freebsd-dev/share/man/man4/scsi.4

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.Dd October 15, 1998
.Dt SCSI 4
.Os FreeBSD 3.0
.Sh NAME
.Nm SCSI ,
.Nm CAM
.Nd CAM SCSI subsystem
.Sh SYNOPSIS
.Cd "controller scbus0"
.Cd "controller scbus1 at ahc0"
.Cd "controller scbus3 at ahc1 bus 0"
.Cd "controller scbus2 at ahc1 bus 1"
.Cd "device cd0"
.Cd "device ch0"
.Cd "device da0"
.Cd "device pass0"
.Cd "device pt0"
.Cd "device sa0"
.Cd "device ch1 at scbus0 target 4 unit 0"
.Cd options		CAMDEBUG
.Cd options		CAM_DEBUG_BUS=-1
.Cd options		CAM_DEBUG_TARGET=-1
.Cd options		CAM_DEBUG_LUN=-1
.Cd options		CAM_DEBUG_FLAGS=CAM_DEBUG_INFO|CAM_DEBUG_CDB
.Cd options		CAM_MAX_HIGHPOWER=4
.Cd options		SCSI_NO_SENSE_STRINGS
.Cd options		SCSI_NO_OP_STRINGS
.Cd options		SCSI_DELAY=8000
.Sh DESCRIPTION
The CAM
.Tn SCSI
subsystem provides a uniform and modular system for the implementation
of drivers to control various
.Tn SCSI
devices, and to utilize different
.Tn SCSI
host adapters through host adapter drivers. When the system probes the 
.Tn SCSI
busses, it attaches any devices it finds to the appropriate
drivers.  The
.Xr pass 4
driver, if it is configured in the kernel, will attach to all
.Tn SCSI
devices.
.Sh KERNEL CONFIGURATION
There are a number of generic kernel configuration options for the
CAM
.Tn SCSI
subsystem:
.Bl -tag -width SCSI_NO_SENSE_STRINGS
.It Dv CAMDEBUG
This option enables the CAM debugging printf code.  This won't actually
cause any debugging information to be printed out when included by itself.
Enabling printouts requires additional configuration.  See below for
details.
.It Dv "CAM_MAX_HIGHPOWER=4"
This sets the maximum allowable number of concurrent "high power" commands.
A "high power" command is a command that takes more electrical power than
most to complete.  An example of this (and the only command currently
tagged as "high power") is the
.Tn SCSI
START UNIT command.  Starting a SCSI disk often takes significantly more
electrical power than normal operation of the disk.  This option allows the
user to specify how many concurrent high power commands may be outstanding
without overloading the power supply on his computer.
.It Dv SCSI_NO_SENSE_STRINGS
This eliminates text descriptions of each
.Tn SCSI
Additional Sense Code and Additional Sense Code Qualifier pair.  Since this
is a fairly large text database, eliminating it reduces the size of the
kernel somewhat.  This is primarily necessary for boot floppies and other
low disk space or low memory space environments.  In most cases, though,
this should be enabled, since it speeds the interpretation of
.Tn SCSI
error messages.  Don't let the "kernel bloat" zealots get to you -- leave
the sense descriptions in your kernel!
.It Dv SCSI_NO_OP_STRINGS
This disables text descriptions of each
.Tn SCSI
opcode.  This option, like the sense string option above, is primarily
useful for environments like a boot floppy where kernel size is critical.
Enabling this option for normal use isn't recommended, since it slows
debugging of
.Tn SCSI
problems.
.It Dv SCSI_DELAY=8000
This is the
.Tn SCSI
"bus settle delay."  In CAM, it is specified in
.Em milliseconds ,
not seconds like the old
.Tn SCSI
layer used to do.  When the kernel boots, it sends a bus reset to each
.Tn SCSI
bus to tell each device to reset itself to a default set of transfer
negotiations and other settings.  Most
.Tn SCSI
devices need some amount of time to recover from a bus reset.  Newer disks
may need as little as 100ms, while old, slow devices may need much longer.
If the
.Dv SCSI_DELAY
isn't specified, it defaults to 2 seconds.  The minimum allowable value for
.Dv SCSI_DELAY
is "100", or 100ms.  One special case is that if the
.Dv SCSI_DELAY
is set to 0, that will be taken to mean the "lowest possible value."  In
that case, the
.Dv SCSI_DELAY
will be reset to 100ms.
.El
.Pp
All devices and the SCSI busses support boot time allocation so that
an upper number of devices and controllers does not need to be configured;
.Cd "device da0"
will suffice for any number of disk drivers.
.Pp
The devices are either
.Em wired
so they appear as a particular device unit or
.Em counted
so that they appear as the next available unused unit.
