Re: pidfd && O_RDWR

[Christian Brauner]

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).