SD(3) SD(3)
NAME
sd - storage device interface
SYNOPSIS
bind #S /dev
/dev/sdctl
/dev/sdCu/ctl
/dev/sdCu/raw
/dev/sdCu/data
...
DESCRIPTION
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 conven-
tion for legacy IDE units names the first controller `C',
and the second `D'. There can be a maximum of 4 IDE con-
trollers and a maximum of 2 units per IDE controller ([01]).
Other ATA controllers start with the first controller being
named `E' There can be a maximum of 16 units per non-legacy
ATA controller ([0-9a-f]). The controller naming convention
for SCSI units starts with the first controller being named
`0', the second `1', 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 individually 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 subdirec-
tory may contain a file per partition. By default, the par-
tition data will exist for such media.
Partitions are added and deleted by writing to the ctl file
part name start-sector end-sector
delpart name
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The default data partition may be deleted. A partition can-
not 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 cor-
responding 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 this is
done.
Reading the ctl file returns at least one line of textual
information about the unit. The first line will always be
prefixed by inquiry and will give a manufacturer and model
number if possible. A line prefixed by config will be
returned for appropriate media, e.g. for IDE units the
remainder of the line contains configuration information
from the device's identify command (config and capabilities)
and also the available I/O transfer options; this is a diag-
nostic aid. A line prefixed by geometry 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 informa-
tion on the geometry line is unit-dependent, for instance,
head, cylinder and sector counts for ATA discs. If any par-
titions are defined for the media, their name, start-sector
and end-sector will be returned, prefixed by part.
% 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 SCSI or ATA
commands on the unit at a low level. SCSI commands are
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submitted as raw CDBs up to 16 bytes long. ATA commands are
formatted as ATA8-AST FISes prefixed by two bytes - an ata
escape 0xff and a byte specifying the ATA protcol. All
devices respond to basic SCSI commands such as inquiry .
This is used by programs such as scuzz(8) and atazz(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 for SCSI commands. ATA com-
mands return the one byte status and response FIS.
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 argu-
ment, 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 argu-
ment corresponding to the named controller, where ctlletter
is a known controller letter such as C or 0.
SOURCE
/sys/src/9/port/devsd.c
/sys/src/9/*/sd*.[hc]
SEE ALSO
atazz(8), sdahci(3), sdaoe(3), scuzz(8)
BUGS
LUNs (logical unit numbers) are not implemented. For ATA
drives, LUNs are not merely ignored but are actively pre-
vented from working except for INQUIRY commands.
The 4 controller limit for IDE is not enforced.
No account is taken of some buggy IDE PCI controllers such
as the CMD640.
IDE units come up with DMA and multi-sector read/write capa-
bility disabled.
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