ext4: convert symlink external data block mapping to bdev

Symlink's external data block is one kind of metadata block, and now
that almost all ext4 metadata block's page cache (e.g. directory blocks,
quota blocks...) belongs to bdev backing inode except the symlink. It
is essentially worked in data=journal mode like other regular file's
data block because probably in order to make it simple for generic VFS
code handling symlinks or some other historical reasons, but the logic
of creating external data block in ext4_symlink() is complicated. and it
also make things confused if user do not want to let the filesystem
worked in data=journal mode. This patch convert the final exceptional
case and make things clean, move the mapping of the symlink's external
data block to bdev like any other metadata block does.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://lore.kernel.org/r/20220424140936.1898920-3-yi.zhang@huawei.com

1 files changed, 43 insertions, 8 deletions

diff --git a/fs/ext4/symlink.c b/fs/ext4/symlink.c
index 69109746e6e2..d281f5bcc526 100644
--- a/fs/ext4/symlink.c
+++ b/fs/ext4/symlink.c
@@ -27,7 +27,7 @@ static const char *ext4_encrypted_get_link(struct dentry *dentry,
 					   struct inode *inode,
 					   struct delayed_call *done)
 {
-	struct page *cpage = NULL;
+	struct buffer_head *bh = NULL;
 	const void *caddr;
 	unsigned int max_size;
 	const char *paddr;
@@ -39,16 +39,19 @@ static const char *ext4_encrypted_get_link(struct dentry *dentry,
 		caddr = EXT4_I(inode)->i_data;
 		max_size = sizeof(EXT4_I(inode)->i_data);
 	} else {
-		cpage = read_mapping_page(inode->i_mapping, 0, NULL);
-		if (IS_ERR(cpage))
-			return ERR_CAST(cpage);
-		caddr = page_address(cpage);
+		bh = ext4_bread(NULL, inode, 0, 0);
+		if (IS_ERR(bh))
+			return ERR_CAST(bh);
+		if (!bh) {
+			EXT4_ERROR_INODE(inode, "bad symlink.");
+			return ERR_PTR(-EFSCORRUPTED);
+		}
+		caddr = bh->b_data;
 		max_size = inode->i_sb->s_blocksize;
 	}
 
 	paddr = fscrypt_get_symlink(inode, caddr, max_size, done);
-	if (cpage)
-		put_page(cpage);
+	brelse(bh);
 	return paddr;
 }
 
@@ -62,6 +65,38 @@ static int ext4_encrypted_symlink_getattr(struct user_namespace *mnt_userns,
 	return fscrypt_symlink_getattr(path, stat);
 }
 
+static void ext4_free_link(void *bh)
+{
+	brelse(bh);
+}
+
+static const char *ext4_get_link(struct dentry *dentry, struct inode *inode,
+				 struct delayed_call *callback)
+{
+	struct buffer_head *bh;
+
+	if (!dentry) {
+		bh = ext4_getblk(NULL, inode, 0, EXT4_GET_BLOCKS_CACHED_NOWAIT);
+		if (IS_ERR(bh))
+			return ERR_CAST(bh);
+		if (!bh || !ext4_buffer_uptodate(bh))
+			return ERR_PTR(-ECHILD);
+	} else {
+		bh = ext4_bread(NULL, inode, 0, 0);
+		if (IS_ERR(bh))
+			return ERR_CAST(bh);
+		if (!bh) {
+			EXT4_ERROR_INODE(inode, "bad symlink.");
+			return ERR_PTR(-EFSCORRUPTED);
+		}
+	}
+
+	set_delayed_call(callback, ext4_free_link, bh);
+	nd_terminate_link(bh->b_data, inode->i_size,
+			  inode->i_sb->s_blocksize - 1);
+	return bh->b_data;
+}
+
 const struct inode_operations ext4_encrypted_symlink_inode_operations = {
 	.get_link	= ext4_encrypted_get_link,
 	.setattr	= ext4_setattr,
@@ -70,7 +105,7 @@ const struct inode_operations ext4_encrypted_symlink_inode_operations = {
 };
 
 const struct inode_operations ext4_symlink_inode_operations = {
-	.get_link	= page_get_link,
+	.get_link	= ext4_get_link,
 	.setattr	= ext4_setattr,
 	.getattr	= ext4_getattr,
 	.listxattr	= ext4_listxattr,