quota: cleanup dquota sync functions (version 4)

Currently the VFS calls vfs_dq_sync to sync out disk quotas for a given
superblock.  This is a small wrapper around sync_dquots which for the
case of a non-NULL superblock is a small wrapper around quota_sync_sb.

Just make quota_sync_sb global (rename it to sync_quota_sb) and call it
directly.  Also call it directly for those cases in quota.c that have a
superblock and leave sync_dquots purely an iterator over sync_quota_sb and
remove it's superblock argument.

To make this nicer move the check for the lack of a quota_sync method
from the callers into sync_quota_sb.

[folded build fix from Alexander Beregalov <a.beregalov@gmail.com>]

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/quota/quota.c

@@ -159,10 +159,14 @@ static int check_quotactl_valid(struct super_block *sb, int type, int cmd,
 	return error;
 }
 
-static void quota_sync_sb(struct super_block *sb, int type)
+#ifdef CONFIG_QUOTA
+void sync_quota_sb(struct super_block *sb, int type)
 {
 	int cnt;
 
+	if (!sb->s_qcop->quota_sync)
+		return;
+
 	sb->s_qcop->quota_sync(sb, type);
 
 	if (sb_dqopt(sb)->flags & DQUOT_QUOTA_SYS_FILE)
@@ -191,17 +195,13 @@ static void quota_sync_sb(struct super_block *sb, int type)
 	}
 	mutex_unlock(&sb_dqopt(sb)->dqonoff_mutex);
 }
+#endif
 
-void sync_dquots(struct super_block *sb, int type)
+static void sync_dquots(int type)
 {
+	struct super_block *sb;
 	int cnt;
 
-	if (sb) {
-		if (sb->s_qcop->quota_sync)
-			quota_sync_sb(sb, type);
-		return;
-	}
-
 	spin_lock(&sb_lock);
 restart:
 	list_for_each_entry(sb, &super_blocks, s_list) {
@@ -222,8 +222,8 @@ restart:
 		sb->s_count++;
 		spin_unlock(&sb_lock);
 		down_read(&sb->s_umount);
-		if (sb->s_root && sb->s_qcop->quota_sync)
-			quota_sync_sb(sb, type);
+		if (sb->s_root)
+			sync_quota_sb(sb, type);
 		up_read(&sb->s_umount);
 		spin_lock(&sb_lock);
 		if (__put_super_and_need_restart(sb))
@@ -301,7 +301,10 @@ static int do_quotactl(struct super_block *sb, int type, int cmd, qid_t id,
 			return sb->s_qcop->set_dqblk(sb, type, id, &idq);
 		}
 		case Q_SYNC:
-			sync_dquots(sb, type);
+			if (sb)
+				sync_quota_sb(sb, type);
+			else
+				sync_dquots(type);
 			return 0;
 
 		case Q_XQUOTAON: