Re: [PATCH hci-8.1 v4 4/5] vhost-blk: create kernel threads with the mainstream worker ioctls

[Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>]

On 10/29/26 11:23 AM, Alexander Ivanov wrote:
> num-threads was passed to our own VHOST_SET_NWORKERS kernel ioctl. The
> kernel drops it with the revert of "drivers/vhost: add ioctl to
> increase the number of workers" in favour of the mainstream worker
> ioctls, which vhost-blk now supports. Create num-threads - 1 workers
> with VHOST_NEW_WORKER and attach them to the virtqueues round-robin
> with VHOST_ATTACH_VRING_WORKER, the layout VHOST_SET_NWORKERS produced.
> 
> Our kernel, unlike mainline, defaults to kthread mode, where
> VHOST_NEW_WORKER fails with -EFAULT rather than -ENOTTY. So switch the
> device to vhost_task mode with VHOST_SET_FORK_FROM_OWNER before
> VHOST_SET_OWNER. With num-threads=1 nothing changes: no worker ioctls,
> kthread mode.
> 
> Released vz10 kernels have VHOST_SET_FORK_FROM_OWNER, but their
> vhost-blk does not handle the worker ioctls and fails VHOST_NEW_WORKER
> with -ENOTTY. Other errors are possible as well, so do not key on the
> errno: if VHOST_SET_FORK_FROM_OWNER fails, keep all virtqueues on the
> default thread; if VHOST_NEW_WORKER fails partway, spread the
> remaining virtqueues over the threads created so far; if attaching a
> virtqueue fails, it stays on the default thread. Either way warn rather
> than fail to start vhost-blk. Unless VHOST_SET_FORK_FROM_OWNER failed,
> the default thread stays a vhost_task, as the mode cannot be changed
> after VHOST_SET_OWNER.
> 
> https://virtuozzo.atlassian.net/browse/VSTOR-107537
> 
> Signed-off-by: Alexander Ivanov <alexander.ivanov@virtuozzo.com>
> ---
>  [...]

LGTM this time.

Reviewed-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>

@Andrey Zhadchenko I'd like your R-b on this one before merging.

Andrey