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Re: [PATCH] vhost-user-scsi: support reconnect to backend
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From: |
Michael S. Tsirkin |
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Subject: |
Re: [PATCH] vhost-user-scsi: support reconnect to backend |
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Date: |
Mon, 24 Jul 2023 16:30:22 -0400 |
On Mon, Jul 24, 2023 at 05:21:37PM +0000, Raphael Norwitz wrote:
> Very excited to see this. High level looks good modulo a few small things.
>
> My major concern is around existing vhost-user-scsi backends which don’t
> support VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD. IMO we should hide the
> reconnect behavior behind a VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD check. We
> may want to do the same for vhost-user-blk.
>
> The question is then what happens if the check is false. IIUC without an
> inflight FD, if a device processes requests out of order, it’s not safe to
> continue execution on reconnect, as there’s no way for the backend to know
> how to replay IO. Should we permanently wedge the device or have QEMU fail
> out? May be nice to have a toggle for this.
No, device itself can store the state somewhere. And if it wants to,
it can check VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD and fail reconnect.
--
MST
[PATCH v2 0/4] Implement reconnect for vhost-user-scsi, Li Feng, 2023/07/25