Re: [RFC][PATCH 0/4] Prepare for supporting more filesystems with fanotify

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On Sat, Apr 29, 2023 at 8:26 PM Amir Goldstein <amir73il@xxxxxxxxx> wrote:
>
> On Sat, Apr 29, 2023 at 5:45 PM Chuck Lever <cel@xxxxxxxxxx> wrote:
> >
> > On Thu, Apr 27, 2023 at 11:13:33AM -0400, Jeff Layton wrote:
> > > On Tue, 2023-04-25 at 16:01 +0300, Amir Goldstein wrote:
> > > > Jan,
> > > >
> > > > Following up on the FAN_REPORT_ANY_FID proposal [1], here is a shot at an
> > > > alternative proposal to seamlessly support more filesystems.
> > > >
> > > > While fanotify relaxes the requirements for filesystems to support
> > > > reporting fid to require only the ->encode_fh() operation, there are
> > > > currently no new filesystems that meet the relaxed requirements.
> > > >
> > > > I will shortly post patches that allow overlayfs to meet the new
> > > > requirements with default overlay configurations.
> > > >
> > > > The overlay and vfs/fanotify patch sets are completely independent.
> > > > The are both available on my github branch [2] and there is a simple
> > > > LTP test variant that tests reporting fid from overlayfs [3], which
> > > > also demonstrates the minor UAPI change of name_to_handle_at(2) for
> > > > requesting a non-decodeable file handle by userspace.
> > > >
> > > > Thanks,
> > > > Amir.
> > > >
> > > > [1] https://lore.kernel.org/linux-fsdevel/20230417162721.ouzs33oh6mb7vtft@quack3/
> > > > [2] https://github.com/amir73il/linux/commits/exportfs_encode_fid
> > > > [3] https://github.com/amir73il/ltp/commits/exportfs_encode_fid
> > > >
> > > > Amir Goldstein (4):
> > > >   exportfs: change connectable argument to bit flags
> > > >   exportfs: add explicit flag to request non-decodeable file handles
> > > >   exportfs: allow exporting non-decodeable file handles to userspace
> > > >   fanotify: support reporting non-decodeable file handles
> > > >
> > > >  Documentation/filesystems/nfs/exporting.rst |  4 +--
> > > >  fs/exportfs/expfs.c                         | 29 ++++++++++++++++++---
> > > >  fs/fhandle.c                                | 20 ++++++++------
> > > >  fs/nfsd/nfsfh.c                             |  5 ++--
> > > >  fs/notify/fanotify/fanotify.c               |  4 +--
> > > >  fs/notify/fanotify/fanotify_user.c          |  6 ++---
> > > >  fs/notify/fdinfo.c                          |  2 +-
> > > >  include/linux/exportfs.h                    | 18 ++++++++++---
> > > >  include/uapi/linux/fcntl.h                  |  5 ++++
> > > >  9 files changed, 67 insertions(+), 26 deletions(-)
> > > >
> > >
> > > This set looks fairly benign to me, so ACK on the general concept.
> >
> > Me also (modulo previous review comments), so
> >
> >   Acked-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> >
> > I assume either Amir or Jeff will take these when they are ready.
> > If I'm wrong, please do let me know and I can take them via the
> > NFSD tree.
> >
>
> With your and Jeff's ACKs I think it would be best if Jan takes
> these changes through the fsnotify tree, because they are only
> meant to improve fanotify at this point.
>
> >
> > > I am starting to dislike how the AT_* flags are turning into a bunch of
> > > flags that only have meanings on certain syscalls. I don't see a cleaner
> > > way to handle it though.
>
> With all the various proposals of file_handle_v2, I still think that the
> AT_HANDLE_FID is the cleanest in terms of API simplicity.
>
> Just trying to document file_handle_v2 and backward compat with
> file_handle_v1 gives me a headache and documenting AT_HANDLE_FID
> is a no brainer.
>

To prove my point, here is the man page draft for AT_HANDLE_FID:

https://github.com/amir73il/man-pages/commit/da7e8dc4749ced85ba692073a42724f2bbe5fe3b

Thanks,
Amir.




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