add patch for rbd cache support

README.md

@@ -30,6 +30,13 @@ It boils down to the following steps:
 
 At least according to my zsh history.
 
+If you are building from an already changed version, but without that particular changelog, use:
+
+- `dch --auto-nmr --newversion $newversion`
+
+Ideally, you copy the old changelog to the new one. Look up the old version number! 
+Add "Non-maintainer upload." manually to your list of changes.
+
 
 ## Patch Details
 
@@ -51,3 +58,10 @@ Removes block devices from lists of mirrored and movable devices. This prevents
 
 This may not solve the general case, but is makes it compatible with our usage.
 
+
+### `add_rbd_cache_support.patch` 
+
+Add caching support for rbd devices. This was disabled for arbritrary external storage.
+But this does not make sense for rbd.
+
+

add_rbd_cache_support.patch

+Index: ganeti-2.15.2/lib/hypervisor/hv_kvm/__init__.py
+===================================================================
+--- ganeti-2.15.2.orig/lib/hypervisor/hv_kvm/__init__.py
++++ ganeti-2.15.2/lib/hypervisor/hv_kvm/__init__.py
+@@ -921,12 +921,13 @@ class KVMHypervisor(hv_base.BaseHypervis
+     disk_cache = up_hvp[constants.HV_DISK_CACHE]
+     for cfdev, link_name, uri in kvm_disks:
+       if cfdev.dev_type in constants.DTS_EXT_MIRROR:
+-        if disk_cache != "none":
++        if disk_cache != "none" and cfdev.dev_type != "rbd":
+           # TODO: make this a hard error, instead of a silent overwrite
+           logging.warning("KVM: overriding disk_cache setting '%s' with 'none'"
+                           " to prevent shared storage corruption on migration",
+                           disk_cache)
+-        cache_val = ",cache=none"
++          disk_cache = "none"
++        cache_val = ",cache=%s" % disk_cache
+       elif disk_cache != constants.HT_CACHE_DEFAULT:
+         cache_val = ",cache=%s" % disk_cache
+       else: