Based on kernel version 5.6.13. Page generated on 2020-05-15 16:46 EST.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 |
Linux Kernel 2.6 series
SCSI mid_level - lower_level driver interface
=============================================
Introduction
============
This document outlines the interface between the Linux SCSI mid level and
SCSI lower level drivers. Lower level drivers (LLDs) are variously called
host bus adapter (HBA) drivers and host drivers (HD). A "host" in this
context is a bridge between a computer IO bus (e.g. PCI or ISA) and a
single SCSI initiator port on a SCSI transport. An "initiator" port
(SCSI terminology, see SAM-3 at http://www.t10.org) sends SCSI commands
to "target" SCSI ports (e.g. disks). There can be many LLDs in a running
system, but only one per hardware type. Most LLDs can control one or more
SCSI HBAs. Some HBAs contain multiple hosts.
In some cases the SCSI transport is an external bus that already has
its own subsystem in Linux (e.g. USB and ieee1394). In such cases the
SCSI subsystem LLD is a software bridge to the other driver subsystem.
Examples are the usb-storage driver (found in the drivers/usb/storage
directory) and the ieee1394/sbp2 driver (found in the drivers/ieee1394
directory).
For example, the aic7xxx LLD controls Adaptec SCSI parallel interface
(SPI) controllers based on that company's 7xxx chip series. The aic7xxx
LLD can be built into the kernel or loaded as a module. There can only be
one aic7xxx LLD running in a Linux system but it may be controlling many
HBAs. These HBAs might be either on PCI daughter-boards or built into
the motherboard (or both). Some aic7xxx based HBAs are dual controllers
and thus represent two hosts. Like most modern HBAs, each aic7xxx host
has its own PCI device address. [The one-to-one correspondence between
a SCSI host and a PCI device is common but not required (e.g. with
ISA adapters).]
The SCSI mid level isolates an LLD from other layers such as the SCSI
upper layer drivers and the block layer.
This version of the document roughly matches linux kernel version 2.6.8 .
Documentation
=============
There is a SCSI documentation directory within the kernel source tree,
typically Documentation/scsi . Most documents are in plain
(i.e. ASCII) text. This file is named scsi_mid_low_api.txt and can be
found in that directory. A more recent copy of this document may be found
at http://web.archive.org/web/20070107183357rn_1/sg.torque.net/scsi/.
Many LLDs are documented there (e.g. aic7xxx.txt). The SCSI mid-level is
briefly described in scsi.txt which contains a url to a document
describing the SCSI subsystem in the lk 2.4 series. Two upper level
drivers have documents in that directory: st.txt (SCSI tape driver) and
scsi-generic.txt (for the sg driver).
Some documentation (or urls) for LLDs may be found in the C source code
or in the same directory as the C source code. For example to find a url
about the USB mass storage driver see the
/usr/src/linux/drivers/usb/storage directory.
Driver structure
================
Traditionally an LLD for the SCSI subsystem has been at least two files in
the drivers/scsi directory. For example, a driver called "xyz" has a header
file "xyz.h" and a source file "xyz.c". [Actually there is no good reason
why this couldn't all be in one file; the header file is superfluous.] Some
drivers that have been ported to several operating systems have more than
two files. For example the aic7xxx driver has separate files for generic
and OS-specific code (e.g. FreeBSD and Linux). Such drivers tend to have
their own directory under the drivers/scsi directory.
When a new LLD is being added to Linux, the following files (found in the
drivers/scsi directory) will need some attention: Makefile and Kconfig .
It is probably best to study how existing LLDs are organized.
As the 2.5 series development kernels evolve into the 2.6 series
production series, changes are being introduced into this interface. An
example of this is driver initialization code where there are now 2 models
available. The older one, similar to what was found in the lk 2.4 series,
is based on hosts that are detected at HBA driver load time. This will be
referred to the "passive" initialization model. The newer model allows HBAs
to be hot plugged (and unplugged) during the lifetime of the LLD and will
be referred to as the "hotplug" initialization model. The newer model is
preferred as it can handle both traditional SCSI equipment that is
permanently connected as well as modern "SCSI" devices (e.g. USB or
IEEE 1394 connected digital cameras) that are hotplugged. Both
initialization models are discussed in the following sections.
An LLD interfaces to the SCSI subsystem several ways:
a) directly invoking functions supplied by the mid level
b) passing a set of function pointers to a registration function
supplied by the mid level. The mid level will then invoke these
functions at some point in the future. The LLD will supply
implementations of these functions.
c) direct access to instances of well known data structures maintained
by the mid level
Those functions in group a) are listed in a section entitled "Mid level
supplied functions" below.
Those functions in group b) are listed in a section entitled "Interface
functions" below. Their function pointers are placed in the members of
"struct scsi_host_template", an instance of which is passed to
scsi_host_alloc() ** . Those interface functions that the LLD does not
wish to supply should have NULL placed in the corresponding member of
struct scsi_host_template. Defining an instance of struct
scsi_host_template at file scope will cause NULL to be placed in function
pointer members not explicitly initialized.
Those usages in group c) should be handled with care, especially in a
"hotplug" environment. LLDs should be aware of the lifetime of instances
that are shared with the mid level and other layers.
All functions defined within an LLD and all data defined at file scope
should be static. For example the slave_alloc() function in an LLD
called "xxx" could be defined as
"static int xxx_slave_alloc(struct scsi_device * sdev) { /* code */ }"
** the scsi_host_alloc() function is a replacement for the rather vaguely
named scsi_register() function in most situations.
Hotplug initialization model
============================
In this model an LLD controls when SCSI hosts are introduced and removed
from the SCSI subsystem. Hosts can be introduced as early as driver
initialization and removed as late as driver shutdown. Typically a driver
will respond to a sysfs probe() callback that indicates an HBA has been
detected. After confirming that the new device is one that the LLD wants
to control, the LLD will initialize the HBA and then register a new host
with the SCSI mid level.
