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 274Also, most C99 enhancements are encouraged to the extent they are supported 275by the relevant gcc compilers. So C99 style structure and array 276initializers are encouraged where appropriate. Don't go too far, 277VLAs are not properly supported yet. An exception to this is the use of 278``//`` style comments; ``/*...*/`` comments are still preferred in Linux. 279 280Well written, tested and documented code, need not be re-formatted to 281comply with the above conventions. For example, the aic7xxx driver 282comes to Linux from FreeBSD and Adaptec's own labs. No doubt FreeBSD 283and Adaptec have their own coding conventions. 284 285 286Mid level supplied functions 287============================ 288These functions are supplied by the SCSI mid level for use by LLDs. 289The names (i.e. entry points) of these functions are exported 290so an LLD that is a module can access them. The kernel will 291arrange for the SCSI mid level to be loaded and initialized before any LLD 292is initialized. The functions below are listed alphabetically and their 293names all start with ``scsi_``. 294 295Summary: 296 297 - scsi_add_device - creates new scsi device (lu) instance 298 - scsi_add_host - perform sysfs registration and set up transport class 299 - scsi_change_queue_depth - change the queue depth on a SCSI device 300 - scsi_bios_ptable - return copy of block device's partition table 301 - scsi_block_requests - prevent further commands being queued to given host 302 - scsi_host_alloc - return a new scsi_host instance whose refcount==1 303 - scsi_host_get - increments Scsi_Host instance's refcount 304 - scsi_host_put - decrements Scsi_Host instance's refcount (free if 0) 305 - scsi_register - create and register a scsi host adapter instance. 306 - scsi_remove_device - detach and remove a SCSI device 307 - scsi_remove_host - detach and remove all SCSI devices owned by host 308 - scsi_report_bus_reset - report scsi _bus_ reset observed 309 - scsi_scan_host - scan SCSI bus 310 - scsi_track_queue_full - track successive QUEUE_FULL events 311 - scsi_unblock_requests - allow further commands to be queued to given host 312 - scsi_unregister - [calls scsi_host_put()] 313 314 315Details:: 316 317 /** 318 * scsi_add_device - creates new scsi device (lu) instance 319 * @shost: pointer to scsi host instance 320 * @channel: channel number (rarely other than 0) 321 * @id: target id number 322 * @lun: logical unit number 323 * 324 * Returns pointer to new struct scsi_device instance or 325 * ERR_PTR(-ENODEV) (or some other bent pointer) if something is 326 * wrong (e.g. no lu responds at given address) 327 * 328 * Might block: yes 329 * 330 * Notes: This call is usually performed internally during a scsi 331 * bus scan when an HBA is added (i.e. scsi_scan_host()). So it 332 * should only be called if the HBA becomes aware of a new scsi 333 * device (lu) after scsi_scan_host() has completed. If successful 334 * this call can lead to slave_alloc() and slave_configure() callbacks 335 * into the LLD. 336 * 337 * Defined in: drivers/scsi/scsi_scan.c 338 **/ 339 struct scsi_device * scsi_add_device(struct Scsi_Host *shost, 340 unsigned int channel, 341 unsigned int id, unsigned int lun) 342 343 344 /** 345 * scsi_add_host - perform sysfs registration and set up transport class 346 * @shost: pointer to scsi host instance 347 * @dev: pointer to struct device of type scsi class 348 * 349 * Returns 0 on success, negative errno of failure (e.g. -ENOMEM) 350 * 351 * Might block: no 352 * 353 * Notes: Only required in "hotplug initialization model" after a 354 * successful call to scsi_host_alloc(). This function does not 355 * scan the bus; this can be done by calling scsi_scan_host() or 356 * in some other transport-specific way. The LLD must set up 357 * the transport template before calling this function and may only 358 * access the transport class data after this function has been called. 359 * 360 * Defined in: drivers/scsi/hosts.c 361 **/ 362 int scsi_add_host(struct Scsi_Host *shost, struct device * dev) 363 364 365 /** 366 * scsi_change_queue_depth - allow LLD to change queue depth on a SCSI device 367 * @sdev: pointer to SCSI device to change queue depth on 368 * @tags Number of tags allowed if tagged queuing enabled, 369 * or number of commands the LLD can queue up 370 * in non-tagged mode (as per cmd_per_lun). 