[PATCH] qemu: don't call qemuMigrationSrcIsAllowedHostdev() from qemuMigrationDstPrepareFresh()

[Jiri Denemark]

On Wed, Jul 27, 2022 at 12:28:23 -0400, Laine Stump wrote:
> This call to qemuMigrationSrcIsAllowedHostdev() (which does a
> hardcoded fail of the migration if there is any PCI or mdev hostdev
> device in the domain) while doing the destination side of migration
> prep was found once the call to that same function was removed from
> the source side migration prep (commit 25883cd5).
> 
> According to jdenemar, for the V2 migration protocol, prep of the
> destination is the first step, so this *was* the proper place to do
> the check, but for V3 migration this is in a way redundant (since we
> will have already done the check on the source side (updated by
> 25883cd5 to query QEMU rather than do a hardcoded fail)).
> 
> Of course it's possible that the source could support migration of a
> particular VFIO device, but the destination doesn't. But the current
> check on the destination side is worthless even in that case, since it
> is just *always* failing rather than querying QEMU; and QEMU can't be
> queried at the point where the destination check is happening, since
> it isn't yet running.
> 
> Anyway QEMU should complain when it's started if it's going to fail,
> so removing this check should just move the failure to happen a bit
> later. So the best solution to this problem is to simply remove the
> hardcoded check/fail from qemuMigrationDstPrepareFresh() and rely on
> QEMU to fail if it needs to.
> 
> Fixes: 25883cd5f0b188f2417f294b7d219a77b219f7c2
> Signed-off-by: Laine Stump <laine at redhat.com>
> ---
>  src/qemu/qemu_migration.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c
> index 20dc91f1ce..85b6b12f92 100644
> --- a/src/qemu/qemu_migration.c
> +++ b/src/qemu/qemu_migration.c
> @@ -3379,9 +3379,6 @@ qemuMigrationDstPrepareFresh(virQEMUDriver *driver,
>                        QEMU_MIGRATION_COOKIE_CAPS;
>      }
>  
> -    if (!qemuMigrationSrcIsAllowedHostdev(*def))
> -        goto cleanup;
> -
>      /* Let migration hook filter domain XML */
>      if (virHookPresent(VIR_HOOK_DRIVER_QEMU)) {
>          g_autofree char *xml = NULL;

Reviewed-by: Jiri Denemark <jdenemar at redhat.com>

And safe for freeze.