During LLD initialization the driver should register itself with the
appropriate IO bus on which it expects to find HBA(s) (e.g. the PCI bus).
This can probably be done via sysfs. Any driver parameters (especially
those that are writable after the driver is loaded) could also be
registered with sysfs at this point. The SCSI mid level first becomes
aware of an LLD when that LLD registers its first HBA.
At some later time, the LLD becomes aware of an HBA and what follows
is a typical sequence of calls between the LLD and the mid level.
This example shows the mid level scanning the newly introduced HBA for 3
scsi devices of which only the first 2 respond:
HBA PROBE: assume 2 SCSI devices found in scan
LLD mid level LLD
===-------------------=========--------------------===------
scsi_host_alloc() -->
scsi_add_host() ---->
scsi_scan_host() -------+
|
slave_alloc()
slave_configure() --> scsi_change_queue_depth()
|
slave_alloc()
slave_configure()
|
slave_alloc() ***
slave_destroy() ***
------------------------------------------------------------
If the LLD wants to adjust the default queue settings, it can invoke
scsi_change_queue_depth() in its slave_configure() routine.
*** For scsi devices that the mid level tries to scan but do not
respond, a slave_alloc(), slave_destroy() pair is called.
When an HBA is being removed it could be as part of an orderly shutdown
associated with the LLD module being unloaded (e.g. with the "rmmod"
command) or in response to a "hot unplug" indicated by sysfs()'s
remove() callback being invoked. In either case, the sequence is the
same:
HBA REMOVE: assume 2 SCSI devices attached
LLD mid level LLD
===----------------------=========-----------------===------
scsi_remove_host() ---------+
|
slave_destroy()
slave_destroy()
scsi_host_put()
------------------------------------------------------------
It may be useful for a LLD to keep track of struct Scsi_Host instances
(a pointer is returned by scsi_host_alloc()). Such instances are "owned"
by the mid-level. struct Scsi_Host instances are freed from
scsi_host_put() when the reference count hits zero.
Hot unplugging an HBA that controls a disk which is processing SCSI
commands on a mounted file system is an interesting situation. Reference
counting logic is being introduced into the mid level to cope with many
of the issues involved. See the section on reference counting below.
The hotplug concept may be extended to SCSI devices. Currently, when an
HBA is added, the scsi_scan_host() function causes a scan for SCSI devices
attached to the HBA's SCSI transport. On newer SCSI transports the HBA
may become aware of a new SCSI device _after_ the scan has completed.
An LLD can use this sequence to make the mid level aware of a SCSI device:
SCSI DEVICE hotplug
LLD mid level LLD
===-------------------=========--------------------===------
scsi_add_device() ------+
|
slave_alloc()
slave_configure() [--> scsi_change_queue_depth()]
------------------------------------------------------------
In a similar fashion, an LLD may become aware that a SCSI device has been
removed (unplugged) or the connection to it has been interrupted. Some
existing SCSI transports (e.g. SPI) may not become aware that a SCSI
device has been removed until a subsequent SCSI command fails which will
probably cause that device to be set offline by the mid level. An LLD that
detects the removal of a SCSI device can instigate its removal from
upper layers with this sequence:
SCSI DEVICE hot unplug
LLD mid level LLD
===----------------------=========-----------------===------
scsi_remove_device() -------+
|
slave_destroy()
------------------------------------------------------------
It may be useful for an LLD to keep track of struct scsi_device instances
(a pointer is passed as the parameter to slave_alloc() and
slave_configure() callbacks). Such instances are "owned" by the mid-level.
struct scsi_device instances are freed after slave_destroy().
Reference Counting
==================
The Scsi_Host structure has had reference counting infrastructure added.
This effectively spreads the ownership of struct Scsi_Host instances
across the various SCSI layers which use them. Previously such instances
were exclusively owned by the mid level. LLDs would not usually need to
directly manipulate these reference counts but there may be some cases
where they do.
There are 3 reference counting functions of interest associated with
struct Scsi_Host:
- scsi_host_alloc(): returns a pointer to new instance of struct
Scsi_Host which has its reference count ^^ set to 1
- scsi_host_get(): adds 1 to the reference count of the given instance
- scsi_host_put(): decrements 1 from the reference count of the given
instance. If the reference count reaches 0 then the given instance
is freed
The scsi_device structure has had reference counting infrastructure added.
This effectively spreads the ownership of struct scsi_device instances
across the various SCSI layers which use them. Previously such instances
were exclusively owned by the mid level. See the access functions declared
towards the end of include/scsi/scsi_device.h . If an LLD wants to keep
a copy of a pointer to a scsi_device instance it should use scsi_device_get()
to bump its reference count. When it is finished with the pointer it can
use scsi_device_put() to decrement its reference count (and potentially
delete it).
^^ struct Scsi_Host actually has 2 reference counts which are manipulated
in parallel by these functions.
Conventions
===========
First, Linus Torvalds's thoughts on C coding style can be found in the
Documentation/process/coding-style.rst file.
Next, there is a movement to "outlaw" typedefs introducing synonyms for
struct tags. Both can be still found in the SCSI subsystem, but
the typedefs have been moved to a single file, scsi_typedefs.h to
make their future removal easier, for example:
"typedef struct scsi_cmnd Scsi_Cmnd;"
Also, most C99 enhancements are encouraged to the extent they are supported
by the relevant gcc compilers. So C99 style structure and array
initializers are encouraged where appropriate. Don't go too far,
VLAs are not properly supported yet. An exception to this is the use of
"//" style comments; /*...*/ comments are still preferred in Linux.
