ext4: online defrag -- Add the EXT4_IOC_SUPER_INFO ioctl

From: Akira Fujita <a-fujita@rs.jp.nec.com>

EXT4_IOC_SUPER_INFO gets super block information on disk.

Super block information is necessary for relevant (-r) and force (-f) defrag.
Non-root user can't get this information by opening the block device directly,
so implement this ioctl newly.

Signed-off-by: Akira Fujita <a-fujita@rs.jp.nec.com>
Signed-off-by: Takashi Sato <t-sato@yk.jp.nec.com>
--- fs/ext4/ext4.h  |    1 +
 fs/ext4/ioctl.c |   10 ++++++++++
 2 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index ccea421..94c4186 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -303,6 +303,7 @@ struct ext4_new_group_data {
 #define EXT4_IOC_MIGRATE		_IO('f', 9)
  /* note ioctl 11 reserved for filesystem-independent FIEMAP ioctl */
 #define EXT4_IOC_DEFRAG			_IOW('f', 15, struct ext4_ext_defrag_data)
+#define EXT4_IOC_SUPER_INFO		_IOR('f', 16, struct ext4_super_block)

 /*
  * ioctl commands in 32 bit emulation
diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index d5e1fe7..f8ce89b 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -246,6 +246,16 @@ setversion_out:
 		return err;
 	}

+	case EXT4_IOC_SUPER_INFO: {
+		struct ext4_super_block es;
+
+		if (copy_to_user((struct ext4_super_block __user *)arg,
+				EXT4_SB(inode->i_sb)->s_es, sizeof(es)))
+			return -EFAULT;
+		else
+			return 0;
+	}
+
 	case EXT4_IOC_GROUP_ADD: {
 		struct ext4_new_group_data input;
 		struct super_block *sb = inode->i_sb;