From: Jeff Layton <jlayton@kernel.org>
To: Amir Goldstein <amir73il@gmail.com>
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 12:36:30 -0400 [thread overview]
Message-ID: <df31058f662fe9ec9ad1cc59838f288b8aff10f0.camel@kernel.org> (raw)
In-Reply-To: <CAOQ4uxjR0cdjW1Pr1DWAn+dkTd3SbV7CUqeGRh2FeDVBGAdtRw@mail.gmail.com>
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;
};
}
__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.
> 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.
--
Jeff Layton <jlayton@kernel.org>
next prev parent reply other threads:[~2023-04-27 16:36 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 [this message]
2023-04-27 19:11 ` Amir Goldstein
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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