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

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Date:   Thu, 1 Jun 2023 12:01:25 +0000
From:   Bernd Schubert <bschubert@....com>
To:     Miklos Szeredi <miklos@...redi.hu>
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 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.


Thanks,
Bernd