371 * 372 * Returns nothing 373 * 374 * Might block: no 375 * 376 * Notes: Can be invoked any time on a SCSI device controlled by this 377 * LLD. [Specifically during and after slave_configure() and prior to 378 * slave_destroy().] Can safely be invoked from interrupt code. 379 * 380 * Defined in: drivers/scsi/scsi.c [see source code for more notes] 381 * 382 **/ 383 int scsi_change_queue_depth(struct scsi_device *sdev, int tags) 384 385 386 /** 387 * scsi_bios_ptable - return copy of block device's partition table 388 * @dev: pointer to block device 389 * 390 * Returns pointer to partition table, or NULL for failure 391 * 392 * Might block: yes 393 * 394 * Notes: Caller owns memory returned (free with kfree() ) 395 * 396 * Defined in: drivers/scsi/scsicam.c 397 **/ 398 unsigned char *scsi_bios_ptable(struct block_device *dev) 399 400 401 /** 402 * scsi_block_requests - prevent further commands being queued to given host 403 * 404 * @shost: pointer to host to block commands on 405 * 406 * Returns nothing 407 * 408 * Might block: no 409 * 410 * Notes: There is no timer nor any other means by which the requests 411 * get unblocked other than the LLD calling scsi_unblock_requests(). 412 * 413 * Defined in: drivers/scsi/scsi_lib.c 414 **/ 415 void scsi_block_requests(struct Scsi_Host * shost) 416 417 418 /** 419 * scsi_host_alloc - create a scsi host adapter instance and perform basic 420 * initialization. 421 * @sht: pointer to scsi host template 422 * @privsize: extra bytes to allocate in hostdata array (which is the 423 * last member of the returned Scsi_Host instance) 424 * 425 * Returns pointer to new Scsi_Host instance or NULL on failure 426 * 427 * Might block: yes 428 * 429 * Notes: When this call returns to the LLD, the SCSI bus scan on 430 * this host has _not_ yet been done. 431 * The hostdata array (by default zero length) is a per host scratch 432 * area for the LLD's exclusive use. 433 * Both associated refcounting objects have their refcount set to 1. 434 * Full registration (in sysfs) and a bus scan are performed later when 435 * scsi_add_host() and scsi_scan_host() are called. 436 * 437 * Defined in: drivers/scsi/hosts.c . 438 **/ 439 struct Scsi_Host * scsi_host_alloc(struct scsi_host_template * sht, 440 int privsize) 441 442 443 /** 444 * scsi_host_get - increment Scsi_Host instance refcount 445 * @shost: pointer to struct Scsi_Host instance 446 * 447 * Returns nothing 448 * 449 * Might block: currently may block but may be changed to not block 450 * 451 * Notes: Actually increments the counts in two sub-objects 452 * 453 * Defined in: drivers/scsi/hosts.c 454 **/ 455 void scsi_host_get(struct Scsi_Host *shost) 456 457 458 /** 459 * scsi_host_put - decrement Scsi_Host instance refcount, free if 0 460 * @shost: pointer to struct Scsi_Host instance 461 * 462 * Returns nothing 463 * 464 * Might block: currently may block but may be changed to not block 465 * 466 * Notes: Actually decrements the counts in two sub-objects. If the 467 * latter refcount reaches 0, the Scsi_Host instance is freed. 468 * The LLD need not worry exactly when the Scsi_Host instance is 469 * freed, it just shouldn't access the instance after it has balanced 470 * out its refcount usage. 471 * 472 * Defined in: drivers/scsi/hosts.c 473 **/ 474 void scsi_host_put(struct Scsi_Host *shost) 475 476 477 /** 478 * scsi_register - create and register a scsi host adapter instance. 479 * @sht: pointer to scsi host template 480 * @privsize: extra bytes to allocate in hostdata array (which is the 481 * last member of the returned Scsi_Host instance) 482 * 483 * Returns pointer to new Scsi_Host instance or NULL on failure 484 * 485 * Might block: yes 486 * 487 * Notes: When this call returns to the LLD, the SCSI bus scan on 488 * this host has _not_ yet been done. 489 * The hostdata array (by default zero length) is a per host scratch 490 * area for the LLD. 491 * 492 * Defined in: drivers/scsi/hosts.c . 493 **/ 494 struct Scsi_Host * scsi_register(struct scsi_host_template * sht, 495 int privsize) 496 497 498 /** 499 * scsi_remove_device - detach and remove a SCSI device 500 * @sdev: a pointer to a scsi device instance 501 * 502 * Returns value: 0 on success, -EINVAL if device not attached 503 * 504 * Might block: yes 505 * 506 * Notes: If an LLD becomes aware that a scsi device (lu) has 507 * been removed but its host is still present then it can request 508 * the removal of that scsi device. If successful this call will 509 * lead to the slave_destroy() callback being invoked. sdev is an 510 * invalid pointer after this call. 511 * 512 * Defined in: drivers/scsi/scsi_sysfs.c . 513 **/ 514 int scsi_remove_device(struct scsi_device *sdev) 515 516 517 /** 518 * scsi_remove_host - detach and remove all SCSI devices owned by host 519 * @shost: a pointer to a scsi host instance 520 * 521 * Returns value: 0 on success, 1 on failure (e.g. LLD busy ??) 522 * 523 * Might block: yes 524 * 525 * Notes: Should only be invoked if the "hotplug initialization 526 * model" is being used. It should be called _prior_ to 527 * scsi_unregister(). 528 * 529 * Defined in: drivers/scsi/hosts.c . 530 **/ 531 int scsi_remove_host(struct Scsi_Host *shost) 532 533 534 /** 535 * scsi_report_bus_reset - report scsi _bus_ reset observed 536 * @shost: a pointer to a scsi host involved 537 * @channel: channel (within) host on which scsi bus reset occurred 538 * 539 * Returns nothing 540 * 541 * Might block: no 542 * 543 * Notes: This only needs to be called if the reset is one which 544 * originates from an unknown location. Resets originated by the 545 * mid level itself don't need to call this, but there should be 546 * no harm. The main purpose of this is to make sure that a 547 * CHECK_CONDITION is properly treated. 