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>

fs/ext4/inode.c

@@ -5295,7 +5295,14 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
 			error = PTR_ERR(handle);
 			goto err_out;
 		}
+
+		/* dquot_transfer() calls back ext4_get_inode_usage() which
+		 * counts xattr inode references.
+		 */
+		down_read(&EXT4_I(inode)->xattr_sem);
 		error = dquot_transfer(inode, attr);
+		up_read(&EXT4_I(inode)->xattr_sem);
+
 		if (error) {
 			ext4_journal_stop(handle);
 			return error;

fs/ext4/ioctl.c

@@ -373,7 +373,13 @@ static int ext4_ioctl_setproject(struct file *filp, __u32 projid)
 
 	transfer_to[PRJQUOTA] = dqget(sb, make_kqid_projid(kprojid));
 	if (!IS_ERR(transfer_to[PRJQUOTA])) {
+
+		/* __dquot_transfer() calls back ext4_get_inode_usage() which
+		 * counts xattr inode references.
+		 */
+		down_read(&EXT4_I(inode)->xattr_sem);
 		err = __dquot_transfer(inode, transfer_to);
+		up_read(&EXT4_I(inode)->xattr_sem);
 		dqput(transfer_to[PRJQUOTA]);
 		if (err)
 			goto out_dirty;

fs/ext4/super.c

@@ -1272,6 +1272,7 @@ static const struct dquot_operations ext4_quota_operations = {
 	.alloc_dquot		= dquot_alloc,
 	.destroy_dquot		= dquot_destroy,
 	.get_projid		= ext4_get_projid,
+	.get_inode_usage	= ext4_get_inode_usage,
 	.get_next_id		= ext4_get_next_id,
 };
 

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;

fs/ext4/xattr.h

@@ -193,3 +193,5 @@ extern void ext4_xattr_inode_set_class(struct inode *ea_inode);
 #else
 static inline void ext4_xattr_inode_set_class(struct inode *ea_inode) { }
 #endif
+
+extern int ext4_get_inode_usage(struct inode *inode, qsize_t *usage);

fs/quota/dquot.c

@@ -1910,6 +1910,7 @@ int __dquot_transfer(struct inode *inode, struct dquot **transfer_to)
 {
 	qsize_t space, cur_space;
 	qsize_t rsv_space = 0;
+	qsize_t inode_usage = 1;
 	struct dquot *transfer_from[MAXQUOTAS] = {};
 	int cnt, ret = 0;
 	char is_valid[MAXQUOTAS] = {};
@@ -1919,6 +1920,13 @@ int __dquot_transfer(struct inode *inode, struct dquot **transfer_to)
 
 	if (IS_NOQUOTA(inode))
 		return 0;
+
+	if (inode->i_sb->dq_op->get_inode_usage) {
+		ret = inode->i_sb->dq_op->get_inode_usage(inode, &inode_usage);
+		if (ret)
+			return ret;
+	}
+
 	/* Initialize the arrays */
 	for (cnt = 0; cnt < MAXQUOTAS; cnt++) {
 		warn_to[cnt].w_type = QUOTA_NL_NOWARN;
@@ -1946,7 +1954,7 @@ int __dquot_transfer(struct inode *inode, struct dquot **transfer_to)
 			continue;
 		is_valid[cnt] = 1;
 		transfer_from[cnt] = i_dquot(inode)[cnt];
-		ret = check_idq(transfer_to[cnt], 1, &warn_to[cnt]);
+		ret = check_idq(transfer_to[cnt], inode_usage, &warn_to[cnt]);
 		if (ret)
 			goto over_quota;
 		ret = check_bdq(transfer_to[cnt], space, 0, &warn_to[cnt]);
@@ -1963,7 +1971,7 @@ int __dquot_transfer(struct inode *inode, struct dquot **transfer_to)
 		/* Due to IO error we might not have transfer_from[] structure */
 		if (transfer_from[cnt]) {
 			int wtype;
-			wtype = info_idq_free(transfer_from[cnt], 1);
+			wtype = info_idq_free(transfer_from[cnt], inode_usage);
 			if (wtype != QUOTA_NL_NOWARN)
 				prepare_warning(&warn_from_inodes[cnt],
 						transfer_from[cnt], wtype);
@@ -1971,13 +1979,13 @@ int __dquot_transfer(struct inode *inode, struct dquot **transfer_to)
 			if (wtype != QUOTA_NL_NOWARN)
 				prepare_warning(&warn_from_space[cnt],
 						transfer_from[cnt], wtype);
-			dquot_decr_inodes(transfer_from[cnt], 1);
+			dquot_decr_inodes(transfer_from[cnt], inode_usage);
 			dquot_decr_space(transfer_from[cnt], cur_space);
 			dquot_free_reserved_space(transfer_from[cnt],
 						  rsv_space);
 		}
 
-		dquot_incr_inodes(transfer_to[cnt], 1);
+		dquot_incr_inodes(transfer_to[cnt], inode_usage);
 		dquot_incr_space(transfer_to[cnt], cur_space);
 		dquot_resv_space(transfer_to[cnt], rsv_space);
 

include/linux/quota.h

@@ -332,6 +332,8 @@ struct dquot_operations {
 	 * quota code only */
 	qsize_t *(*get_reserved_space) (struct inode *);
 	int (*get_projid) (struct inode *, kprojid_t *);/* Get project ID */
+	/* Get number of inodes that were charged for a given inode */
+	int (*get_inode_usage) (struct inode *, qsize_t *);
 	/* Get next ID with active quota structure */
 	int (*get_next_id) (struct super_block *sb, struct kqid *qid);
 };