Well written, tested and documented code, need not be re-formatted to
comply with the above conventions. For example, the aic7xxx driver
comes to Linux from FreeBSD and Adaptec's own labs. No doubt FreeBSD
and Adaptec have their own coding conventions.
Mid level supplied functions
============================
These functions are supplied by the SCSI mid level for use by LLDs.
The names (i.e. entry points) of these functions are exported
so an LLD that is a module can access them. The kernel will
arrange for the SCSI mid level to be loaded and initialized before any LLD
is initialized. The functions below are listed alphabetically and their
names all start with "scsi_".
Summary:
scsi_add_device - creates new scsi device (lu) instance
scsi_add_host - perform sysfs registration and set up transport class
scsi_change_queue_depth - change the queue depth on a SCSI device
scsi_bios_ptable - return copy of block device's partition table
scsi_block_requests - prevent further commands being queued to given host
scsi_host_alloc - return a new scsi_host instance whose refcount==1
scsi_host_get - increments Scsi_Host instance's refcount
scsi_host_put - decrements Scsi_Host instance's refcount (free if 0)
scsi_partsize - parse partition table into cylinders, heads + sectors
scsi_register - create and register a scsi host adapter instance.
scsi_remove_device - detach and remove a SCSI device
scsi_remove_host - detach and remove all SCSI devices owned by host
scsi_report_bus_reset - report scsi _bus_ reset observed
scsi_scan_host - scan SCSI bus
scsi_track_queue_full - track successive QUEUE_FULL events
scsi_unblock_requests - allow further commands to be queued to given host
scsi_unregister - [calls scsi_host_put()]
Details:
/**
* scsi_add_device - creates new scsi device (lu) instance
* @shost: pointer to scsi host instance
* @channel: channel number (rarely other than 0)
* @id: target id number
* @lun: logical unit number
*
* Returns pointer to new struct scsi_device instance or
* ERR_PTR(-ENODEV) (or some other bent pointer) if something is
* wrong (e.g. no lu responds at given address)
*
* Might block: yes
*
* Notes: This call is usually performed internally during a scsi
* bus scan when an HBA is added (i.e. scsi_scan_host()). So it
* should only be called if the HBA becomes aware of a new scsi
* device (lu) after scsi_scan_host() has completed. If successful
* this call can lead to slave_alloc() and slave_configure() callbacks
* into the LLD.
*
* Defined in: drivers/scsi/scsi_scan.c
**/
struct scsi_device * scsi_add_device(struct Scsi_Host *shost,
unsigned int channel,
unsigned int id, unsigned int lun)
/**
* scsi_add_host - perform sysfs registration and set up transport class
* @shost: pointer to scsi host instance
* @dev: pointer to struct device of type scsi class
*
* Returns 0 on success, negative errno of failure (e.g. -ENOMEM)
*
* Might block: no
*
* Notes: Only required in "hotplug initialization model" after a
* successful call to scsi_host_alloc(). This function does not
* scan the bus; this can be done by calling scsi_scan_host() or
* in some other transport-specific way. The LLD must set up
* the transport template before calling this function and may only
* access the transport class data after this function has been called.
*
* Defined in: drivers/scsi/hosts.c
**/
int scsi_add_host(struct Scsi_Host *shost, struct device * dev)
/**
* scsi_change_queue_depth - allow LLD to change queue depth on a SCSI device
* @sdev: pointer to SCSI device to change queue depth on
* @tags Number of tags allowed if tagged queuing enabled,
* or number of commands the LLD can queue up
* in non-tagged mode (as per cmd_per_lun).
*
* Returns nothing
*
* Might block: no
*
* Notes: Can be invoked any time on a SCSI device controlled by this
* LLD. [Specifically during and after slave_configure() and prior to
* slave_destroy().] Can safely be invoked from interrupt code.
*
* Defined in: drivers/scsi/scsi.c [see source code for more notes]
*
**/
int scsi_change_queue_depth(struct scsi_device *sdev, int tags)
/**
* scsi_bios_ptable - return copy of block device's partition table
* @dev: pointer to block device
*
* Returns pointer to partition table, or NULL for failure
*
* Might block: yes
*
* Notes: Caller owns memory returned (free with kfree() )
*
* Defined in: drivers/scsi/scsicam.c
**/
unsigned char *scsi_bios_ptable(struct block_device *dev)
/**
* scsi_block_requests - prevent further commands being queued to given host
*
* @shost: pointer to host to block commands on
*
* Returns nothing
*
* Might block: no
*
* Notes: There is no timer nor any other means by which the requests
* get unblocked other than the LLD calling scsi_unblock_requests().
*
* Defined in: drivers/scsi/scsi_lib.c
**/
void scsi_block_requests(struct Scsi_Host * shost)
/**
* scsi_host_alloc - create a scsi host adapter instance and perform basic
* initialization.
* @sht: pointer to scsi host template
* @privsize: extra bytes to allocate in hostdata array (which is the
* last member of the returned Scsi_Host instance)
*
* Returns pointer to new Scsi_Host instance or NULL on failure
*
* Might block: yes
*
* Notes: When this call returns to the LLD, the SCSI bus scan on
* this host has _not_ yet been done.
* The hostdata array (by default zero length) is a per host scratch
* area for the LLD's exclusive use.
* Both associated refcounting objects have their refcount set to 1.
* Full registration (in sysfs) and a bus scan are performed later when
* scsi_add_host() and scsi_scan_host() are called.
*
* Defined in: drivers/scsi/hosts.c .
**/
struct Scsi_Host * scsi_host_alloc(struct scsi_host_template * sht,
int privsize)
/**
* scsi_host_get - increment Scsi_Host instance refcount
* @shost: pointer to struct Scsi_Host instance
*
* Returns nothing
*
* Might block: currently may block but may be changed to not block
*
* Notes: Actually increments the counts in two sub-objects
*
* Defined in: drivers/scsi/hosts.c
**/
void scsi_host_get(struct Scsi_Host *shost)
/**
* scsi_host_put - decrement Scsi_Host instance refcount, free if 0
* @shost: pointer to struct Scsi_Host instance
*
* Returns nothing
*
* Might block: currently may block but may be changed to not block
*
* Notes: Actually decrements the counts in two sub-objects. If the
* latter refcount reaches 0, the Scsi_Host instance is freed.
