quota: Allow each filesystem to specify which quota types it supports

Currently all filesystems supporting VFS quota support user and group
quotas. With introduction of project quotas this is going to change so
make sure filesystem isn't called for quota type it doesn't support by
introduction of a bitmask determining which quota types each filesystem
supports.
Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/quota/quota.c

@@ -47,8 +47,11 @@ static int check_quotactl_permission(struct super_block *sb, int type, int cmd,
 
 static void quota_sync_one(struct super_block *sb, void *arg)
 {
-	if (sb->s_qcop && sb->s_qcop->quota_sync)
-		sb->s_qcop->quota_sync(sb, *(int *)arg);
+	int type = *(int *)arg;
+
+	if (sb->s_qcop && sb->s_qcop->quota_sync &&
+	    (sb->s_quota_types & (1 << type)))
+		sb->s_qcop->quota_sync(sb, type);
 }
 
 static int quota_sync_all(int type)
@@ -297,8 +300,14 @@ static int do_quotactl(struct super_block *sb, int type, int cmd, qid_t id,
 
 	if (type >= (XQM_COMMAND(cmd) ? XQM_MAXQUOTAS : MAXQUOTAS))
 		return -EINVAL;
+	/*
+	 * Quota not supported on this fs? Check this before s_quota_types
+	 * since they needn't be set if quota is not supported at all.
+	 */
 	if (!sb->s_qcop)
 		return -ENOSYS;
+	if (!(sb->s_quota_types & (1 << type)))
+		return -EINVAL;
 
 	ret = check_quotactl_permission(sb, type, cmd, id);
 	if (ret < 0)

fs/super.c

@@ -218,6 +218,12 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags)
 	atomic_set(&s->s_active, 1);
 	mutex_init(&s->s_vfs_rename_mutex);
 	lockdep_set_class(&s->s_vfs_rename_mutex, &type->s_vfs_rename_key);
+	/*
+	 * For now MAXQUOTAS check in do_quotactl() will limit quota type
+	 * appropriately. When each fs sets allowed_types, we can remove the
+	 * line below
+	 */
+	s->s_quota_types = QTYPE_MASK_USR | QTYPE_MASK_GRP | QTYPE_MASK_PRJ;
 	mutex_init(&s->s_dquot.dqio_mutex);
 	mutex_init(&s->s_dquot.dqonoff_mutex);
 	s->s_maxbytes = MAX_NON_LFS;

include/linux/fs.h

@@ -1224,6 +1224,7 @@ struct super_block {
 	struct backing_dev_info *s_bdi;
 	struct mtd_info		*s_mtd;
 	struct hlist_node	s_instances;
+	unsigned int		s_quota_types;	/* Bitmask of supported quota types */
 	struct quota_info	s_dquot;	/* Diskquota specific options */
 
 	struct sb_writers	s_writers;

include/linux/quota.h

@@ -56,6 +56,11 @@ enum quota_type {
 	PRJQUOTA = 2,		/* element used for project quotas */
 };
 
+/* Masks for quota types when used as a bitmask */
+#define QTYPE_MASK_USR (1 << USRQUOTA)
+#define QTYPE_MASK_GRP (1 << GRPQUOTA)
+#define QTYPE_MASK_PRJ (1 << PRJQUOTA)
+
 typedef __kernel_uid32_t qid_t; /* Type in which we store ids in memory */
 typedef long long qsize_t;	/* Type in which we store sizes */