nilfs2: add support for FS_IOC_GETFSLABEL

Implement support for FS_IOC_GETFSLABEL ioctl to read filesystem label.

Link: https://lkml.kernel.org/r/20240815074408.5550-4-konishi.ryusuke@gmail.com
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/fs/nilfs2/nilfs.h b/fs/nilfs2/nilfs.h
index 4017f7856440..3097490b6621 100644
--- a/fs/nilfs2/nilfs.h
+++ b/fs/nilfs2/nilfs.h
@@ -103,6 +103,18 @@ enum {
 	NILFS_SB_COMMIT_ALL	/* Commit both super blocks */
 };
 
+/**
+ * define NILFS_MAX_VOLUME_NAME - maximum number of characters (bytes) in a
+ *                                file system volume name
+ *
+ * Defined by the size of the volume name field in the on-disk superblocks.
+ * This volume name does not include the terminating NULL byte if the string
+ * length matches the field size, so use (NILFS_MAX_VOLUME_NAME + 1) for the
+ * size of the buffer that requires a NULL byte termination.
+ */
+#define NILFS_MAX_VOLUME_NAME  \
+	sizeof_field(struct nilfs_super_block, s_volume_name)
+
 /*
  * Macros to check inode numbers
  */