On Thu, 2017-06-29 at 11:46 -0400, J. Bruce Fields wrote:
> On Thu, Jun 29, 2017 at 06:34:49AM -0700, Christoph Hellwig wrote:
> > this resurrects parts of an old series to add open by handle
> > support to
> > NFS. The prime intent here is to support the actual open by handle
> > ioctls, although it will also allow very crude re-
> > exporting. Without
> > the other patches from Jeff's series that re-exporting will suck
> > badly
> > though.
>
> Why do we want this?
>
> Any re-export support is going to have some major limitations. (No
> file
> locking, and re-export of NFSv4 probably not possible?)
>
> Last I heard the only motivation was extremely specific to Primary
> Data's setup. I'm happy to help them, but I think we need *some*
> evidence this will be useful to upstream users.
>
The main use case for open by filehandle was (and still should be) the
promise of being able to do the sort of tricks you normally associate
with object storage on a standard filesystem.
Imagine that you are trying to build an application for indexing and
searching the data on your storage. You basically want to trawl through
the filesystem on a regular basis and build up a database of key words
and other metadata to tell you what is in the files. For that kind of
application, the namespace is a real PITA to deal with, because files
get renamed, moved and deleted all the time; so if you can store
something that is independent of the namespace and that will give you
access to the file contents, then why wouldn't you do so? Normally,
applications like that use the inode number, but you can't open a file
by inode number, and you have the same problems with inode number reuse
that a NFS server has.
That's the sort of thing I'd think we want to allow through open by
filehandle, and I see no reason why NFS should be excluded from that
type of application.
--
Trond Myklebust
Linux NFS client maintainer, PrimaryData
trond.myklebust@xxxxxxxxxxxxxxx
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