Re: [Fwd: Serious problem with mount(8)]

On Wed, 2007-05-23 at 09:30 +0200, Dag-Erling Smørgrav wrote:
> Joe Marcus Clarke <marcus_at_FreeBSD.org> writes:
> > Dag-Erling Smørgrav <des_at_des.no> writes:
> > > Better yet, extend the pidfile API with a function which reads the
> > > contents of a PID file and also checks whether it's locked.
> > I'd be happy to do this.  Is my approach with this code sound (i.e. can
> > I simply port this to pidfile(3)), or should I take another approach?
> > Thanks.
> 
> You expose yourself to all sorts of race conditions by opening the file
> twice...  what you should do is something like (off the top of my head):
> 
>         fd = open(pidfile, O_RDONLY);
>         fcntl(fd, F_GETLK, &fl)
>         if (fl.l_type == F_UNLCK)
>                 return (-1)
>         fstat(fd, &fsb);
>         read(fd, buf, fsb.st_len);
>         if (atoi(buf) != fl.l_pid)
>                 return (-1);
> #ifdef OPTIONAL
>         stat(pidfile, &sb);
>         if (sb.st_dev != fsb.st_dev || sb.st_ino != fsb.st_ino)
>                 return (-1);
> #endif
>         return (fl.l_pid);
> 
> with appropriate error checking, of course.

Thanks for the tip, but this is moot now that flopen(3) has been fixed,
and pidfile_open(3) operates as documented.

Joe

-- 
Joe Marcus Clarke
FreeBSD GNOME Team      ::      gnome_at_FreeBSD.org
FreeNode / #freebsd-gnome
http://www.FreeBSD.org/gnome