linux-kernel - Re: [PATCH v5 0/3] FUSE: Implement atomic lookup + open/create

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Date:   Thu, 1 Jun 2023 14:18:17 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Bernd Schubert <bschubert@....com>
Cc:     Dharmendra Singh <dharamhans87@...il.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        fuse-devel <fuse-devel@...ts.sourceforge.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Horst Birthelmer <horst@...thelmer.com>
Subject: Re: [PATCH v5 0/3] FUSE: Implement atomic lookup + open/create

On Thu, 1 Jun 2023 at 14:01, Bernd Schubert <bschubert@....com> wrote:
>
> On 6/1/23 13:50, Miklos Szeredi wrote:
> > On Thu, 1 Jun 2023 at 13:17, Bernd Schubert <bschubert@....com> wrote:
> >>
> >> Hi Miklos,
> >>
> >> On 5/19/22 11:39, Miklos Szeredi wrote:
> >>> On Tue, 17 May 2022 at 12:08, Dharmendra Singh <dharamhans87@...il.com> wrote:
> >>>>
> >>>> In FUSE, as of now, uncached lookups are expensive over the wire.
> >>>> E.g additional latencies and stressing (meta data) servers from
> >>>> thousands of clients. These lookup calls possibly can be avoided
> >>>> in some cases. Incoming three patches address this issue.
> >>>>
> >>>>
> >>>> Fist patch handles the case where we are creating a file with O_CREAT.
> >>>> Before we go for file creation, we do a lookup on the file which is most
> >>>> likely non-existent. After this lookup is done, we again go into libfuse
> >>>> to create file. Such lookups where file is most likely non-existent, can
> >>>> be avoided.
> >>>
> >>> I'd really like to see a bit wider picture...
> >>>
> >>> We have several cases, first of all let's look at plain O_CREAT
> >>> without O_EXCL (assume that there were no changes since the last
> >>> lookup for simplicity):
> >>>
> >>> [not cached, negative]
> >>>      ->atomic_open()
> >>>         LOOKUP
> >>>         CREATE
> >>>
> >>
> >> [...]
> >>
> >>> [not cached]
> >>>      ->atomic_open()
> >>>          OPEN_ATOMIC
> >>
> >> new patch version is eventually going through xfstests (and it finds
> >> some issues), but I have a question about wording here. Why
> >> "OPEN_ATOMIC" and not "ATOMIC_OPEN". Based on your comment  @Dharmendra
> >> renamed all functions and this fuse op "open atomic" instead of "atomic
> >> open" - for my non native English this sounds rather weird. At best it
> >> should be "open atomically"?
> >
> > FUSE_OPEN_ATOMIC is a specialization of FUSE_OPEN.  Does that explain
> > my thinking?
>
> Yeah, just the vfs function is also called atomic_open. We now have
>
>
> static int fuse_atomic_open(struct inode *dir, struct dentry *entry,
>                  struct file *file, unsigned flags,
>                  umode_t mode)
> {
>      struct fuse_conn *fc = get_fuse_conn(dir);
>
>      if (fc->no_open_atomic)
>          return fuse_open_nonatomic(dir, entry, file, flags, mode);
>      else
>          return fuse_open_atomic(dir, entry, file, flags, mode);
> }
>
>
> Personally I would use something like _fuse_atomic_open() and
> fuse_create_open() (instead of fuse_open_nonatomic). The order of "open
> atomic" also made it into libfuse and comments - it just sounds a bit
> weird ;) I have to live with it, if you prefer it like this.

I'd prefer FUSE_OPEN_ATOMIC for the API, but I don't care about
function names, as long as the purpose is clear.

Thanks,
Miklos