linux-kernel - Re: [PATCH RFC v2] fhandle: expose u64 mount id to name_to_handle

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Message-ID: <20240528-gipfel-dilemma-948a590a36fd@brauner>
Date: Tue, 28 May 2024 14:04:16 +0200
From: Christian Brauner <brauner@...nel.org>
To: Christoph Hellwig <hch@...radead.org>
Cc: Jan Kara <jack@...e.cz>, Aleksa Sarai <cyphar@...har.com>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Chuck Lever <chuck.lever@...cle.com>, 
	Jeff Layton <jlayton@...nel.org>, Amir Goldstein <amir73il@...il.com>, 
	Alexander Aring <alex.aring@...il.com>, linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org
Subject: Re: [PATCH RFC v2] fhandle: expose u64 mount id to
 name_to_handle_at(2)

On Tue, May 28, 2024 at 03:55:29AM -0700, Christoph Hellwig wrote:
> On Tue, May 28, 2024 at 11:17:58AM +0200, Christian Brauner wrote:
> > As I've said earlier, independent of the new handle type returning the
> > new mount id is useful and needed because it allows the caller to
> > reliably generate a mount fd for use with open_by_handle_at() via
> > statmount(). That won't be solved by a new handle type and is racy with
> > the old mount id. So I intend to accept a version of this patch.
> 
> The whole point is that with the fsid in the handle we do not even need
> a mount fd for open_by_handle_at.

Can you please explain how opening an fd based on a handle returned from
name_to_handle_at() and not using a mount file descriptor for
open_by_handle_at() would work?