548 * 549 * Defined in: drivers/scsi/scsi_error.c . 550 **/ 551 void scsi_report_bus_reset(struct Scsi_Host * shost, int channel) 552 553 554 /** 555 * scsi_scan_host - scan SCSI bus 556 * @shost: a pointer to a scsi host instance 557 * 558 * Might block: yes 559 * 560 * Notes: Should be called after scsi_add_host() 561 * 562 * Defined in: drivers/scsi/scsi_scan.c 563 **/ 564 void scsi_scan_host(struct Scsi_Host *shost) 565 566 567 /** 568 * scsi_track_queue_full - track successive QUEUE_FULL events on given 569 * device to determine if and when there is a need 570 * to adjust the queue depth on the device. 571 * @sdev: pointer to SCSI device instance 572 * @depth: Current number of outstanding SCSI commands on this device, 573 * not counting the one returned as QUEUE_FULL. 574 * 575 * Returns 0 - no change needed 576 * >0 - adjust queue depth to this new depth 577 * -1 - drop back to untagged operation using host->cmd_per_lun 578 * as the untagged command depth 579 * 580 * Might block: no 581 * 582 * Notes: LLDs may call this at any time and we will do "The Right 583 * Thing"; interrupt context safe. 584 * 585 * Defined in: drivers/scsi/scsi.c . 586 **/ 587 int scsi_track_queue_full(struct scsi_device *sdev, int depth) 588 589 590 /** 591 * scsi_unblock_requests - allow further commands to be queued to given host 592 * 593 * @shost: pointer to host to unblock commands on 594 * 595 * Returns nothing 596 * 597 * Might block: no 598 * 599 * Defined in: drivers/scsi/scsi_lib.c . 600 **/ 601 void scsi_unblock_requests(struct Scsi_Host * shost) 602 603 604 /** 605 * scsi_unregister - unregister and free memory used by host instance 606 * @shp: pointer to scsi host instance to unregister. 607 * 608 * Returns nothing 609 * 610 * Might block: no 611 * 612 * Notes: Should not be invoked if the "hotplug initialization 613 * model" is being used. Called internally by exit_this_scsi_driver() 614 * in the "passive initialization model". Hence a LLD has no need to 615 * call this function directly. 616 * 617 * Defined in: drivers/scsi/hosts.c . 618 **/ 619 void scsi_unregister(struct Scsi_Host * shp) 620 621 622 623 624Interface Functions 625=================== 626Interface functions are supplied (defined) by LLDs and their function 627pointers are placed in an instance of struct scsi_host_template which 628is passed to scsi_host_alloc() [or scsi_register() / init_this_scsi_driver()]. 629Some are mandatory. Interface functions should be declared static. The 630accepted convention is that driver "xyz" will declare its slave_configure() 631function as:: 632 633 static int xyz_slave_configure(struct scsi_device * sdev); 634 635and so forth for all interface functions listed below. 636 637A pointer to this function should be placed in the 'slave_configure' member 638of a "struct scsi_host_template" instance. A pointer to such an instance 639should be passed to the mid level's scsi_host_alloc() [or scsi_register() / 640init_this_scsi_driver()]. 641 642The interface functions are also described in the include/scsi/scsi_host.h 643file immediately above their definition point in "struct scsi_host_template". 644In some cases more detail is given in scsi_host.h than below. 645 646The interface functions are listed below in alphabetical order. 647 648Summary: 649 650 - bios_param - fetch head, sector, cylinder info for a disk 651 - eh_timed_out - notify the host that a command timer expired 652 - eh_abort_handler - abort given command 653 - eh_bus_reset_handler - issue SCSI bus reset 654 - eh_device_reset_handler - issue SCSI device reset 655 - eh_host_reset_handler - reset host (host bus adapter) 656 - info - supply information about given host 657 - ioctl - driver can respond to ioctls 658 - proc_info - supports /proc/scsi/{driver_name}/{host_no} 659 - queuecommand - queue scsi command, invoke 'done' on completion 660 - slave_alloc - prior to any commands being sent to a new device 661 - slave_configure - driver fine tuning for given device after attach 662 - slave_destroy - given device is about to be shut down 663 664 665Details:: 666 667 /** 668 * bios_param - fetch head, sector, cylinder info for a disk 669 * @sdev: pointer to scsi device context (defined in 670 * include/scsi/scsi_device.h) 671 * @bdev: pointer to block device context (defined in fs.h) 672 * @capacity: device size (in 512 byte sectors) 673 * @params: three element array to place output: 674 * params[0] number of heads (max 255) 675 * params[1] number of sectors (max 63) 676 * params[2] number of cylinders 677 * 678 * Return value is ignored 679 * 680 * Locks: none 681 * 682 * Calling context: process (sd) 683 * 684 * Notes: an arbitrary geometry (based on READ CAPACITY) is used 685 * if this function is not provided. The params array is 686 * pre-initialized with made up values just in case this function 687 * doesn't output anything. 