[libvirt PATCH] qemu: fixing auto-detecting binary in domain capabilities

[Richard W.M. Jones]

On Fri, Jan 17, 2020 at 01:29:36PM +0000, Daniel P. Berrangé wrote:
> The virConnectGetDomainCapabilities API accepts either a binary path
> to the emulator, or desired guest arch. If guest arch is not given,
> then the host arch is assumed.
> 
> In the case where the binary is not given, the code tried to find the
> emulator binary in the existing list of cached emulator capabilities.
> This is not valid since we switched to lazy population of the cache in:
> 
>   commit 3dd91af01f30c5bda6328454ef49f3afece755d6
>   Author: Daniel P. Berrangé <berrange at redhat.com>
>   Date:   Mon Dec 2 13:04:26 2019 +0000
> 
>     qemu: stop creating capabilities at driver startup
> 
> As a result of this change, if there are no persistent guests defined
> using the requested guest architecture, virConnectGetDomainCapabilities
> will fail to find an emulator binary.
> 
> The solution is to stop relying on the cached capabilities to find the
> binary and instead use the same logic we use to pick default a binary
> per arch when populating capabilities.
> 
> Signed-off-by: Daniel P. Berrangé <berrange at redhat.com>

Fixes the problem over here, so:

Tested-by: Richard W.M. Jones <rjones at redhat.com>

Thanks,

Rich.

> ---
>  src/qemu/qemu_capabilities.c | 42 ++++++++++++++++--------------------
>  1 file changed, 19 insertions(+), 23 deletions(-)
> 
> diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
> index 498348ad58..9017e8d920 100644
> --- a/src/qemu/qemu_capabilities.c
> +++ b/src/qemu/qemu_capabilities.c
> @@ -5280,10 +5280,12 @@ virQEMUCapsCacheLookupDefault(virFileCachePtr cache,
>                                const char **retMachine)
>  {
>      int virttype = VIR_DOMAIN_VIRT_NONE;
> -    int arch = virArchFromHost();
> +    virArch hostarch = virArchFromHost();
> +    virArch arch = hostarch;
>      virDomainVirtType capsType;
>      virQEMUCapsPtr qemuCaps = NULL;
>      virQEMUCapsPtr ret = NULL;
> +    virArch arch_from_caps;
>  
>      if (virttypeStr &&
>          (virttype = virDomainVirtTypeFromString(virttypeStr)) < 0) {
> @@ -5299,31 +5301,25 @@ virQEMUCapsCacheLookupDefault(virFileCachePtr cache,
>          goto cleanup;
>      }
>  
> -    if (binary) {
> -        virArch arch_from_caps;
> +    if (!binary)
> +        binary = virQEMUCapsGetDefaultEmulator(hostarch, arch);
>  
> -        if (!(qemuCaps = virQEMUCapsCacheLookup(cache, binary)))
> -            goto cleanup;
> +    if (!(qemuCaps = virQEMUCapsCacheLookup(cache, binary)))
> +        goto cleanup;
>  
> -        arch_from_caps = virQEMUCapsGetArch(qemuCaps);
> +    arch_from_caps = virQEMUCapsGetArch(qemuCaps);
>  
> -        if (arch_from_caps != arch &&
> -            !((ARCH_IS_X86(arch) && ARCH_IS_X86(arch_from_caps)) ||
> -              (ARCH_IS_PPC(arch) && ARCH_IS_PPC(arch_from_caps)) ||
> -              (ARCH_IS_ARM(arch) && ARCH_IS_ARM(arch_from_caps)) ||
> -              (ARCH_IS_S390(arch) && ARCH_IS_S390(arch_from_caps)))) {
> -            virReportError(VIR_ERR_INVALID_ARG,
> -                           _("architecture from emulator '%s' doesn't "
> -                             "match given architecture '%s'"),
> -                           virArchToString(arch_from_caps),
> -                           virArchToString(arch));
> -            goto cleanup;
> -        }
> -    } else {
> -        if (!(qemuCaps = virQEMUCapsCacheLookupByArch(cache, arch)))
> -            goto cleanup;
> -
> -        binary = virQEMUCapsGetBinary(qemuCaps);
> +    if (arch_from_caps != arch &&
> +        !((ARCH_IS_X86(arch) && ARCH_IS_X86(arch_from_caps)) ||
> +          (ARCH_IS_PPC(arch) && ARCH_IS_PPC(arch_from_caps)) ||
> +          (ARCH_IS_ARM(arch) && ARCH_IS_ARM(arch_from_caps)) ||
> +          (ARCH_IS_S390(arch) && ARCH_IS_S390(arch_from_caps)))) {
> +        virReportError(VIR_ERR_INVALID_ARG,
> +                       _("architecture from emulator '%s' doesn't "
> +                         "match given architecture '%s'"),
> +                       virArchToString(arch_from_caps),
> +                       virArchToString(arch));
> +        goto cleanup;
>      }
>  
>      if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_KVM))
> -- 
> 2.23.0

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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