btrfs: qgroup: add new quota mode for simple quotas

Add a new quota mode called "simple quotas". It can be enabled by the
existing quota enable ioctl via a new command, and sets an incompat
bit, as the implementation of simple quotas will make backwards
incompatible changes to the disk format of the extent tree.
Signed-off-by: Boris Burkov <boris@bur.io>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/delayed-ref.c

@@ -959,8 +959,7 @@ int btrfs_add_delayed_tree_ref(struct btrfs_trans_handle *trans,
 		return -ENOMEM;
 	}
 
-	if (test_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags) &&
-	    !generic_ref->skip_qgroup) {
+	if (btrfs_qgroup_enabled(fs_info) && !generic_ref->skip_qgroup) {
 		record = kzalloc(sizeof(*record), GFP_NOFS);
 		if (!record) {
 			kmem_cache_free(btrfs_delayed_tree_ref_cachep, ref);
@@ -1063,8 +1062,7 @@ int btrfs_add_delayed_data_ref(struct btrfs_trans_handle *trans,
 		return -ENOMEM;
 	}
 
-	if (test_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags) &&
-	    !generic_ref->skip_qgroup) {
+	if (btrfs_qgroup_enabled(fs_info) && !generic_ref->skip_qgroup) {
 		record = kzalloc(sizeof(*record), GFP_NOFS);
 		if (!record) {
 			kmem_cache_free(btrfs_delayed_data_ref_cachep, ref);

fs/btrfs/fs.h

@@ -220,7 +220,8 @@ enum {
 	 BTRFS_FEATURE_INCOMPAT_NO_HOLES	|	\
 	 BTRFS_FEATURE_INCOMPAT_METADATA_UUID	|	\
 	 BTRFS_FEATURE_INCOMPAT_RAID1C34	|	\
-	 BTRFS_FEATURE_INCOMPAT_ZONED)
+	 BTRFS_FEATURE_INCOMPAT_ZONED		|	\
+	 BTRFS_FEATURE_INCOMPAT_SIMPLE_QUOTA)
 
 #ifdef CONFIG_BTRFS_DEBUG
 	/*

fs/btrfs/ioctl.c

@@ -3697,7 +3697,8 @@ static long btrfs_ioctl_quota_ctl(struct file *file, void __user *arg)
 
 	switch (sa->cmd) {
 	case BTRFS_QUOTA_CTL_ENABLE:
-		ret = btrfs_quota_enable(fs_info);
+	case BTRFS_QUOTA_CTL_ENABLE_SIMPLE_QUOTA:
+		ret = btrfs_quota_enable(fs_info, sa);
 		break;
 	case BTRFS_QUOTA_CTL_DISABLE:
 		ret = btrfs_quota_disable(fs_info);

fs/btrfs/qgroup.h

@@ -101,8 +101,15 @@
  *     subtree rescan for them.
  */
 
-#define BTRFS_QGROUP_RUNTIME_FLAG_CANCEL_RESCAN		(1UL << 3)
-#define BTRFS_QGROUP_RUNTIME_FLAG_NO_ACCOUNTING		(1UL << 4)
+/*
+ * These flags share the flags field of the btrfs_qgroup_status_item with the
+ * persisted flags defined in btrfs_tree.h.
+ *
+ * To minimize the chance of collision with new persisted status flags, these
+ * count backwards from the MSB.
+ */
+#define BTRFS_QGROUP_RUNTIME_FLAG_CANCEL_RESCAN		(1ULL << 63)
+#define BTRFS_QGROUP_RUNTIME_FLAG_NO_ACCOUNTING		(1ULL << 62)
 
 /*
  * Record a dirty extent, and info qgroup to update quota on it
@@ -276,13 +283,17 @@ enum {
 	ENUM_BIT(QGROUP_FREE),
 };
 
