exportfs: add explicit flag to request non-decodeable file handles

So far, all callers of exportfs_encode_inode_fh(), except for fsnotify's
show_mark_fhandle(), check that filesystem can decode file handles, but
we would like to add more callers that do not require a file handle that
can be decoded.

Introduce a flag to explicitly request a file handle that may not to be
decoded later and a wrapper exportfs_encode_fid() that sets this flag
and convert show_mark_fhandle() to use the new wrapper.

This will be used to allow adding fanotify support to filesystems that
do not support NFS export.

Acked-by: Jeff Layton <jlayton@kernel.org>
Acked-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Message-Id: <20230502124817.3070545-3-amir73il@gmail.com>

1 files changed, 18 insertions, 2 deletions

diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c
index ab7feffe2d19..40e624cf7e92 100644
--- a/fs/exportfs/expfs.c
+++ b/fs/exportfs/expfs.c
@@ -381,11 +381,27 @@ static int export_encode_fh(struct inode *inode, struct fid *fid,
 	return type;
 }
 
+/**
+ * exportfs_encode_inode_fh - encode a file handle from inode
+ * @inode:   the object to encode
+ * @fid:     where to store the file handle fragment
+ * @max_len: maximum length to store there
+ * @flags:   properties of the requested file handle
+ *
+ * Returns an enum fid_type or a negative errno.
+ */
 int exportfs_encode_inode_fh(struct inode *inode, struct fid *fid,
-			     int *max_len, struct inode *parent)
+			     int *max_len, struct inode *parent, int flags)
 {
 	const struct export_operations *nop = inode->i_sb->s_export_op;
 
+	/*
+	 * If a decodeable file handle was requested, we need to make sure that
+	 * filesystem can decode file handles.
+	 */
+	if (nop && !(flags & EXPORT_FH_FID) && !nop->fh_to_dentry)
+		return -EOPNOTSUPP;
+
 	if (nop && nop->encode_fh)
 		return nop->encode_fh(inode, fid->raw, max_len, parent);
 
@@ -418,7 +434,7 @@ int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len,
 		parent = p->d_inode;
 	}
 
-	error = exportfs_encode_inode_fh(inode, fid, max_len, parent);
+	error = exportfs_encode_inode_fh(inode, fid, max_len, parent, flags);
 	dput(p);
 
 	return error;