* The LLD need not worry exactly when the Scsi_Host instance is
* freed, it just shouldn't access the instance after it has balanced
* out its refcount usage.
*
* Defined in: drivers/scsi/hosts.c
**/
void scsi_host_put(struct Scsi_Host *shost)
/**
* scsi_partsize - parse partition table into cylinders, heads + sectors
* @buf: pointer to partition table
* @capacity: size of (total) disk in 512 byte sectors
* @cyls: outputs number of cylinders calculated via this pointer
* @hds: outputs number of heads calculated via this pointer
* @secs: outputs number of sectors calculated via this pointer
*
* Returns 0 on success, -1 on failure
*
* Might block: no
*
* Notes: Caller owns memory returned (free with kfree() )
*
* Defined in: drivers/scsi/scsicam.c
**/
int scsi_partsize(unsigned char *buf, unsigned long capacity,
unsigned int *cyls, unsigned int *hds, unsigned int *secs)
/**
* scsi_register - create and register a scsi host adapter instance.
* @sht: pointer to scsi host template
* @privsize: extra bytes to allocate in hostdata array (which is the
* last member of the returned Scsi_Host instance)
*
* Returns pointer to new Scsi_Host instance or NULL on failure
*
* Might block: yes
*
* Notes: When this call returns to the LLD, the SCSI bus scan on
* this host has _not_ yet been done.
* The hostdata array (by default zero length) is a per host scratch
* area for the LLD.
*
* Defined in: drivers/scsi/hosts.c .
**/
struct Scsi_Host * scsi_register(struct scsi_host_template * sht,
int privsize)
/**
* scsi_remove_device - detach and remove a SCSI device
* @sdev: a pointer to a scsi device instance
*
* Returns value: 0 on success, -EINVAL if device not attached
*
* Might block: yes
*
* Notes: If an LLD becomes aware that a scsi device (lu) has
* been removed but its host is still present then it can request
* the removal of that scsi device. If successful this call will
* lead to the slave_destroy() callback being invoked. sdev is an
* invalid pointer after this call.
*
* Defined in: drivers/scsi/scsi_sysfs.c .
**/
int scsi_remove_device(struct scsi_device *sdev)
/**
* scsi_remove_host - detach and remove all SCSI devices owned by host
* @shost: a pointer to a scsi host instance
*
* Returns value: 0 on success, 1 on failure (e.g. LLD busy ??)
*
* Might block: yes
*
* Notes: Should only be invoked if the "hotplug initialization
* model" is being used. It should be called _prior_ to
* scsi_unregister().
*
* Defined in: drivers/scsi/hosts.c .
**/
int scsi_remove_host(struct Scsi_Host *shost)
/**
* scsi_report_bus_reset - report scsi _bus_ reset observed
* @shost: a pointer to a scsi host involved
* @channel: channel (within) host on which scsi bus reset occurred
*
* Returns nothing
*
* Might block: no
*
* Notes: This only needs to be called if the reset is one which
* originates from an unknown location. Resets originated by the
* mid level itself don't need to call this, but there should be
* no harm. The main purpose of this is to make sure that a
* CHECK_CONDITION is properly treated.
*
* Defined in: drivers/scsi/scsi_error.c .
**/
void scsi_report_bus_reset(struct Scsi_Host * shost, int channel)
/**
* scsi_scan_host - scan SCSI bus
* @shost: a pointer to a scsi host instance
*
* Might block: yes
*
* Notes: Should be called after scsi_add_host()
*
* Defined in: drivers/scsi/scsi_scan.c
**/
void scsi_scan_host(struct Scsi_Host *shost)
/**
* scsi_track_queue_full - track successive QUEUE_FULL events on given
* device to determine if and when there is a need
* to adjust the queue depth on the device.
* @sdev: pointer to SCSI device instance
* @depth: Current number of outstanding SCSI commands on this device,
* not counting the one returned as QUEUE_FULL.
*
* Returns 0 - no change needed
* >0 - adjust queue depth to this new depth
* -1 - drop back to untagged operation using host->cmd_per_lun
* as the untagged command depth
*
* Might block: no
*
* Notes: LLDs may call this at any time and we will do "The Right
* Thing"; interrupt context safe.
*
* Defined in: drivers/scsi/scsi.c .
**/
int scsi_track_queue_full(struct scsi_device *sdev, int depth)
/**
* scsi_unblock_requests - allow further commands to be queued to given host
*
* @shost: pointer to host to unblock commands on
*
* Returns nothing
*
* Might block: no
*
* Defined in: drivers/scsi/scsi_lib.c .
**/
void scsi_unblock_requests(struct Scsi_Host * shost)
/**
* scsi_unregister - unregister and free memory used by host instance
* @shp: pointer to scsi host instance to unregister.
*
* Returns nothing
*
* Might block: no
*
* Notes: Should not be invoked if the "hotplug initialization
* model" is being used. Called internally by exit_this_scsi_driver()
* in the "passive initialization model". Hence a LLD has no need to
* call this function directly.
*
* Defined in: drivers/scsi/hosts.c .
**/
void scsi_unregister(struct Scsi_Host * shp)
Interface Functions
===================
Interface functions are supplied (defined) by LLDs and their function
pointers are placed in an instance of struct scsi_host_template which
is passed to scsi_host_alloc() [or scsi_register() / init_this_scsi_driver()].
