[PATCH] ext2fs: add ext2fs_read_sb that returns superblock

[Artem Blagodarenko <artem.blagodarenko@gmail.com>]

tune2fs is used to make e2label duties.  ext2fs_open2() reads group
descriptors which are not used during disk label obtaining, but takes
a lot of time on large partitions.

This patch adds ext2fs_read_sb(), there only initialized superblock
is returned This saves time dramatically.

Signed-off-by: Artem Blagodarenko <c17828@cray.com>
Cray-bug-id: LUS-5777
---
 lib/ext2fs/ext2fs.h |  2 ++
 lib/ext2fs/openfs.c | 16 ++++++++++++++++
 misc/tune2fs.c      | 23 +++++++++++++++--------
 3 files changed, 33 insertions(+), 8 deletions(-)

diff --git a/lib/ext2fs/ext2fs.h b/lib/ext2fs/ext2fs.h
index 59fd9742..3a63b74d 100644
--- a/lib/ext2fs/ext2fs.h
+++ b/lib/ext2fs/ext2fs.h
@@ -1630,6 +1630,8 @@ extern int ext2fs_journal_sb_start(int blocksize);
 extern errcode_t ext2fs_open(const char *name, int flags, int superblock,
 			     unsigned int block_size, io_manager manager,
 			     ext2_filsys *ret_fs);
+extern errcode_t ext2fs_read_sb(const char *name, io_manager manager,
+				struct ext2_super_block * super);
 extern errcode_t ext2fs_open2(const char *name, const char *io_options,
 			      int flags, int superblock,
 			      unsigned int block_size, io_manager manager,
diff --git a/lib/ext2fs/openfs.c b/lib/ext2fs/openfs.c
index 51b54a44..95f45d84 100644
--- a/lib/ext2fs/openfs.c
+++ b/lib/ext2fs/openfs.c
@@ -99,6 +99,22 @@ static void block_sha_map_free_entry(void *data)
 	return;
 }
 
+errcode_t ext2fs_read_sb(const char *name, io_manager manager,
+			 struct ext2_super_block * super)
+{
+	io_channel	io;
+	errcode_t	retval = 0;
+
+	retval = manager->open(name, 0, &io);
+	if (!retval) {
+		retval = io_channel_read_blk(io, 1, -SUPERBLOCK_SIZE,
+				     super);
+		io_channel_close(io);
+	}
+
+	return retval;
+}
+
 /*
  *  Note: if superblock is non-zero, block-size must also be non-zero.
  * 	Superblock and block_size can be zero to use the default size.
diff --git a/misc/tune2fs.c b/misc/tune2fs.c
index 7d2d38d7..fea607e1 100644
--- a/misc/tune2fs.c
+++ b/misc/tune2fs.c
@@ -2879,6 +2879,21 @@ int tune2fs_main(int argc, char **argv)
 #endif
 		io_ptr = unix_io_manager;
 
+	if (print_label) {
+		/* For e2label emulation */
+		struct ext2_super_block sb;
+
+		/* Read only superblock. Nothing else metters.*/
+		retval = ext2fs_read_sb(device_name, io_ptr, &sb);
+		if (!retval) {
+			printf("%.*s\n", (int) sizeof(sb.s_volume_name),
+			       sb.s_volume_name);
+		}
+
+		remove_error_table(&et_ext2_error_table);
+		return retval;
+	}
+
 retry_open:
 	if ((open_flag & EXT2_FLAG_RW) == 0 || f_flag)
 		open_flag |= EXT2_FLAG_SKIP_MMP;
@@ -2972,14 +2987,6 @@ retry_open:
 	sb = fs->super;
 	fs->flags &= ~EXT2_FLAG_MASTER_SB_ONLY;
 
-	if (print_label) {
-		/* For e2label emulation */
-		printf("%.*s\n", (int) sizeof(sb->s_volume_name),
-		       sb->s_volume_name);
-		remove_error_table(&et_ext2_error_table);
-		goto closefs;
-	}
-
 	retval = ext2fs_check_if_mounted(device_name, &mount_flags);
 	if (retval) {
 		com_err("ext2fs_check_if_mount", retval,
-- 
2.14.3