btrfs: add support for processing pending changes

There are some actions that modify global filesystem state but cannot be
performed at the time of request, but later at the transaction commit
time when the filesystem is in a known state.

For example enabling new incompat features on-the-fly or issuing
transaction commit from unsafe contexts (sysfs handlers).

Signed-off-by: David Sterba <dsterba@suse.cz>

fs/btrfs/ctree.h

@@ -1402,6 +1402,11 @@ struct btrfs_fs_info {
 	 */
 	u64 last_trans_log_full_commit;
 	unsigned long mount_opt;
+	/*
+	 * Track requests for actions that need to be done during transaction
+	 * commit (like for some mount options).
+	 */
+	unsigned long pending_changes;
 	unsigned long compress_type:4;
 	int commit_interval;
 	/*
@@ -2103,6 +2108,7 @@ struct btrfs_ioctl_defrag_range_args {
 #define btrfs_raw_test_opt(o, opt)	((o) & BTRFS_MOUNT_##opt)
 #define btrfs_test_opt(root, opt)	((root)->fs_info->mount_opt & \
 					 BTRFS_MOUNT_##opt)
+
 #define btrfs_set_and_info(root, opt, fmt, args...)			\
 {									\
 	if (!btrfs_test_opt(root, opt))					\
@@ -2117,6 +2123,45 @@ struct btrfs_ioctl_defrag_range_args {
 	btrfs_clear_opt(root->fs_info->mount_opt, opt);			\
 }
 
+/*
+ * Requests for changes that need to be done during transaction commit.
+ *
+ * Internal mount options that are used for special handling of the real
+ * mount options (eg. cannot be set during remount and have to be set during
+ * transaction commit)
+ */
+
+#define btrfs_test_pending(info, opt)	\
+	test_bit(BTRFS_PENDING_##opt, &(info)->pending_changes)
+#define btrfs_set_pending(info, opt)	\
+	set_bit(BTRFS_PENDING_##opt, &(info)->pending_changes)
+#define btrfs_clear_pending(info, opt)	\
+	clear_bit(BTRFS_PENDING_##opt, &(info)->pending_changes)
+
+/*
+ * Helpers for setting pending mount option changes.
+ *
+ * Expects corresponding macros
+ * BTRFS_PENDING_SET_ and CLEAR_ + short mount option name
+ */
+#define btrfs_set_pending_and_info(info, opt, fmt, args...)            \
+do {                                                                   \
+       if (!btrfs_raw_test_opt((info)->mount_opt, opt)) {              \
+               btrfs_info((info), fmt, ##args);                        \
+               btrfs_set_pending((info), SET_##opt);                   \
+               btrfs_clear_pending((info), CLEAR_##opt);               \
+       }                                                               \
+} while(0)
+
+#define btrfs_clear_pending_and_info(info, opt, fmt, args...)          \
+do {                                                                   \
+       if (btrfs_raw_test_opt((info)->mount_opt, opt)) {               \
+               btrfs_info((info), fmt, ##args);                        \
+               btrfs_set_pending((info), CLEAR_##opt);                 \
+               btrfs_clear_pending((info), SET_##opt);                 \
+       }                                                               \
+} while(0)
+
 /*
  * Inode flags
  */

fs/btrfs/disk-io.c

@@ -2834,6 +2834,12 @@ retry_root_backup:
 	if (btrfs_test_opt(tree_root, CHANGE_INODE_CACHE))
 		btrfs_set_opt(tree_root->fs_info->mount_opt, INODE_MAP_CACHE);
 
+	/*
+	 * Mount does not set all options immediatelly, we can do it now and do
+	 * not have to wait for transaction commit
+	 */
+	btrfs_apply_pending_changes(fs_info);
+
 #ifdef CONFIG_BTRFS_FS_CHECK_INTEGRITY
 	if (btrfs_test_opt(tree_root, CHECK_INTEGRITY)) {
 		ret = btrfsic_mount(tree_root, fs_devices,

fs/btrfs/transaction.c

@@ -1850,6 +1850,8 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 	else
 		btrfs_clear_opt(root->fs_info->mount_opt, INODE_MAP_CACHE);
 
+	btrfs_apply_pending_changes(root->fs_info);
+
 	/* commit_fs_roots gets rid of all the tree log roots, it is now
 	 * safe to free the root of tree log roots
 	 */
@@ -2019,3 +2021,17 @@ int btrfs_clean_one_deleted_snapshot(struct btrfs_root *root)
 
 	return (ret < 0) ? 0 : 1;
 }
+
+void btrfs_apply_pending_changes(struct btrfs_fs_info *fs_info)
+{
+	unsigned long prev;
+	unsigned long bit;
+
+	prev = cmpxchg(&fs_info->pending_changes, 0, 0);
+	if (!prev)
+		return;
+
+	if (prev)
+		btrfs_warn(fs_info,
+			"unknown pending changes left 0x%lx, ignoring", prev);
+}

fs/btrfs/transaction.h

@@ -170,4 +170,6 @@ int btrfs_wait_marked_extents(struct btrfs_root *root,
 int btrfs_transaction_blocked(struct btrfs_fs_info *info);
 int btrfs_transaction_in_commit(struct btrfs_fs_info *info);
 void btrfs_put_transaction(struct btrfs_transaction *transaction);
+void btrfs_apply_pending_changes(struct btrfs_fs_info *fs_info);
+
 #endif