erofs: use dsb instead of layout for ondisk super_block

As Christoph pointed out [1], "Why is the variable name
for the on-disk subperblock layout? We usually still
calls this something with sb in the name, e.g. dsb.
for disksuper block. " Let's fix it.

[1] https://lore.kernel.org/r/20190829101545.GC20598@infradead.org/Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Link: https://lore.kernel.org/r/20190904020912.63925-14-gaoxiang25@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/erofs/super.c

@@ -49,9 +49,9 @@ static void free_inode(struct inode *inode)
 }
 
 static bool check_layout_compatibility(struct super_block *sb,
-				       struct erofs_super_block *layout)
+				       struct erofs_super_block *dsb)
 {
-	const unsigned int feature = le32_to_cpu(layout->feature_incompat);
+	const unsigned int feature = le32_to_cpu(dsb->feature_incompat);
 
 	EROFS_SB(sb)->feature_incompat = feature;
 
@@ -68,7 +68,7 @@ static int superblock_read(struct super_block *sb)
 {
 	struct erofs_sb_info *sbi;
 	struct buffer_head *bh;
-	struct erofs_super_block *layout;
+	struct erofs_super_block *dsb;
 	unsigned int blkszbits;
 	int ret;
 
@@ -80,16 +80,15 @@ static int superblock_read(struct super_block *sb)
 	}
 
 	sbi = EROFS_SB(sb);
-	layout = (struct erofs_super_block *)((u8 *)bh->b_data
-		 + EROFS_SUPER_OFFSET);
+	dsb = (struct erofs_super_block *)(bh->b_data + EROFS_SUPER_OFFSET);
 
 	ret = -EINVAL;
-	if (le32_to_cpu(layout->magic) != EROFS_SUPER_MAGIC_V1) {
+	if (le32_to_cpu(dsb->magic) != EROFS_SUPER_MAGIC_V1) {
 		errln("cannot find valid erofs superblock");
 		goto out;
 	}
 
-	blkszbits = layout->blkszbits;
+	blkszbits = dsb->blkszbits;
 	/* 9(512 bytes) + LOG_SECTORS_PER_BLOCK == LOG_BLOCK_SIZE */
 	if (blkszbits != LOG_BLOCK_SIZE) {
 		errln("blksize %u isn't supported on this platform",
@@ -97,25 +96,25 @@ static int superblock_read(struct super_block *sb)
 		goto out;
 	}
 
-	if (!check_layout_compatibility(sb, layout))
+	if (!check_layout_compatibility(sb, dsb))
 		goto out;
 
-	sbi->blocks = le32_to_cpu(layout->blocks);
-	sbi->meta_blkaddr = le32_to_cpu(layout->meta_blkaddr);
+	sbi->blocks = le32_to_cpu(dsb->blocks);
+	sbi->meta_blkaddr = le32_to_cpu(dsb->meta_blkaddr);
 #ifdef CONFIG_EROFS_FS_XATTR
-	sbi->xattr_blkaddr = le32_to_cpu(layout->xattr_blkaddr);
+	sbi->xattr_blkaddr = le32_to_cpu(dsb->xattr_blkaddr);
 #endif
 	sbi->islotbits = ilog2(sizeof(struct erofs_inode_compact));
-	sbi->root_nid = le16_to_cpu(layout->root_nid);
-	sbi->inos = le64_to_cpu(layout->inos);
+	sbi->root_nid = le16_to_cpu(dsb->root_nid);
+	sbi->inos = le64_to_cpu(dsb->inos);
 
-	sbi->build_time = le64_to_cpu(layout->build_time);
-	sbi->build_time_nsec = le32_to_cpu(layout->build_time_nsec);
+	sbi->build_time = le64_to_cpu(dsb->build_time);
+	sbi->build_time_nsec = le32_to_cpu(dsb->build_time_nsec);
 
-	memcpy(&sb->s_uuid, layout->uuid, sizeof(layout->uuid));
+	memcpy(&sb->s_uuid, dsb->uuid, sizeof(dsb->uuid));
 
-	ret = strscpy(sbi->volume_name, layout->volume_name,
-		      sizeof(layout->volume_name));
+	ret = strscpy(sbi->volume_name, dsb->volume_name,
+		      sizeof(dsb->volume_name));
 	if (ret < 0) {	/* -E2BIG */
 		errln("bad volume name without NIL terminator");
 		ret = -EFSCORRUPTED;