.Pp
To configure a driver in the kernel without wiring down the device use a
config line similar to
.Cd "device ch0"
to include the changer driver.
.Pp
To wire down a unit use a config line similar to
.Cd "device ch1 at scbus0 target 4 unit 0"
to assign changer 1 as the changer with SCSI ID 4,
SCSI logical unit 0 on SCSI bus 0.
Individual scbuses can be wired down to specific controllers with
a config line similar to
.Cd "controller scbus0 at ahc0"
which assigns scsi bus 0 to the first unit using the ahc driver.
For controllers supporting more than one bus,
the particular bus can be specified as in
.Cd "controller scbus3 at ahc1 bus 1"
which assigns scbus 1 to the second bus probed on the ahc1 device.
.Pp
When you have a mixture of wired down and counted devices then the
counting begins with the first non-wired down unit for a particular
type.  That is, if you have a disk wired down as
.Em "device da1" ,
then the first non-wired disk shall come on line as
.Em da2 .
.Sh ADAPTERS
The system allows common device drivers to work through many different
types of adapters. The adapters take requests from the upper layers and do
all IO between the 
.Em SCSI
bus and the system. The maximum size of a transfer is governed by the
adapter. Most adapters can transfer 64KB in a single operation, however
many can transfer larger amounts.
.Sh TARGET MODE
Some adapters support 
.Em target mode
in which the system is capable of operating as a device, responding to
operations initiated by another system. Target mode is supported for
some adapters, but is not yet complete for this version of the CAM
.Tn SCSI
subsystem.
.Sh FILES
see other scsi device entries.
.Sh DIAGNOSTICS
When the kernel is compiled with options CAMDEBUG, an XPT_DEBUG CCB can be
used to enable various amounts of tracing information on any 
specific device. Devices not being traced will not produce trace information.
There are currently four debugging flags that may be turned on:
.Bl -tag -width CAM_DEBUG_SUBTRACE
.It Dv CAM_DEBUG_INFO
This debugging flag enables general informational printfs for the device
or devices in question.
.It Dv CAM_DEBUG_TRACE
This debugging flag enables function-level command flow tracing.  i.e.
kernel printfs will happen at the entrance and exit of various functions.
.It Dv CAM_DEBUG_SUBTRACE
This debugging flag enables debugging output internal to various functions.
.It Dv CAM_DEBUG_CDB
This debugging flag will cause the kernel to print out all
.Tn SCSI
commands sent to a particular device or devices.
.El
.Pp
Some of these flags, most notably
.Dv CAM_DEBUG_TRACE
and
.Dv CAM_DEBUG_SUBTRACE
will produce kernel printfs in EXTREME numbers.  Because of that, they
aren't especially useful.  There aren't many things logged at the
.Dv CAM_DEBUG_INFO
level, so it isn't especially useful.  The most useful debugging flag is
the
.Dv CAM_DEBUG_CDB
flag.  Users can enable debugging from their kernel config file, by using
the following kernel config options:
.Bl -tag -width CAM_DEBUG_TARGET
.It Dv CAMDEBUG
This enables CAM debugging.  Without this option, users will not even be able
to turn on debugging from userland via
.Xr camcontrol 8 .
.It Dv CAM_DEBUG_FLAGS
This allows the user to set the various debugging flags described above
in a kernel config file.  Flags may be ORed together if the user wishes to
see printfs for multiple debugging levels.
.It Dv CAM_DEBUG_BUS
Specify a bus to debug.  To debug all busses, set this to -1.
.It Dv CAM_DEBUG_TARGET
Specify a target to debug.  To debug all targets, set this to -1.
.It Dv CAM_DEBUG_LUN
Specify a lun to debug.  To debug all luns, set this to -1.
.El
.Pp
When specifying a bus, target or lun to debug, you
.Em MUST
specify all three bus/target/lun options above.  Using wildcards, you
should be able to enable debugging on most anything.
.Pp
Users may also enable debugging printfs on the fly, if the
.Dv CAMDEBUG
option is their config file, by using the
.Xr camcontrol 8
utility.  See
.Xr camcontrol 8
for details.
.Sh SEE ALSO
.Xr aha 4 ,
.Xr ahb 4 ,
.Xr ahc 4 ,
.Xr bt 4 ,
.Xr cd 4 ,
.Xr ch 4 ,
.Xr da 4 ,
.Xr pass 4 ,
.Xr pt 4 ,
.Xr sa 4 ,
.Xr xpt 4 ,
.Xr camcontrol 8
.Sh HISTORY
The CAM
.Tn SCSI
subsystem first appeared in
.Fx 3.0 .
.Sh AUTHORS
The CAM
.Tn SCSI
subsystem was written by
.An Justin Gibbs
and
.An Kenneth Merry .