688 * 689 * Optionally defined in: LLD 690 **/ 691 int bios_param(struct scsi_device * sdev, struct block_device *bdev, 692 sector_t capacity, int params[3]) 693 694 695 /** 696 * eh_timed_out - The timer for the command has just fired 697 * @scp: identifies command timing out 698 * 699 * Returns: 700 * 701 * EH_HANDLED: I fixed the error, please complete the command 702 * EH_RESET_TIMER: I need more time, reset the timer and 703 * begin counting again 704 * EH_NOT_HANDLED Begin normal error recovery 705 * 706 * 707 * Locks: None held 708 * 709 * Calling context: interrupt 710 * 711 * Notes: This is to give the LLD an opportunity to do local recovery. 712 * This recovery is limited to determining if the outstanding command 713 * will ever complete. You may not abort and restart the command from 714 * this callback. 715 * 716 * Optionally defined in: LLD 717 **/ 718 int eh_timed_out(struct scsi_cmnd * scp) 719 720 721 /** 722 * eh_abort_handler - abort command associated with scp 723 * @scp: identifies command to be aborted 724 * 725 * Returns SUCCESS if command aborted else FAILED 726 * 727 * Locks: None held 728 * 729 * Calling context: kernel thread 730 * 731 * Notes: If 'no_async_abort' is defined this callback 732 * will be invoked from scsi_eh thread. No other commands 733 * will then be queued on current host during eh. 734 * Otherwise it will be called whenever scsi_times_out() 735 * is called due to a command timeout. 736 * 737 * Optionally defined in: LLD 738 **/ 739 int eh_abort_handler(struct scsi_cmnd * scp) 740 741 742 /** 743 * eh_bus_reset_handler - issue SCSI bus reset 744 * @scp: SCSI bus that contains this device should be reset 745 * 746 * Returns SUCCESS if command aborted else FAILED 747 * 748 * Locks: None held 749 * 750 * Calling context: kernel thread 751 * 752 * Notes: Invoked from scsi_eh thread. No other commands will be 753 * queued on current host during eh. 754 * 755 * Optionally defined in: LLD 756 **/ 757 int eh_bus_reset_handler(struct scsi_cmnd * scp) 758 759 760 /** 761 * eh_device_reset_handler - issue SCSI device reset 762 * @scp: identifies SCSI device to be reset 763 * 764 * Returns SUCCESS if command aborted else FAILED 765 * 766 * Locks: None held 767 * 768 * Calling context: kernel thread 769 * 770 * Notes: Invoked from scsi_eh thread. No other commands will be 771 * queued on current host during eh. 772 * 773 * Optionally defined in: LLD 774 **/ 775 int eh_device_reset_handler(struct scsi_cmnd * scp) 776 777 778 /** 779 * eh_host_reset_handler - reset host (host bus adapter) 780 * @scp: SCSI host that contains this device should be reset 781 * 782 * Returns SUCCESS if command aborted else FAILED 783 * 784 * Locks: None held 785 * 786 * Calling context: kernel thread 787 * 788 * Notes: Invoked from scsi_eh thread. No other commands will be 789 * queued on current host during eh. 790 * With the default eh_strategy in place, if none of the _abort_, 791 * _device_reset_, _bus_reset_ or this eh handler function are 792 * defined (or they all return FAILED) then the device in question 793 * will be set offline whenever eh is invoked. 794 * 795 * Optionally defined in: LLD 796 **/ 797 int eh_host_reset_handler(struct scsi_cmnd * scp) 798 799 800 /** 801 * info - supply information about given host: driver name plus data 802 * to distinguish given host 803 * @shp: host to supply information about 804 * 805 * Return ASCII null terminated string. [This driver is assumed to 806 * manage the memory pointed to and maintain it, typically for the 807 * lifetime of this host.] 808 * 809 * Locks: none 810 * 811 * Calling context: process 812 * 813 * Notes: Often supplies PCI or ISA information such as IO addresses 814 * and interrupt numbers. If not supplied struct Scsi_Host::name used 815 * instead. It is assumed the returned information fits on one line 816 * (i.e. does not included embedded newlines). 817 * The SCSI_IOCTL_PROBE_HOST ioctl yields the string returned by this 818 * function (or struct Scsi_Host::name if this function is not 819 * available). 820 * In a similar manner, init_this_scsi_driver() outputs to the console 821 * each host's "info" (or name) for the driver it is registering. 822 * Also if proc_info() is not supplied, the output of this function 823 * is used instead. 824 * 825 * Optionally defined in: LLD 826 **/ 827 const char * info(struct Scsi_Host * shp) 828 829 830 /** 831 * ioctl - driver can respond to ioctls 832 * @sdp: device that ioctl was issued for 833 * @cmd: ioctl number 834 * @arg: pointer to read or write data from. Since it points to 835 * user space, should use appropriate kernel functions 836 * (e.g. copy_from_user() ). In the Unix style this argument 837 * can also be viewed as an unsigned long. 838 * 839 * Returns negative "errno" value when there is a problem. 