driver may 936 * call scp->scsi_done before returning zero, but after it has 937 * called scp->scsi_done, it may not return any value other than 938 * zero. If the driver makes a non-zero return, it must not 939 * execute the command's scsi_done callback at any time. 940 * 941 * Locks: up to and including 2.6.36, struct Scsi_Host::host_lock 942 * held on entry (with "irqsave") and is expected to be 943 * held on return. From 2.6.37 onwards, queuecommand is 944 * called without any locks held. 945 * 946 * Calling context: in interrupt (soft irq) or process context 947 * 948 * Notes: This function should be relatively fast. Normally it 949 * will not wait for IO to complete. Hence the scp->scsi_done 950 * callback is invoked (often directly from an interrupt service 951 * routine) some time after this function has returned. In some 952 * cases (e.g. pseudo adapter drivers that manufacture the 953 * response to a SCSI INQUIRY) the scp->scsi_done callback may be 954 * invoked before this function returns. If the scp->scsi_done 955 * callback is not invoked within a certain period the SCSI mid 956 * level will commence error processing. If a status of CHECK 957 * CONDITION is placed in "result" when the scp->scsi_done 958 * callback is invoked, then the LLD driver should perform 959 * autosense and fill in the struct scsi_cmnd::sense_buffer 960 * array. The scsi_cmnd::sense_buffer array is zeroed prior to 961 * the mid level queuing a command to an LLD. 962 * 963 * Defined in: LLD 964 **/ 965 int queuecommand(struct Scsi_Host *shost, struct scsi_cmnd * scp) 966 967 968 /** 969 * slave_alloc - prior to any commands being sent to a new device 970 * (i.e. just prior to scan) this call is made 971 * @sdp: pointer to new device (about to be scanned) 972 * 973 * Returns 0 if ok. Any other return is assumed to be an error and 974 * the device is ignored. 975 * 976 * Locks: none 977 * 978 * Calling context: process 979 * 980 * Notes: Allows the driver to allocate any resources for a device 981 * prior to its initial scan. The corresponding scsi device may not 982 * exist but the mid level is just about to scan for it (i.e. send 983 * and INQUIRY command plus ...). If a device is found then 984 * slave_configure() will be called while if a device is not found 985 * slave_destroy() is called. 986 * For more details see the include/scsi/scsi_host.h file. 987 * 988 * Optionally defined in: LLD 989 **/ 990 int slave_alloc(struct scsi_device *sdp) 991 992 993 /** 994 * slave_configure - driver fine tuning for given device just after it 995 * has been first scanned (i.e. it responded to an 996 * INQUIRY) 997 * @sdp: device that has just been attached 998 * 999 * Returns 0 if ok. Any other return is assumed to be an error and 1000 * the device is taken offline. [offline devices will _not_ have 1001 * slave_destroy() called on them so clean up resources.] 1002 * 1003 * Locks: none 1004 * 1005 * Calling context: process 1006 * 1007 * Notes: Allows the driver to inspect the response to the initial 1008 * INQUIRY done by the scanning code and take appropriate action. 1009 * For more details see the include/scsi/scsi_host.h file. 1010 * 1011 * Optionally defined in: LLD 1012 **/ 1013 int slave_configure(struct scsi_device *sdp) 1014 1015 1016 /** 1017 * slave_destroy - given device is about to be shut down. All 1018 * activity has ceased on this device. 1019 * @sdp: device that is about to be shut down 1020 * 1021 * Returns nothing 1022 * 1023 * Locks: none 1024 * 1025 * Calling context: process 1026 * 1027 * Notes: Mid level structures for given device are still in place 1028 * but are about to be torn down. Any per device resources allocated 1029 * by this driver for given device should be freed now. No further 1030 * commands will be sent for this sdp instance. [However the device 1031 * could be re-attached in the future in which case a new instance 1032 * of struct scsi_device would be supplied by future slave_alloc() 1033 * and slave_configure() calls.] 