2 .\" Julian Elischer <julian@FreeBSD.org>. All rights reserved.
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
7 .\" 1. Redistributions of source code must retain the above copyright
8 .\" notice, this list of conditions and the following disclaimer.
10 .\" 2. Redistributions in binary form must reproduce the above copyright
11 .\" notice, this list of conditions and the following disclaimer in the
12 .\" documentation and/or other materials provided with the distribution.
14 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 .Nd Common Access Method Storage subsystem
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"
55 subsystem provides a uniform and modular system for the implementation
56 of drivers to control various
62 devices, and to utilize different
68 host adapters through host adapter drivers.
69 When the system probes buses, it attaches any devices it finds to the
73 driver, if it is configured in the kernel, will attach to all devices.
74 .Sh KERNEL CONFIGURATION
75 There are a number of generic kernel configuration options for the
78 .Bl -tag -width SCSI_NO_SENSE_STRINGS
80 Additional time to wait after the static parts of the kernel have run to allow
81 for discovery of additional devices which may take time to connect,
82 such as USB attached storage.
83 .It Dv CAM_IOSCHED_DYNAMIC
84 Enable dynamic decisions in the I/O scheduler based on hints and the current
85 performance of the storage devices.
87 Enable collection of statistics for periph devices.
88 .It Dv CAM_TEST_FAILURE
89 Enable ability to simulate I/O failures.
91 This option compiles in all the
93 debugging printf code.
94 This will not actually
95 cause any debugging information to be printed out when included by itself.
96 See below for details.
97 .It Dv "CAM_MAX_HIGHPOWER=4"
98 This sets the maximum allowable number of concurrent "high power" commands.
99 A "high power" command is a command that takes more electrical power than
101 An example of this is the
104 Starting a disk often takes significantly more electrical power than normal
106 This option allows the
107 user to specify how many concurrent high power commands may be outstanding
108 without overloading the power supply on his computer.
109 .It Dv SCSI_NO_SENSE_STRINGS
110 This eliminates text descriptions of each
112 Additional Sense Code and Additional Sense Code Qualifier pair.
114 is a fairly large text database, eliminating it reduces the size of the
116 This is primarily necessary for boot floppies and other
117 low disk space or low memory space environments.
118 In most cases, though,
119 this should be enabled, since it speeds the interpretation of
122 Do not let the "kernel bloat" zealots get to you -- leave
123 the sense descriptions in your kernel!
124 .It Dv SCSI_NO_OP_STRINGS
125 This disables text descriptions of each
128 This option, like the sense string option above, is primarily
129 useful for environments like a boot floppy where kernel size is critical.
130 Enabling this option for normal use is not recommended, since it slows
134 .It Dv SCSI_DELAY=8000
142 not seconds like the old
145 When the kernel boots, it sends a bus reset to each
147 bus to tell each device to reset itself to a default set of transfer
148 negotiations and other settings.
151 devices need some amount of time to recover from a bus reset.
153 may need as little as 100ms, while old, slow devices may need much longer.
156 is not specified, it defaults to 2 seconds.
157 The minimum allowable value for
160 One special case is that if the
162 is set to 0, that will be taken to mean the "lowest possible value."
165 will be reset to 100ms.
168 All devices and buses support dynamic allocation so that
169 an upper number of devices and controllers does not need to be configured;
171 will suffice for any number of disk drivers.
173 The devices are either
175 so they appear as a particular device unit or
177 so that they appear as the next available unused unit.
179 Units are wired down by setting kernel environment hints.
180 This is usually done either interactively from the
182 or automatically via the
183 .Pa /boot/device.hints
186 .Bd -literal -offset indent
187 hint.device.unit.property="value"
192 bus numbers can be wired down to specific controllers with
193 a config line similar to the following:
194 .Bd -literal -offset indent
195 hint.scbus.0.at="ahd1"
203 For controllers supporting more than one bus, a particular bus can be assigned
205 .Bd -literal -offset indent
206 hint.scbus.0.at="ahc1"
212 bus 0 to the bus 1 instance on
214 Peripheral drivers can be wired to a specific bus, target, and lun as so:
215 .Bd -literal -offset indent
216 hint.da.0.at="scbus0"
223 to target 0, unit (lun) 0 of scbus 0.
224 Omitting the target or unit hints will instruct
226 to treat them as wildcards
227 and use the first respective counted instances.
228 These examples can be combined together to allow a peripheral device to be
229 wired to any particular controller, bus, target, and/or unit instance.
234 .Bd -literal -offset indent
235 hint.nvme.4.at="pci7:0:0"
236 hint.scbus.10.at="nvme4"
237 hint.nda.10.at="scbus10"
238 hint.nda.10.target="1"
239 hint.nda.10.unit="12"
240 hint.nda.11.at="scbus10"
241 hint.nda.11.target="1"
245 This assigns the NVMe card living at PCI bus 7 slot 0 function 1 to scbus 10.
249 The unit is the namespace identifier from the drive.
250 The namespace id 1 is exported as
252 and namespace id 2 is exported as
255 For devices that provide a serial number, units may be wired to that serial
256 number without regard where the drive is attached:
257 .Bd -literal -offset indent
258 hint.nda.3.sn="CY0AN07101120B12P"
259 hint.da.44.sn="143282400011"
260 hint.ada.2.sn="A065D591"
267 to drives with the specified serial numbers.