Some are mandatory. Interface functions should be declared static. The
accepted convention is that driver "xyz" will declare its slave_configure()
function as:
static int xyz_slave_configure(struct scsi_device * sdev);
and so forth for all interface functions listed below.
A pointer to this function should be placed in the 'slave_configure' member
of a "struct scsi_host_template" instance. A pointer to such an instance
should be passed to the mid level's scsi_host_alloc() [or scsi_register() /
init_this_scsi_driver()].
The interface functions are also described in the include/scsi/scsi_host.h
file immediately above their definition point in "struct scsi_host_template".
In some cases more detail is given in scsi_host.h than below.
The interface functions are listed below in alphabetical order.
Summary:
bios_param - fetch head, sector, cylinder info for a disk
eh_timed_out - notify the host that a command timer expired
eh_abort_handler - abort given command
eh_bus_reset_handler - issue SCSI bus reset
eh_device_reset_handler - issue SCSI device reset
eh_host_reset_handler - reset host (host bus adapter)
info - supply information about given host
ioctl - driver can respond to ioctls
proc_info - supports /proc/scsi/{driver_name}/{host_no}
queuecommand - queue scsi command, invoke 'done' on completion
slave_alloc - prior to any commands being sent to a new device
slave_configure - driver fine tuning for given device after attach
slave_destroy - given device is about to be shut down
Details:
/**
* bios_param - fetch head, sector, cylinder info for a disk
* @sdev: pointer to scsi device context (defined in
* include/scsi/scsi_device.h)
* @bdev: pointer to block device context (defined in fs.h)
* @capacity: device size (in 512 byte sectors)
* @params: three element array to place output:
* params[0] number of heads (max 255)
* params[1] number of sectors (max 63)
* params[2] number of cylinders
*
* Return value is ignored
*
* Locks: none
*
* Calling context: process (sd)
*
* Notes: an arbitrary geometry (based on READ CAPACITY) is used
* if this function is not provided. The params array is
* pre-initialized with made up values just in case this function
* doesn't output anything.
*
* Optionally defined in: LLD
**/
int bios_param(struct scsi_device * sdev, struct block_device *bdev,
sector_t capacity, int params[3])
/**
* eh_timed_out - The timer for the command has just fired
* @scp: identifies command timing out
*
* Returns:
*
* EH_HANDLED: I fixed the error, please complete the command
* EH_RESET_TIMER: I need more time, reset the timer and
* begin counting again
* EH_NOT_HANDLED Begin normal error recovery
*
*
* Locks: None held
*
* Calling context: interrupt
*
* Notes: This is to give the LLD an opportunity to do local recovery.
* This recovery is limited to determining if the outstanding command
* will ever complete. You may not abort and restart the command from
* this callback.
*
* Optionally defined in: LLD
**/
int eh_timed_out(struct scsi_cmnd * scp)
/**
* eh_abort_handler - abort command associated with scp
* @scp: identifies command to be aborted
*
* Returns SUCCESS if command aborted else FAILED
*
* Locks: None held
*
* Calling context: kernel thread
*
* Notes: If 'no_async_abort' is defined this callback
* will be invoked from scsi_eh thread. No other commands
* will then be queued on current host during eh.
* Otherwise it will be called whenever scsi_times_out()
* is called due to a command timeout.
*
* Optionally defined in: LLD
**/
int eh_abort_handler(struct scsi_cmnd * scp)
/**
* eh_bus_reset_handler - issue SCSI bus reset
* @scp: SCSI bus that contains this device should be reset
*
* Returns SUCCESS if command aborted else FAILED
*
* Locks: None held
*
* Calling context: kernel thread
*
* Notes: Invoked from scsi_eh thread. No other commands will be
* queued on current host during eh.
*
* Optionally defined in: LLD
**/
int eh_bus_reset_handler(struct scsi_cmnd * scp)
/**
* eh_device_reset_handler - issue SCSI device reset
* @scp: identifies SCSI device to be reset
*
* Returns SUCCESS if command aborted else FAILED
*
* Locks: None held
*
* Calling context: kernel thread
*
* Notes: Invoked from scsi_eh thread. No other commands will be
* queued on current host during eh.
*
* Optionally defined in: LLD
**/
int eh_device_reset_handler(struct scsi_cmnd * scp)
/**
* eh_host_reset_handler - reset host (host bus adapter)
* @scp: SCSI host that contains this device should be reset
*
* Returns SUCCESS if command aborted else FAILED
*
* Locks: None held
*
* Calling context: kernel thread
*
* Notes: Invoked from scsi_eh thread. No other commands will be
* queued on current host during eh.
* With the default eh_strategy in place, if none of the _abort_,
* _device_reset_, _bus_reset_ or this eh handler function are
* defined (or they all return FAILED) then the device in question
* will be set offline whenever eh is invoked.
*
* Optionally defined in: LLD
**/
int eh_host_reset_handler(struct scsi_cmnd * scp)
/**
* info - supply information about given host: driver name plus data
* to distinguish given host
* @shp: host to supply information about
*
* Return ASCII null terminated string. [This driver is assumed to
* manage the memory pointed to and maintain it, typically for the
* lifetime of this host.]
*
* Locks: none
*
* Calling context: process
*
* Notes: Often supplies PCI or ISA information such as IO addresses
* and interrupt numbers. If not supplied struct Scsi_Host::name used
* instead. It is assumed the returned information fits on one line
* (i.e. does not included embedded newlines).
* The SCSI_IOCTL_PROBE_HOST ioctl yields the string returned by this
* function (or struct Scsi_Host::name if this function is not
* available).
* In a similar manner, init_this_scsi_driver() outputs to the console
* each host's "info" (or name) for the driver it is registering.
* Also if proc_info() is not supplied, the output of this function
* is used instead.
