Re: [Qemu-devel] [PATCH 11/18] migration: introduce capability localhost

[Paolo Bonzini]

Il 22/08/2013 22:50, Michael R. Hines ha scritto:
> On 08/21/2013 11:18 AM, Paolo Bonzini wrote:
>> Il 21/08/2013 09:18, Lei Li ha scritto:
>>>       } else if (strstart(uri, "unix:", &p)) {
>>> +        if (s->enabled_capabilities[MIGRATION_CAPABILITY_LOCALHOST]) {
>>> +            local_start_outgoing_migration(s, p, &local_err);
>>> +        }
>>>           unix_start_outgoing_migration(s, p, &local_err);
>>>       } else if (strstart(uri, "fd:", &p)) {
>>>           fd_start_outgoing_migration(s, p, &local_err);
>>> @@ -521,6 +524,15 @@ int migrate_use_xbzrle(void)
>>>       return s->enabled_capabilities[MIGRATION_CAPABILITY_XBZRLE];
>>>   }
>>>   +bool migrate_is_localhost(void)
>>> +{
>>> +    MigrationState *s;
>>> +
>>> +    s = migrate_get_current();
>>> +
>>> +    return s->enabled_capabilities[MIGRATION_CAPABILITY_LOCALHOST];
>>> +}
>> I think this is a bad name, too.  There is nothing more "local" in this
>> migration than in "unix:" migration.
>>
>> Let's call the capability according to what it does, for example
>> unix-page-flipping.
> 
> Why is there a capability at all? Isn't that what the "local" URI is for?

Because in these patches, the local URI is only present in the
destination (which is wrong: the destination should autodetect local
mode using the load-page hook).  As you can see above, a "unix" URI will
examine the capability and pick the appropriate migration method.

However, this is also the wrong place to look at the capability.  It is
the save-page hook that should examine the capability.  It will then do
nothing if it is disabled, and do page-flipping if the capability is on.

Paolo