0 or a 840 * positive value indicates success and is returned to the user space. 841 * 842 * Locks: none 843 * 844 * Calling context: process 845 * 846 * Notes: The SCSI subsystem uses a "trickle down" ioctl model. 847 * The user issues an ioctl() against an upper level driver 848 * (e.g. /dev/sdc) and if the upper level driver doesn't recognize 849 * the 'cmd' then it is passed to the SCSI mid level. If the SCSI 850 * mid level does not recognize it, then the LLD that controls 851 * the device receives the ioctl. According to recent Unix standards 852 * unsupported ioctl() 'cmd' numbers should return -ENOTTY. 853 * 854 * Optionally defined in: LLD 855 **/ 856 int ioctl(struct scsi_device *sdp, int cmd, void *arg) 857 858 859 /** 860 * proc_info - supports /proc/scsi/{driver_name}/{host_no} 861 * @buffer: anchor point to output to (0==writeto1_read0) or fetch from 862 * (1==writeto1_read0). 863 * @start: where "interesting" data is written to. Ignored when 864 * 1==writeto1_read0. 865 * @offset: offset within buffer 0==writeto1_read0 is actually 866 * interested in. Ignored when 1==writeto1_read0 . 867 * @length: maximum (or actual) extent of buffer 868 * @host_no: host number of interest (struct Scsi_Host::host_no) 869 * @writeto1_read0: 1 -> data coming from user space towards driver 870 * (e.g. "echo some_string > /proc/scsi/xyz/2") 871 * 0 -> user what data from this driver 872 * (e.g. "cat /proc/scsi/xyz/2") 873 * 874 * Returns length when 1==writeto1_read0. Otherwise number of chars 875 * output to buffer past offset. 876 * 877 * Locks: none held 878 * 879 * Calling context: process 880 * 881 * Notes: Driven from scsi_proc.c which interfaces to proc_fs. proc_fs 882 * support can now be configured out of the scsi subsystem. 883 * 884 * Optionally defined in: LLD 885 **/ 886 int proc_info(char * buffer, char ** start, off_t offset, 887 int length, int host_no, int writeto1_read0) 888 889 890 /** 891 * queuecommand - queue scsi command, invoke scp->scsi_done on completion 892 * @shost: pointer to the scsi host object 893 * @scp: pointer to scsi command object 894 * 895 * Returns 0 on success. 896 * 897 * If there's a failure, return either: 898 * 899 * SCSI_MLQUEUE_DEVICE_BUSY if the device queue is full, or 900 * SCSI_MLQUEUE_HOST_BUSY if the entire host queue is full 901 * 902 * On both of these returns, the mid-layer will requeue the I/O 903 * 904 * - if the return is SCSI_MLQUEUE_DEVICE_BUSY, only that particular 905 * device will be paused, and it will be unpaused when a command to 906 * the device returns (or after a brief delay if there are no more 907 * outstanding commands to it). Commands to other devices continue 908 * to be processed normally. 909 * 910 * - if the return is SCSI_MLQUEUE_HOST_BUSY, all I/O to the host 911 * is paused and will be unpaused when any command returns from 912 * the host (or after a brief delay if there are no outstanding 913 * commands to the host). 914 * 915 * For compatibility with earlier versions of queuecommand, any 916 * other return value is treated the same as 917 * SCSI_MLQUEUE_HOST_BUSY. 918 * 919 * Other types of errors that are detected immediately may be 920 * flagged by setting scp->result to an appropriate value, 921 * invoking the scp->scsi_done callback, and then returning 0 922 * from this function. If the command is not performed 923 * immediately (and the LLD is starting (or will start) the given 924 * command) then this function should place 0 in scp->result and 925 * return 0. 926 * 927 * Command ownership. If the driver returns zero, it owns the 928 * command and must take responsibility for ensuring the 929 * scp->scsi_done callback is executed. Note: the driver may 930 * call scp->scsi_done before returning zero, but after it has 931 * called scp->scsi_done, it may not return any value other than 932 * zero. If the driver makes a non-zero return, it must not 933 * execute the command's scsi_done callback at any time. 934 * 935 * Locks: up to and including 2.6.36, struct Scsi_Host::host_lock 936 * held on entry (with "irqsave") and is expected to be 937 * held on return. From 2.6.37 onwards, queuecommand is 938 * called without any locks held. 939 * 940 * Calling context: in interrupt (soft irq) or process context 941 * 942 * Notes: This function should be relatively fast. Normally it 943 * will not wait for IO to complete. Hence the scp->scsi_done 944 * callback is invoked (often directly from an interrupt service 945 * routine) some time after this function has returned. In some 946 * cases (e.g. pseudo adapter drivers that manufacture the 947 * response to a SCSI INQUIRY) the scp->scsi_done callback may be 948 * invoked before this function returns. If the scp->scsi_done 949 * callback is not invoked within a certain period the SCSI mid 950 * level will commence error processing. If a status of CHECK 951 * CONDITION is placed in "result" when the scp->scsi_done 952 * callback is invoked, then the LLD driver should perform 953 * autosense and fill in the struct scsi_cmnd::sense_buffer 954 * array. The scsi_cmnd::sense_buffer array is zeroed prior to 955 * the mid level queuing a command to an LLD. 956 * 957 * Defined in: LLD 958 **/ 959 int queuecommand(struct Scsi_Host *shost, struct scsi_cmnd * scp) 960 961 962 /** 963 * slave_alloc - prior to any commands being sent to a new device 964 * (i.e. just prior to scan) this call is made 965 * @sdp: pointer to new device (about to be scanned) 966 * 967 * Returns 0 if ok. Any other return is assumed to be an error and 968 * the device is ignored. 