Re: [RFC PATCH v2 0/8] block-backend: Introduce I/O hang

[Ying Fang]

On 10/10/2020 10:27 AM, cenjiahui wrote:
> Hi Kevin,
>
> Could you please spend some time reviewing and commenting on this patch series.
>
> Thanks,
> Jiahui Cen

This feature is confirmed effective in a cloud storage environment since
it can help to improve the availability without pausing the entire
guest. Hope it won't be lost on the thread. Any comments or reviews
are welcome.

> On 2020/9/30 17:45, Jiahui Cen wrote:
> > A VM in the cloud environment may use a virutal disk as the backend storage,
> > and there are usually filesystems on the virtual block device. When backend
> > storage is temporarily down, any I/O issued to the virtual block device will
> > cause an error. For example, an error occurred in ext4 filesystem would make
> > the filesystem readonly. However a cloud backend storage can be soon recovered.
> > For example, an IP-SAN may be down due to network failure and will be online
> > soon after network is recovered. The error in the filesystem may not be
> > recovered unless a device reattach or system restart. So an I/O rehandle is
> > in need to implement a self-healing mechanism.
> >
> > This patch series propose a feature called I/O hang. It can rehandle AIOs
> > with EIO error without sending error back to guest. From guest's perspective
> > of view it is just like an IO is hanging and not returned. Guest can get
> > back running smoothly when I/O is recovred with this feature enabled.
> >
> > v1->v2:
> > * Rebase to fix compile problems.
> > * Fix incorrect remove of rehandle list.
> > * Provide rehandle pause interface.
> >
> > Jiahui Cen (8):
> >    block-backend: introduce I/O rehandle info
> >    block-backend: rehandle block aios when EIO
> >    block-backend: add I/O hang timeout
> >    block-backend: add I/O rehandle pause/unpause
> >    block-backend: enable I/O hang when timeout is set
> >    virtio-blk: pause I/O hang when resetting
> >    qemu-option: add I/O hang timeout option
> >    qapi: add I/O hang and I/O hang timeout qapi event
> >
> >   block/block-backend.c          | 300 +++++++++++++++++++++++++++++++++
> >   blockdev.c                     |  11 ++
> >   hw/block/virtio-blk.c          |   8 +
> >   include/sysemu/block-backend.h |   5 +
> >   qapi/block-core.json           |  26 +++
> >   5 files changed, 350 insertions(+)
> .