quota: add get_inode_usage callback to transfer multi-inode charges

Ext4 ea_inode feature allows storing xattr values in external inodes to
be able to store values that are bigger than a block in size. Ext4 also
has deduplication support for these type of inodes. With deduplication,
the actual storage waste is eliminated but the users of such inodes are
still charged full quota for the inodes as if there was no sharing
happening in the background.

This design requires ext4 to manually charge the users because the
inodes are shared.

An implication of this is that, if someone calls chown on a file that
has such references we need to transfer the quota for the file and xattr
inodes. Current dquot_transfer() function implicitly transfers one inode
charge. With ea_inode feature, we would like to transfer multiple inode
charges.

Add get_inode_usage callback which can interrogate the total number of
inodes that were charged for a given inode.

[ Applied fix from Colin King to make sure the 'ret' variable is
  initialized on the successful return path.  Detected by
  CoverityScan, CID#1446616 ("Uninitialized scalar variable") --tytso]

Signed-off-by: Tahsin Erdogan <tahsin@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Jan Kara <jack@suse.cz>

1 files changed, 55 insertions, 0 deletions

diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index a4c8fe3692a2..22bfb6221a2d 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -733,6 +733,61 @@ static void ext4_xattr_update_super_block(handle_t *handle,
 	}
 }
 
+int ext4_get_inode_usage(struct inode *inode, qsize_t *usage)
+{
+	struct ext4_iloc iloc = { .bh = NULL };
+	struct buffer_head *bh = NULL;
+	struct ext4_inode *raw_inode;
+	struct ext4_xattr_ibody_header *header;
+	struct ext4_xattr_entry *entry;
+	qsize_t ea_inode_refs = 0;
+	void *end;
+	int ret;
+
+	lockdep_assert_held_read(&EXT4_I(inode)->xattr_sem);
+
+	if (ext4_test_inode_state(inode, EXT4_STATE_XATTR)) {
+		ret = ext4_get_inode_loc(inode, &iloc);
+		if (ret)
+			goto out;
+		raw_inode = ext4_raw_inode(&iloc);
+		header = IHDR(inode, raw_inode);
+		end = (void *)raw_inode + EXT4_SB(inode->i_sb)->s_inode_size;
+		ret = xattr_check_inode(inode, header, end);
+		if (ret)
+			goto out;
+
+		for (entry = IFIRST(header); !IS_LAST_ENTRY(entry);
+		     entry = EXT4_XATTR_NEXT(entry))
+			if (entry->e_value_inum)
+				ea_inode_refs++;
+	}
+
+	if (EXT4_I(inode)->i_file_acl) {
+		bh = sb_bread(inode->i_sb, EXT4_I(inode)->i_file_acl);
+		if (!bh) {
+			ret = -EIO;
+			goto out;
+		}
+
+		if (ext4_xattr_check_block(inode, bh)) {
+			ret = -EFSCORRUPTED;
+			goto out;
+		}
+
+		for (entry = BFIRST(bh); !IS_LAST_ENTRY(entry);
+		     entry = EXT4_XATTR_NEXT(entry))
+			if (entry->e_value_inum)
+				ea_inode_refs++;
+	}
+	*usage = ea_inode_refs + 1;
+	ret = 0;
+out:
+	brelse(iloc.bh);
+	brelse(bh);
+	return ret;
+}
+
 static inline size_t round_up_cluster(struct inode *inode, size_t length)
 {
 	struct super_block *sb = inode->i_sb;