969 * 970 * Locks: none 971 * 972 * Calling context: process 973 * 974 * Notes: Allows the driver to allocate any resources for a device 975 * prior to its initial scan. The corresponding scsi device may not 976 * exist but the mid level is just about to scan for it (i.e. send 977 * and INQUIRY command plus ...). If a device is found then 978 * slave_configure() will be called while if a device is not found 979 * slave_destroy() is called. 980 * For more details see the include/scsi/scsi_host.h file. 981 * 982 * Optionally defined in: LLD 983 **/ 984 int slave_alloc(struct scsi_device *sdp) 985 986 987 /** 988 * slave_configure - driver fine tuning for given device just after it 989 * has been first scanned (i.e. it responded to an 990 * INQUIRY) 991 * @sdp: device that has just been attached 992 * 993 * Returns 0 if ok. Any other return is assumed to be an error and 994 * the device is taken offline. [offline devices will _not_ have 995 * slave_destroy() called on them so clean up resources.] 996 * 997 * Locks: none 998 * 999 * Calling context: process 1000 * 1001 * Notes: Allows the driver to inspect the response to the initial 1002 * INQUIRY done by the scanning code and take appropriate action. 1003 * For more details see the include/scsi/scsi_host.h file. 1004 * 1005 * Optionally defined in: LLD 1006 **/ 1007 int slave_configure(struct scsi_device *sdp) 1008 1009 1010 /** 1011 * slave_destroy - given device is about to be shut down. All 1012 * activity has ceased on this device. 1013 * @sdp: device that is about to be shut down 1014 * 1015 * Returns nothing 1016 * 1017 * Locks: none 1018 * 1019 * Calling context: process 1020 * 1021 * Notes: Mid level structures for given device are still in place 1022 * but are about to be torn down. Any per device resources allocated 1023 * by this driver for given device should be freed now. No further 1024 * commands will be sent for this sdp instance. [However the device 1025 * could be re-attached in the future in which case a new instance 1026 * of struct scsi_device would be supplied by future slave_alloc() 1027 * and slave_configure() calls.] 1028 * 1029 * Optionally defined in: LLD 1030 **/ 1031 void slave_destroy(struct scsi_device *sdp) 1032 1033 1034 1035Data Structures 1036=============== 1037struct scsi_host_template 1038------------------------- 1039There is one "struct scsi_host_template" instance per LLD [#]_. It is 1040typically initialized as a file scope static in a driver's header file. That 1041way members that are not explicitly initialized will be set to 0 or NULL. 1042Member of interest: 1043 1044 name 1045 - name of driver (may contain spaces, please limit to 1046 less than 80 characters) 1047 1048 proc_name 1049 - name used in "/proc/scsi/<proc_name>/<host_no>" and 1050 by sysfs in one of its "drivers" directories. Hence 1051 "proc_name" should only contain characters acceptable 1052 to a Unix file name. 1053 1054 ``(*queuecommand)()`` 1055 - primary callback that the mid level uses to inject 1056 SCSI commands into an LLD. 1057 1058The structure is defined and commented in include/scsi/scsi_host.h 1059 1060.. [#] In extreme situations a single driver may have several instances 1061 if it controls several different classes of hardware (e.g. an LLD 1062 that handles both ISA and PCI cards and has a separate instance of 1063 struct scsi_host_template for each class). 1064 1065struct Scsi_Host 1066---------------- 1067There is one struct Scsi_Host instance per host (HBA) that an LLD 1068controls. The struct Scsi_Host structure has many members in common 1069with "struct scsi_host_template". When a new struct Scsi_Host instance 1070is created (in scsi_host_alloc() in hosts.c) those common members are 1071initialized from the driver's struct scsi_host_template instance. Members 1072of interest: 1073 1074 host_no 1075 - system wide unique number that is used for identifying 1076 this host. Issued in ascending order from 0. 1077 can_queue 1078 - must be greater than 0; do not send more than can_queue 1079 commands to the adapter. 1080 this_id 1081 - scsi id of host (scsi initiator) or -1 if not known 1082 sg_tablesize 1083 - maximum scatter gather elements allowed by host. 1084 Set this to SG_ALL or less to avoid chained SG lists. 1085 Must be at least 1. 