Re: [Qemu-devel] [PATCH 13/47] block: introduce block job error

[Kevin Wolf <kwolf@redhat.com>]

Am 24.07.2012 13:03, schrieb Paolo Bonzini:
> The following behaviors are possible:
> 
> 'report': The behavior is the same as in 1.1.  An I/O error,
> respectively during a read or a write, will complete the job immediately
> with an error code.
> 
> 'ignore': An I/O error, respectively during a read or a write, will be
> ignored.  For streaming, the job will complete with an error and the
> backing file will be left in place.  For mirroring, the sector will be
> marked again as dirty and re-examined later.
> 
> 'stop': The job will be paused and the job iostatus will be set to
> failed or nospace, while the VM will keep running.  This can only be
> specified if the block device has rerror=stop and werror=stop or enospc.
> 
> 'enospc': Behaves as 'stop' for ENOSPC errors, 'report' for others.
> 
> In all cases, even for 'report', the I/O error is reported as a QMP
> event BLOCK_JOB_ERROR, with the same arguments as BLOCK_IO_ERROR.
> 
> It is possible that while stopping the VM a BLOCK_IO_ERROR event will be
> reported and will clobber the event from BLOCK_JOB_ERROR, or vice versa.
> This is not really avoidable since stopping the VM completes all pending
> I/O requests.  In fact, it is already possible now that a series of
> BLOCK_IO_ERROR events are reported with rerror=stop, because vm_stop
> calls bdrv_drain_all and this can generate further errors.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

If we want to switch to named target block devices later, it would
probably make sense to use the io_status of that block device rather
than adding it to the job.

Maybe what results is a duplication that can be tolerated, though.

> +BlockErrorAction block_job_error_action(BlockJob *job, BlockDriverState *bs,
> +                                        BlockdevOnError on_err,
> +                                        int is_read, int error)
> +{
> +    BlockErrorAction action;
> +
> +    switch (on_err) {
> +    case BLOCKDEV_ON_ERROR_ENOSPC:
> +        action = (error == ENOSPC) ? BDRV_ACTION_STOP : BDRV_ACTION_REPORT;
> +        break;
> +    case BLOCKDEV_ON_ERROR_STOP:
> +        action = BDRV_ACTION_STOP;
> +        break;
> +    case BLOCKDEV_ON_ERROR_REPORT:
> +        action = BDRV_ACTION_REPORT;
> +        break;
> +    case BLOCKDEV_ON_ERROR_IGNORE:
> +        action = BDRV_ACTION_IGNORE;
> +        break;
> +    default:
> +        abort();
> +    }
> +    bdrv_emit_qmp_error_event(job->bs, QEVENT_BLOCK_JOB_ERROR, action, is_read);
> +    if (action == BDRV_ACTION_STOP) {
> +        block_job_pause(job);
> +        if (bs == job->bs) {
> +            block_job_iostatus_set_err(job, error);
> +        } else {
> +            bdrv_iostatus_set_err(bs, error);
> +        }

However, so that everything just falls into place once we make the
target block device visible, I'd make the bdrv_iostatus_set_err() call
unconditional then.

Kevin