btrfs: cleanup extent buffer readahead

We're going to pass around more information when we allocate extent
buffers, in order to make that cleaner how we do readahead.  Most of the
callers have the parent node that we're getting our blockptr from, with
the sole exception of relocation which simply has the bytenr it wants to
read.

Add a helper that takes the current arguments that we need (bytenr and
gen), and add another helper for simply reading the slot out of a node.
In followup patches the helper that takes all the extra arguments will
be expanded, and the simpler helper won't need to have it's arguments
adjusted.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 47 insertions, 0 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 1dfbe859c650..973254b1f216 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -6123,3 +6123,50 @@ int try_release_extent_buffer(struct page *page)
 
 	return release_extent_buffer(eb);
 }
+
+/*
+ * btrfs_readahead_tree_block - attempt to readahead a child block
+ * @fs_info:	the fs_info
+ * @bytenr:	bytenr to read
+ * @gen:	generation for the uptodate check, can be 0
+ *
+ * Attempt to readahead a tree block at @bytenr.  If @gen is 0 then we do a
+ * normal uptodate check of the eb, without checking the generation.  If we have
+ * to read the block we will not block on anything.
+ */
+void btrfs_readahead_tree_block(struct btrfs_fs_info *fs_info,
+				u64 bytenr, u64 gen)
+{
+	struct extent_buffer *eb;
+	int ret;
+
+	eb = btrfs_find_create_tree_block(fs_info, bytenr);
+	if (IS_ERR(eb))
+		return;
+
+	if (btrfs_buffer_uptodate(eb, gen, 1)) {
+		free_extent_buffer(eb);
+		return;
+	}
+
+	ret = read_extent_buffer_pages(eb, WAIT_NONE, 0);
+	if (ret < 0)
+		free_extent_buffer_stale(eb);
+	else
+		free_extent_buffer(eb);
+}
+
+/*
+ * btrfs_readahead_node_child - readahead a node's child block
+ * @node:	parent node we're reading from
+ * @slot:	slot in the parent node for the child we want to read
+ *
+ * A helper for btrfs_readahead_tree_block, we simply read the bytenr pointed at
+ * the slot in the node provided.
+ */
+void btrfs_readahead_node_child(struct extent_buffer *node, int slot)
+{
+	btrfs_readahead_tree_block(node->fs_info,
+				   btrfs_node_blockptr(node, slot),
+				   btrfs_node_ptr_generation(node, slot));
+}