[Qemu-devel] n ways block filters

["Benoît Canet" <benoit.canet@irqsave.net>]

Hello list,

I plan to convert throttling to a block filter and write n way throttling
support.

I discussed a bit with Stefan on the list and we came to the conclusion that the
block filter API need group support.

filter group:
-------------

My current plan to implement this is to add the following fields to the BlockDriver
structure.

int bdrv_add_filter_group(const char *name, QDict options);
int bdrv_reconfigure_filter_group(const char *name, QDict options);
int bdrv_destroy_filter_group(const char *name);

These three extra method would allow to create, reconfigure or destroy a block
filter group. A block filter group contain the shared or non shared state of the
blockfilter. For throttling it would contains the ThrottleState structure.

Each block filter driver would contains a linked list of linked list where the
BDS are registered grouped by filter groups state.

The regular bdrv_open callback would be used to instantiate a block filter and
add it to a filter group. This method would also take a new-node-name for the new
filter. This node-name would become the name of the new filter.
bdrv_close would cleanup and deregister from a filter group.

An extra filter-group field in the option dict would allow the bdrv_open method
to register the newly opened block filter in it's filter group.
The BDS structure would have a direct pointer to it's filter group state.

Utility methods to do the bdrv_add_filter_group bdrv_open then bdrv_swap to
install a new filter can be provided by block.c. The same can be done for filter
close and desinstallation.

Legacy throttling QMP API
-------------------------

The legacy throttling API would create throttling filters groups containing only
one BDS.

By default for every 1 way block filter block.c would create a filter group
using the BDS id or node-name as group name. This allow for easy filer removal
with the bds reference.

Group throttling API
--------------------

Commands would be added to create throttling filter groups reconfigure and remove
them.

Two additional commands would be added to create and insert a block filter in a
given group or close and remove it.

Before I start implementing something what are your thougths on this ?

Best regards

Benoît