Hi libvirt comuninty’s developers. I will try the fast explain. We’re working on kvm for a project and we tried get current machine’s memory usages. The code we tried to use for this operation is as shown in the below.

irb(main):002:0> conn = Libvirt::open("qemu:///system")

=> #<Libvirt::Connect:0x000055d1c66de398>

irb(main):003:0> domain = conn.lookup_domain_by_name("2_2").memory_stats

=> [#<Libvirt::Domain::MemoryStats:0x000055d1c6621a68 @tag=6, @val=1048576>, #<Libvirt::Domain::MemoryStats:0x000055d1c6621978 @tag=7, @val=1180796>]

irb(main):004:0> domain.first.val

Traceback (most recent call last):

16: from /root/.rbenv/versions/2.5.1/bin/bundle:23:in `load'

15: from /root/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/bundler-1.16.6/exe/bundle:22:in `<top (required)>'

14: from /root/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/bundler-1.16.6/lib/bundler/friendly_errors.rb:124:in `with_friendly_errors'

13: from /root/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/bundler-1.16.6/exe/bundle:30:in `block in <top (required)>'

12: from /root/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/bundler-1.16.6/lib/bundler/cli.rb:18:in `start'

11: from /root/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/bundler-1.16.6/lib/bundler/vendor/thor/lib/thor/base.rb:466:in `start'

10: from /root/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/bundler-1.16.6/lib/bundler/cli.rb:27:in `dispatch'

9: from /root/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/bundler-1.16.6/lib/bundler/vendor/thor/lib/thor.rb:387:in `dispatch'

8: from /root/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/bundler-1.16.6/lib/bundler/vendor/thor/lib/thor/invocation.rb:126:in `invoke_command'

7: from /root/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/bundler-1.16.6/lib/bundler/vendor/thor/lib/thor/command.rb:27:in `run'

6: from /root/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/bundler-1.16.6/lib/bundler/cli.rb:424:in `exec'

5: from /root/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/bundler-1.16.6/lib/bundler/cli/exec.rb:28:in `run'

4: from /root/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/bundler-1.16.6/lib/bundler/cli/exec.rb:74:in `kernel_load'

3: from /root/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/bundler-1.16.6/lib/bundler/cli/exec.rb:74:in `load'

2: from bin/console:13:in `<top (required)>'

1: from (irb):4

NoMethodError (undefined method `val' for #<Libvirt::Domain::MemoryStats:0x000055d1c6621a68>)

Did you mean? value

irb(main):005:0> domain.first.value

=> nil

As you see, when we want the use memory_usage’s val parameter but Libvirt throwing up undefined method error. Our fix proffer is memory_stats function's return @val parameter enough be update as shown in the below.

diff --git a/ext/libvirt/domain.c b/ext/libvirt/domain.c

index d665907..d458e98 100644

--- a/ext/libvirt/domain.c

+++ b/ext/libvirt/domain.c

@@ -675,7 +675,7 @@ static VALUE libvirt_domain_memory_stats(int argc, VALUE *argv, VALUE d)

for (i = 0; i < r; i++) {

tmp = rb_class_new_instance(0, NULL, c_domain_memory_stats);

rb_iv_set(tmp, "@tag", INT2NUM(stats[i].tag));

- rb_iv_set(tmp, "@val", ULL2NUM(stats[i].val));

+ rb_iv_set(tmp, "@value", ULL2NUM(stats[i].val));

rb_ary_store(result, i, tmp);

}

After that change memory_stats method’s val error will solved as shown in the below.

irb(main):002:0> conn = Libvirt::open("qemu:///system")

=> #<Libvirt::Connect:0x0000562ecf943320>

irb(main):003:0> memory_stats = conn.lookup_domain_by_name("2_2").memory_stats

=> [#<Libvirt::Domain::MemoryStats:0x0000562ecf976f68 @tag=6, @value=1048576>, #<Libvirt::Domain::MemoryStats:0x0000562ecf976f40 @tag=7, @value=1182952>]

irb(main):004:0> memory_stats.first.value

=> 1048576