On Tue, Apr 25, 2023 at 04:36:27PM +0200, Christian Brauner wrote:
> On Tue, Apr 25, 2023 at 02:54:29PM +0100, Al Viro wrote:
> > On Tue, Apr 25, 2023 at 02:34:15PM +0200, Christian Brauner wrote:
> >
> > > It is rife with misunderstandings just looking at what we did in
> > > kernel/fork.c earlier:
> > >
> > > retval = get_unused_fd_flags(O_RDWR | O_CLOEXEC);
> > > [...]
> > > pidfile = anon_inode_getfile("[pidfd]", &pidfd_fops, pid,
> > > O_RDWR | O_CLOEXEC);
> > >
> > > seeing where both get_unused_fd_flags() and both *_getfile() take flag
> > > arguments. Sure, for us this is pretty straightforward since we've seen
> > > that code a million times. For others it's confusing why there's two
> > > flag arguments. Sure, we could use one flags argument but it still be
> > > weird to look at.
> >
> > First of all, get_unused_fd_flags() doesn't give a damn about O_RDWR and
> > anon_inode_getfile() - about O_CLOEXEC. Duplicating the expression in
> > places like that is cargo-culting.
>
> I distinctly remember us having that conversation about how to do this
> nicely back then and fwiw this is your patch... ;)
> 6fd2fe494b17 ("copy_process(): don't use ksys_close() on cleanups")
Should've followed with "no need to pass nonsense flags to get_unused_fd_flags()
and anon_inode_getfile()"...
> So sure, that was my point: people are confused why there's two flag
> arguments and what exactly has to go into them and just copy-paste
> whatever other users already have.
> There's definitely one where people allocate a file descriptor early on
> and then sometimes maybe way later allocate a struct file and install
> it. And that's where exposing and using get_unused_fd_flags() and
> fd_install() is great and works fine.
FWIW, there's something I toyed with a while ago - a primitive along the
lines of
fd_set_file(fd, file)
{
if (IS_ERR(file)) {
put_unused_fd(fd);
return ERR_PTR(file);
}
fd_install(fd, file);
return fd;
}
That simplifies quite a few places, collapsing failure exit handling.
Not sure how many can be massaged into that form, though...
