[Xen-devel] [OSSTEST PATCH 1/2] libvirt: Check migration capabilities using proper XML parser

[Ian Jackson <ian.jackson@xxxxxxxxxxxxx>]

Do not grep the virsh capabilities output (!)  Instead, parse the XML
using perl's XML modules and look for the specific feature flag using
an XPATH pattern.

AFAICT from looking at the XML, that's

    <capabilities>
      <host>
        <migration_features>
          <live/>

But the original code does not test for <live/>.

Xen could in principle (and AIUI might in the future, on ARM) support
save/restore but not live migration.  Currently it supports neither.

I don't know whether libvirt's capabilities system can capture this
distinction.  libvirt.git#1d37a4c4 "libxl: detect support for save and
restore" suggests not.

Perhaps relatedly, I am not sure whether this test should be changed
to look for the xpath
  /capabilities/host/migration_features/live
instead.  The schema (libvirt.git/docs/schemas/capability.rng) seems
to suggest that it probably should.

For now, this osstest commit has no ultimate functional change (with
libvirt output as it currently appears to be on real hosts).

Signed-off-by: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
CC: Julien Grall <julien.grall@xxxxxxx>
CC: Jim Fehlig <jfehlig@xxxxxxxx>
---
 Osstest/Toolstack/libvirt.pm | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/Osstest/Toolstack/libvirt.pm b/Osstest/Toolstack/libvirt.pm
index 69ff0bb..b7db7af 100644
--- a/Osstest/Toolstack/libvirt.pm
+++ b/Osstest/Toolstack/libvirt.pm
@@ -21,6 +21,8 @@ use strict;
 use warnings;
 
 use Osstest::TestSupport;
+use XML::LibXML::XPathContext;
+use XML::LibXML;
 
 sub new {
     my ($class, $ho, $methname,$asset) = @_;
@@ -72,6 +74,17 @@ sub shutdown_wait ($$$) {
     guest_await_destroy($gho,$timeout);
 }
 
+sub _check_capability ($$) {
+    my ($self, $xpath) = @_;
+    my $ho = $self->{Host};
+    my $caps = target_cmd_output_root($ho, 'virsh capabilities');
+    my $stash = open_unique_stashfile('virsh-capabilities');
+    my $dom = XML::LibXML->load_xml(string => $caps);
+    my $xc = XML::LibXML::XPathContext->new($dom);
+    my @nodes = $xc->findnodes($xpath);
+    return !!@nodes;
+}
+
 sub migrate_check ($$) {
     my ($self, $local) = @_;
     my $rc;
@@ -80,9 +93,7 @@ sub migrate_check ($$) {
         # local migration is not supported
         $rc = 1;
     } else {
-       my $ho = $self->{Host};
-       my $caps = target_cmd_output_root($ho, "virsh capabilities");
-       $rc = ($caps =~ m/<migration_features>/) ? 0 : 1
+       $rc = $self->check_capability('/capabilities/host/migration_features');
     }
 
     logm("rc=$rc");
-- 
2.1.4


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