Re: [Qemu-block] [RFC patch 3/3] blockjob: add devops to blockjob backends

[Kevin Wolf]

Am 16.03.2017 um 01:46 hat John Snow geschrieben:
> This lets us hook into drained_begin and drained_end requests from the
> backend level, which is particularly useful for making sure that all
> jobs associated with a particular node (whether the source or the target)
> receive a drain request.
> 
> Suggested-by: Kevin Wolf <address@hidden>
> Signed-off-by: John Snow <address@hidden>
> 
> --
> 
> RFC topics:
> 
> - BlkDevOps is traditionally only for Qdev devices, and a BlockJob is not
>   currently a 'device'... Do we want to loosen this restriction, find another
>   way to deliver callbacks to BlockJobs attached to BlkBackends, or do 
> something
>   crazy like make a BlockJob device object?
> 
>   struct JobDevice {
>     DeviceState parent_obj;
>     BlockJob *job;
>   } ...??

We should probably rename BlkDevOps to something that works not only for
devices, but for any user of a BlockBackend. I don't think the
implementation has to be changed, it's just a struct of callbacks and an
opaque pointer that is actually properly treated as opaque.

BlockBackend also has a dev field, which is indeed supposed to be a
DeviceState and is sometimes casted to one (if we can assert
!blk->legacy_dev), but it's a concept completely separate from
BlkDevOps. So we just need to be sure not to call blk_attach_dev() or
blk_attach_dev_legacy().

Kevin