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exportfs: allow exporting non-decodeable file handles to userspace

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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.

Acked-by: Jeff Layton <jlayton@kernel.org>
Acked-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Message-Id: <20230502124817.3070545-4-amir73il@gmail.com>
This commit is contained in:
Amir Goldstein
2023-05-02 15:48:16 +03:00
committed by Jan Kara
parent 304e9c83e8
commit 96b2b072ee
2 changed files with 19 additions and 8 deletions
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5
include/uapi/linux/fcntl.h
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@@ -112,4 +112,9 @@
#define AT_RECURSIVE 0x8000 /* Apply to the entire subtree */
/* Flags for name_to_handle_at(2). We reuse AT_ flag space to save bits... */
#define AT_HANDLE_FID AT_REMOVEDIR /* file handle is needed to
compare object identity and may not
be usable to open_by_handle_at(2) */
#endif /* _UAPI_LINUX_FCNTL_H */