SCSI(4) | Device Drivers Manual | SCSI(4)

# NAME

`scsi`, `scsibus` —
Small Computer Systems Interface (SCSI) bus driver

# SYNOPSIS

`scsibus* at scsi?`
`atapibus* at atapi?`
`options SCSIDEBUG`
`options SCSIVERBOSE`

# DESCRIPTION

The `scsi` driver is the top, machine-independent layer of the two-layer software system that provides an interface for the implementation of drivers to control various SCSI or ATAPI bus devices, and to use different SCSI bus host adapters or EIDE controllers. SCSI bus is capable of supporting a wide variety of peripherals, including hard disks, removable disks, CD-ROMs, scanners, tape drives, and other miscellaneous high-speed devices.

The bottom layer is composed of the drivers for individual EIDE or SCSI bus controller chips (e.g. NCR 5380), accessed through various host bus interfaces, including, but not limited to PCI, ISA, Sbus, TURBOchannel, and NuBus. These individual devices are referred to as “host adaptors” in SCSI terminology, because they connect the SCSI bus to the host computer.

When NetBSD probes the SCSI busses, it “attaches” any devices it finds to the appropriate drivers.

sd(4)
  hard disks
cd(4)
  CD-ROM drives
st(4)
  tape drives
ch(4)
  media changers
ss(4)
  scanners

If no specific driver matches the device, then `scsi` attaches the device to the uk(4) driver so that user level SCSI ioctl(2) calls may still be performed against the device. Currently, only sd(4), cd(4), st(4), and uk(4) can attach to an atapi bus.

Please see the intro(4) manual page to see which SCSI bus host adaptors are supported by NetBSD on your computer system.

# KERNEL CONFIGURATION

The `scsi` software supports some NetBSD kernel config(1) options. They are:

`SCSIDEBUG`
  Compile in a wide variety of `printf`() statements that can be turned on by ioctl(2).
`SCSIVERBOSE`
  Enable additional and more descriptive error and status messages from the `scsi` software.

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.

The devices are either wired so they appear at a particular device unit number or counted so that they appear as the next available unused unit number.

To configure a driver in the kernel without wiring down the device use a config line similar to

`ch* at scsibus? target ? lun ?`

to include the ch(4) 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, logical unit 0, on bus 0. Individual SCSI busses 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(4) driver.

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

`sd1 at scsibus0 target 1 lun 0`

then the first non-wired disk shall come on line as sd2.

# IOCTLS

There are a number of ioctl(2) calls 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 ioctl(2) calls may be applied to a specific device.

`SCIOCRESET`
  Reset a SCSI device.
`SCIOCDEBUG`
  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`
  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(2) call 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`
  Ask the driver what its bus, target and LUN are.
`SCIOCDECONFIG`
  Ask the device to disappear. This may not happen if the device is in use.

# 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 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.

# TARGET MODE

Some adapters support Target Mode in which the system is capable of operating as a device, responding to operations initiated by another system. Target Mode will be supported for some host adapters, but is not yet complete for this version of the SCSI system.

# DIAGNOSTICS

When the kernel is compiled with option `SCSIDEBUG`, the `SCIOCDEBUG` ioctl(2) 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.

# SEE ALSO

config(1), ioctl(2), ata(4), cd(4), ch(4), intro(4), sd(4), se(4), ss(4), st(4), uk(4), scsictl(8)

# HISTORY

This `scsi` system appeared in MACH 2.5 at TRW.

This man page was originally written by Julian Elischer ⟨julian@freebsd.org⟩ for FreeBSD and extensively modified by Erik Fair ⟨fair@NetBSD.org⟩ for NetBSD.

# BUGS

Not every device obeys the SCSI specification as faithfully as it should. As such devices are discovered by the NetBSD Project, their names are added to a quirk list compiled into the `scsi` driver along a list of flags indicating which particular bad behaviors the device exhibits (and that the driver should be prepared to work around).

August 18, 2019 | NetBSD 10.1