librbd: add explicit management of cacheshistoric/rbd-multi-cache

Allow librbd users to create in-memory cache pools, and open images using
those caches.  This lets you control the total amount of memory consumed
for some number of open images.  It also lets you individually control
the writeback behavior for individual images (e.g., have some write-thru,
some write-back).

This doesn't let you specify max_dirty limits on a per-image basis, tho,
unless you give that image its own cache.

Note that doing rbd_open on an image when 'rbd cache' is true is
equivalent to creating a separate cache for that image using the
'rbd cache *' tunables.  This API is meant to be used in leiu of the
'rbd cache*' options.

Signed-off-by: Sage Weil <sage@newdream.net>

1 files changed, 32 insertions, 0 deletions

diff --git a/src/librbd.cc b/src/librbd.cc
index 36b93cf7df5..f89ff6ff584 100644
--- a/src/librbd.cc
+++ b/src/librbd.cc
@@ -2420,6 +2420,19 @@ extern "C" int rbd_open(rados_ioctx_t p, const char *name, rbd_image_t *image, c
   return r;
 }
 
+extern "C" int rbd_open_cached(rados_ioctx_t p, const char *name, rbd_image_t *image, const char *snap_name,
+			       rbd_cache_t cache)
+{
+  librados::IoCtx io_ctx;
+  librados::IoCtx::from_rados_ioctx_t(p, io_ctx);
+  librbd::ImageCtx *ictx = new librbd::ImageCtx(name, snap_name, io_ctx, (librbd::CacheCtx *)cache);
+  if (!ictx)
+    return -ENOMEM;
+  int r = librbd::open_image(ictx);
+  *image = (rbd_image_t)ictx;
+  return r;
+}
+
 extern "C" int rbd_close(rbd_image_t image)
 {
   librbd::ImageCtx *ctx = (librbd::ImageCtx *)image;
@@ -2448,6 +2461,25 @@ extern "C" int rbd_stat(rbd_image_t image, rbd_image_info_t *info, size_t infosi
   return librbd::info(ictx, *info, infosize);
 }
 
+/* cache */
+
+extern "C" int rbd_cache_create(rados_t cluster, rbd_cache_t *pcache,
+				uint64_t max_size, uint64_t max_dirty, uint64_t target_dirty)
+{
+  librbd::CacheCtx *cache = new librbd::CacheCtx((CephContext *)rados_cct(cluster), "rbd_cache");
+  cache->object_cacher->set_max_size(max_size);
+  cache->object_cacher->set_max_dirty(max_dirty);
+  cache->object_cacher->set_target_dirty(target_dirty);
+  *pcache = cache;
+  return 0;
+}
+
+extern "C" int rbd_cache_destroy(rbd_cache_t cache)
+{
+  delete (librbd::CacheCtx *)cache;
+  return 0;
+}
+
 /* snapshots */
 extern "C" int rbd_snap_create(rbd_image_t image, const char *snap_name)
 {