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

[Martin Kletzander]

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 at redhat.com>
>Signed-off-by: Yang Hang <yanghang44 at huawei.com>
>Signed-off-by: Wang Xin <wangxinxin.wang at huawei.com>
>
>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) {

>+                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 at redhat.com>

but I'll wait after the release since this is a feature.
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