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Re: [PATCH v2] libxl: Retry QMP PCI device_add
- To: Jason Andryuk <jandryuk@xxxxxxxxx>
- From: Anthony PERARD <anthony.perard@xxxxxxxxxx>
- Date: Tue, 26 Apr 2022 15:23:07 +0100
- Authentication-results: esa5.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none
- Cc: <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Juergen Gross <jgross@xxxxxxxx>
- Delivery-date: Tue, 26 Apr 2022 14:23:23 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Fri, Apr 22, 2022 at 10:07:03AM -0400, Jason Andryuk wrote:
> PCI device assignment to an HVM with stubdom is potentially racy. First
> the PCI device is assigned to the stubdom via the PV PCI protocol. Then
> QEMU is sent a QMP command to attach the PCI device to QEMU running
> within the stubdom. However, the sysfs entries within the stubdom may
> not have appeared by the time QEMU receives the device_add command
> resulting in errors like:
>
> libxl_qmp.c:1838:qmp_ev_parse_error_messages:Domain 10:Could not open
> '/sys/bus/pci/devices/0000:00:1f.3/config': No such file or directory
>
> This patch retries the device assignment up to 10 times with a 1 second
> delay between. That roughly matches the overall hotplug timeout for
> pci_add_timeout. pci_add_timeout's initialization is moved to
> do_pci_add since retries call into pci_add_qmp_device_add again.
>
> The qmp_ev_parse_error_messages error is still printed since it happens
> at a lower level than the pci code controlling the retries. With that,
> the "Retrying PCI add %d" message is also printed at ERROR level to
> clarify what is happening.
>
> Signed-off-by: Jason Andryuk <jandryuk@xxxxxxxxx>
> ---
> v2:
> Only retry when a stubdom is present.
> Move pci_add_timeout initialization.
> Use pas->aodev->ao directly.
Reviewed-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
Thanks,
--
Anthony PERARD
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