Re: [Xen-devel] [PATCH v1 2/2] libxl: add removing XS backend path for PV devices on domain destroy

[Ian Jackson <ian.jackson@xxxxxxxxxx>]

Oleksandr Grytsov writes ("[PATCH v1 2/2] libxl: add removing XS backend path 
for PV devices on domain destroy"):
> From: Oleksandr Grytsov <oleksandr_grytsov@xxxxxxxx>
> 
> Currently backend path is remove for specific devices: VBD, VIF, QDISK.
> This commit adds removing backend path for: VDISPL, VSND, VINPUT.

Thanks for this and your previous patch.

This one looks to me like it is probably correct.  But I have not been
able to understand why this code was limited to vbds and vifs before
so I am hesitant.

Searching the git history, I think this has been like this since
a0eaa86e7537
 "libxl: add device backend listener in order to launch backends"
and subsequent commits have just reorganised things but not
fundamentally changed them.  I've CC'd Roger who wrote this code.

I think:

>      switch(ddev->dev->backend_kind) {
> +    case LIBXL__DEVICE_KIND_VDISPL:
> +    case LIBXL__DEVICE_KIND_VSND:
> +    case LIBXL__DEVICE_KIND_VINPUT:
>      case LIBXL__DEVICE_KIND_VBD:
>      case LIBXL__DEVICE_KIND_VIF:

If we do want this to handle *all* kinds of device, maybe it should
have a fallback that aborts, or something ?  (I don't think it is
easy to make it a compile error to forget to add an entry here but if
we could do that it would probably be best.)

All of that assuming that the basic idea is right, which I would like
Roger's opinion about.

Thanks,
Ian.

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