RE: [PATCH v3 1/2] qemu: add support for shmem-{plain, doorbell} role

On Mon, Aug 03, 2020 at 09:26:19AM +0000, Wangxin (Alexander) wrote: >> On Fri, Jul 24, 2020 at 11:34:11AM +0800, Wang Xin wrote: >> >Role(master or peer) controls how the domain behaves on migration. >> >For more details about migration with ivshmem, see >> >https://git.qemu.org/?p=qemu.git;a=blob_plain;f=docs/system/ivshmem.rst;hb=HEAD >> > >> >It's a optional attribute in libvirt, and qemu will choose default >> >role for ivshmem device if the user is not specified. >> > >> >With device property 'role', the value can be 'master' or 'peer'. >> > - 'master' (means 'master=on' in qemu), the guest will copy >> > the shared memory on migration to the destination host. >> > - 'peer' (means 'master=off' in qemu), the migration is disabled. >> > >> >Signed-off-by: Martin Kletzander <mkletzan(a)redhat.com&gt; >> >Signed-off-by: Yang Hang <yanghang44(a)huawei.com&gt; >> >Signed-off-by: Wang Xin <wangxinxin.wang(a)huawei.com&gt; >> > >> >diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c >> >index 2c7bf349c3..e588b74c2f 100644 >> >--- a/src/qemu/qemu_migration.c >> >+++ b/src/qemu/qemu_migration.c >> >@@ -1261,10 +1261,22 @@ qemuMigrationSrcIsAllowed(virQEMUDriverPtr driver, >> > } >> > } >> > >> >- if (vm->def->nshmems) { >> >- virReportError(VIR_ERR_OPERATION_INVALID, "%s", >> >- _("migration with shmem device is not supported")); >> >- return false; >> >+ for (i = 0; i < vm->def->nshmems; i++) { >> >+ virDomainShmemDefPtr shmem = vm->def->shmems[i]; >> >+ >> >+ if (shmem->model == VIR_DOMAIN_SHMEM_MODEL_IVSHMEM) { >> >+ virReportError(VIR_ERR_OPERATION_INVALID, "%s", >> >+ _("migration with legacy shmem device is not supported")); >> >+ return false; >> >+ } >> >+ if (shmem->role == VIR_DOMAIN_SHMEM_ROLE_PEER) { >> >> This allows migration with the default role which you leave to be chosen by the >> hypervisor. In that case we need to change this to: >> >> if (shmem->role != VIR_DOMAIN_SHMEM_ROLE_MASTER) { > >In fact, the hypervisor will also check weather the ivshmem device is migratable(by >using migration blocker) or not. >If 'role' is not specified in libvirt, the default role may 'master' or 'peer', we don't kown it, >so, I think it's better to check it in hypervisor. > We strive to prevent any errors in QEMU "just in case". Users could start doubting our backwards compatibility if their `default` role shmem stopped migrating in the future, for example. And by being strict we avoid any possible future issues like this.

>> >> >+ virReportError(VIR_ERR_OPERATION_INVALID, >> >+ _("shmem device '%s' with role='%s', " >> >+ "cannot be migrated"), >> >> and this accordingly. >> >> But that's fine, I can change that before pushing. With that change:

>> >> Reviewed-by: Martin Kletzander <mkletzan(a)redhat.com&gt; >> >> but I'll wait after the release since this is a feature. > >