1086 max_sectors 1087 - maximum number of sectors (usually 512 bytes) allowed 1088 in a single SCSI command. The default value of 0 leads 1089 to a setting of SCSI_DEFAULT_MAX_SECTORS (defined in 1090 scsi_host.h) which is currently set to 1024. So for a 1091 disk the maximum transfer size is 512 KB when max_sectors 1092 is not defined. Note that this size may not be sufficient 1093 for disk firmware uploads. 1094 cmd_per_lun 1095 - maximum number of commands that can be queued on devices 1096 controlled by the host. Overridden by LLD calls to 1097 scsi_change_queue_depth(). 1098 no_async_abort 1099 - 1=>Asynchronous aborts are not supported 1100 - 0=>Timed-out commands will be aborted asynchronously 1101 hostt 1102 - pointer to driver's struct scsi_host_template from which 1103 this struct Scsi_Host instance was spawned 1104 hostt->proc_name 1105 - name of LLD. This is the driver name that sysfs uses 1106 transportt 1107 - pointer to driver's struct scsi_transport_template instance 1108 (if any). FC and SPI transports currently supported. 1109 sh_list 1110 - a double linked list of pointers to all struct Scsi_Host 1111 instances (currently ordered by ascending host_no) 1112 my_devices 1113 - a double linked list of pointers to struct scsi_device 1114 instances that belong to this host. 1115 hostdata[0] 1116 - area reserved for LLD at end of struct Scsi_Host. Size 1117 is set by the second argument (named 'xtr_bytes') to 1118 scsi_host_alloc() or scsi_register(). 1119 vendor_id 1120 - a unique value that identifies the vendor supplying 1121 the LLD for the Scsi_Host. Used most often in validating 1122 vendor-specific message requests. Value consists of an 1123 identifier type and a vendor-specific value. 1124 See scsi_netlink.h for a description of valid formats. 1125 1126The scsi_host structure is defined in include/scsi/scsi_host.h 1127 1128struct scsi_device 1129------------------ 1130Generally, there is one instance of this structure for each SCSI logical unit 1131on a host. Scsi devices connected to a host are uniquely identified by a 1132channel number, target id and logical unit number (lun). 1133The structure is defined in include/scsi/scsi_device.h 1134 1135struct scsi_cmnd 1136---------------- 1137Instances of this structure convey SCSI commands to the LLD and responses 1138back to the mid level. The SCSI mid level will ensure that no more SCSI 1139commands become queued against the LLD than are indicated by 1140scsi_change_queue_depth() (or struct Scsi_Host::cmd_per_lun). There will 1141be at least one instance of struct scsi_cmnd available for each SCSI device. 1142Members of interest: 1143 1144 cmnd 1145 - array containing SCSI command 1146 cmnd_len 1147 - length (in bytes) of SCSI command 1148 sc_data_direction 1149 - direction of data transfer in data phase. See 1150 "enum dma_data_direction" in include/linux/dma-mapping.h 1151 request_bufflen 1152 - number of data bytes to transfer (0 if no data phase) 1153 use_sg 1154 - ==0 -> no scatter gather list, hence transfer data 1155 to/from request_buffer 1156 - >0 -> scatter gather list (actually an array) in 1157 request_buffer with use_sg elements 1158 request_buffer 1159 - either contains data buffer or scatter gather list 1160 depending on the setting of use_sg. Scatter gather 1161 elements are defined by 'struct scatterlist' found 1162 in include/linux/scatterlist.h . 1163 done 1164 - function pointer that should be invoked by LLD when the 1165 SCSI command is completed (successfully or otherwise). 1166 Should only be called by an LLD if the LLD has accepted 1167 the command (i.e. queuecommand() returned or will return 1168 0). The LLD may invoke 'done' prior to queuecommand() 1169 finishing. 1170 result 1171 - should be set by LLD prior to calling 'done'. A value 1172 of 0 implies a successfully completed command (and all 1173 data (if any) has been transferred to or from the SCSI 1174 target device). 'result' is a 32 bit unsigned integer that 1175 can be viewed as 4 related bytes. The SCSI status value is 1176 in the LSB. See include/scsi/scsi.h status_byte(), 1177 msg_byte(), host_byte() and driver_byte() macros and 1178 related constants. 1179 sense_buffer 1180 - an array (maximum size: SCSI_SENSE_BUFFERSIZE bytes) that 1181 should be written when the SCSI status (LSB of 'result') 1182 is set to CHECK_CONDITION (2). When CHECK_CONDITION is 1183 set, if the top nibble of sense_buffer[0] has the value 7 1184 then the mid level will assume the sense_buffer array 1185 contains a valid SCSI sense buffer; otherwise the mid 1186 level will issue a REQUEST_SENSE SCSI command to 1187 retrieve the sense buffer. The latter strategy is error 1188 prone in the presence of command queuing so the LLD should 1189 always "auto-sense". 1190 device 1191 - pointer to scsi_device object that this command is 1192 associated with. 1193 resid 1194 - an LLD should set this signed integer to the requested 1195 transfer length (i.e. 