SD(3)SD(3)NAMEsd - storage device interface
bind #S /dev
The storage device interface serves a two-level directory giving access
to multiple storage units, typically ATA(PI) or SCSI discs. Each unit
is accessed via files in the directory named by the controller to which
it is attached, C, and by its unit number u. The controller naming
convention for ATA(PI) units starts with the first controller being
named the second etc. up to a maximum of 4 controllers ([C-F]); legacy
controllers are always 'C' and 'D'. There can be a maximum of 2 units
per ATA(PI) controller (). The controller naming convention for
SCSI units starts with the first controller being named the second etc.
up to a maximum of 16 controllers ([0-9a-f]). There can be a maximum
of 16 units per SCSI controller ([0-9a-f]).
Units are not accessed before the first attach. Units may be individu‐
ally attached using the attach specifier, for example
bind -a '#SsdD0' /dev
An attach without a specifier will cause the driver to scan for all
possible units before processing the rest of the name.
The subdirectory for each unit contains two files, ctl and raw. In
addition, if the unit is a direct-access disc of some type it may be
split into partitions and the subdirectory may contain a file per par‐
tition. By default, the partition data will exist for such media.
ctl and partitions
Partitions are added and deleted by writing to the ctl file
part name start-sector end-sector
The default data partition may be deleted. A partition cannot be
deleted if a process has it open. If a change of removable media is
detected, the new media cannot be opened until all open partitions on
the old media are closed.
Partitions are usually created using fdisk and prep(8); the convention
is to name non-Plan 9 partitions after their corresponding operating
systems (e.g., /dev/sdC0/dos) and Plan 9 partitions according to their
function (e.g., /dev/sdC0/swap). The example in prep(8) shows how.
Reading the ctl file returns at least one line of textual information
about the unit. The first line will always be prefixed by and will
give a manufacturer and model number if possible. A line prefixed by
will be returned for appropriate media, e.g. for ATA(PI) units the
remainder of the line contains configuration information from the
device's identify command (config and capabilities) and also the avail‐
able I/O transfer options; this is a diagnostic aid. A line prefixed
by will be returned for appropriate media; at least two numbers will
follow, the first being the number of sectors contained in the unit and
the second the sector size in bytes. Any remaining information on the
geometry line is unit-dependent, for instance, head, cylinder and sec‐
tor counts for ATA discs. If any partitions are defined for the media,
their name, start-sector and end-sector will be returned, prefixed by
% cat /dev/sdD0/ctl
inquiry KENWOOD CD-ROM UCR-421 208E10/20/99 7.39 2 M0
config 85C0 capabilities 0F00 dma 00550004 dmactl 00000000
geometry 242725 2352
part data 0 242725
The use of DMA and multi-sector read/write commands may be enabled and
disabled on ATA(PI) units by writing to the ctl file dma and rwm
respectively followed by on or off. For example, to enable DMA on a
unit that supports it:
% echo 'dma on'>/dev/sd00/ctl
If supported by the unit, the standby timer may be enabled:
% echo 'standby T'>/dev/sdC0/ctl
where T is the standby timer period in seconds. T must be between 30
and 1200, or can be 0 to disable the timer.
The raw file is used to execute an arbitrary command on the unit at a
low level. This is used by programs such as scuzz(8) to manipulate
devices that do not fit the simple storage model or for maintenance
purposes. The following steps may be taken to execute a command
- Write the command to the raw file;
- Read or write data associated with the command, according to the
direction of the transfer.
- Read the raw file to retrieve the status of the command, returned as
a text integer.
Reading /dev/sdctl yields information about each controller, one line
per controller. Writing `config message' to /dev/sdctl passes message
to the legacy configuration machinery, used to set attributes such as
IRQ, port and size. Writing `ctltype message' to /dev/sdctl passes
message to ctltype's wtopctl function with a nil sdev argument, where
ctltype is a known controller type such as ata or scsi. Writing
`sdctlletter message' to /dev/sdctl passes message to sdctlletter's
wtopctl function with an sdev argument corresponding to the named con‐
troller, where ctlletter is a known controller letter such as C or 0.
LUNs (logical unit numbers) are not implemented. For (S)ATA drives,
LUNs are not merely ignored but are actively prevented from working
except for INQUIRY commands.
The 4 controller limit for ATA(PI) is not enforced.
No account is taken of some buggy ATA PCI controllers such as the
ATA(PI) units come up with DMA and multi-sector read/write capability