*
* Optionally defined in: LLD
**/
const char * info(struct Scsi_Host * shp)
/**
* ioctl - driver can respond to ioctls
* @sdp: device that ioctl was issued for
* @cmd: ioctl number
* @arg: pointer to read or write data from. Since it points to
* user space, should use appropriate kernel functions
* (e.g. copy_from_user() ). In the Unix style this argument
* can also be viewed as an unsigned long.
*
* Returns negative "errno" value when there is a problem. 0 or a
* positive value indicates success and is returned to the user space.
*
* Locks: none
*
* Calling context: process
*
* Notes: The SCSI subsystem uses a "trickle down" ioctl model.
* The user issues an ioctl() against an upper level driver
* (e.g. /dev/sdc) and if the upper level driver doesn't recognize
* the 'cmd' then it is passed to the SCSI mid level. If the SCSI
* mid level does not recognize it, then the LLD that controls
* the device receives the ioctl. According to recent Unix standards
* unsupported ioctl() 'cmd' numbers should return -ENOTTY.
*
* Optionally defined in: LLD
**/
int ioctl(struct scsi_device *sdp, int cmd, void *arg)
/**
* proc_info - supports /proc/scsi/{driver_name}/{host_no}
* @buffer: anchor point to output to (0==writeto1_read0) or fetch from
* (1==writeto1_read0).
* @start: where "interesting" data is written to. Ignored when
* 1==writeto1_read0.
* @offset: offset within buffer 0==writeto1_read0 is actually
* interested in. Ignored when 1==writeto1_read0 .
* @length: maximum (or actual) extent of buffer
* @host_no: host number of interest (struct Scsi_Host::host_no)
* @writeto1_read0: 1 -> data coming from user space towards driver
* (e.g. "echo some_string > /proc/scsi/xyz/2")
* 0 -> user what data from this driver
* (e.g. "cat /proc/scsi/xyz/2")
*
* Returns length when 1==writeto1_read0. Otherwise number of chars
* output to buffer past offset.
*
* Locks: none held
*
* Calling context: process
*
* Notes: Driven from scsi_proc.c which interfaces to proc_fs. proc_fs
* support can now be configured out of the scsi subsystem.
*
* Optionally defined in: LLD
**/
int proc_info(char * buffer, char ** start, off_t offset,
int length, int host_no, int writeto1_read0)
/**
* queuecommand - queue scsi command, invoke scp->scsi_done on completion
* @shost: pointer to the scsi host object
* @scp: pointer to scsi command object
*
* Returns 0 on success.
*
* If there's a failure, return either:
*
* SCSI_MLQUEUE_DEVICE_BUSY if the device queue is full, or
* SCSI_MLQUEUE_HOST_BUSY if the entire host queue is full
*
* On both of these returns, the mid-layer will requeue the I/O
*
* - if the return is SCSI_MLQUEUE_DEVICE_BUSY, only that particular
* device will be paused, and it will be unpaused when a command to
* the device returns (or after a brief delay if there are no more
* outstanding commands to it). Commands to other devices continue
* to be processed normally.
*
* - if the return is SCSI_MLQUEUE_HOST_BUSY, all I/O to the host
* is paused and will be unpaused when any command returns from
* the host (or after a brief delay if there are no outstanding
* commands to the host).
*
* For compatibility with earlier versions of queuecommand, any
* other return value is treated the same as
* SCSI_MLQUEUE_HOST_BUSY.
*
* Other types of errors that are detected immediately may be
* flagged by setting scp->result to an appropriate value,
* invoking the scp->scsi_done callback, and then returning 0
* from this function. If the command is not performed
* immediately (and the LLD is starting (or will start) the given
* command) then this function should place 0 in scp->result and
* return 0.
*
* Command ownership. If the driver returns zero, it owns the
* command and must take responsibility for ensuring the
* scp->scsi_done callback is executed. Note: the driver may
* call scp->scsi_done before returning zero, but after it has
* called scp->scsi_done, it may not return any value other than
* zero. If the driver makes a non-zero return, it must not
* execute the command's scsi_done callback at any time.
*
* Locks: up to and including 2.6.36, struct Scsi_Host::host_lock
* held on entry (with "irqsave") and is expected to be
* held on return. From 2.6.37 onwards, queuecommand is
* called without any locks held.
*
* Calling context: in interrupt (soft irq) or process context
*
* Notes: This function should be relatively fast. Normally it
* will not wait for IO to complete. Hence the scp->scsi_done
* callback is invoked (often directly from an interrupt service
* routine) some time after this function has returned. In some
* cases (e.g. pseudo adapter drivers that manufacture the
* response to a SCSI INQUIRY) the scp->scsi_done callback may be
* invoked before this function returns. If the scp->scsi_done
* callback is not invoked within a certain period the SCSI mid
* level will commence error processing. If a status of CHECK
* CONDITION is placed in "result" when the scp->scsi_done
* callback is invoked, then the LLD driver should perform
* autosense and fill in the struct scsi_cmnd::sense_buffer
* array. The scsi_cmnd::sense_buffer array is zeroed prior to
* the mid level queuing a command to an LLD.
*
* Defined in: LLD
**/
int queuecommand(struct Scsi_Host *shost, struct scsi_cmnd * scp)
/**
* slave_alloc - prior to any commands being sent to a new device
* (i.e. just prior to scan) this call is made
* @sdp: pointer to new device (about to be scanned)
*
* Returns 0 if ok. Any other return is assumed to be an error and
* the device is ignored.
*
* Locks: none
*
* Calling context: process
*
* Notes: Allows the driver to allocate any resources for a device
* prior to its initial scan. The corresponding scsi device may not
* exist but the mid level is just about to scan for it (i.e. send
* and INQUIRY command plus ...). If a device is found then
* slave_configure() will be called while if a device is not found
* slave_destroy() is called.
* For more details see the include/scsi/scsi_host.h file.
