/share/man/man4/scsi.4

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  1. .\" Copyright (c) 1996
  2. .\" Julian Elischer <julian@FreeBSD.org>. All rights reserved.
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  26. .\" $FreeBSD$
  27. .Dd June 7, 2012
  28. .Dt CAM 4
  29. .Os
  30. .Sh NAME
  31. .Nm CAM
  32. .Nd Common Access Method SCSI/ATA subsystem
  33. .Sh SYNOPSIS
  34. .Cd "device scbus"
  35. .Cd "device ada"
  36. .Cd "device cd"
  37. .Cd "device ch"
  38. .Cd "device da"
  39. .Cd "device pass"
  40. .Cd "device pt"
  41. .Cd "device sa"
  42. .Cd "options CAMDEBUG"
  43. .Cd "options CAM_DEBUG_BUS=-1"
  44. .Cd "options CAM_DEBUG_TARGET=-1"
  45. .Cd "options CAM_DEBUG_LUN=-1"
  46. .Cd "options CAM_DEBUG_COMPILE=CAM_DEBUG_INFO|CAM_DEBUG_CDB|CAM_DEBUG_PROBE"
  47. .Cd "options CAM_DEBUG_FLAGS=CAM_DEBUG_INFO|CAM_DEBUG_CDB"
  48. .Cd "options CAM_MAX_HIGHPOWER=4"
  49. .Cd "options SCSI_NO_SENSE_STRINGS"
  50. .Cd "options SCSI_NO_OP_STRINGS"
  51. .Cd "options SCSI_DELAY=8000"
  52. .Sh DESCRIPTION
  53. The
  54. .Nm
  55. subsystem provides a uniform and modular system for the implementation
  56. of drivers to control various
  57. .Tn SCSI
  58. and
  59. .Tn ATA
  60. devices, and to utilize different
  61. .Tn SCSI
  62. and
  63. .Tn ATA
  64. host adapters through host adapter drivers.
  65. When the system probes busses, it attaches any devices it finds to the
  66. appropriate drivers.
  67. The
  68. .Xr pass 4
  69. driver, if it is configured in the kernel, will attach to all devices.
  70. .Sh KERNEL CONFIGURATION
  71. There are a number of generic kernel configuration options for the
  72. .Nm
  73. subsystem:
  74. .Bl -tag -width SCSI_NO_SENSE_STRINGS
  75. .It Dv CAMDEBUG
  76. This option compiles in all the
  77. .Nm
  78. debugging printf code.
  79. This will not actually
  80. cause any debugging information to be printed out when included by itself.
  81. See below for details.
  82. .It Dv "CAM_MAX_HIGHPOWER=4"
  83. This sets the maximum allowable number of concurrent "high power" commands.
  84. A "high power" command is a command that takes more electrical power than
  85. most to complete.
  86. An example of this is the
  87. .Tn SCSI
  88. START UNIT command.
  89. Starting a disk often takes significantly more electrical power than normal
  90. operation.
  91. This option allows the
  92. user to specify how many concurrent high power commands may be outstanding
  93. without overloading the power supply on his computer.
  94. .It Dv SCSI_NO_SENSE_STRINGS
  95. This eliminates text descriptions of each
  96. .Tn SCSI
  97. Additional Sense Code and Additional Sense Code Qualifier pair.
  98. Since this
  99. is a fairly large text database, eliminating it reduces the size of the
  100. kernel somewhat.
  101. This is primarily necessary for boot floppies and other
  102. low disk space or low memory space environments.
  103. In most cases, though,
  104. this should be enabled, since it speeds the interpretation of
  105. .Tn SCSI
  106. error messages.
  107. Do not let the "kernel bloat" zealots get to you -- leave
  108. the sense descriptions in your kernel!
  109. .It Dv SCSI_NO_OP_STRINGS
  110. This disables text descriptions of each
  111. .Tn SCSI
  112. opcode.
  113. This option, like the sense string option above, is primarily
  114. useful for environments like a boot floppy where kernel size is critical.
  115. Enabling this option for normal use is not recommended, since it slows
  116. debugging of
  117. .Tn SCSI
  118. problems.
  119. .It Dv SCSI_DELAY=8000
  120. This is the
  121. .Tn SCSI
  122. "bus settle delay."
