[RFC][PATCH 4/4] fanotify: support reporting non-decodeable file handles

[Amir Goldstein <amir73il@gmail.com>]

fanotify users do not always need to decode the file handles reported
with FAN_REPORT_FID.

Relax the restriction that filesystem needs to support NFS export and
allow reporting file handles from filesystems that only support ecoding
unique file handles.

For such filesystems, users will have to use the AT_HANDLE_FID of
name_to_handle_at(2) if they want to compare the object in path to the
object fid reported in an event.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/notify/fanotify/fanotify.c      | 4 ++--
 fs/notify/fanotify/fanotify_user.c | 6 ++----
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index d1a49f5b6e6d..d2bbf1445a9e 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -380,7 +380,7 @@ static int fanotify_encode_fh_len(struct inode *inode)
 	if (!inode)
 		return 0;
 
-	exportfs_encode_inode_fh(inode, NULL, &dwords, NULL, 0);
+	exportfs_encode_fid(inode, NULL, &dwords);
 	fh_len = dwords << 2;
 
 	/*
@@ -443,7 +443,7 @@ static int fanotify_encode_fh(struct fanotify_fh *fh, struct inode *inode,
 	}
 
 	dwords = fh_len >> 2;
-	type = exportfs_encode_inode_fh(inode, buf, &dwords, NULL, 0);
+	type = exportfs_encode_fid(inode, buf, &dwords);
 	err = -EINVAL;
 	if (!type || type == FILEID_INVALID || fh_len != dwords << 2)
 		goto out_err;
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 8f430bfad487..a5af84cbb30d 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -1586,11 +1586,9 @@ static int fanotify_test_fid(struct dentry *dentry)
 	 * We need to make sure that the file system supports at least
 	 * encoding a file handle so user can use name_to_handle_at() to
 	 * compare fid returned with event to the file handle of watched
-	 * objects. However, name_to_handle_at() requires that the
-	 * filesystem also supports decoding file handles.
+	 * objects, but it does not need to support decoding file handles.
 	 */
-	if (!dentry->d_sb->s_export_op ||
-	    !dentry->d_sb->s_export_op->fh_to_dentry)
+	if (!dentry->d_sb->s_export_op)
 		return -EOPNOTSUPP;
 
 	return 0;
-- 
2.34.1