On Tue 02-05-23 15:48:16, Amir Goldstein wrote:
> Some userspace programs use st_ino as a unique object identifier, even
> though inode numbers may be recycable.
>
> This issue has been addressed for NFS export long ago using the exportfs
> file handle API and the unique file handle identifiers are also exported
> to userspace via name_to_handle_at(2).
>
> fanotify also uses file handles to identify objects in events, but only
> for filesystems that support NFS export.
>
> Relax the requirement for NFS export support and allow more filesystems
> to export a unique object identifier via name_to_handle_at(2) with the
> flag AT_HANDLE_FID.
>
> A file handle requested with the AT_HANDLE_FID flag, may or may not be
> usable as an argument to open_by_handle_at(2).
>
> To allow filesystems to opt-in to supporting AT_HANDLE_FID, a struct
> export_operations is required, but even an empty struct is sufficient
> for encoding FIDs.
Christian (or Al), are you OK with sparing one AT_ flag for this
functionality? Otherwise the patch series looks fine to me so I'd like to
queue it into my tree. Thanks!
Honza
>
> Acked-by: Jeff Layton <jlayton@xxxxxxxxxx>
> Acked-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
> ---
> fs/fhandle.c | 22 ++++++++++++++--------
> include/uapi/linux/fcntl.h | 5 +++++
> 2 files changed, 19 insertions(+), 8 deletions(-)
>
> diff --git a/fs/fhandle.c b/fs/fhandle.c
> index f2bc27d1975e..4a635cf787fc 100644
> --- a/fs/fhandle.c
> +++ b/fs/fhandle.c
> @@ -16,7 +16,7 @@
>
> static long do_sys_name_to_handle(const struct path *path,
> struct file_handle __user *ufh,
> - int __user *mnt_id)
> + int __user *mnt_id, int fh_flags)
> {
> long retval;
> struct file_handle f_handle;
> @@ -24,11 +24,14 @@ static long do_sys_name_to_handle(const struct path *path,
> struct file_handle *handle = NULL;
>
> /*
> - * We need to make sure whether the file system
> - * support decoding of the file handle
> + * We need to make sure whether the file system support decoding of
> + * the file handle if decodeable file handle was requested.
> + * Otherwise, even empty export_operations are sufficient to opt-in
> + * to encoding FIDs.
> */
> if (!path->dentry->d_sb->s_export_op ||
> - !path->dentry->d_sb->s_export_op->fh_to_dentry)
> + (!(fh_flags & EXPORT_FH_FID) &&
> + !path->dentry->d_sb->s_export_op->fh_to_dentry))
> return -EOPNOTSUPP;
>
> if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
> @@ -45,10 +48,10 @@ static long do_sys_name_to_handle(const struct path *path,
> /* convert handle size to multiple of sizeof(u32) */
> handle_dwords = f_handle.handle_bytes >> 2;
>
> - /* we ask for a non connected handle */
> + /* we ask for a non connectable maybe decodeable file handle */
> retval = exportfs_encode_fh(path->dentry,
> (struct fid *)handle->f_handle,
> - &handle_dwords, 0);
> + &handle_dwords, fh_flags);
> handle->handle_type = retval;
> /* convert handle size to bytes */
> handle_bytes = handle_dwords * sizeof(u32);
> @@ -84,6 +87,7 @@ static long do_sys_name_to_handle(const struct path *path,
> * @handle: resulting file handle
> * @mnt_id: mount id of the file system containing the file
> * @flag: flag value to indicate whether to follow symlink or not
> + * and whether a decodable file handle is required.
> *
> * @handle->handle_size indicate the space available to store the
> * variable part of the file handle in bytes. If there is not
> @@ -96,17 +100,19 @@ SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
> {
> struct path path;
> int lookup_flags;
> + int fh_flags;
> int err;
>
> - if ((flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
> + if (flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH | AT_HANDLE_FID))
> return -EINVAL;
>
> lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
> + fh_flags = (flag & AT_HANDLE_FID) ? EXPORT_FH_FID : 0;
> if (flag & AT_EMPTY_PATH)
> lookup_flags |= LOOKUP_EMPTY;
> err = user_path_at(dfd, name, lookup_flags, &path);
> if (!err) {
> - err = do_sys_name_to_handle(&path, handle, mnt_id);
> + err = do_sys_name_to_handle(&path, handle, mnt_id, fh_flags);
> path_put(&path);
> }
> return err;
> diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
> index e8c07da58c9f..3091080db069 100644
> --- a/include/uapi/linux/fcntl.h
> +++ b/include/uapi/linux/fcntl.h
> @@ -112,4 +112,9 @@
>
> #define AT_RECURSIVE 0x8000 /* Apply to the entire subtree */
>
> +/* Flags for name_to_handle_at(2) */
> +#define AT_HANDLE_FID 0x10000 /* file handle is needed to compare
> + object indentity and may not be
> + usable to open_by_handle_at(2) */
> +
> #endif /* _UAPI_LINUX_FCNTL_H */
> --
> 2.34.1
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
