[Virtio-fs] [PATCH v3 10/10] virtiofsd: Add lazy lo_do_find()

[Hanna Reitz]

On 09.08.21 21:08, Vivek Goyal wrote:
> On Fri, Jul 30, 2021 at 05:01:34PM +0200, Max Reitz wrote:
>> lo_find() right now takes two lookup keys for two maps, namely the file
>> handle for inodes_by_handle and the statx information for inodes_by_ids.
>> However, we only need the statx information if looking up the inode by
>> the file handle failed.
>>
>> There are two callers of lo_find(): The first one, lo_do_lookup(), has
>> both keys anyway, so passing them does not incur any additional cost.
>> The second one, lookup_name(), though, needs to explicitly invoke
>> name_to_handle_at() (through get_file_handle()) and statx() (through
>> do_statx()).  We need to try to get a file handle as the primary key, so
>> we cannot get rid of get_file_handle(), but we only need the statx
>> information if looking up an inode by handle failed; so we can defer
>> that until the lookup has indeed failed.
> So IIUC, this patch seems to be all about avoiding do_statx()
> call in lookup_name() if file handle could be successfully
> generated.
>
> So can't we just not modify lookup_name() to not call statx()
> if file handle could be generated. And also modfiy lo_find()
> to use st/mnt_id only if fhandle==NULL.
>
> That probably is much simpler change as compared to passing function
> pointers around.

Definitely, but I don’t know whether it’s correct.

Or, we can just drop this patch and say that we don’t need to 
over-optimize C virtiofsd.

Hanna