'request_bufflen') less the number 1196 of bytes that are actually transferred. 'resid' is 1197 preset to 0 so an LLD can ignore it if it cannot detect 1198 underruns (overruns should be rare). If possible an LLD 1199 should set 'resid' prior to invoking 'done'. The most 1200 interesting case is data transfers from a SCSI target 1201 device (e.g. READs) that underrun. 1202 underflow 1203 - LLD should place (DID_ERROR << 16) in 'result' if 1204 actual number of bytes transferred is less than this 1205 figure. Not many LLDs implement this check and some that 1206 do just output an error message to the log rather than 1207 report a DID_ERROR. Better for an LLD to implement 1208 'resid'. 1209 1210It is recommended that a LLD set 'resid' on data transfers from a SCSI 1211target device (e.g. READs). It is especially important that 'resid' is set 1212when such data transfers have sense keys of MEDIUM ERROR and HARDWARE ERROR 1213(and possibly RECOVERED ERROR). In these cases if a LLD is in doubt how much 1214data has been received then the safest approach is to indicate no bytes have 1215been received. For example: to indicate that no valid data has been received 1216a LLD might use these helpers:: 1217 1218 scsi_set_resid(SCpnt, scsi_bufflen(SCpnt)); 1219 1220where 'SCpnt' is a pointer to a scsi_cmnd object. To indicate only three 512 1221bytes blocks has been received 'resid' could be set like this:: 1222 1223 scsi_set_resid(SCpnt, scsi_bufflen(SCpnt) - (3 * 512)); 1224 1225The scsi_cmnd structure is defined in include/scsi/scsi_cmnd.h 1226 1227 1228Locks 1229===== 1230Each struct Scsi_Host instance has a spin_lock called struct 1231Scsi_Host::default_lock which is initialized in scsi_host_alloc() [found in 1232hosts.c]. Within the same function the struct Scsi_Host::host_lock pointer 1233is initialized to point at default_lock. Thereafter lock and unlock 1234operations performed by the mid level use the struct Scsi_Host::host_lock 1235pointer. Previously drivers could override the host_lock pointer but 1236this is not allowed anymore. 1237 1238 1239Autosense 1240========= 1241Autosense (or auto-sense) is defined in the SAM-2 document as "the 1242automatic return of sense data to the application client coincident 1243with the completion of a SCSI command" when a status of CHECK CONDITION 1244occurs. LLDs should perform autosense. This should be done when the LLD 1245detects a CHECK CONDITION status by either: 1246 1247 a) instructing the SCSI protocol (e.g. SCSI Parallel Interface (SPI)) 1248 to perform an extra data in phase on such responses 1249 b) or, the LLD issuing a REQUEST SENSE command itself 1250 1251Either way, when a status of CHECK CONDITION is detected, the mid level 1252decides whether the LLD has performed autosense by checking struct 1253scsi_cmnd::sense_buffer[0] . If this byte has an upper nibble of 7 (or 0xf) 1254then autosense is assumed to have taken place. If it has another value (and 1255this byte is initialized to 0 before each command) then the mid level will 1256issue a REQUEST SENSE command. 1257 1258In the presence of queued commands the "nexus" that maintains sense 1259buffer data from the command that failed until a following REQUEST SENSE 1260may get out of synchronization. This is why it is best for the LLD 1261to perform autosense. 1262 1263 1264Changes since lk 2.4 series 1265=========================== 1266io_request_lock has been replaced by several finer grained locks. The lock 1267relevant to LLDs is struct Scsi_Host::host_lock and there is 1268one per SCSI host. 1269 1270The older error handling mechanism has been removed. This means the 1271LLD interface functions abort() and reset() have been removed. 1272The struct scsi_host_template::use_new_eh_code flag has been removed. 1273 1274In the 2.4 series the SCSI subsystem configuration descriptions were 1275aggregated with the configuration descriptions from all other Linux 1276subsystems in the Documentation/Configure.help file. In the 2.6 series, 1277the SCSI subsystem now has its own (much smaller) drivers/scsi/Kconfig 1278file that contains both configuration and help information. 1279 1280struct SHT has been renamed to struct scsi_host_template. 1281 1282Addition of the "hotplug initialization model" and many extra functions 1283to support it. 1284 1285 1286Credits 1287======= 1288The following people have contributed to this document: 1289 1290 - Mike Anderson <andmike at us dot ibm dot com> 1291 - James Bottomley <James dot Bottomley at hansenpartnership dot com> 1292 - Patrick Mansfield <patmans at us dot ibm dot com> 1293 - Christoph Hellwig <hch at infradead dot org> 1294 - Doug Ledford <dledford at redhat dot com> 1295 - Andries Brouwer <Andries dot Brouwer at cwi dot nl> 1296 - Randy Dunlap <rdunlap at xenotime dot net> 1297 - Alan Stern <stern at rowland dot harvard dot edu> 1298 1299 1300Douglas Gilbert 1301dgilbert at interlog dot com 1302 130321st September 2004 1304