qemu: fix hang in p2p + xbzrle compression + parallel migration

When we do parallel migration, The multifd-channels migration parameter
needs to be set on the destination side as well before incoming migration
URI, unless we accept the default number of connections(2).

Usually, This can be correctly handled by libvirtd. But in this case if
we use p2p + xbzrle compression without parameter '--comp-xbzrle-cache',
qemuMigrationParamsDump returns too early, The corresponding migration
parameter will not be set on the destination side, It results QEMU hangs.

Reproducer:
virsh migrate --live --p2p --comp-methods xbzrle \
--parallel --parallel-connections 3 GUEST qemu+ssh://dsthost/system

or

virsh migrate --live --p2p --compressed \
--parallel --parallel-connections 3 GUEST qemu+ssh://dsthost/system

Signed-off-by: Lin Ma <lma@suse.com>
Message-Id: <20200416044451.21134-1-lma@suse.com>
Reviewed-by: Jiri Denemark <jdenemar@redhat.com>

diff --git a/src/qemu/qemu_migration_params.c b/src/qemu/qemu_migration_params.c
index dd5e2ce1b62712ea28431e2d4931df3ba0221958..810199370fd5941140eba53ec9c3623d0aa5b2f2 100644 (file)
--- a/src/qemu/qemu_migration_params.c
+++ b/src/qemu/qemu_migration_params.c
@@ -630,7 +630,6 @@ qemuMigrationParamsDump(qemuMigrationParamsPtr migParams,
     if (migParams->compMethods == 1ULL << QEMU_MIGRATION_COMPRESS_XBZRLE &&
         !migParams->params[QEMU_MIGRATION_PARAM_XBZRLE_CACHE_SIZE].set) {
         *flags |= VIR_MIGRATE_COMPRESSED;
-        return 0;
     }
 
     for (i = 0; i < QEMU_MIGRATION_COMPRESS_LAST; ++i) {