Re: [PATCH 1/2] io: open pipes in non-blocking mode

[Dave Chinner <david@fromorbit.com>]

On Mon, Dec 03, 2018 at 08:20:30AM -0800, Darrick J. Wong wrote:
> On Mon, Dec 03, 2018 at 07:53:42AM +1100, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@redhat.com>
> > 
> > So that O_RDONLY open commands (such as from copy_range) do not
> > block forever waiting on a non-existent writer.
> > 
> > Signed-off-by: Dave Chinner <dchinner@redhat.com>
> > ---
> >  io/open.c | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > diff --git a/io/open.c b/io/open.c
> > index 6ea3e9a2019f..b1d9a0fa317c 100644
> > --- a/io/open.c
> > +++ b/io/open.c
> > @@ -56,6 +56,7 @@ openfile(
> >  	struct fs_path	*fs_path)
> >  {
> >  	struct fs_path	*fsp;
> > +	struct stat	st;
> >  	int		fd;
> >  	int		oflags;
> >  
> > @@ -79,6 +80,18 @@ openfile(
> >  	if (flags & IO_NOFOLLOW)
> >  		oflags |= O_NOFOLLOW;
> >  
> > +	/*
> > +	 * if we've been passed a pipe to open, don't block waiting for a
> > +	 * reader or writer to appear. We want to either succeed or error out
> > +	 * immediately.
> > +	 */
> > +	if (stat(path, &st) < 0 && errno != ENOENT) {
> > +		perror("stat");
> > +		return -1;
> > +	}
> > +	if (S_ISFIFO(st.st_mode))
> 
> Hmm... does stat() set st.st_mode even if it returns ENOENT?  Or are we
> possibly branching on an uninitialized st here?
> 
> struct stat	st = { 0 }; ?

Yeah, I'll fix that.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com