*
* Optionally defined in: LLD
**/
int slave_alloc(struct scsi_device *sdp)
/**
* slave_configure - driver fine tuning for given device just after it
* has been first scanned (i.e. it responded to an
* INQUIRY)
* @sdp: device that has just been attached
*
* Returns 0 if ok. Any other return is assumed to be an error and
* the device is taken offline. [offline devices will _not_ have
* slave_destroy() called on them so clean up resources.]
*
* Locks: none
*
* Calling context: process
*
* Notes: Allows the driver to inspect the response to the initial
* INQUIRY done by the scanning code and take appropriate action.
* For more details see the include/scsi/scsi_host.h file.
*
* Optionally defined in: LLD
**/
int slave_configure(struct scsi_device *sdp)
/**
* slave_destroy - given device is about to be shut down. All
* activity has ceased on this device.
* @sdp: device that is about to be shut down
*
* Returns nothing
*
* Locks: none
*
* Calling context: process
*
* Notes: Mid level structures for given device are still in place
* but are about to be torn down. Any per device resources allocated
* by this driver for given device should be freed now. No further
* commands will be sent for this sdp instance. [However the device
* could be re-attached in the future in which case a new instance
* of struct scsi_device would be supplied by future slave_alloc()
* and slave_configure() calls.]
*
* Optionally defined in: LLD
**/
void slave_destroy(struct scsi_device *sdp)
Data Structures
===============
struct scsi_host_template
-------------------------
There is one "struct scsi_host_template" instance per LLD ***. It is
typically initialized as a file scope static in a driver's header file. That
way members that are not explicitly initialized will be set to 0 or NULL.
Member of interest:
name - name of driver (may contain spaces, please limit to
less than 80 characters)
proc_name - name used in "/proc/scsi/<proc_name>/<host_no>" and
by sysfs in one of its "drivers" directories. Hence
"proc_name" should only contain characters acceptable
to a Unix file name.
(*queuecommand)() - primary callback that the mid level uses to inject
SCSI commands into an LLD.
The structure is defined and commented in include/scsi/scsi_host.h
*** In extreme situations a single driver may have several instances
if it controls several different classes of hardware (e.g. an LLD
that handles both ISA and PCI cards and has a separate instance of
struct scsi_host_template for each class).
struct Scsi_Host
----------------
There is one struct Scsi_Host instance per host (HBA) that an LLD
controls. The struct Scsi_Host structure has many members in common
with "struct scsi_host_template". When a new struct Scsi_Host instance
is created (in scsi_host_alloc() in hosts.c) those common members are
initialized from the driver's struct scsi_host_template instance. Members
of interest:
host_no - system wide unique number that is used for identifying
this host. Issued in ascending order from 0.
can_queue - must be greater than 0; do not send more than can_queue
commands to the adapter.
this_id - scsi id of host (scsi initiator) or -1 if not known
sg_tablesize - maximum scatter gather elements allowed by host.
Set this to SG_ALL or less to avoid chained SG lists.
Must be at least 1.
max_sectors - maximum number of sectors (usually 512 bytes) allowed
in a single SCSI command. The default value of 0 leads
to a setting of SCSI_DEFAULT_MAX_SECTORS (defined in
scsi_host.h) which is currently set to 1024. So for a
disk the maximum transfer size is 512 KB when max_sectors
is not defined. Note that this size may not be sufficient
for disk firmware uploads.
cmd_per_lun - maximum number of commands that can be queued on devices
controlled by the host. Overridden by LLD calls to
scsi_change_queue_depth().
unchecked_isa_dma - 1=>only use bottom 16 MB of ram (ISA DMA addressing
restriction), 0=>can use full 32 bit (or better) DMA
address space
no_async_abort - 1=>Asynchronous aborts are not supported
0=>Timed-out commands will be aborted asynchronously
hostt - pointer to driver's struct scsi_host_template from which
this struct Scsi_Host instance was spawned
hostt->proc_name - name of LLD. This is the driver name that sysfs uses
transportt - pointer to driver's struct scsi_transport_template instance
(if any). FC and SPI transports currently supported.
sh_list - a double linked list of pointers to all struct Scsi_Host
instances (currently ordered by ascending host_no)
my_devices - a double linked list of pointers to struct scsi_device
instances that belong to this host.
hostdata[0] - area reserved for LLD at end of struct Scsi_Host. Size
is set by the second argument (named 'xtr_bytes') to
scsi_host_alloc() or scsi_register().
vendor_id - a unique value that identifies the vendor supplying
the LLD for the Scsi_Host. Used most often in validating
vendor-specific message requests. Value consists of an
identifier type and a vendor-specific value.
See scsi_netlink.h for a description of valid formats.
The scsi_host structure is defined in include/scsi/scsi_host.h
struct scsi_device
------------------
Generally, there is one instance of this structure for each SCSI logical unit
on a host. Scsi devices connected to a host are uniquely identified by a
channel number, target id and logical unit number (lun).
The structure is defined in include/scsi/scsi_device.h
struct scsi_cmnd
----------------
Instances of this structure convey SCSI commands to the LLD and responses
back to the mid level. The SCSI mid level will ensure that no more SCSI
commands become queued against the LLD than are indicated by
scsi_change_queue_depth() (or struct Scsi_Host::cmd_per_lun). There will
be at least one instance of struct scsi_cmnd available for each SCSI device.
Members of interest:
cmnd - array containing SCSI command
cmnd_len - length (in bytes) of SCSI command
sc_data_direction - direction of data transfer in data phase. See
"enum dma_data_direction" in include/linux/dma-mapping.h
request_bufflen - number of data bytes to transfer (0 if no data phase)
use_sg - ==0 -> no scatter gather list, hence transfer data
to/from request_buffer
- >0 -> scatter gather list (actually an array) in
request_buffer with use_sg elements
request_buffer - either contains data buffer or scatter gather list
depending on the setting of use_sg. Scatter gather
elements are defined by 'struct scatterlist' found
in include/linux/scatterlist.h .
done - function pointer that should be invoked by LLD when the
SCSI command is completed (successfully or otherwise).
