Re: pidfd && O_RDWR

[Oleg Nesterov <oleg@redhat.com>]

On 02/23, Christian Brauner wrote:
>
> On Mon, Feb 23, 2026 at 08:21:02PM +0100, Oleg Nesterov wrote:
> > On 02/23, Oleg Nesterov wrote:
> > >
> > > pidfd_prepare() does pidfs_alloc_file(pid, flags | O_RDWR) and "| O_RDWR"
> > > makes no sense because pidfs_alloc_file() itself does
> > >
> > > 	flags |= O_RDWR;
> > >
> > > I was going to send the trivial cleanup, but why a pidfs file needs
> > > O_RDWR/FMODE_WRITE ?
> > >
> > > Actually the same question about some anon_inode_getfile_fmode(O_RDWR)
> > > users, for example signalfd.c.
> >
> > perhaps an accidental legacy from 628ff7c1d8d8 ("anonfd: Allow making anon
> > files read-only") ?
>
> It was always a possibility that we would support some form of
> write-like operation eventually. And we have support for setting trusted
> extended attributes on pidfds for some time now (trusted xattrs require
> global cap_sys_admin).

But why do we need O_RDWR right now? That was my question.

I can be easily wrong, but I think that pidfs_xattr_handlers logic doesn't
need it...

OK, I won't pretend I understand fs, I'll send the trivial cleanup which just
removes the unnecessary "flags | O_RDWR" in pidfd_prepare().

Oleg.