On Thu, Apr 27, 2023 at 6:13 PM Jeff Layton <jlayton@xxxxxxxxxx> 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. 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. Thanks, Amir.
