Anthony Liguori <address@hidden> wrote:
On 10/04/2011 09:49 AM, Juan Quintela wrote:
Anthony Liguori<address@hidden> wrote:
On 09/23/2011 07:57 AM, Juan Quintela wrote:
[ much more stuff ]
It avoids s==NULL checks,
In favor of s->state == MIG_STATE_NONE.
and it also avoids having to have new
variables (max_throotle) just because we don't have a migration state
handy.
The intention of the global variable is to set a default for new
sessions. I can imagine a world where if you had parallel migrations,
you could either toggle the default (the global variable) or the
specific parameter within a single migration session.
But it's not about features. It's a general reluctances to heavily
modify the code to rely on a global instead of passing the state
around. Here's a pretty good short write up of why this is a Bad
Thing.
http://stackoverflow.com/questions/1392315/problems-with-singleton-pattern
Ultimately, MIG_STATE_NONE shouldn't be needed because we should not
be relying on a singleton accessor to get the MigrationState. A
better cleanup would be to further pass MigrationState between
functions and eliminate the need for a global at all.
I understand the singleton problem, but the reason to put STATE_NONE is
not for that O:-) (it just happens that we only have a migration now).
Why I want it?
Just now, the only thing that we are "setting" for a migration before it
starts is the "bandwidth". I see the future when migration becomes
something like:
migration_set_speed ....
migration_set_target ....
migration_set_<whatever else>
migrate
as you can see, we are "preparing" migration, and we don't have a
"STATE" now that describes this state, migration not started, but we
want to prepare it.
Perhaps a better name that STATE_NONE is in order. I got NONE in the
sense that "migration" has not been attemted yet.