  123. In
  124. .Nm ,
  125. it is specified in
  126. .Em milliseconds ,
  127. not seconds like the old
  128. .Tn SCSI
  129. layer used to do.
  130. When the kernel boots, it sends a bus reset to each
  131. .Tn SCSI
  132. bus to tell each device to reset itself to a default set of transfer
  133. negotiations and other settings.
  134. Most
  135. .Tn SCSI
  136. devices need some amount of time to recover from a bus reset.
  137. Newer disks
  138. may need as little as 100ms, while old, slow devices may need much longer.
  139. If the
  140. .Dv SCSI_DELAY
  141. is not specified, it defaults to 2 seconds.
  142. The minimum allowable value for
  143. .Dv SCSI_DELAY
  144. is "100", or 100ms.
  145. One special case is that if the
  146. .Dv SCSI_DELAY
  147. is set to 0, that will be taken to mean the "lowest possible value."
  148. In that case, the
  149. .Dv SCSI_DELAY
  150. will be reset to 100ms.
  151. .El
  152. .Pp
  153. All devices and busses support dynamic allocation so that
  154. an upper number of devices and controllers does not need to be configured;
  155. .Cd "device da"
  156. will suffice for any number of disk drivers.
  157. .Pp
  158. The devices are either
  159. .Em wired
  160. so they appear as a particular device unit or
  161. .Em counted
  162. so that they appear as the next available unused unit.
  163. .Pp
  164. Units are wired down by setting kernel environment hints.
  165. This is usually done either interactively from the
  166. .Xr loader 8 ,
  167. or automatically via the
  168. .Pa /boot/device.hints
  169. file.
  170. The basic syntax is:
  171. .Bd -literal -offset indent
  172. hint.device.unit.property="value"
  173. .Ed
  174. .Pp
  175. Individual
  176. .Nm
  177. bus numbers can be wired down to specific controllers with
  178. a config line similar to the following:
  179. .Bd -literal -offset indent
  180. hint.scbus.0.at="ahd1"
  181. .Ed
  182. .Pp
  183. This assigns
  184. .Nm
  185. bus number 0 to the
  186. .Em ahd1
  187. driver instance.
  188. For controllers supporting more than one bus, a particular bus can be assigned
  189. as follows:
  190. .Bd -literal -offset indent
  191. hint.scbus.0.at="ahc1"
  192. hint.scbus.0.bus="1"
  193. .Ed
  194. .Pp
  195. This assigns
  196. .Nm
  197. bus 0 to the bus 1 instance on
  198. .Em ahc0 .
  199. Peripheral drivers can be wired to a specific bus, target, and lun as so:
  200. .Bd -literal -offset indent
  201. hint.da.0.at="scbus0"
  202. hint.da.0.target="0"
  203. hint.da.0.unit="0"
  204. .Ed
  205. .Pp
  206. This assigns
  207. .Em da0
  208. to target 0, unit (lun) 0 of scbus 0.
  209. Omitting the target or unit hints will instruct
  210. .Nm
  211. to treat them as wildcards
  212. and use the first respective counted instances.
  213. These examples can be combined together to allow a peripheral device to be
  214. wired to any particular controller, bus, target, and/or unit instance.
  215. .Pp
  216. When you have a mixture of wired down and counted devices then the
  217. counting begins with the first non-wired down unit for a particular
  218. type.
  219. That is, if you have a disk wired down as
  220. .Em "device da1" ,
  221. then the first non-wired disk shall come on line as
  222. .Em da2 .
  223. .Sh ADAPTERS
  224. The system allows common device drivers to work through many different
  225. types of adapters.
  226. The adapters take requests from the upper layers and do
  227. all IO between the
  228. .Tn SCSI
  229. or
  230. .Tn ATA
  231. bus and the system.
  232. The maximum size of a transfer is governed by the
  233. adapter.
  234. Most adapters can transfer 64KB in a single operation, however
  235. many can transfer larger amounts.
  236. .Sh TARGET MODE
  237. Some adapters support
  238. .Em target mode
  239. in which the system is capable of operating as a device, responding to
  240. operations initiated by another system.
  241. Target mode is supported for
  242. some adapters, but is not yet complete for this version of the
  243. .Nm
  244. .Tn SCSI
  245. subsystem.
