[svlug] What is /dev/shmfs and how does it relate to API's?

M. Drew Streib dtype at dtype.org
Thu Jul 31 13:44:58 PDT 2003


On Thu, Jul 31, 2003 at 08:28:04PM +0000, M. Drew Streib wrote:
> /dev/shmfs is 'Shared Memory Filesystem'
> 
> A direct mapping to a SysV-style shared memory segment of some sort.
> I'm not sure why you'd want to use a file like this rather than normal
> APIs. Debug maybe?

After looking this up more, and with help from Brian Chrisman...

shmfs is similar to tmpfs in that it is an all RAM/swap filesystem. It
is basically a ramdisk that can be swapped out, and with variable size.
It shouldn't need a /dev entry, afaik, as it is fully virtual. Unlike a
ramdisk, it can be created at any time, and its size is variable depending
on use (basically limited by swap and ram size).

It is specified somewhat in SuS2 and in POSIX.4. 

Original announcment to Linux kernel list:
http://lwn.net/1998/0409/a/shmfs.html

It is currently supported in 2.4+ Linux kernels.

-drew

-- 
M. Drew Streib <dtype at dtype.org>
Independent Rambler, Software/Standards/Freedom/Law -- http://dtype.org/
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