10 a.m.
On Fri, Apr 5, 2019 at 10:49 AM Frank Filz <ffilzlnx(a)mindspring.com> wrote:
> On Thu, Apr 4, 2019 at 11:41 AM Wyllys Ingersoll
> <wyllys.ingersoll(a)keepertech.com> wrote:
> >
> > I have a cephfs filesystem and I want to export a subdirectory of my
cephfs
> tree. Is this possible or do I have to export the entire tree from the
root?
> >
>
> You can export a subdirectory, but there is no subtree checking. It's
possible for
> someone to guess filehandles and access files outside the exported
directory.
> See the "no_subtree_check" section in the linux
> exports(5) manpage. It is generally best to export along filesystem
boundaries
> for that reason.
Most cephfs filesystems I've encountered are vast and wide and I have seen
many cases where one wants to export multiple subdirectories with different
parameters and restrictions. Only supporting the top of the tree seems
like a really basic starting point. If thats a real concern, it should be
spelled out explicitly in the documentation. It's not at all clear from
what I've read.
>
> > If it is possible, then is it also possible to define exports for
multiple
> subdirectories of my cephfs FS such as /cephfs/exports/foo and
> /cephfs/exports/bar as 2 separate exports?
>
> Yes. They will each get their own cephfs client though, so in the event
that two
> clients end up accessing the same inodes via two different exports,
performance
> may suffer. The clients will end up competing with one another for caps.
I guess thats possible with hard links, but I think that's an edge case at
best. Doesn't that problem also exist if the subdirectories are exported
using the basic fsal_vfs ?
Hmm, if this was something we actually wanted to generally support (I'm
not convinced it would be a good idea), we could use the fsal_filesystem
infrastructure to share the cephfs client.
Are you saying that ganesha does NOT officially support exporting
subdirectories using fsal ceph?
Im just trying to understand the limitations and future direction of the
project in this area. Consider an implementation where a large cephfs
filesystem is used as part of a NAS server and multiple subdirectories of
it are exported using NFS and SMB to a variety of clients.