[btr] Add a comment to btr_pool_available().

diff --git a/buffer_tree.c b/buffer_tree.c
index 5571b4338fd841343034892c3591080806691734..4160646da483bff8c8b0eea6c754d05fe17cf895 100644 (file)
--- a/buffer_tree.c
+++ b/buffer_tree.c
@@ -100,6 +100,10 @@ size_t btr_pool_unused(struct btr_pool *btrp)
        return btr_pool_size(btrp) - btr_pool_filled(btrp);
 }
 
+/*
+ * Return maximal size available for one read. This is
+ * smaller than the value returned by btr_pool_unused().
+ */
 size_t btr_pool_available(struct btr_pool *btrp)
 {
        if (!btrp->whead)