[PATCH 7/9] fhandle: add EXPORT_OP_AUTONOMOUS_HANDLES marker

[Christian Brauner <brauner@kernel.org>]

Allow a filesystem to indicate that it supports encoding autonomous file
handles that can be decoded without having to pass a filesystem for the
filesystem. In other words, the file handle uniquely identifies the
filesystem.

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 fs/fhandle.c             | 7 ++++++-
 include/linux/exportfs.h | 4 +++-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/fs/fhandle.c b/fs/fhandle.c
index 22edced83e4c..ab4891925b52 100644
--- a/fs/fhandle.c
+++ b/fs/fhandle.c
@@ -23,12 +23,13 @@ static long do_sys_name_to_handle(const struct path *path,
 	struct file_handle f_handle;
 	int handle_dwords, handle_bytes;
 	struct file_handle *handle = NULL;
+	const struct export_operations *eops = path->dentry->d_sb->s_export_op;
 
 	/*
 	 * We need to make sure whether the file system support decoding of
 	 * the file handle if decodeable file handle was requested.
 	 */
-	if (!exportfs_can_encode_fh(path->dentry->d_sb->s_export_op, fh_flags))
+	if (!exportfs_can_encode_fh(eops, fh_flags))
 		return -EOPNOTSUPP;
 
 	/*
@@ -90,6 +91,10 @@ static long do_sys_name_to_handle(const struct path *path,
 			if (d_is_dir(path->dentry))
 				handle->handle_type |= FILEID_IS_DIR;
 		}
+
+		/* Filesystems supports autonomous file handles. */
+		if (eops->flags & EXPORT_OP_AUTONOMOUS_HANDLES)
+			handle->handle_type |= FILEID_IS_AUTONOMOUS;
 		retval = 0;
 	}
 	/* copy the mount id */
diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
index 45b38a29643f..959a1f7d46d0 100644
--- a/include/linux/exportfs.h
+++ b/include/linux/exportfs.h
@@ -194,7 +194,8 @@ struct handle_to_path_ctx {
 /* Flags supported in encoded handle_type that is exported to user */
 #define FILEID_IS_CONNECTABLE	0x10000
 #define FILEID_IS_DIR		0x20000
-#define FILEID_VALID_USER_FLAGS	(FILEID_IS_CONNECTABLE | FILEID_IS_DIR)
+#define FILEID_IS_AUTONOMOUS	0x40000
+#define FILEID_VALID_USER_FLAGS	(FILEID_IS_CONNECTABLE | FILEID_IS_DIR | FILEID_IS_AUTONOMOUS)
 
 /**
  * struct export_operations - for nfsd to communicate with file systems
@@ -291,6 +292,7 @@ struct export_operations {
 						*/
 #define EXPORT_OP_FLUSH_ON_CLOSE	(0x20) /* fs flushes file data on close */
 #define EXPORT_OP_NOLOCKS		(0x40) /* no file locking support */
+#define EXPORT_OP_AUTONOMOUS_HANDLES	(0x80) /* filesystem supports autonomous file handles */
 	unsigned long	flags;
 };
 

-- 
2.47.2