Re: ipc: object information data in proc and sysfs

From: Andrew Morton
Date: Mon Nov 19 2012 - 19:12:40 EST


On Sun, 18 Nov 2012 12:31:08 +0000
Sami Kerola <kerolasa@xxxxxx> wrote:

> Hello,
>
> While back I started to look how to get util-linux ipcs(1) tool to
> read values from /proc instead of using IPC multiplex functions. Most
> of the data ipcs(1) is interested is available in /proc, but there are
> few exceptions, such as
>
> msgctl q_qbytes
> semctl getval
> semctl sempid
> semctl semncnt
> semctl semzcnt
>
> The simplest thing to do would be to add values in /proc/sysvipc/msg
> and /proc/sysvipc/sem as additional fields, but that does not seem
> right, as it would result to ABI change.
>
> More effort requiring change would be to add information in new sysfs
> paths. The IPC facilities are using id's which could be used as
> placeholder directories for the data needed. Something like
>
> /proc/sys/kernel/ipc/{m,s,q}/id/info
> ^^^^^^^^^^^^^^^^^^^
>
> That sort of structure would allow future extensions IPC data without
> much pain. I also assume that subdirectories could allow a little
> more precise controls, and perhaps some selected values might be made
> writable in future. If nothing else at least expressing in sensible
> format semaphore lock wait queues could make debugging tools, such as
> lslocks(8), more useful.
>
> I could give a try this change, but not without hearing the concept
> makes sense and could be considered part of upstream kernel (assuming
> my coding meets the usual quality criteria).
>
> Any thoughts, comments, recommendations?

Where's the benefit in switching ipcs over to using /proc?

procfs reads are probably slower than the syscalls?
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