linux-kernel - Re: [GIT PULL] vfs pidfd

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Date: Tue, 12 Mar 2024 15:15:56 +0100
From: Christian Brauner <brauner@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL] vfs pidfd

On Mon, Mar 11, 2024 at 01:05:06PM -0700, Linus Torvalds wrote:
> On Fri, 8 Mar 2024 at 02:14, Christian Brauner <brauner@...nel.org> wrote:
> >
> > * Move pidfds from the anonymous inode infrastructure to a tiny
> >   pseudo filesystem. This will unblock further work that we weren't able
> >   to do simply because of the very justified limitations of anonymous
> >   inodes. Moving pidfds to a tiny pseudo filesystem allows for statx on
> >   pidfds to become useful for the first time. They can now be compared
> >   by inode number which are unique for the system lifetime.
> 
> So I obviously pulled this already, but I did have one question - we
> don't make nsfs conditional, and I'm not convinced we should make
> pidfs conditional either.
> 
> I think (and *hope*) all the semantic annoyances got sorted out, and I
> don't think there are any realistic size advantages to not enabling
> CONFIG_FS_PID.
> 
> Is there some fundamental reason for that config entry to exist?

No, the size of struct pid was the main reason but I don't think it
matters. A side-effect was that we could easily enforce 64bit inode
numbers. But realistically it's trivial enough to workaround. Here's a
patch for what I think is pretty simple appended. Does that work?

View attachment "0001-pidfs-remove-config-option.patch" of type "text/x-diff" (5465 bytes)