On Wed, Oct 18, 2023 at 01:00:00PM +0300, Amir Goldstein wrote:
> AT_HANDLE_FID was added as an API for name_to_handle_at() that request
> the encoding of a file id, which is not intended to be decoded.
>
> This file id is used by fanotify to describe objects in events.
>
> So far, overlayfs is the only filesystem that supports encoding
> non-decodeable file ids, by providing export_operations with an
> ->encode_fh() method and without a ->decode_fh() method.
>
> Add support for encoding non-decodeable file ids to all the filesystems
> that do not provide export_operations, by encoding a file id of type
> FILEID_INO64_GEN from { i_ino, i_generation }.
>
> A filesystem may that does not support NFS export, can opt-out of
> encoding non-decodeable file ids for fanotify by defining an empty
> export_operations struct (i.e. with a NULL ->encode_fh() method).
>
> This allows the use of fanotify events with file ids on filesystems
> like 9p which do not support NFS export to bring fanotify in feature
> parity with inotify on those filesystems.
>
> Note that fanotify also requires that the filesystems report a non-null
> fsid. Currently, many simple filesystems that have support for inotify
> (e.g. debugfs, tracefs, sysfs) report a null fsid, so can still not be
> used with fanotify in file id reporting mode.
>
> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
> ---
> fs/exportfs/expfs.c | 30 +++++++++++++++++++++++++++---
> include/linux/exportfs.h | 10 +++++++---
> 2 files changed, 34 insertions(+), 6 deletions(-)
>
> diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c
> index 30da4539e257..34e7d835d4ef 100644
> --- a/fs/exportfs/expfs.c
> +++ b/fs/exportfs/expfs.c
> @@ -383,6 +383,30 @@ int generic_encode_ino32_fh(struct inode *inode, __u32 *fh, int *max_len,
> }
> EXPORT_SYMBOL_GPL(generic_encode_ino32_fh);
>
> +/**
> + * exportfs_encode_ino64_fid - encode non-decodeable 64bit ino file id
> + * @inode: the object to encode
> + * @fid: where to store the file handle fragment
> + * @max_len: maximum length to store there
Length in what units? Is the 3 below in units of bytes or
sizeof(__be32) ? I'm guessing it's the latter; if so, it should
be mentioned here. (We have XDR_UNIT for this purpose, btw).
export_encode_fh() isn't exactly clear about that either, sadly.
> + *
> + * This generic function is used to encode a non-decodeable file id for
> + * fanotify for filesystems that do not support NFS export.
> + */
> +static int exportfs_encode_ino64_fid(struct inode *inode, struct fid *fid,
> + int *max_len)
> +{
> + if (*max_len < 3) {
> + *max_len = 3;
Let's make this a symbolic constant rather than a naked integer.
> + return FILEID_INVALID;
> + }
> +
> + fid->i64.ino = inode->i_ino;
> + fid->i64.gen = inode->i_generation;
> + *max_len = 3;
> +
> + return FILEID_INO64_GEN;
> +}
> +
> /**
> * exportfs_encode_inode_fh - encode a file handle from inode
> * @inode: the object to encode
> @@ -401,10 +425,10 @@ int exportfs_encode_inode_fh(struct inode *inode, struct fid *fid,
> if (!exportfs_can_encode_fh(nop, flags))
> return -EOPNOTSUPP;
>
> - if (nop && nop->encode_fh)
> - return nop->encode_fh(inode, fid->raw, max_len, parent);
> + if (!nop && (flags & EXPORT_FH_FID))
> + return exportfs_encode_ino64_fid(inode, fid, max_len);
>
> - return -EOPNOTSUPP;
> + return nop->encode_fh(inode, fid->raw, max_len, parent);
> }
> EXPORT_SYMBOL_GPL(exportfs_encode_inode_fh);
>
> diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
> index 21eeb9f6bdbd..6688e457da64 100644
> --- a/include/linux/exportfs.h
> +++ b/include/linux/exportfs.h
> @@ -134,7 +134,11 @@ struct fid {
> u32 parent_ino;
> u32 parent_gen;
> } i32;
> - struct {
> + struct {
> + u64 ino;
> + u32 gen;
> + } __packed i64;
> + struct {
> u32 block;
> u16 partref;
> u16 parent_partref;
> @@ -246,7 +250,7 @@ extern int exportfs_encode_fh(struct dentry *dentry, struct fid *fid,
>
> static inline bool exportfs_can_encode_fid(const struct export_operations *nop)
> {
> - return nop && nop->encode_fh;
> + return !nop || nop->encode_fh;
> }
>
> static inline bool exportfs_can_decode_fh(const struct export_operations *nop)
> @@ -259,7 +263,7 @@ static inline bool exportfs_can_encode_fh(const struct export_operations *nop,
> {
> /*
> * If a non-decodeable file handle was requested, we only need to make
> - * sure that filesystem can encode file handles.
> + * sure that filesystem did not opt-out of encoding fid.
> */
> if (fh_flags & EXPORT_FH_FID)
> return exportfs_can_encode_fid(nop);
> --
> 2.34.1
>
>
--
Chuck Lever
