SIGBUS on wl_shm clients (Re: Newest git version of Wayland is even worse)

[Pekka Paalanen]

On Sat, 8 Dec 2012 17:52:46 -0500
darxus at chaosreigns.com wrote:

> On 12/08, Bill Spitzak wrote:
> > On 12/08/2012 12:23 AM, Pekka Paalanen wrote:
> > 
> > >FWIW, I have seen a bus error (SIGBUS) before. One way to trigger
> > >it is to run out of space on the tmpfs, where your XDG_RUNTIME_DIR
> > >points to. Maybe you should check that?
> > >
> > >I think it needs at least 20-30 MB, to not run out too soon with
> > >shm clients, and the more the better. Of course depends quite a lot
> > >on whether toytoolkit is mainly using shm or EGL buffers. If
> > >you are still on proprietary drivers, it is definitely shm buffers.
> > 
> > Indeed that was it. I had XDG_RUNTIME_DIR set to /var/lock which
> > only has 5M on it. Changing it to /var/tmp makes things work again.
> 
> Is there a way to get a better error message for that?  Or maybe throw a
> warning at startup?

Not really, unless you start checking the free space of the mount
where the XDG_RUNTIME_DIR happens to be on, and have some arbitrary
threshold. Or catch SIGBUS, and print an error saying that please
check free space.

These should be in all the clients, and it is quite ugly anyway.
Libwayland-client certainly should not add signal handlers on its
own, and we cannot really come up with a good number for the free
space, either. Whatever the number, you may still hit the limit, or
then the number is ridiculous.

Since it is a signal, instead of, say, ftruncate() failing, there's
very little we can sanely do, TTBOMK.


Thanks,
pq