Re: [PATCH v4 1/4] pidfd: extend pidfd_get_pid() and de-duplicate pid lookup

[Shakeel Butt <shakeel.butt@linux.dev>]

On Thu, Oct 17, 2024 at 10:05:49PM GMT, Lorenzo Stoakes wrote:
> The means by which a pid is determined from a pidfd is duplicated, with
> some callers holding a reference to the (pid)fd, and others explicitly
> pinning the pid.
> 
> Introduce __pidfd_get_pid() which narrows this to one approach of pinning
> the pid, with an optional output parameters for file->f_flags to avoid the
> need to hold onto a file to retrieve this.
> 
> Additionally, allow the ability to open a pidfd by opening a /proc/<pid>
> directory, utilised by the pidfd_send_signal() system call, providing a
> pidfd_get_pid_proc() helper function to do so.
> 
> Doing this allows us to eliminate open-coded pidfd pid lookup and to
> consistently handle this in one place.
> 
> This lays the groundwork for a subsequent patch which adds a new sentinel
> pidfd to explicitly reference the current process (i.e. thread group
> leader) without the need for a pidfd.
> 
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>