Re: [libvirt PATCH v4 1/3] add QEMU_CAPS_TCG_DISABLED and probe conditionally

[Michal Privoznik <mprivozn@xxxxxxxxxx>]

On 4/22/20 11:50 PM, Tobin Feldman-Fitzthum wrote:
> Only probe QEMU binary with accel=tcg if TCG is not disabled.
> Similarly, only add a VIR_DOMAIN_VIRT_QEMU guest if TCG
> is available.
>
> Signed-off-by: Tobin Feldman-Fitzthum <tobin@xxxxxxxxxxxxxxxxxx>
> ---
>   src/qemu/qemu_capabilities.c | 22 ++++++++++++++--------
>   src/qemu/qemu_capabilities.h |  1 +
>   2 files changed, 15 insertions(+), 8 deletions(-)
>
> diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
> index fe311048d4..c56b2d8f0e 100644
> --- a/src/qemu/qemu_capabilities.c
> +++ b/src/qemu/qemu_capabilities.c
> @@ -573,6 +573,7 @@ VIR_ENUM_IMPL(virQEMUCaps,
>                 "fsdev.multidevs",
>                 "virtio.packed",
>                 "pcie-root-port.hotplug",
> +              "tcg-disabled",
>       );
>   
>   
> @@ -1014,13 +1015,16 @@ virQEMUCapsInitGuestFromBinary(virCapsPtr caps,
>       virCapabilitiesAddGuestFeatureWithToggle(guest, VIR_CAPS_GUEST_FEATURE_TYPE_DISKSNAPSHOT,
>                                                true, false);
>   
> -    if (virCapabilitiesAddGuestDomain(guest,
> -                                      VIR_DOMAIN_VIRT_QEMU,
> -                                      NULL,
> -                                      NULL,
> -                                      0,
> -                                      NULL) == NULL)
> -        goto cleanup;
> +    if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_TCG_DISABLED)) {
> +        if (virCapabilitiesAddGuestDomain(guest,
> +                                          VIR_DOMAIN_VIRT_QEMU,
> +                                          NULL,
> +                                          NULL,
> +                                          0,
> +                                          NULL) == NULL) {
> +            goto cleanup;
> +        }
> +    }
>   
>       if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_KVM)) {
>           if (virCapabilitiesAddGuestDomain(guest,
> @@ -2295,7 +2299,8 @@ bool
>   virQEMUCapsIsVirtTypeSupported(virQEMUCapsPtr qemuCaps,
>                                  virDomainVirtType virtType)
>   {
> -    if (virtType == VIR_DOMAIN_VIRT_QEMU)
> +    if (virtType == VIR_DOMAIN_VIRT_QEMU &&
> +        !virQEMUCapsGet(qemuCaps, QEMU_CAPS_TCG_DISABLED))
>           return true;
>   
>       if (virtType == VIR_DOMAIN_VIRT_KVM &&
> @@ -5150,6 +5155,7 @@ virQEMUCapsInitQMP(virQEMUCapsPtr qemuCaps,
>        * off.
>        */
>       if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_KVM) &&
> +        !virQEMUCapsGet(qemuCaps, QEMU_CAPS_TCG_DISABLED) &&
>           virQEMUCapsInitQMPSingle(qemuCaps, libDir, runUid, runGid, true) < 0)
>           return -1;
>   
> diff --git a/src/qemu/qemu_capabilities.h b/src/qemu/qemu_capabilities.h
> index 1681fc79a8..abc4ee82cb 100644
> --- a/src/qemu/qemu_capabilities.h
> +++ b/src/qemu/qemu_capabilities.h
> @@ -554,6 +554,7 @@ typedef enum { /* virQEMUCapsFlags grouping marker for syntax-check */
>       QEMU_CAPS_FSDEV_MULTIDEVS, /* fsdev.multidevs */
>       QEMU_CAPS_VIRTIO_PACKED_QUEUES, /* virtio.packed */
>       QEMU_CAPS_PCIE_ROOT_PORT_HOTPLUG, /* pcie-root-port.hotplug */
> +    QEMU_CAPS_TCG_DISABLED, /* QEMU does not support TCG */

Actually, I think this should be a positive capability, e.g. 
QEMU_CAPS_TCG to reflect whether QEMU supports TCG or not. I can do the 
change locally before pushing, if you agree with the change.

Michal