Re: [PATCH v4 2/6] xen: backends: don't overwrite XenStore nodes created by toolstack

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Sat, Dec 02, 2023 at 01:41:21AM +0000, Volodymyr Babchuk wrote:
> Xen PV devices in QEMU can be created in two ways: either by QEMU
> itself, if they were passed via command line, or by Xen toolstack. In
> the latter case, QEMU scans XenStore entries and configures devices
> accordingly.
> 
> In the second case we don't want QEMU to write/delete front-end
> entries for two reasons: it might have no access to those entries if
> it is running in un-privileged domain and it is just incorrect to
> overwrite entries already provided by Xen toolstack, because toolstack
> manages those nodes. For example, it might read backend- or frontend-
> state to be sure that they are both disconnected and it is safe to
> destroy a domain.
> 
> This patch checks presence of xendev->backend to check if Xen PV
> device was configured by Xen toolstack to decide if it should touch
> frontend entries in XenStore. Also, when we need to remove XenStore
> entries during device teardown only if they weren't created by Xen
> toolstack. If they were created by toolstack, then it is toolstack's
> job to do proper clean-up.
> 
> Suggested-by: Paul Durrant <xadimgnik@xxxxxxxxx>
> Suggested-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
> Co-Authored-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
> Reviewed-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
> 

Hi Volodymyr,

There's something wrong with this patch. The block backend doesn't work
when creating a guest via libxl, an x86 hvm guest with qdisk.

Error from guest kernel:
"2 reading backend fields at /local/domain/0/backend/qdisk/23/768"

It seems that "sector-size" is missing for the disk.

Thanks,

-- 
Anthony PERARD