Re: noexec on /dev/shm

On Thu, 2010-12-23 at 22:59 +0100, Lennart Poettering wrote:

On Mon, 20.12.10 19:16, Fernando Lopez-Lezcano (nando@ccrma.Stanford.EDU) wrote:

...

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)

If this uses O_NOATIME it shouldnt matter whether the backing fs is tmpfs or real disk.

Sadly this turns out not to be the case, at least if I'm reading fs/pipe.c correctly. O_NOATIME will turn off atime updates, but mtime and ctime are still modified on every pipe write, and there's no such thing as O_NOCMTIME even though the filesystem layer does have the concept internally. Which means device-backed filesystems will see write traffic just for using named pipes.

Heck of lame. Someone should fix that.

- ajax