linux-kernel - Re: [LSF/MM/BPF TOPIC] making O

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Date:   Mon, 9 May 2022 15:47:49 +0000
From:   Chuck Lever III <chuck.lever@...cle.com>
To:     Miklos Szeredi <miklos@...redi.hu>,
        Steve French <smfrench@...il.com>
CC:     lsf-pc <lsf-pc@...ts.linux-foundation.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [LSF/MM/BPF TOPIC] making O_TMPFILE more atomic



> On May 3, 2022, at 2:52 PM, Miklos Szeredi <miklos@...redi.hu> wrote:
> 
> On Thu, 24 Feb 2022 at 06:33, Steve French <smfrench@...il.com> wrote:
>> 
>> Currently creating tmpfiles on Linux can be problematic because the
>> tmpfile is not created and opened at the same time  (vfs_tmpfile calls
>> into the fs, then later vfs_open is called to open the tmpfile).   For
>> some filesystems it would be more natural to create and open the
>> tmpfile as one operation (because the action of creating the file on
>> some filesystems returns an open handle, so closing it then reopening
>> it would cause the tmpfile to be deleted).
>> 
>> I would like to discuss whether the function do_tmpfile (which creates
>> and then opens the tmpfile) could have an option for a filesystem to
>> do this as one operation which would allow it to be more atomic and
>> allow it to work on a wider variety of filesystems.
> 
> A related thread:
> 
> https://lore.kernel.org/all/20201109100343.3958378-3-chirantan@chromium.org/#r
> 
> There was no conclusion in the end. Not sure how hacky it would be to
> store the open file in the inode...

I just proposed adding a VFS API to make open/create atomic.
See 8/8 in this thread:

https://lore.kernel.org/linux-nfs/20220420192418.GB27805@fieldses.org/T/#m505a59ad4e4ed1413ffc055a088de3182fb50bb4

It adds a sibling API to dentry_open(). I didn't have
O_TMPFILE in mind when I created this API.


--
Chuck Lever