1034 * 1035 * Optionally defined in: LLD 1036 **/ 1037 void slave_destroy(struct scsi_device *sdp) 1038 1039 1040 1041Data Structures 1042=============== 1043struct scsi_host_template 1044------------------------- 1045There is one "struct scsi_host_template" instance per LLD [#]_. It is 1046typically initialized as a file scope static in a driver's header file. That 1047way members that are not explicitly initialized will be set to 0 or NULL. 1048Member of interest: 1049 1050 name 1051 - name of driver (may contain spaces, please limit to 1052 less than 80 characters) 1053 1054 proc_name 1055 - name used in "/proc/scsi/<proc_name>/<host_no>" and 1056 by sysfs in one of its "drivers" directories. Hence 1057 "proc_name" should only contain characters acceptable 1058 to a Unix file name. 1059 1060 ``(*queuecommand)()`` 1061 - primary callback that the mid level uses to inject 1062 SCSI commands into an LLD. 1063 1064The structure is defined and commented in include/scsi/scsi_host.h 1065 1066.. [#] In extreme situations a single driver may have several instances 1067 if it controls several different classes of hardware (e.g. an LLD 1068 that handles both ISA and PCI cards and has a separate instance of 1069 struct scsi_host_template for each class). 1070 1071struct Scsi_Host 1072---------------- 1073There is one struct Scsi_Host instance per host (HBA) that an LLD 1074controls. The struct Scsi_Host structure has many members in common 1075with "struct scsi_host_template". When a new struct Scsi_Host instance 1076is created (in scsi_host_alloc() in hosts.c) those common members are 1077initialized from the driver's struct scsi_host_template instance. Members 1078of interest: 1079 1080 host_no 1081 - system wide unique number that is used for identifying 1082 this host. Issued in ascending order from 0. 1083 can_queue 1084 - must be greater than 0; do not send more than can_queue 1085 commands to the adapter. 1086 this_id 1087 - scsi id of host (scsi initiator) or -1 if not known 1088 sg_tablesize 1089 - maximum scatter gather elements allowed by host. 1090 Set this to SG_ALL or less to avoid chained SG lists. 1091 Must be at least 1. 1092 max_sectors 1093 - maximum number of sectors (usually 512 bytes) allowed 1094 in a single SCSI command. The default value of 0 leads 1095 to a setting of SCSI_DEFAULT_MAX_SECTORS (defined in 1096 scsi_host.h) which is currently set to 1024. So for a 1097 disk the maximum transfer size is 512 KB when max_sectors 1098 is not defined. Note that this size may not be sufficient 1099 for disk firmware uploads. 1100 cmd_per_lun 1101 - maximum number of commands that can be queued on devices 1102 controlled by the host. Overridden by LLD calls to 1103 scsi_change_queue_depth(). 1104 unchecked_isa_dma 1105 - 1=>only use bottom 16 MB of ram (ISA DMA addressing 1106 restriction), 0=>can use full 32 bit (or better) DMA 1107 address space 1108 no_async_abort 1109 - 1=>Asynchronous aborts are not supported 1110 - 0=>Timed-out commands will be aborted asynchronously 1111 hostt 1112 - pointer to driver's struct scsi_host_template from which 1113 this struct Scsi_Host instance was spawned 1114 hostt->proc_name 1115 - name of LLD. This is the driver name that sysfs uses 1116 transportt 1117 - pointer to driver's struct scsi_transport_template instance 1118 (if any). FC and SPI transports currently supported. 1119 sh_list 1120 - a double linked list of pointers to all struct Scsi_Host 1121 instances (currently ordered by ascending host_no) 1122 my_devices 1123 - a double linked list of pointers to struct scsi_device 1124 instances that belong to this host. 1125 hostdata[0] 1126 - area reserved for LLD at end of struct Scsi_Host. Size 1127 is set by the second argument (named 'xtr_bytes') to 1128 scsi_host_alloc() or scsi_register(). 1129 vendor_id 1130 - a unique value that identifies the vendor supplying 1131 the LLD for the Scsi_Host. Used most often in validating 1132 vendor-specific message requests. Value consists of an 1133 identifier type and a vendor-specific value. 1134 See scsi_netlink.h for a description of valid formats. 