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From: Miklos Szeredi <miklos@szeredi.hu>
Date: Tue, 28 May 2024 15:28:18 +0200
Message-ID: <CAJfpegvznUGTYxxTzB5QQHWtNrCfSkWvGscacfZ67Gn+6XoD8w@mail.gmail.com>
Subject: Re: [PATCH RFC v2] fhandle: expose u64 mount id to name_to_handle_at(2)
To: Christoph Hellwig <hch@infradead.org>
Cc: Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>, Aleksa Sarai <cyphar@cyphar.com>, 
	Alexander Viro <viro@zeniv.linux.org.uk>, Chuck Lever <chuck.lever@oracle.com>, 
	Jeff Layton <jlayton@kernel.org>, Amir Goldstein <amir73il@gmail.com>, 
	Alexander Aring <alex.aring@gmail.com>, linux-fsdevel@vger.kernel.org, 
	linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, 
	linux-api@vger.kernel.org
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On Tue, 28 May 2024 at 15:24, Christoph Hellwig <hch@infradead.org> wrote:
>
> On Tue, May 28, 2024 at 02:04:16PM +0200, Christian Brauner wrote:
> > 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?
>
> Same as NFS file handles:
>
> name_to_handle_at returns a handle that includes a file system
> identifier.
>
> open_by_handle_at looks up the superblock based on that identifier.

The open file needs a specific mount, holding the superblock is not sufficient.

Thanks,
Miklos