plan9fox/sys/man/3/sd

.TH SD 3
.SH NAME
sd \- storage device interface
.SH SYNOPSIS
.nf
.B bind #S /dev

.B /dev/sdctl
.BI /dev/sd Cu /ctl
.BI /dev/sd Cu /raw
.BI /dev/sd Cu /data
\&...
.fi
.SH 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,
.IR C  ,
and by its unit number
.IR u .
The controller naming convention for ATA(PI) units starts
with the first controller being named
.LR C ,
the second
.LR D ,
etc. up to a maximum of 4 controllers
.RB ([ C-F ]);
legacy controllers are always 'C' and 'D'.
There can be a maximum of 2 units per ATA(PI) controller
.RB ([ 01 ]).
The controller naming convention for SCSI units starts with
the first controller being named
.LR 0 ,
the second
.LR 1 ,
etc. up to a maximum of 16 controllers
.RB ([ 0-9a-f ]).
There can be a maximum of 16 units per SCSI controller
.RB ([ 0-9a-f ]).
.PP
Units are not accessed before the first attach.
Units may be individually attached using the attach specifier,
for example
.IP
.EX
bind -a '#SsdD0' /dev
.EE
.PP
An attach without a specifier will cause the driver to scan for all possible
units before processing the rest of the name.
.PP
The subdirectory for each unit contains two files,
.I ctl
and
.IR 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 partition.
By default,
the partition
.I data
will exist for such media.
.PP
Partitions are added and deleted by writing to the
.I ctl
file
.IP
.EX
part \f2name start-sector end-sector\fP
delpart \f2name\fP
.EE
.PP
The default
.I 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.
.PP
Partitions are usually created using
.I fdisk
and
.IR prep (8);
the convention is to name non-Plan 9 partitions after their corresponding operating systems
(e.g.,
.BR /dev/sdC0/dos )
and Plan 9 partitions according to their function
(e.g.,
.BR /dev/sdC0/swap ).
The example in
.IR prep (8)
shows how this is done.
.PP
Reading the
.I ctl
file returns at least one line of textual information about
the unit.
The first line will always be prefixed by
.B inquiry
and will give a manufacturer and model number if possible.
A line prefixed by
.B config
will be returned for appropriate media,
e.g. for ATA(PI) units the remainder of the line contains
configuration information from the device's
.I identify
command (config and capabilities)
and also the available I/O transfer options;
this is a diagnostic aid.
A line prefixed by
.B 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 information on the
.B geometry
line is unit-dependent,
for instance, head,
cylinder and sector counts for ATA discs.
If any partitions are defined for the media,
their name, start-sector and end-sector will be returned,
prefixed by
.BR part .
.IP
.EX
% 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
%
.EE
.PP
The use of DMA and multi-sector read/write commands may be
enabled and disabled on ATA(PI) units by writing to the
.B ctl
file
.B dma
and
.B rwm
respectively followed by
.B on
or
.BR off .
For example, to enable DMA on a unit that supports it:
.IP
.EX
% echo 'dma on'>/dev/sd00/ctl
.EE
.PP
If supported by the unit,
the standby timer may be enabled:
.IP
.EX
% echo 'standby \f2T\fP'>/dev/sdC0/ctl
.EE
.PP
where
.I T
is the standby timer period in seconds.
.I T
must be between 30 and 1200,
or can be 0 to disable the timer.
.PP
The
.B raw
file is used to execute an arbitrary command on the unit at
a low level.
This is used by programs such as
.IR 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
.IP \- 3
Write the command to the
.I raw
file;
.IP \-
Read or write data associated with the command, according to the direction of the transfer.
.IP \-
Read the
.I raw
file to retrieve the status of the command,
returned as a text integer.
.LP
Reading
.B /dev/sdctl
yields information about each controller,
one line per controller.
Writing `\fLconfig \fImessage\fR' to
.B /dev/sdctl
passes
.I message
to the legacy configuration machinery,
used to set attributes such as IRQ, port and size.
Writing `\fIctltype message\fR' to
.B /dev/sdctl
passes
.I message
to
.IR ctltype 's
.B wtopctl
function with a nil
.B sdev
argument,
where
.I ctltype
is a known controller type such as
.B ata
or
.BR scsi .
Writing `\c
.BI sd "ctlletter message\fR'
to
.B /dev/sdctl
passes
.I message
to
.BI sd ctlletter\fR's
.B wtopctl
function with an
.B sdev
argument corresponding to the named controller,
where
.I ctlletter
is a known controller letter such as
.B C
or
.BR 0 .
.SH SOURCE
.B /sys/src/9/port/devsd.c
.br
.B /sys/src/9/*/sd*.[hc]
.SH SEE ALSO
.IR scuzz (8)
.SH BUGS
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.
.PP
The 4 controller limit for ATA(PI) is not enforced.
.PP
No account is taken of some buggy ATA PCI controllers
such as the CMD640.
.PP
ATA(PI) units come up with DMA and multi-sector read/write
capability disabled.