1135 1136The scsi_host structure is defined in include/scsi/scsi_host.h 1137 1138struct scsi_device 1139------------------ 1140Generally, there is one instance of this structure for each SCSI logical unit 1141on a host. Scsi devices connected to a host are uniquely identified by a 1142channel number, target id and logical unit number (lun). 1143The structure is defined in include/scsi/scsi_device.h 1144 1145struct scsi_cmnd 1146---------------- 1147Instances of this structure convey SCSI commands to the LLD and responses 1148back to the mid level. The SCSI mid level will ensure that no more SCSI 1149commands become queued against the LLD than are indicated by 1150scsi_change_queue_depth() (or struct Scsi_Host::cmd_per_lun). There will 1151be at least one instance of struct scsi_cmnd available for each SCSI device. 1152Members of interest: 1153 1154 cmnd 1155 - array containing SCSI command 1156 cmnd_len 1157 - length (in bytes) of SCSI command 1158 sc_data_direction 1159 - direction of data transfer in data phase. See 1160 "enum dma_data_direction" in include/linux/dma-mapping.h 1161 request_bufflen 1162 - number of data bytes to transfer (0 if no data phase) 1163 use_sg 1164 - ==0 -> no scatter gather list, hence transfer data 1165 to/from request_buffer 1166 - >0 -> scatter gather list (actually an array) in 1167 request_buffer with use_sg elements 1168 request_buffer 1169 - either contains data buffer or scatter gather list 1170 depending on the setting of use_sg. Scatter gather 1171 elements are defined by 'struct scatterlist' found 1172 in include/linux/scatterlist.h . 1173 done 1174 - function pointer that should be invoked by LLD when the 1175 SCSI command is completed (successfully or otherwise). 1176 Should only be called by an LLD if the LLD has accepted 1177 the command (i.e. queuecommand() returned or will return 1178 0). The LLD may invoke 'done' prior to queuecommand() 1179 finishing. 1180 result 1181 - should be set by LLD prior to calling 'done'. A value 1182 of 0 implies a successfully completed command (and all 1183 data (if any) has been transferred to or from the SCSI 1184 target device). 'result' is a 32 bit unsigned integer that 1185 can be viewed as 4 related bytes. The SCSI status value is 1186 in the LSB. See include/scsi/scsi.h status_byte(), 1187 msg_byte(), host_byte() and driver_byte() macros and 1188 related constants. 1189 sense_buffer 1190 - an array (maximum size: SCSI_SENSE_BUFFERSIZE bytes) that 1191 should be written when the SCSI status (LSB of 'result') 1192 is set to CHECK_CONDITION (2). When CHECK_CONDITION is 1193 set, if the top nibble of sense_buffer[0] has the value 7 1194 then the mid level will assume the sense_buffer array 1195 contains a valid SCSI sense buffer; otherwise the mid 1196 level will issue a REQUEST_SENSE SCSI command to 1197 retrieve the sense buffer. The latter strategy is error 1198 prone in the presence of command queuing so the LLD should 1199 always "auto-sense". 1200 device 1201 - pointer to scsi_device object that this command is 1202 associated with. 1203 resid 1204 - an LLD should set this signed integer to the requested 1205 transfer length (i.e. 'request_bufflen') less the number 1206 of bytes that are actually transferred. 'resid' is 1207 preset to 0 so an LLD can ignore it if it cannot detect 1208 underruns (overruns should be rare). If possible an LLD 1209 should set 'resid' prior to invoking 'done'. The most 1210 interesting case is data transfers from a SCSI target 1211 device (e.g. READs) that underrun. 1212 underflow 1213 - LLD should place (DID_ERROR << 16) in 'result' if 1214 actual number of bytes transferred is less than this 1215 figure. Not many LLDs implement this check and some that 1216 do just output an error message to the log rather than 1217 report a DID_ERROR. Better for an LLD to implement 1218 'resid'. 