From: Amir Goldstein <amir73il@gmail.com>
To: Jeff Layton <jlayton@kernel.org>
Cc: Jan Kara <jack@suse.cz>, Christian Brauner <brauner@kernel.org>,
Miklos Szeredi <miklos@szeredi.hu>,
linux-unionfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-api@vger.kernel.org
Subject: Re: [RFC][PATCH 0/4] Prepare for supporting more filesystems with fanotify
Date: Thu, 27 Apr 2023 22:11:46 +0300 [thread overview]
Message-ID: <CAOQ4uxhWzV7YJ_kPGg_4wHhWAd79_Xgo2uoDY+1K9sEtJcH_cA@mail.gmail.com> (raw)
In-Reply-To: <df31058f662fe9ec9ad1cc59838f288b8aff10f0.camel@kernel.org>
handle_bytes
On Thu, Apr 27, 2023 at 7:36 PM Jeff Layton <jlayton@kernel.org> wrote:
>
> On Thu, 2023-04-27 at 18:52 +0300, Amir Goldstein wrote:
> > On Thu, Apr 27, 2023 at 6:13 PM Jeff Layton <jlayton@kernel.org> 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.
> >
> > Thanks!
> >
> > >
> > > 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.
> >
> > Yeh, it's not great.
> >
> > There is also a way to extend the existing API with:
> >
> > Perhstruct file_handle {
> > unsigned int handle_bytes:8;
> > unsigned int handle_flags:24;
> > int handle_type;
> > unsigned char f_handle[];
> > };
> >
> > AFAICT, this is guaranteed to be backward compat
> > with old kernels and old applications.
> >
>
> That could work. It would probably look cleaner as a union though.
> Something like this maybe?
>
> union {
> unsigned int legacy_handle_bytes;
> struct {
> u8 handle_bytes;
> u8 __reserved;
> u16 handle_flags;
> };
> }
I have no problem with the union, but does this struct
guarantee that the lowest byte of legacy_handle_bytes
is in handle_bytes for all architectures?
That's the reason I went with
struct {
unsigned int handle_bytes:8;
unsigned int handle_flags:24;
}
Is there a problem with this approach?
> > unsigned int handle_bytes:8;
> > unsigned int handle_flags:24;
>
> __reserved must be zeroed (for now). You could consider using it for
> some other purpose later.
>
> It's a little ugly as an API but it would be backward compatible, given
> that we never use the high bits today anyway.
>
> Callers might need to deal with an -EINVAL when they try to pass non-
> zero handle_flags to existing kernels, since you'd trip the
> MAX_HANDLE_SZ check that's there today.
>
Exactly.
> > It also may not be a bad idea that the handle_flags could
> > be used to request specific fh properties (FID) and can also
> > describe the properties of the returned fh (i.e. non-decodeable)
> > that could also be respected by open_by_handle_at().
> >
> > For backward compact, kernel will only set handle_flags in
> > response if new flags were set in the request.
> >
> > Do you consider this extension better than AT_HANDLE_FID
> > or worse? At least it is an API change that is contained within the
> > exportfs subsystem, without polluting the AT_ flags global namespace.
> >
>
> Personally, yes. I think adding a struct file_handle_v2 would be cleaner
> and allows for expanding the API later through new flags.
I agree.
I will give it a try.
Thanks,
Amir.
next prev parent reply other threads:[~2023-04-27 19:12 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-25 13:01 [RFC][PATCH 0/4] Prepare for supporting more filesystems with fanotify Amir Goldstein
2023-04-25 13:01 ` [RFC][PATCH 1/4] exportfs: change connectable argument to bit flags Amir Goldstein
2023-04-26 14:16 ` Chuck Lever
2023-04-25 13:01 ` [RFC][PATCH 2/4] exportfs: add explicit flag to request non-decodeable file handles Amir Goldstein
2023-04-26 14:18 ` Chuck Lever
2023-04-27 15:00 ` Jeff Layton
2023-04-27 15:13 ` Amir Goldstein
2023-04-25 13:01 ` [RFC][PATCH 3/4] exportfs: allow exporting non-decodeable file handles to userspace Amir Goldstein
2023-04-25 13:01 ` [RFC][PATCH 4/4] fanotify: support reporting non-decodeable file handles Amir Goldstein
2023-04-27 11:48 ` Jan Kara
2023-04-27 12:28 ` Amir Goldstein
2023-04-27 14:34 ` Amir Goldstein
2023-04-27 16:34 ` Jan Kara
2023-04-26 13:47 ` [RFC][PATCH 0/4] Prepare for supporting more filesystems with fanotify Chuck Lever
2023-04-27 4:57 ` Amir Goldstein
2023-04-27 15:13 ` Jeff Layton
2023-04-27 15:52 ` Amir Goldstein
2023-04-27 16:36 ` Jeff Layton
2023-04-27 19:11 ` Amir Goldstein [this message]
2023-04-27 19:26 ` Jeff Layton
2023-04-28 11:40 ` Jan Kara
2023-04-28 12:15 ` Jeff Layton
2023-04-28 12:31 ` Jan Kara
2023-04-28 12:33 ` Amir Goldstein
2023-04-29 14:45 ` Chuck Lever
2023-04-29 17:26 ` Amir Goldstein
2023-05-01 18:48 ` Amir Goldstein
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