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Re: [Xen-devel] [PATCH v3 2/2] qdisk - hw/block/xen_disk: grant copy implementation





On 07/14/2016 12:37 PM, Wei Liu wrote:
On Wed, Jun 22, 2016 at 10:38:53AM +0200, Paulina Szubarczyk wrote:
diff --git a/configure b/configure
index e41876a..355d3fa 100755
--- a/configure
+++ b/configure
@@ -1843,7 +1843,7 @@ fi
  # xen probe

  if test "$xen" != "no" ; then
-  xen_libs="-lxenstore -lxenctrl -lxenguest"
+  xen_libs="-lxenstore -lxenctrl -lxenguest -lxengnttab"


First thing, -lxengnttab should be in xen_stable_libs.

Do I understand correctly that I should add a new variable "xen_stable_libs"? I could not find it in the qemu tree used anywhere else.

The probing needs to be more sophisticated.

You need to probe the new function your added as well. Just a few lines
below xen_stable_libs there is a section for hand-coded probing source
code, which you would need to modify.

Assuming your gnttab change will be merged into 4.8 (the release under
development at the moment), you need to have a separate program for it.

I will add that.

After you've done proper probing, you will know which version of Xen
this qemu is compiling against.  And then, there should be some fallback
mechanism to compile and run this qemu with older version of xen. This
is not too hard because you can guard your code with feature flag or
ifdef (please consult Stefan and Anthony which method to use).

Feel free to ask questions. I will try my best to explain.


+    blkdev->feature_grant_copy =
+                (xengnttab_grant_copy(blkdev->xendev.gnttabdev, 0, NULL) == 0);

This is a bit problematic. As this patch stands, it won't compile on
older version of Xen because there is no such function there.

There is a variable CONFIG_XEN_CTRL_INTERFACE_VERSION holding current version of the Xen control library this qemu is configured with. It is set from the configure file. The feature could be guarded with ifdef by a new variable CONFIG_XEN_LIBS_INTERFACE_VERSION or they could be unified to CONFIG_XEN_TOOLS_INTERFACE_VERSION to not fill the same value twice.

Paulina

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