Re: [RFC PATCH 1/7] FUSE: Add the fsnotify opcode and in/out structs to FUSE

Amir Goldstein
2021-10-26T18:28:19Z

On Tue, Oct 26, 2021 at 5:56 PM Amir Goldstein <amir73il@gmail.com> wrote:
>
> On Mon, Oct 25, 2021 at 11:47 PM Ioannis Angelakopoulos
> <iangelak@redhat.com> wrote:
> >
> > Since fsnotify is the backend for the inotify subsystem all the backend
> > code implementation we add is related to fsnotify.
> >
> > To support an fsnotify request in FUSE and specifically virtiofs we add a
> > new opcode for the FSNOTIFY (51) operation request in the "fuse.h" header.
> >
> > Also add the "fuse_notify_fsnotify_in" and "fuse_notify_fsnotify_out"
> > structs that are responsible for passing the fsnotify/inotify related data
> > to and from the FUSE server.
> >
> > Signed-off-by: Ioannis Angelakopoulos <iangelak@redhat.com>
> > ---
> > include/uapi/linux/fuse.h | 23 ++++++++++++++++++++++-
> > 1 file changed, 22 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
> > index 46838551ea84..418b7fc72417 100644
> > --- a/include/uapi/linux/fuse.h
> > +++ b/include/uapi/linux/fuse.h
> > @@ -186,6 +186,9 @@
> > * - add FUSE_SYNCFS
> > * 7.35
> > * - add FUSE_NOTIFY_LOCK
> > + * 7.36
> > + * - add FUSE_HAVE_FSNOTIFY
> > + * - add fuse_notify_fsnotify_(in,out)
> > */
> >
> > #ifndef _LINUX_FUSE_H
> > @@ -221,7 +224,7 @@
> > #define FUSE_KERNEL_VERSION 7
> >
> > /** Minor version number of this interface */
> > -#define FUSE_KERNEL_MINOR_VERSION 35
> > +#define FUSE_KERNEL_MINOR_VERSION 36
> >
> > /** The node ID of the root inode */
> > #define FUSE_ROOT_ID 1
> > @@ -338,6 +341,7 @@ struct fuse_file_lock {
> > * write/truncate sgid is killed only if file has group
> > * execute permission. (Same as Linux VFS behavior).
> > * FUSE_SETXATTR_EXT: Server supports extended struct fuse_setxattr_in
> > + * FUSE_HAVE_FSNOTIFY: remote fsnotify/inotify event subsystem support
> > */
> > #define FUSE_ASYNC_READ (1 << 0)
> > #define FUSE_POSIX_LOCKS (1 << 1)
> > @@ -369,6 +373,7 @@ struct fuse_file_lock {
> > #define FUSE_SUBMOUNTS (1 << 27)
> > #define FUSE_HANDLE_KILLPRIV_V2 (1 << 28)
> > #define FUSE_SETXATTR_EXT (1 << 29)
> > +#define FUSE_HAVE_FSNOTIFY (1 << 30)
> >
> > /**
> > * CUSE INIT request/reply flags
> > @@ -515,6 +520,7 @@ enum fuse_opcode {
> > FUSE_SETUPMAPPING = 48,
> > FUSE_REMOVEMAPPING = 49,
> > FUSE_SYNCFS = 50,
> > + FUSE_FSNOTIFY = 51,
> >
> > /* CUSE specific operations */
> > CUSE_INIT = 4096,
> > @@ -532,6 +538,7 @@ enum fuse_notify_code {
> > FUSE_NOTIFY_RETRIEVE = 5,
> > FUSE_NOTIFY_DELETE = 6,
> > FUSE_NOTIFY_LOCK = 7,
> > + FUSE_NOTIFY_FSNOTIFY = 8,
> > FUSE_NOTIFY_CODE_MAX,
> > };
> >
> > @@ -571,6 +578,20 @@ struct fuse_getattr_in {
> > uint64_t fh;
> > };
> >
> > +struct fuse_notify_fsnotify_out {
> > + uint64_t inode;
>
> 64bit inode is not a good unique identifier of the object.
> you need to either include the generation in object identifier
> or much better use the object's nfs file handle, the same way
> that fanotify stores object identifiers.
>
> > + uint64_t mask;
> > + uint32_t namelen;
> > + uint32_t cookie;
>
> I object to persisting with the two-events-joined-by-cookie design.
> Any new design should include a single event for rename
> with information about src and dst.
>
> I know this is inconvenient, but we are NOT going to create a "remote inotify"
> interface, we need to create a "remote fsnotify" interface and if server wants
> to use inotify, it will need to join the disjoined MOVE_FROM/TO event into
> a single "remote event", that FUSE will use to call fsnotify_move().
>

TBH, the disjoint vs. joint from/to event is an unfinished business
for fanotify.
So my objection above is more of a strong wish.
But I admit that if existing network protocols already encode the disjoint
from/to events semantics, I may need to fold back on that objection.

Thanks,
Amir.