[Qemu-devel] KVM Forum 2012 Block BoF minutes

[Markus Armbruster <armbru@redhat.com>]

Attendees:

Kevin Wolf <kwolf@redhat.com>
Stefan Hajnoczi <stefanha@redhat.com>
Jeff Cody <jcody@redhat.com>
Markus Armbruster <armbru@redhat.com>

and a few people dropping in and out.

Minutes are basically a TODO list.  Could be a bit terse in places; if
anything's unclear, please ask.


Block layer data structure cleanup:

- Split block backend off BlockDriverState

- Turn block backend into a proper ADT (besides other good things, this
  makes it possible to replace its implementation by a test harness for
  unit testing of its customers)

- Get rid of BlockDriverState opaque (driver private state), inherit the
  common part into driver state

Convert open to QemuOpts (or perhaps QDict?)

Avoid double open for probing (update: patches posted)

Block jobs:

- Rate limiting is broken in general (it works for the single
  BlockDriverState case)

- Block jobs should be jobs: generally available instead of tied to a
  (single) BlockDriverState; get rid of the block job pointer in
  BlockDriverState

- Migration should probably be a job

Block migration needs to die after its replacement is ready

BlockDriverState member in_use and DriveInfo member refcount are a mess:

- in_use is used to avoid running certain things concurrently, but the
  rules are unclear, except they're clearly incomplete; possible rules
  could be about need for consistent views of image contents

- refcount is only used together with in_use, and appears to be for
  avoiding premature deletion

AHCI:

- Same IDE device models connect to different kinds of controllers just
  fine

- Use links to connect controller device model and drive device models;
  the link serves as generic address replacing bus, unit, index

- Make -drive if!=none true sugar for suitable -device (details depend
  on machine)

- Checking legacy bus, unit, index needs to be delayed until machine's
  limits are known

- Add "enough" -hdX to cover common usage (got 4 now, want 6 for q35)

- Some AHCI controllers can optionally mimick a legacy IDE controller,
  and expose some of their ports there (controlled by BIOS for real
  hardware, by controller qdev property for us)

- Convenience machine option to control that qdev property of an onboard
  controller would be nice (should not apply to additional controllers
  plugged in with -device)

- if=ahci is not necessary