Should only be called by an LLD if the LLD has accepted
the command (i.e. queuecommand() returned or will return
0). The LLD may invoke 'done' prior to queuecommand()
finishing.
result - should be set by LLD prior to calling 'done'. A value
of 0 implies a successfully completed command (and all
data (if any) has been transferred to or from the SCSI
target device). 'result' is a 32 bit unsigned integer that
can be viewed as 4 related bytes. The SCSI status value is
in the LSB. See include/scsi/scsi.h status_byte(),
msg_byte(), host_byte() and driver_byte() macros and
related constants.
sense_buffer - an array (maximum size: SCSI_SENSE_BUFFERSIZE bytes) that
should be written when the SCSI status (LSB of 'result')
is set to CHECK_CONDITION (2). When CHECK_CONDITION is
set, if the top nibble of sense_buffer[0] has the value 7
then the mid level will assume the sense_buffer array
contains a valid SCSI sense buffer; otherwise the mid
level will issue a REQUEST_SENSE SCSI command to
retrieve the sense buffer. The latter strategy is error
prone in the presence of command queuing so the LLD should
always "auto-sense".
device - pointer to scsi_device object that this command is
associated with.
resid - an LLD should set this signed integer to the requested
transfer length (i.e. 'request_bufflen') less the number
of bytes that are actually transferred. 'resid' is
preset to 0 so an LLD can ignore it if it cannot detect
underruns (overruns should be rare). If possible an LLD
should set 'resid' prior to invoking 'done'. The most
interesting case is data transfers from a SCSI target
device (e.g. READs) that underrun.
underflow - LLD should place (DID_ERROR << 16) in 'result' if
actual number of bytes transferred is less than this
figure. Not many LLDs implement this check and some that
do just output an error message to the log rather than
report a DID_ERROR. Better for an LLD to implement
'resid'.
It is recommended that a LLD set 'resid' on data transfers from a SCSI
target device (e.g. READs). It is especially important that 'resid' is set
when such data transfers have sense keys of MEDIUM ERROR and HARDWARE ERROR
(and possibly RECOVERED ERROR). In these cases if a LLD is in doubt how much
data has been received then the safest approach is to indicate no bytes have
been received. For example: to indicate that no valid data has been received
a LLD might use these helpers:
scsi_set_resid(SCpnt, scsi_bufflen(SCpnt));
where 'SCpnt' is a pointer to a scsi_cmnd object. To indicate only three 512
bytes blocks has been received 'resid' could be set like this:
scsi_set_resid(SCpnt, scsi_bufflen(SCpnt) - (3 * 512));
The scsi_cmnd structure is defined in include/scsi/scsi_cmnd.h
Locks
=====
Each struct Scsi_Host instance has a spin_lock called struct
Scsi_Host::default_lock which is initialized in scsi_host_alloc() [found in
hosts.c]. Within the same function the struct Scsi_Host::host_lock pointer
is initialized to point at default_lock. Thereafter lock and unlock
operations performed by the mid level use the struct Scsi_Host::host_lock
pointer. Previously drivers could override the host_lock pointer but
this is not allowed anymore.
Autosense
=========
Autosense (or auto-sense) is defined in the SAM-2 document as "the
automatic return of sense data to the application client coincident
with the completion of a SCSI command" when a status of CHECK CONDITION
occurs. LLDs should perform autosense. This should be done when the LLD
detects a CHECK CONDITION status by either:
a) instructing the SCSI protocol (e.g. SCSI Parallel Interface (SPI))
to perform an extra data in phase on such responses
b) or, the LLD issuing a REQUEST SENSE command itself
Either way, when a status of CHECK CONDITION is detected, the mid level
decides whether the LLD has performed autosense by checking struct
scsi_cmnd::sense_buffer[0] . If this byte has an upper nibble of 7 (or 0xf)
then autosense is assumed to have taken place. If it has another value (and
this byte is initialized to 0 before each command) then the mid level will
issue a REQUEST SENSE command.
In the presence of queued commands the "nexus" that maintains sense
buffer data from the command that failed until a following REQUEST SENSE
may get out of synchronization. This is why it is best for the LLD
to perform autosense.
Changes since lk 2.4 series
===========================
io_request_lock has been replaced by several finer grained locks. The lock
relevant to LLDs is struct Scsi_Host::host_lock and there is
one per SCSI host.
The older error handling mechanism has been removed. This means the
LLD interface functions abort() and reset() have been removed.
The struct scsi_host_template::use_new_eh_code flag has been removed.
In the 2.4 series the SCSI subsystem configuration descriptions were
aggregated with the configuration descriptions from all other Linux
subsystems in the Documentation/Configure.help file. In the 2.6 series,
the SCSI subsystem now has its own (much smaller) drivers/scsi/Kconfig
file that contains both configuration and help information.
struct SHT has been renamed to struct scsi_host_template.
Addition of the "hotplug initialization model" and many extra functions
to support it.
Credits
=======
The following people have contributed to this document:
Mike Anderson <andmike at us dot ibm dot com>
James Bottomley <James dot Bottomley at hansenpartnership dot com>
Patrick Mansfield <patmans at us dot ibm dot com>
Christoph Hellwig <hch at infradead dot org>
Doug Ledford <dledford at redhat dot com>
Andries Brouwer <Andries dot Brouwer at cwi dot nl>
Randy Dunlap <rdunlap at xenotime dot net>
Alan Stern <stern at rowland dot harvard dot edu>
Douglas Gilbert
dgilbert at interlog dot com
21st September 2004
|