Re: debian (1.2.22-3~bpo8+1) package build failure

Olly Betts <[email protected]> wrote:
> On Sat, Aug 06, 2016 at 03:43:48AM +0000, Eric Wong wrote:
> > Eric Wong <[email protected]> wrote:
> > > I'm trying to test a trivial patch to set FD_CLOEXEC on the
> > > flintlock lockfd when using F_OFD_SETLK
> > 
> > Fwiw, this is the patch I was originally going to test.
> > (but now I see maybe my F_SETFD might only need to be
> >  called on F_OFD_SETLK success)   Description at bottom.
> > 
> > --- a/backends/flint_lock.cc
> > +++ b/backends/flint_lock.cc
> > @@ -108,6 +108,10 @@ FlintLock::lock(bool exclusive, string & explanation) {
> >  	return ((errno == EMFILE || errno == ENFILE) ? FDLIMIT : UNKNOWN);
> >      }
> >  
> > +#ifdef FD_CLOEXEC
> > +    (void)fcntl(lockfd, F_SETFD, FD_CLOEXEC);
> > +#endif
> > +
> 
> This is fixed in master and 1.4.0, which set CLOEXEC for all relevant
> FDs.  Those changes weren't backported as they were rather pervasive
> and we'd had no user reports of issues due to this, but since the
> CLOEXEC changes we now we lock in process on a modern Linux kernel and
> that change got backported - as you've noticed that can cause more major
> issues without CLOEXEC, and I think we ought to backport CLOEXEC for the
> lock file to 1.2.x.

Thanks for the response.   Is this the svn/1.2 branch in
the git repo?  Currently at:

	commit 76e09ea726d9666462567b5839899fc53f53cebe
	("Fix typo in POD docs for Search::Xapian")

Did you get a chance to look into the build failure?
No worries if not, I've been busy, too; I'm just happy
that https://public-inbox.org/git/
(git mailing list archives with Xapian)
seems to be holding up :)

> I'd suggest comparing backends/flint_lock.cc with the version on git
> master - the CLOEXEC-related changes are easy to see, and a bit more
> rigorous than your patch (CLOEXEC is applied when the lock file is
> opened, at least on platforms which support that, which means there's
> no window in which fork()+exec() can occur in another thread while
> the FD is unprotected).
> 
> Arguably we ought to avoid using OFD locks if we don't have CLOEXEC
> (then we use a child process to hold the lock, which also means that
> fork()+exec() doesn't end up with a locked FD open).  Currently
> only Linux supports OFD locks, and has CLOEXEC so right now it's
> not an issue.  OFD locks have been proposed for POSIX standardisation,
> but since CLOEXEC is in POSIX.1-2008, I suspect any platform which adds
> support for OFD locks would actually support CLOEXEC anyway.

Yes, I doubt anybody would implement OFD before CLOEXEC :)