From 5d340d26dd70192eb0e4f3f240e3433fb9a24154 Mon Sep 17 00:00:00 2001
From: Josh Durgin <josh.durgin@inktank.com>
Date: Thu, 24 Apr 2014 14:47:24 -0700
Subject: [PATCH] librbd: add an interface to invalidate cached data

This is useful for qemu to guarantee live migration with caching is
safe, by invalidating the cache on the destination before starting it.

Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
---
 src/include/rbd/librbd.h    |  9 +++++++++
 src/include/rbd/librbd.hpp  |  8 ++++++++
 src/librbd/internal.cc      | 13 +++++++++++++
 src/librbd/internal.h       |  1 +
 src/librbd/librbd.cc        | 12 ++++++++++++
 src/pybind/rbd.py           |  8 ++++++++
 src/test/pybind/test_rbd.py |  6 ++++++
 7 files changed, 57 insertions(+)

diff --git a/src/include/rbd/librbd.h b/src/include/rbd/librbd.h
index 5be82033390..1e87af9d194 100644
--- a/src/include/rbd/librbd.h
+++ b/src/include/rbd/librbd.h
@@ -39,6 +39,7 @@ extern "C" {
 
 #define LIBRBD_SUPPORTS_WATCH 0
 #define LIBRBD_SUPPORTS_AIO_FLUSH 1
+#define LIBRBD_SUPPORTS_INVALIDATE 1
 
 typedef void *rbd_snap_t;
 typedef void *rbd_image_t;
@@ -376,6 +377,14 @@ int rbd_flush(rbd_image_t image);
  */
 int rbd_aio_flush(rbd_image_t image, rbd_completion_t c);
 
+/**
+ * Drop any cached data for an image
+ *
+ * @param image the image to invalidate cached data for
+ * @returns 0 on success, negative error code on failure
+ */
+int rbd_invalidate_cache(rbd_image_t image);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/src/include/rbd/librbd.hpp b/src/include/rbd/librbd.hpp
index 697fc6ccc41..caf61a65f70 100644
--- a/src/include/rbd/librbd.hpp
+++ b/src/include/rbd/librbd.hpp
@@ -216,6 +216,14 @@ public:
    */
   int aio_flush(RBD::AioCompletion *c);
 
+  /**
+   * Drop any cached data for an image
+   *
+   * @param image the image to invalidate cached data for
+   * @returns 0 on success, negative error code on failure
+   */
+  int invalidate_cache();
+
 private:
   friend class RBD;
 
diff --git a/src/librbd/internal.cc b/src/librbd/internal.cc
index b13ff97cd9a..e56ef0897f4 100644
--- a/src/librbd/internal.cc
+++ b/src/librbd/internal.cc
@@ -2881,6 +2881,19 @@ reprotect_and_return_err:
     return r;
   }
 
+  int invalidate_cache(ImageCtx *ictx)
+  {
+    CephContext *cct = ictx->cct;
+    ldout(cct, 20) << "invalidate_cache " << ictx << dendl;
+
+    int r = ictx_check(ictx);
+    if (r < 0)
+      return r;
+
+    RWLock::WLocker l(ictx->md_lock);
+    return ictx->invalidate_cache();
+  }
+
   int aio_write(ImageCtx *ictx, uint64_t off, size_t len, const char *buf,
 		AioCompletion *c)
   {
diff --git a/src/librbd/internal.h b/src/librbd/internal.h
index 43458886b43..6fb1af46175 100644
--- a/src/librbd/internal.h
+++ b/src/librbd/internal.h
@@ -188,6 +188,7 @@ namespace librbd {
   int aio_flush(ImageCtx *ictx, AioCompletion *c);
   int flush(ImageCtx *ictx);
   int _flush(ImageCtx *ictx);
+  int invalidate_cache(ImageCtx *ictx);
 
   ssize_t handle_sparse_read(CephContext *cct,
 			     ceph::bufferlist data_bl,
diff --git a/src/librbd/librbd.cc b/src/librbd/librbd.cc
index cad0c5eb172..658f24b85ca 100644
--- a/src/librbd/librbd.cc
+++ b/src/librbd/librbd.cc
@@ -514,6 +514,12 @@ namespace librbd {
     return librbd::aio_flush(ictx, (librbd::AioCompletion *)c->pc);
   }
 
+  int Image::invalidate_cache()
+  {
+    ImageCtx *ictx = (ImageCtx *)ctx;
+    return librbd::invalidate_cache(ictx);
+  }
+
 } // namespace librbd
 
 extern "C" void rbd_version(int *major, int *minor, int *extra)
@@ -1130,6 +1136,12 @@ extern "C" int rbd_aio_flush(rbd_image_t image, rbd_completion_t c)
   return librbd::aio_flush(ictx, (librbd::AioCompletion *)comp->pc);
 }
 
+extern "C" int rbd_invalidate_cache(rbd_image_t image)
+{
+  librbd::ImageCtx *ictx = (librbd::ImageCtx *)image;
+  return librbd::invalidate_cache(ictx);
+}
+
 extern "C" int rbd_aio_is_complete(rbd_completion_t c)
 {
   librbd::RBD::AioCompletion *comp = (librbd::RBD::AioCompletion *)c;
diff --git a/src/pybind/rbd.py b/src/pybind/rbd.py
index bf075769d8b..ab093ce30ab 100644
--- a/src/pybind/rbd.py
+++ b/src/pybind/rbd.py
@@ -750,6 +750,14 @@ written." % (self.name, ret, length))
         if ret < 0:
             raise make_ex(ret, 'error flushing image')
 
+    def invalidate_cache(self):
+        """
+        Drop any cached data for the image.
+        """
+        ret = self.librbd.rbd_invalidate_cache(self.image)
+        if ret < 0:
+            raise make_ex(ret, 'error invalidating cache')
+
     def stripe_unit(self):
         """
         Returns the stripe unit used for the image.
diff --git a/src/test/pybind/test_rbd.py b/src/test/pybind/test_rbd.py
index e098805b615..144c4293cc8 100644
--- a/src/test/pybind/test_rbd.py
+++ b/src/test/pybind/test_rbd.py
@@ -229,6 +229,12 @@ class TestImage(object):
         self.image.close()
         remove_image()
 
+    def test_invalidate_cache(self):
+        self.image.write('abc', 0)
+        eq('abc', self.image.read(0, 3))
+        self.image.invalidate_cache()
+        eq('abc', self.image.read(0, 3))
+
     def test_stat(self):
         info = self.image.stat()
         check_stat(info, IMG_SIZE, IMG_ORDER)