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Re: [libvirt] [PATCH 4/4] virQEMUCapsHasPCIMultiBus: assume true if we have no version information



On Wed, Nov 29, 2017 at 03:58:57PM +0100, Ján Tomko wrote:
> In status XML, we do not store the QEMU version information, we only
> format all the capabilities. We dropped QEMU_CAPS_PCI_MULTIBUS
> in commit 5b783379 which was released in libvirt 3.2.0.
> 
> Therefore the only way of telling if the already running domain
> at the time of daemon restart has been started with a QEMU that does
> use 'pci.0' or not on PPC is to look at the pci-root controller's
> alias. This is not an option if the domain has a user-specified alias
> for the pci-root.
> 
> Instead of reintroducing the capability, assume 'pci.0' when we have
> no version information. That way the only left broken use case would
> be the combination of user aliases and very old QEMU.
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=1518148
> ---
>  src/qemu/qemu_capabilities.c | 16 ++++++++--------
>  src/qemu/qemu_capspriv.h     |  4 ----
>  tests/qemuxml2argvtest.c     |  5 -----
>  3 files changed, 8 insertions(+), 17 deletions(-)
> 
> diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
> index c9d0a66d8..7b52d1a71 100644
> --- a/src/qemu/qemu_capabilities.c
> +++ b/src/qemu/qemu_capabilities.c
> @@ -2436,6 +2436,14 @@ bool virQEMUCapsHasPCIMultiBus(virQEMUCapsPtr qemuCaps,
>           *     ppce500: 1.6.0
>           */
>  
> +        /* We do not store the qemu version in domain status XML.
> +         * Hope the user is using a QEMU new enough to use 'pci.0',
> +         * otherwise the results of this function will be wrong
> +         * for domains already running at the time of daemon
> +         * restart */
> +        if (qemuCaps->version == 0)
> +            return true;
> +

I don't like this that we will hope that QEMU is new enough, but I
cannot think of a better way how to check it and this definitely
improves current code.

For the whole series:
Reviewed-by: Pavel Hrdina <phrdina redhat com>

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