[libvirt] [PATCH] qemu: fix hang in p2p + xbzrle compression + parallel migration

[Lin Ma]

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 at suse.com>
---
 src/qemu/qemu_migration_params.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/qemu/qemu_migration_params.c b/src/qemu/qemu_migration_params.c
index dd5e2ce1b6..810199370f 100644
--- 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) {
-- 
2.23.0