scsi, scsibus —
SCSI system
cd* at scsibus?
ch* at scsibus?
safte* at scsibus?
sd* at scsibus?
ses* at scsibus?
st* at scsibus?
uk* at scsibus?
# multipath support
emc* at scsibus?
hds* at scsibus?
rdac* at scsibus?
sym* at scsibus?
TABLE OF CONTENTS
The SCSI system provides a uniform and modular system for the
implementation of drivers to control various SCSI devices, and to utilize
different SCSI host adapters through host adapter drivers. When the system
probes the SCSI buses, it attaches any devices it finds to
the appropriate drivers. If no driver seems appropriate, then it attaches the
device to the uk (unknown) driver so that user level SCSI ioctls may still be
performed against the device.
The option SCSIDEBUG enables the debug ioctl.
All devices and the SCSI buses support boot time allocation so
that an upper number of devices and controllers does not need to be
configured; sd* at scsibus? will suffice for any
number of disk drivers.
The devices are either wired so they appear as a
particular device unit or counted so that they appear as
the next available unused unit.
To configure a driver in the kernel without wiring down the device
use a config line similar to ch* at scsibus? to
include the changer driver.
To wire down a unit use a config line similar to
ch1 at scsibus0 target 4 lun 0 to assign changer 1
as the changer with SCSI ID 4, SCSI logical unit 0 on SCSI bus 0. Individual
scsibuses can be wired down to specific controllers with a config line
similar to scsibus0 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 scsibus3
at ahc1 bus 1 which assigns scsibus 1 to the second bus probed on the
ahc1 device.
When there is 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 a disk is wired down as sd1 at scsibus?,
then the first non-wired disk shall come on line as
sd2.
There are a number of ioctls that work on any SCSI device.
They are defined in
<sys/scsiio.h> and can be
applied against any SCSI device that permits them. For the tape, it must be
applied against the control device. See the manual page for each device type
for more information about how generic SCSI ioctls may be applied to a
specific device.
SCIOCRESET- Reset a device.
SCIOCDEBUG
int *- Turn on debugging. All SCSI operations originating from this device's
driver will be traced to the console, along with other information.
Debugging is controlled by four bits, described in the header file. If no
debugging is configured into the kernel, debugging will have no effect.
SCSI debugging is controlled by the configuration option
SCSIDEBUG.
SCIOCCOMMAND
scsireq_t *- Take a SCSI command and data from a user process and apply them to the
SCSI device. Return all status information and return data to the process.
The ioctl will return a successful status even if the device rejected the
command. As all status is returned to the user, it is up to the user
process to examine this information to decide the success of the
command.
SCIOCIDENTIFY
struct scsi_addr *- Ask the driver what its bus, target and lun are. In addition, the device
type, ATAPI or SCSI, is returned.
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 I/O
between the 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, and many can transfer larger amounts.
When the kernel is compiled with option SCSIDEBUG, the SCIOCDEBUG ioctl can be
used to enable various amounts of tracing information on any specific device.
Devices not being traced will not produce trace information. The four bits
that make up the debug level each control certain types of debugging
information.
Bit
0- shows all SCSI bus operations including SCSI commands, error information
and the first 48 bytes of any data transferred.
Bit
1- shows routines called.
Bit
2- shows information about what branches are taken and often some of the
return values of functions.
Bit
3- shows more detailed information including DMA scatter-gather logs.
cd(4),
ch(4),
emc(4),
hds(4),
intro(4),
mpath(4),
rdac(4),
safte(4),
sd(4),
ses(4),
st(4),
sym(4),
uk(4),
scsi(8)
This scsi system appeared in MACH 2.5 at TRW.
![[OpenBSD]](/openbsd.gif){kind=small}