btrfs: use a negative value for BTRFS_LOG_FORCE_COMMIT

Currently we use the value 1 for BTRFS_LOG_FORCE_COMMIT, but that value
has a few inconveniences:

1) If it's ever used by btrfs_log_inode(), or any function down the call
   chain, we have to remember to btrfs_set_log_full_commit(), which is
   repetitive and has a chance to be forgotten in future use cases.
   btrfs_log_inode_parent() only calls btrfs_set_log_full_commit() when
   it gets a negative value from btrfs_log_inode();

2) Down the call chain of btrfs_log_inode(), we may have functions that
   need to force a log commit, but can return either an error (negative
   value), false (0) or true (1). So they are forced to return some
   random negative to force a log commit - using BTRFS_LOG_FORCE_COMMIT
   would make the intention more clear. Currently the only example is
   flush_dir_items_batch().

So turn BTRFS_LOG_FORCE_COMMIT into a negative value. The chosen value
is -(MAX_ERRNO + 1), so that it does not overlap any errno value and makes
it easier to debug.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/tree-log.c

@@ -3652,11 +3652,10 @@ static int flush_dir_items_batch(struct btrfs_trans_handle *trans,
 
 	/*
 	 * If for some unexpected reason the last item's index is not greater
-	 * than the last index we logged, warn and return an error to fallback
-	 * to a transaction commit.
+	 * than the last index we logged, warn and force a transaction commit.
 	 */
 	if (WARN_ON(last_index <= inode->last_dir_index_offset))
-		ret = -EUCLEAN;
+		ret = BTRFS_LOG_FORCE_COMMIT;
 	else
 		inode->last_dir_index_offset = last_index;
 out:
@@ -5604,10 +5603,8 @@ static int add_conflicting_inode(struct btrfs_trans_handle *trans,
 	 * LOG_INODE_EXISTS mode) and slow down other fsyncs or transaction
 	 * commits.
 	 */
-	if (ctx->num_conflict_inodes >= MAX_CONFLICT_INODES) {
-		btrfs_set_log_full_commit(trans);
+	if (ctx->num_conflict_inodes >= MAX_CONFLICT_INODES)
 		return BTRFS_LOG_FORCE_COMMIT;
-	}
 
 	inode = btrfs_iget(root->fs_info->sb, ino, root);
 	/*
@@ -6466,7 +6463,6 @@ static int btrfs_log_inode(struct btrfs_trans_handle *trans,
 	 * result in losing the file after a log replay.
 	 */
 	if (full_dir_logging && inode->last_unlink_trans >= trans->transid) {
-		btrfs_set_log_full_commit(trans);
 		ret = BTRFS_LOG_FORCE_COMMIT;
 		goto out_unlock;
 	}

fs/btrfs/tree-log.h

@@ -13,8 +13,13 @@
 /* return value for btrfs_log_dentry_safe that means we don't need to log it at all */
 #define BTRFS_NO_LOG_SYNC 256
 
-/* We can't use the tree log for whatever reason, force a transaction commit */
-#define BTRFS_LOG_FORCE_COMMIT				(1)
+/*
+ * We can't use the tree log for whatever reason, force a transaction commit.
+ * We use a negative value because there are functions through the logging code
+ * that need to return an error (< 0 value), false (0) or true (1). Any negative
+ * value will do, as it will cause the log to be marked for a full sync.
+ */
+#define BTRFS_LOG_FORCE_COMMIT				(-(MAX_ERRNO + 1))
 
 struct btrfs_log_ctx {
 	int log_ret;