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Under GNU General Public License
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RAW(8) RAW(8)
NAME
raw - bind a Linux raw character device
SYNOPSIS
raw /dev/raw/raw<N> <major> <minor>
raw /dev/raw/raw<N> /dev/<blockdev>
raw -q /dev/raw/raw<N>
raw -qa
WARNING
Although Linux includes support for rawio, it is now a deprecated interface. If
your application performs device access using this interface, Red Hat encourages
you to modify your application to open the block device with the O_DIRECT flag. The
rawio interface will exist for the life of Red Hat Enterprise Linux 5, but is a
candidate for removal from future releases.
DESCRIPTION
raw is used to bind a Linux raw character device to a block device. Any block
device may be used: at the time of binding, the device driver does not even have to
be accessible (it may be loaded on demand as a kernel module later).
raw is used in two modes: it either sets raw device bindings, or it queries exist-
ing bindings. When setting a raw device, /dev/raw/raw<N> is the device name of an
existing raw device node in the filesystem. The block device to which it is to be
bound can be specified either in terms of its major and minor device numbers, or as
a path name /dev/<blockdev> to an existing block device file.
The bindings already in existence can be queried with the -q option, with is used
either with a raw device filename to query that one device, or with the -a option
to query all bound raw devices.
Unbinding can be done by specifying major and minor 0.
Once bound to a block device, a raw device can be opened, read and written, just
like the block device it is bound to. However, the raw device does not behave
exactly like the block device. In particular, access to the raw device bypasses
the kernel's block buffer cache entirely: all I/O is done directly to and from the
address space of the process performing the I/O. If the underlying block device
driver can support DMA, then no data copying at all is required to complete the
I/O.
Because raw I/O involves direct hardware access to a process's memory, a few extra
restrictions must be observed. All I/Os must be correctly aligned in memory and on
disk: they must start at a sector offset on disk, they must be an exact number of
sectors long, and the data buffer in virtual memory must also be aligned to a mul-
tiple of the sector size. The sector size is 512 bytes for most devices.
Use the /etc/sysconfig/rawdevices file to define the set of raw device mappings
automatically created during the system startup sequence. The format of the file is
the same used in the command line with the exception that the "raw" command itself
is omitted.
OPTIONS
-q Set query mode. raw will query an existing binding instead of setting a new
one.
-a With -q , specifies that all bound raw devices should be queried.
-h provides a usage summary.
BUGS
The Linux dd (1) command should be used without bs= option or the blocksize needs
to be a multiple of the sector size of the device (512 bytes usually) otherwise it
will fail with "Invalid Argument" messages (EINVAL).
Raw I/O devices do not maintain cache coherency with the Linux block device buffer
cache. If you use raw I/O to overwrite data already in the buffer cache, the
buffer cache will no longer correspond to the contents of the actual storage device
underneath. This is deliberate, but is regarded either a bug or a feature depend-
ing on who you ask!
AUTHOR
Stephen Tweedie (sct AT redhat.com)
Version 0.1 Aug 1999 RAW(8)
Generated by $Id: phpMan.php,v 4.49 2006/02/26 13:18:18 chedong Exp $ Author: Che Dong
On Apache/1.3.37 (Unix) mod_throttle/3.1.2 FrontPage/5.0.2.2635 mod_psoft_traffic/0.2 mod_ssl/2.8.28 OpenSSL/0.9.8b
Under GNU General Public License
2008-11-21 06:39 @38.103.63.55 Crawled by CCBot/1.0 (+http://www.commoncrawl.org/bot.html)