  246. .Sh FILES
  247. see other
  248. .Nm
  249. device entries.
  250. .Sh DIAGNOSTICS
  251. An XPT_DEBUG CCB can be used to enable various amounts of tracing information
  252. on any specific bus/device from the list of options compiled into the kernel.
  253. There are currently seven debugging flags that may be compiled in and used:
  254. .Bl -tag -width CAM_DEBUG_SUBTRACE
  255. .It Dv CAM_DEBUG_INFO
  256. This flag enables general informational printfs for the device
  257. or devices in question.
  258. .It Dv CAM_DEBUG_TRACE
  259. This flag enables function-level command flow tracing.
  260. i.e.\&
  261. kernel printfs will happen at the entrance and exit of various functions.
  262. .It Dv CAM_DEBUG_SUBTRACE
  263. This flag enables debugging output internal to various functions.
  264. .It Dv CAM_DEBUG_CDB
  265. This flag will cause the kernel to print out all
  266. .Tn ATA
  267. and
  268. .Tn SCSI
  269. commands sent to a particular device or devices.
  270. .It Dv CAM_DEBUG_XPT
  271. This flag will enable command scheduler tracing.
  272. .It Dv CAM_DEBUG_PERIPH
  273. This flag will enable peripheral drivers messages.
  274. .It Dv CAM_DEBUG_PROBE
  275. This flag will enable devices probe process tracing.
  276. .El
  277. .Pp
  278. Some of these flags, most notably
  279. .Dv CAM_DEBUG_TRACE
  280. and
  281. .Dv CAM_DEBUG_SUBTRACE ,
  282. will produce kernel printfs in EXTREME numbers.
  283. .Pp
  284. Users can enable debugging from their kernel config file, by using
  285. the following kernel config options:
  286. .Bl -tag -width CAM_DEBUG_COMPILE
  287. .It Dv CAMDEBUG
  288. This builds into the kernel all possible
  289. .Nm
  290. debugging.
  291. .It Dv CAM_DEBUG_COMPILE
  292. This allows to specify support for which debugging flags described above
  293. should be built into the kernel.
  294. Flags may be ORed together if the user wishes to
  295. see printfs for multiple debugging levels.
  296. .It Dv CAM_DEBUG_FLAGS
  297. This allows to set the various debugging flags from a kernel config file.
  298. .It Dv CAM_DEBUG_BUS
  299. Specify a bus to debug.
  300. To debug all busses, set this to -1.
  301. .It Dv CAM_DEBUG_TARGET
  302. Specify a target to debug.
  303. To debug all targets, set this to -1.
  304. .It Dv CAM_DEBUG_LUN
  305. Specify a lun to debug.
  306. To debug all luns, set this to -1.
  307. .El
  308. .Pp
  309. Users may also enable debugging on the fly by using the
  310. .Xr camcontrol 8
  311. utility, if wanted options built into the kernel.
  312. See
  313. .Xr camcontrol 8
  314. for details.
  315. .Sh SEE ALSO
  316. .Xr ada 4 ,
  317. .Xr aha 4 ,
  318. .Xr ahb 4 ,
  319. .Xr ahc 4 ,
  320. .Xr ahci 4 ,
  321. .Xr ata 4 ,
  322. .Xr bt 4 ,
  323. .Xr cd 4 ,
  324. .Xr ch 4 ,
  325. .Xr da 4 ,
  326. .Xr pass 4 ,
  327. .Xr pt 4 ,
  328. .Xr sa 4 ,
  329. .Xr xpt 4 ,
  330. .Xr camcontrol 8
  331. .Sh HISTORY
  332. The
  333. .Nm
  334. .Tn SCSI
  335. subsystem first appeared in
  336. .Fx 3.0 .
  337. The
  338. .Nm
  339. ATA support was added in
  340. .Fx 8.0 .
  341. .Sh AUTHORS
  342. .An -nosplit
  343. The
  344. .Nm
  345. .Tn SCSI
  346. subsystem was written by
  347. .An Justin Gibbs
  348. and
  349. .An Kenneth Merry .
  350. The
  351. .Nm
  352. .Tn ATA
  353. support was added by
  354. .An Alexander Motin Aq mav@FreeBSD.org .