Re: pidfd && O_RDWR

[David Laight <david.laight.linux@gmail.com>]

On Mon, 23 Feb 2026 22:39:22 +0100
Christian Brauner <brauner@kernel.org> 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).
> 

Isn't 'sending a signal' a write-like operation?

	David