[Xen-devel] [PATCH] tools: libxl: do not set the PoD target on ARM

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

ARM does not implemented PoD and so returns ENOSYS from XENMEM_set_pod_target.

The correct solution here would be to check for ENOSYS in libxl, unfortunately
xc_domain_set_pod_target suffers from the same broken error reporting as the
rest of libxc and throws away the errno.

So for now conditionally define xc_domain_set_pod_target to return success
(which is what PoD does if nothing needs doing). xc_domain_get_pod_target sets
errno==-1 and returns -1, which matches the broken error reporting of the
existing function. It appears to have no in tree callers in any case.

The conditional should be removed once libxc has been fixed.

This makes ballooning (xl mem-set) work for ARM domains.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: george.dunlap@xxxxxxxxxx
---
I'd be generally wary of modifying the error handling in a piecemeal way, but
certainly doing so for 4.4 now would be inapropriate.

IIRC Ian J was planning a thorough sweep of the libxc error paths in 4.5 time
frame, at which point this conditional stuff could be dropped.

In terms of the 4.4 release, obviously ballooning would be very nice to have
for ARM guests, on the other hand I'm aware that while the patch is fairly
small/contained and safe it is also pretty skanky and likely wouldn't be
accepted outside of the rc period.
---
 tools/libxc/xc_domain.c |   28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/tools/libxc/xc_domain.c b/tools/libxc/xc_domain.c
index c2fdd74..e1d1bec 100644
--- a/tools/libxc/xc_domain.c
+++ b/tools/libxc/xc_domain.c
@@ -986,6 +986,12 @@ out:
     return rc;
 }
 
+/* Currently only implemented on x86. This cannot be handled in the
+ * caller, e.g. by looking for errno==ENOSYS because of the broken
+ * error reporting style. Once this is fixed then this condition can
+ * be removed.
+ */
+#if defined(__i386__)||defined(__x86_64__)
 static int xc_domain_pod_target(xc_interface *xch,
                                 int op,
                                 uint32_t domid,
@@ -1055,6 +1061,28 @@ int xc_domain_get_pod_target(xc_interface *xch,
                                 pod_cache_pages,
                                 pod_entries);
 }
+#else
+int xc_domain_set_pod_target(xc_interface *xch,
+                             uint32_t domid,
+                             uint64_t target_pages,
+                             uint64_t *tot_pages,
+                             uint64_t *pod_cache_pages,
+                             uint64_t *pod_entries)
+{
+    return 0;
+}
+int xc_domain_get_pod_target(xc_interface *xch,
+                             uint32_t domid,
+                             uint64_t *tot_pages,
+                             uint64_t *pod_cache_pages,
+                             uint64_t *pod_entries)
+{
+    /* On x86 (above) xc_domain_pod_target will incorrectly return -1
+     * with errno==-1 on error. Do the same for least surprise. */
+    errno = -1;
+    return -1;
+}
+#endif
 
 int xc_domain_max_vcpus(xc_interface *xch, uint32_t domid, unsigned int max)
 {
-- 
1.7.10.4


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel