ext4: introduce ext4_sb_bread_unmovable() to replace sb_bread_unmovable()

Now we only use sb_bread_unmovable() to read superblock and descriptor
block at mount time, so there is no opportunity that we need to clear
buffer verified bit and also handle buffer write_io error bit. But for
the sake of unification, let's introduce ext4_sb_bread_unmovable() to
replace all sb_bread_unmovable(). After this patch, we stop using read
helpers in fs/buffer.c.
Signed-off-by: zhangyi (F) <yi.zhang@huawei.com>
Link: https://lore.kernel.org/r/20200924073337.861472-8-yi.zhang@huawei.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -2823,6 +2823,8 @@ extern int ext4_resize_fs(struct super_block *sb, ext4_fsblk_t n_blocks_count);
 /* super.c */
 extern struct buffer_head *ext4_sb_bread(struct super_block *sb,
 					 sector_t block, int op_flags);
+extern struct buffer_head *ext4_sb_bread_unmovable(struct super_block *sb,
+						   sector_t block);
 extern void ext4_read_bh_nowait(struct buffer_head *bh, int op_flags,
 				bh_end_io_t *end_io);
 extern int ext4_read_bh(struct buffer_head *bh, int op_flags,

fs/ext4/super.c

@@ -204,18 +204,19 @@ int ext4_read_bh_lock(struct buffer_head *bh, int op_flags, bool wait)
 }
 
 /*
- * This works like sb_bread() except it uses ERR_PTR for error
+ * This works like __bread_gfp() except it uses ERR_PTR for error
  * returns.  Currently with sb_bread it's impossible to distinguish
  * between ENOMEM and EIO situations (since both result in a NULL
  * return.
  */
-struct buffer_head *
-ext4_sb_bread(struct super_block *sb, sector_t block, int op_flags)
+static struct buffer_head *__ext4_sb_bread_gfp(struct super_block *sb,
+					       sector_t block, int op_flags,
+					       gfp_t gfp)
 {
 	struct buffer_head *bh;
 	int ret;
 
-	bh = sb_getblk(sb, block);
+	bh = sb_getblk_gfp(sb, block, gfp);
 	if (bh == NULL)
 		return ERR_PTR(-ENOMEM);
 	if (ext4_buffer_uptodate(bh))
@@ -229,6 +230,18 @@ ext4_sb_bread(struct super_block *sb, sector_t block, int op_flags)
 	return bh;
 }
 
+struct buffer_head *ext4_sb_bread(struct super_block *sb, sector_t block,
+				   int op_flags)
+{
+	return __ext4_sb_bread_gfp(sb, block, op_flags, __GFP_MOVABLE);
+}
+
+struct buffer_head *ext4_sb_bread_unmovable(struct super_block *sb,
+					    sector_t block)
+{
+	return __ext4_sb_bread_gfp(sb, block, 0, 0);
+}
+
 void ext4_sb_breadahead_unmovable(struct super_block *sb, sector_t block)
 {
 	struct buffer_head *bh = sb_getblk_gfp(sb, block, 0);
@@ -3954,8 +3967,11 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 		logical_sb_block = sb_block;
 	}
 
-	if (!(bh = sb_bread_unmovable(sb, logical_sb_block))) {
+	bh = ext4_sb_bread_unmovable(sb, logical_sb_block);
+	if (IS_ERR(bh)) {
 		ext4_msg(sb, KERN_ERR, "unable to read superblock");
+		ret = PTR_ERR(bh);
+		bh = NULL;
 		goto out_fail;
 	}
 	/*
@@ -4351,10 +4367,12 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 		brelse(bh);
 		logical_sb_block = sb_block * EXT4_MIN_BLOCK_SIZE;
 		offset = do_div(logical_sb_block, blocksize);
-		bh = sb_bread_unmovable(sb, logical_sb_block);
-		if (!bh) {
+		bh = ext4_sb_bread_unmovable(sb, logical_sb_block);
+		if (IS_ERR(bh)) {
 			ext4_msg(sb, KERN_ERR,
 			       "Can't read superblock on 2nd try");
+			ret = PTR_ERR(bh);
+			bh = NULL;
 			goto failed_mount;
 		}
 		es = (struct ext4_super_block *)(bh->b_data + offset);
@@ -4573,11 +4591,13 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 		struct buffer_head *bh;
 
 		block = descriptor_loc(sb, logical_sb_block, i);
-		bh = sb_bread_unmovable(sb, block);
-		if (!bh) {
+		bh = ext4_sb_bread_unmovable(sb, block);
+		if (IS_ERR(bh)) {
 			ext4_msg(sb, KERN_ERR,
 			       "can't read group descriptor %d", i);
 			db_count = i;
+			ret = PTR_ERR(bh);
+			bh = NULL;
 			goto failed_mount2;
 		}
 		rcu_read_lock();