noexec on /dev/shm

[Fernando Lopez-Lezcano]

On 12/20/2010 05:26 PM, Fernando Lopez-Lezcano wrote:
> On 12/20/2010 02:17 PM, Adam Jackson wrote:
>> On Mon, 2010-12-20 at 13:07 -0800, Fernando Lopez-Lezcano wrote:
>>
>>> I would like to bring to the attention of the list another current usage
>>> of the tmpfs mounted on /dev/shm in Fedora packages:
>>>
>>> Jack (the Jack Audio Connection Kit, jackaudio.org) has been using the
>>> file api (apologies if my wording is not absolutely correct in unix
>>> terms) on the tmpfs filesystem that is mounted on /dev/shm for a very
>>> long time (10 years?). "/tmp" is not useful to Jack because Jack's
>>> internal communication pipes can't be stored in any disk based journaled
>>> filesystem as the latencies involved in accessing them cause glitches in
>>> the audio streams handled by Jack.
>>
>> This is right and wrong.
>
> Right! Thanks very much for looking at this in such detail (I presume
> you looked at the 1.9.6 code base?).

This is from Paul Davis, the main architect of Jack (I forwarded him 
your post):

----
this isn't exactly correct.

in /dev/shm on linux we have:

    (a) unix-domain sockets for non-RT communication with the server
    (b) FIFOs for RT wakeups (this could use semaphores now)
    (c) shared memory created via either the sysv or posix shm API

we don't care about the unix domain sockets' performance
characteristics, but its convenient to have them in a known location
that happens to be close to where (b) is located.

we do care about the performance of (b)

(c) just works.
----

-- Fernando