Re: [libvirt] [PATCH] qemu: Warn when using vhost-user without shared memory

When user configures vhost-user interface and forgets to also configure any shared memory, the search for the root cause of non-operational interface might take unpleasantly long time. Let's enhance user experience by emitting a warning in the logs. Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1266982 Signed-off-by: Martin Kletzander <mkletzan(a)redhat.com&gt; --- src/qemu/qemu_process.c | 44 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 44 insertions(+) diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c index 420196264685..fb471342e790 100644 --- a/src/qemu/qemu_process.c +++ b/src/qemu/qemu_process.c @@ -4542,6 +4542,7 @@ qemuProcessLaunch(virConnectPtr conn, unsigned int hostdev_flags = 0; size_t nnicindexes = 0; int *nicindexes = NULL; + bool check_shmem = false; VIR_DEBUG("vm=%p name=%s id=%d asyncJob=%d " "incoming.launchURI=%s incoming.deferredURI=%s " @@ -4749,6 +4750,49 @@ qemuProcessLaunch(virConnectPtr conn, goto cleanup; } + VIR_DEBUG("Checking for any possible (non-fatal) issues"); + + /* + * For vhost-user to work, the domain has to have some type of + * shared memory configured. We're not the proper once to judge

+ * whether shared hugepages or shm are enough and will be in the + * future, so we'll just warn in case there is none of that

+ * configured. Moreover failing would give the false illusion + * that libvirt is really checking that everything works before + * running the domain and not only we are unable to do that, but + * it's also not our aim to do so. + */ + for (i = 0; i < vm->def->nnets; i++) { + if (virDomainNetGetActualType(vm->def->nets[i]) == + VIR_DOMAIN_NET_TYPE_VHOSTUSER) { + check_shmem = true; + break; + } + } + + if (check_shmem) { + bool shmem = vm->def->nshmems; + + /* + * This check is by no means complete. We merely check + * whetere there are *some* hugepages enabled and *some* NUMA + * nodes with shared memory access. + */ + if (!shmem && vm->def->mem.nhugepages) { + for (i = 0; i < virDomainNumaGetNodeCount(vm->def->numa); i++) { + if (virDomainNumaGetNodeMemoryAccessMode(vm->def->numa, i) == + VIR_NUMA_MEM_ACCESS_SHARED) + shmem = true; + break; + } + } + + if (!shmem) { + VIR_WARN("Detected vhost-user interface without any shared memory. " + "The interface might not be operational");

+ } + } + VIR_DEBUG("Building emulator command line"); if (!(cmd = qemuBuildCommandLine(conn, driver, vm->def, priv->monConfig, priv->monJSON, priv->qemuCaps,