Re: [PATCH v4 2/2] efi: an sysfs interface for user to update efi firmware

[James Bottomley <James.Bottomley-d9PhHud1JfjCXq6kfMZ53/egYHeGw8Jk@public.gmane.org>]

On Wed, 2015-04-22 at 09:50 -0700, Andy Lutomirski wrote:
> On Apr 21, 2015 9:51 PM, "James Bottomley"
> <James.Bottomley-JuX6DAaQMKPCXq6kfMZ53/egYHeGw8Jk@public.gmane.org> wrote:
> >
> > On Tue, 2015-04-21 at 20:24 -0700, Andy Lutomirski wrote:
> > > On Tue, Apr 21, 2015 at 7:20 PM, James Bottomley
> > > <James.Bottomley-JuX6DAaQMKPCXq6kfMZ53/egYHeGw8Jk@public.gmane.org> wrote:
> > > > On Tue, 2015-04-21 at 18:58 -0700, Andy Lutomirski wrote:
> > > >> On Tue, Apr 21, 2015 at 6:21 PM, James Bottomley
> > > >> <James.Bottomley-JuX6DAaQMKPCXq6kfMZ53/egYHeGw8Jk@public.gmane.org> wrote:
> > > >> > Andy, just on the misc device idea, what about triggering the capsule
> > > >> > update from close()?  In theory close returns an error code (not sure if
> > > >> > most tools actually check this, though).  That means we can do the write
> > > >> > in chunks but pass it in atomically on the close and cat will work
> > > >> > (provided it checks the return code of close).
> > > >>
> > > >> I thought about this but IIRC cat doesn't check the return value from close.
> > > >
> > > > It does in my copy (coreutils-8.23) :
> > > >
> > > >       if (!STREQ (infile, "-") && close (input_desc) < 0)
> > > >         {
> > > >           error (0, errno, "%s", infile);
> > > >           ok = false;
> > > >         }
> > > > [...]
> > > >   if (have_read_stdin && close (STDIN_FILENO) < 0)
> > > >     error (EXIT_FAILURE, errno, _("closing standard input"));
> > > >
> > >
> > > True, but it's stdout that we care about, not stdin :(
> >
> > Gosh you're determined to force me to wade through this source code,
> > aren't you?  That's handled in lib/closeout.c:
> >
> > /* Close standard output.  On error, issue a diagnostic and _exit
> >    with status 'exit_failure'.
> >
> > ...
> >
> >
> > The point is that, admittedly much to my surprise, it all looks to be
> > handled by cat ... so we could proceed to have the transaction completed
> > in close in a misc device (or a sysfs file).
> >
> > Unless there are any other rabbits you'd like to pull out of the hat?
> 
> No, maybe it's okay, unless there's an issue where the error would
> only be returned on the close of the last reference of the struct
> file.  After all, 'cat foo >/sys/bar' doesn't fully close /sys/bar
> until after cat exits.

No, cat handles that too.  It has an atexit() handler for closing
stdout.

James