[PATCH v2 00/14] Fix signal-unsafe logging

[Peter Hutterer]

On Mon, Jun 04, 2012 at 10:20:44AM -0700, Chase Douglas wrote:
> On 06/03/2012 09:20 PM, Peter Hutterer wrote:
> > On Wed, Apr 11, 2012 at 06:33:26PM -0700, Chase Douglas wrote:
> >> On 04/11/2012 04:53 PM, Peter Hutterer wrote:
> >>> On Mon, Apr 09, 2012 at 11:17:26AM -0700, Chase Douglas wrote:
> > [...]
> >>> - the API is rather shocking, replacing one vararg function with a number of
> >>>   mixed calls makes it really hard to grep for the message.
> >>>   a poor man's printf parsing that searches for %d, %s and %x would help
> >>>   here.
> >>
> >> Variadic argument implementation is some of the blackest magic of C
> >> code, and varies a great deal even between architectures of glibc. I
> >> don't know if we can be sure that variadic arguments will always be
> >> signal safe. They aren't mentioned in the POSIX signal(7) man page as
> >> safe functions.
> >>
> >> I doubt we would actually support Interix SUA, for example, but it is
> >> POSIX compliant and its man page says va_* functions are not signal
> >> safe: http://www.suacommunity.com/man/3/varargs.3.html.
> >>
> >>> - given that input drivers almost always use signal-sensitive processing,
> >>>   making xf86IDrvMsg signal safe would go a long way 
> >>
> >> It's variadic, so I don't think that will be possible. I know there's
> >> bound to be some pain here that reaches device drivers, but I don't see
> >> a way around it.
> > 
> > sorry to pick this up so late. I've been banging my head against the wacom
> > driver, finding a good way to log debug messages while parsing events and
> > the crux of the matter is the vararg stuff. I went searching again and found
> > that signal(7) lists execle() and that function takes a variable number of
> > parameters. execle is a POSIX requirement, va_list and friends must be
> > vararg-compatible, which means we can have a normal implementation of the
> > log messaging functions.
> 
> Your logic seems sound, albeit not an exceptionally strong proof that
> varargs are always signal safe :). At this point, I don't have the time
> to rewrite the patches again. Can I hand them off to you to finish?

yeah, I have most of the patches fixed up now, need some more testing now.

Cheers,
  Peter