-int btrfs_quota_enable(struct btrfs_fs_info *fs_info);
 enum btrfs_qgroup_mode {
 	BTRFS_QGROUP_MODE_DISABLED,
 	BTRFS_QGROUP_MODE_FULL,
+	BTRFS_QGROUP_MODE_SIMPLE
 };
 
 enum btrfs_qgroup_mode btrfs_qgroup_mode(struct btrfs_fs_info *fs_info);
+bool btrfs_qgroup_enabled(struct btrfs_fs_info *fs_info);
+bool btrfs_qgroup_full_accounting(struct btrfs_fs_info *fs_info);
+int btrfs_quota_enable(struct btrfs_fs_info *fs_info,
+		       struct btrfs_ioctl_quota_ctl_args *quota_ctl_args);
 int btrfs_quota_disable(struct btrfs_fs_info *fs_info);
 int btrfs_qgroup_rescan(struct btrfs_fs_info *fs_info);
 void btrfs_qgroup_rescan_resume(struct btrfs_fs_info *fs_info);

fs/btrfs/root-tree.c

@@ -510,7 +510,7 @@ int btrfs_subvolume_reserve_metadata(struct btrfs_root *root,
 	struct btrfs_fs_info *fs_info = root->fs_info;
 	struct btrfs_block_rsv *global_rsv = &fs_info->global_block_rsv;
 
-	if (test_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags)) {
+	if (btrfs_qgroup_enabled(fs_info)) {
 		/* One for parent inode, two for dir entries */
 		qgroup_num_bytes = 3 * fs_info->nodesize;
 		ret = btrfs_qgroup_reserve_meta_prealloc(root,

fs/btrfs/transaction.c

@@ -1620,11 +1620,10 @@ static int qgroup_account_snapshot(struct btrfs_trans_handle *trans,
 	int ret;
 
 	/*
-	 * Save some performance in the case that qgroups are not
-	 * enabled. If this check races with the ioctl, rescan will
-	 * kick in anyway.
+	 * Save some performance in the case that full qgroups are not enabled.
+	 * If this check races with the ioctl, rescan will kick in anyway.
 	 */
-	if (!test_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags))
+	if (!btrfs_qgroup_full_accounting(fs_info))
 		return 0;
 
 	/*

include/uapi/linux/btrfs.h

@@ -334,6 +334,7 @@ struct btrfs_ioctl_fs_info_args {
 #define BTRFS_FEATURE_INCOMPAT_ZONED		(1ULL << 12)
 #define BTRFS_FEATURE_INCOMPAT_EXTENT_TREE_V2	(1ULL << 13)
 #define BTRFS_FEATURE_INCOMPAT_RAID_STRIPE_TREE	(1ULL << 14)
+#define BTRFS_FEATURE_INCOMPAT_SIMPLE_QUOTA	(1ULL << 16)
 
 struct btrfs_ioctl_feature_flags {
 	__u64 compat_flags;
@@ -754,6 +755,7 @@ struct btrfs_ioctl_get_dev_stats {
 #define BTRFS_QUOTA_CTL_ENABLE	1
 #define BTRFS_QUOTA_CTL_DISABLE	2
 #define BTRFS_QUOTA_CTL_RESCAN__NOTUSED	3
+#define BTRFS_QUOTA_CTL_ENABLE_SIMPLE_QUOTA 4
 struct btrfs_ioctl_quota_ctl_args {
 	__u64 cmd;
 	__u64 status;

include/uapi/linux/btrfs_tree.h

@@ -1233,9 +1233,17 @@ static inline __u16 btrfs_qgroup_level(__u64 qgroupid)
  */
 #define BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT	(1ULL << 2)
 
+/*
+ * Whether or not this filesystem is using simple quotas.  Not exactly the
+ * incompat bit, because we support using simple quotas, disabling it, then
+ * going back to full qgroup quotas.
+ */
+#define BTRFS_QGROUP_STATUS_FLAG_SIMPLE_MODE	(1ULL << 3)
+
 #define BTRFS_QGROUP_STATUS_FLAGS_MASK	(BTRFS_QGROUP_STATUS_FLAG_ON |		\
 					 BTRFS_QGROUP_STATUS_FLAG_RESCAN |	\
-					 BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT)
+					 BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT | \
+					 BTRFS_QGROUP_STATUS_FLAG_SIMPLE_MODE)
 
 #define BTRFS_QGROUP_STATUS_VERSION        1