268 One need not specify an
270 line when serial numbers are used.
272 The system allows common device drivers to work through many different
274 The adapters take requests from the upper layers and do
282 The maximum size of a transfer is governed by the
284 Most adapters can transfer 64KB in a single operation, however
285 many can transfer larger amounts.
287 Some adapters support
289 in which the system is capable of operating as a device, responding to
290 operations initiated by another system.
291 Target mode is supported for
292 some adapters, but is not yet complete for this version of the
299 subsystem glues together the upper layers of the system to the storage devices.
300 PERIPH devices accept storage requests from GEOM and other upper layers of the
301 system and translates them into protocol requests.
302 XPT (transport) dispatches these protocol requests to a SIM driver.
303 A SIM driver takes protocol requests and translates them into hardware commands
304 the host adapter understands to transfer the protocol requests, and data (if
305 any) to the storage device.
306 The CCB transports these requests around as messages.
308 The Common Access Method was a standard defined in the 1990s to talk to disk
311 is one of the few operating systems to fully implement this model.
312 The interface between different parts of CAM is the CCB (or CAM Control Block).
313 Each CCB has a standard header, which contains the type of request and dispatch
314 information, and a command specific portion.
315 A CAM Periph generates requests.
316 The XPT layer dispatches these requests to the appropriate SIM.
317 Some CCBs are sent directly to the SIM for immediate processing, while others
318 are queued and complete when the I/O has finished.
319 A SIM takes CCBs and translates them into hardware specific commands to push the
320 SCSI CDB or other protocol control block to the peripheral, along with setting
321 up the DMA for the associated data.
323 A periph driver knows how to translate standard requests into protocol messages
324 that a SIM can deliver to hardware.
325 These requests can come from any upper layer source, but primarily come in via
326 GEOM as a bio request.
327 They can also come in directly from character device requests for tapes and pass
330 Disk devices, or direct access (da) in CAM, are one type of peripheral.
331 These devices present themselves to the kernel a device ending in
333 Each protocol has a unique device name:
336 SCSI or SAS device, or devices that accept SCSI CDBs for I/O.
342 An SD or MMC block storage device.
345 Tape devices are called serial access
350 They interface to the system via a character device and provide
352 control for tape drives.
356 device will pass through CCB requests from userland to the SIM directly.
357 The device is used to send commands other than read, write, trim or flush to a
361 command uses this device.
363 The transport driver connects the periph to the SIM.
364 It is not configured separately.
365 It is also responsible for device discovery for those SIM drivers that do not
366 enumerate themselves.
368 SIM used to stand for SCSI Interface Module.
369 Now it is just SIM because it understands protocols other than SCSI.
370 There are two types of SIM drivers: virtual and physical.
371 Physical SIMs are typically called host bus adapters (HBA), but not universally.
372 Virtual SIM drivers are for communicating with virtual machine hosts.
378 An XPT_DEBUG CCB can be used to enable various amounts of tracing information
379 on any specific bus/device from the list of options compiled into the kernel.
380 There are currently seven debugging flags that may be compiled in and used:
381 .Bl -tag -width CAM_DEBUG_SUBTRACE
382 .It Dv CAM_DEBUG_INFO
383 This flag enables general informational printfs for the device
384 or devices in question.
385 .It Dv CAM_DEBUG_TRACE
386 This flag enables function-level command flow tracing i.e.,
387 kernel printfs will happen at the entrance and exit of various functions.
388 .It Dv CAM_DEBUG_SUBTRACE
389 This flag enables debugging output internal to various functions.
391 This flag will cause the kernel to print out all
395 commands sent to a particular device or devices.
397 This flag will enable command scheduler tracing.
398 .It Dv CAM_DEBUG_PERIPH
399 This flag will enable peripheral drivers messages.
400 .It Dv CAM_DEBUG_PROBE
401 This flag will enable devices probe process tracing.
404 Some of these flags, most notably
407 .Dv CAM_DEBUG_SUBTRACE ,
408 will produce kernel printfs in EXTREME numbers.
410 Users can enable debugging from their kernel config file, by using
411 the following kernel config options:
412 .Bl -tag -width CAM_DEBUG_COMPILE
414 This builds into the kernel all possible
417 .It Dv CAM_DEBUG_COMPILE
418 This specifies support for which debugging flags described above
419 should be built into the kernel.
420 Flags may be ORed together if the user wishes to
421 see printfs for multiple debugging levels.
422 .It Dv CAM_DEBUG_FLAGS
423 This sets the various debugging flags from a kernel config file.
425 Specify a bus to debug.
426 To debug all buses, set this to -1.
427 .It Dv CAM_DEBUG_TARGET
428 Specify a target to debug.
429 To debug all targets, set this to -1.
431 Specify a lun to debug.
432 To debug all luns, set this to -1.
435 Users may also enable debugging on the fly by using the
437 utility, if wanted options built into the kernel.
448 .It Sy Periph Drivers:
482 .It Sy Deprecated or Poorly Supported SIM Devices:
504 subsystem first appeared in
508 ATA support was added in
515 subsystem was written by
523 .An Alexander Motin Aq Mt mav@FreeBSD.org .
528 .An Warner Losh Aq Mt imp@FreeBSD.org .