1219 1220It is recommended that a LLD set 'resid' on data transfers from a SCSI 1221target device (e.g. READs). It is especially important that 'resid' is set 1222when such data transfers have sense keys of MEDIUM ERROR and HARDWARE ERROR 1223(and possibly RECOVERED ERROR). In these cases if a LLD is in doubt how much 1224data has been received then the safest approach is to indicate no bytes have 1225been received. For example: to indicate that no valid data has been received 1226a LLD might use these helpers:: 1227 1228 scsi_set_resid(SCpnt, scsi_bufflen(SCpnt)); 1229 1230where 'SCpnt' is a pointer to a scsi_cmnd object. To indicate only three 512 1231bytes blocks has been received 'resid' could be set like this:: 1232 1233 scsi_set_resid(SCpnt, scsi_bufflen(SCpnt) - (3 * 512)); 1234 1235The scsi_cmnd structure is defined in include/scsi/scsi_cmnd.h 1236 1237 1238Locks 1239===== 1240Each struct Scsi_Host instance has a spin_lock called struct 1241Scsi_Host::default_lock which is initialized in scsi_host_alloc() [found in 1242hosts.c]. Within the same function the struct Scsi_Host::host_lock pointer 1243is initialized to point at default_lock. Thereafter lock and unlock 1244operations performed by the mid level use the struct Scsi_Host::host_lock 1245pointer. Previously drivers could override the host_lock pointer but 1246this is not allowed anymore. 1247 1248 1249Autosense 1250========= 1251Autosense (or auto-sense) is defined in the SAM-2 document as "the 1252automatic return of sense data to the application client coincident 1253with the completion of a SCSI command" when a status of CHECK CONDITION 1254occurs. LLDs should perform autosense. This should be done when the LLD 1255detects a CHECK CONDITION status by either: 1256 1257 a) instructing the SCSI protocol (e.g. SCSI Parallel Interface (SPI)) 1258 to perform an extra data in phase on such responses 1259 b) or, the LLD issuing a REQUEST SENSE command itself 1260 1261Either way, when a status of CHECK CONDITION is detected, the mid level 1262decides whether the LLD has performed autosense by checking struct 1263scsi_cmnd::sense_buffer[0] . If this byte has an upper nibble of 7 (or 0xf) 1264then autosense is assumed to have taken place. If it has another value (and 1265this byte is initialized to 0 before each command) then the mid level will 1266issue a REQUEST SENSE command. 1267 1268In the presence of queued commands the "nexus" that maintains sense 1269buffer data from the command that failed until a following REQUEST SENSE 1270may get out of synchronization. This is why it is best for the LLD 1271to perform autosense. 1272 1273 1274Changes since lk 2.4 series 1275=========================== 1276io_request_lock has been replaced by several finer grained locks. The lock 1277relevant to LLDs is struct Scsi_Host::host_lock and there is 1278one per SCSI host. 1279 1280The older error handling mechanism has been removed. This means the 1281LLD interface functions abort() and reset() have been removed. 1282The struct scsi_host_template::use_new_eh_code flag has been removed. 1283 1284In the 2.4 series the SCSI subsystem configuration descriptions were 1285aggregated with the configuration descriptions from all other Linux 1286subsystems in the Documentation/Configure.help file. In the 2.6 series, 1287the SCSI subsystem now has its own (much smaller) drivers/scsi/Kconfig 1288file that contains both configuration and help information. 1289 1290struct SHT has been renamed to struct scsi_host_template. 1291 1292Addition of the "hotplug initialization model" and many extra functions 1293to support it. 1294 1295 1296Credits 1297======= 1298The following people have contributed to this document: 1299 1300 - Mike Anderson <andmike at us dot ibm dot com> 1301 - James Bottomley <James dot Bottomley at hansenpartnership dot com> 1302 - Patrick Mansfield <patmans at us dot ibm dot com> 1303 - Christoph Hellwig <hch at infradead dot org> 1304 - Doug Ledford <dledford at redhat dot com> 1305 - Andries Brouwer <Andries dot Brouwer at cwi dot nl> 1306 - Randy Dunlap <rdunlap at xenotime dot net> 1307 - Alan Stern <stern at rowland dot harvard dot edu> 1308 1309 1310Douglas Gilbert 1311dgilbert at interlog dot com 1312 131321st September 2004 1314