Btrfs: write out free space cache

This is a simple bit, just dump the free space cache out to our preallocated
inode when we're writing out dirty block groups.  There are a bunch of changes
in inode.c in order to account for special cases.  Mostly when we're doing the
writeout we're holding trans_mutex, so we need to use the nolock transacation
functions.  Also we can't do asynchronous completions since the async thread
could be blocked on already completed IO waiting for the transaction lock.  This
has been tested with xfstests and btrfs filesystem balance, as well as my ENOSPC
tests.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>

1 files changed, 48 insertions, 0 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index aab40fb3faed..d5455a2bf60b 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2847,6 +2847,8 @@ again:
 			continue;
 		}
 
+		if (cache->disk_cache_state == BTRFS_DC_SETUP)
+			cache->disk_cache_state = BTRFS_DC_NEED_WRITE;
 		cache->dirty = 0;
 		last = cache->key.objectid + cache->key.offset;
 
@@ -2855,6 +2857,52 @@ again:
 		btrfs_put_block_group(cache);
 	}
 
+	while (1) {
+		/*
+		 * I don't think this is needed since we're just marking our
+		 * preallocated extent as written, but just in case it can't
+		 * hurt.
+		 */
+		if (last == 0) {
+			err = btrfs_run_delayed_refs(trans, root,
+						     (unsigned long)-1);
+			BUG_ON(err);
+		}
+
+		cache = btrfs_lookup_first_block_group(root->fs_info, last);
+		while (cache) {
+			/*
+			 * Really this shouldn't happen, but it could if we
+			 * couldn't write the entire preallocated extent and
+			 * splitting the extent resulted in a new block.
+			 */
+			if (cache->dirty) {
+				btrfs_put_block_group(cache);
+				goto again;
+			}
+			if (cache->disk_cache_state == BTRFS_DC_NEED_WRITE)
+				break;
+			cache = next_block_group(root, cache);
+		}
+		if (!cache) {
+			if (last == 0)
+				break;
+			last = 0;
+			continue;
+		}
+
+		btrfs_write_out_cache(root, trans, cache, path);
+
+		/*
+		 * If we didn't have an error then the cache state is still
+		 * NEED_WRITE, so we can set it to WRITTEN.
+		 */
+		if (cache->disk_cache_state == BTRFS_DC_NEED_WRITE)
+			cache->disk_cache_state = BTRFS_DC_WRITTEN;
+		last = cache->key.objectid + cache->key.offset;
+		btrfs_put_block_group(cache);
+	}
+
 	btrfs_free_path(path);
 	return 0;
 }