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(a)redhat.com&gt; 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. Tested-by: Richard W.M. Jones <rjones(a)redhat.com&gt; Signed-off-by: Daniel P. Berrangé <berrange(a)redhat.com&gt; --- src/qemu/qemu_capabilities.c | 45 ++++++++++++++++++------------------ 1 file changed, 22 insertions(+), 23 deletions(-) diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c index 498348ad58..14c2aa34d2 100644 --- a/src/qemu/qemu_capabilities.c +++ b/src/qemu/qemu_capabilities.c @@ -5280,10 +5280,13 @@ 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; + g_autofree char *probedbinary = NULL; if (virttypeStr && (virttype = virDomainVirtTypeFromString(virttypeStr)) < 0) { @@ -5299,31 +5302,27 @@ virQEMUCapsCacheLookupDefault(virFileCachePtr cache, goto cleanup; } - if (binary) { - virArch arch_from_caps; + if (!binary) { + probedbinary = virQEMUCapsGetDefaultEmulator(hostarch, arch); + binary = probedbinary; + } - 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))