f2fs: save device node number into f2fs_inode

This patch stores inode->i_rdev into on-disk inode structure.

Alun reported that:
 aspire tmp # mount -t f2fs /dev/sdb mnt
 aspire tmp # mknod mnt/sda1 b 8 1
 aspire tmp # mknod mnt/null c 1 3
 aspire tmp # mknod mnt/console c 5 1
 aspire tmp # ls -l mnt
 total 2
 crw-r--r-- 1 root root 5, 1 Jan 22 18:44 console
 crw-r--r-- 1 root root 1, 3 Jan 22 18:44 null
 brw-r--r-- 1 root root 8, 1 Jan 22 18:44 sda1
 aspire tmp # umount mnt
 aspire tmp # mount -t f2fs /dev/sdb mnt
 aspire tmp # ls -l mnt
 total 2
 crw-r--r-- 1 root root 0, 0 Jan 22 18:44 console
 crw-r--r-- 1 root root 0, 0 Jan 22 18:44 null
 brw-r--r-- 1 root root 0, 0 Jan 22 18:44 sda1

In this report, f2fs lost the major/minor numbers of device files after umount.
The reason was revealed that f2fs does not store the inode->i_rdev to the
on-disk inode data structure.

So, as the other file systems do, f2fs also stores i_rdev into the i_addr fields
in on-disk inode structure without any on-disk layout changes.
Note that, this bug is limited to device files made by mknod().
Reported-and-Tested-by: Alun Jones <alun.linux@ty-penguin.org.uk>
Signed-off-by: Changman Lee <cm224.lee@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/inode.c

@@ -100,6 +100,10 @@ static int do_read_inode(struct inode *inode)
 	inode->i_ctime.tv_nsec = le32_to_cpu(ri->i_ctime_nsec);
 	inode->i_mtime.tv_nsec = le32_to_cpu(ri->i_mtime_nsec);
 	inode->i_generation = le32_to_cpu(ri->i_generation);
+	if (ri->i_addr[0])
+		inode->i_rdev = old_decode_dev(le32_to_cpu(ri->i_addr[0]));
+	else
+		inode->i_rdev = new_decode_dev(le32_to_cpu(ri->i_addr[1]));
 
 	fi->i_current_depth = le32_to_cpu(ri->i_current_depth);
 	fi->i_xattr_nid = le32_to_cpu(ri->i_xattr_nid);
@@ -203,6 +207,20 @@ void update_inode(struct inode *inode, struct page *node_page)
 	ri->i_flags = cpu_to_le32(F2FS_I(inode)->i_flags);
 	ri->i_pino = cpu_to_le32(F2FS_I(inode)->i_pino);
 	ri->i_generation = cpu_to_le32(inode->i_generation);
+
+	if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode)) {
+		if (old_valid_dev(inode->i_rdev)) {
+			ri->i_addr[0] =
+				cpu_to_le32(old_encode_dev(inode->i_rdev));
+			ri->i_addr[1] = 0;
+		} else {
+			ri->i_addr[0] = 0;
+			ri->i_addr[1] =
+				cpu_to_le32(new_encode_dev(inode->i_rdev));
+			ri->i_addr[2] = 0;
+		}
+	}
+
 	set_cold_node(inode, node_page);
 	set_page_dirty(node_page);
 }