[RFC PATCH v2 8/9] migration/multifd: Don't send ram data during SYNC

[Fabiano Rosas]

Skip saving and loading any ram data in the packet in the case of a
SYNC. This fixes a shortcoming of the current code which requires a
reset of the MultiFDPages_t fields right after the previous
pending_job finishes, otherwise the very next job might be a SYNC and
multifd_send_fill_packet() will put the stale values in the packet.

By not calling multifd_ram_fill_packet(), we can stop resetting
MultiFDPages_t in the multifd core and leave that to the client code.

Actually moving the reset function is not yet done because
pages->num==0 is used by the client code to determine whether the
MultiFDPages_t needs to be flushed. The subsequent patches will
replace that with a generic flag that is not dependent on
MultiFDPages_t.

Signed-off-by: Fabiano Rosas <farosas@suse.de>
---
 migration/multifd.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/migration/multifd.c b/migration/multifd.c
index d25b8658b2..4394ca6ade 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -438,6 +438,7 @@ void multifd_send_fill_packet(MultiFDSendParams *p)
 {
     MultiFDPacket_t *packet = p->packet;
     uint64_t packet_num;
+    bool sync_packet = p->flags & MULTIFD_FLAG_SYNC;
 
     memset(packet, 0, p->packet_len);
 
@@ -452,7 +453,9 @@ void multifd_send_fill_packet(MultiFDSendParams *p)
 
     p->packets_sent++;
 
-    multifd_ram_fill_packet(p);
+    if (!sync_packet) {
+        multifd_ram_fill_packet(p);
+    }
 
     trace_multifd_send(p->id, packet_num,
                        be32_to_cpu(packet->normal_pages),
@@ -563,7 +566,12 @@ static int multifd_recv_unfill_packet(MultiFDRecvParams 
*p, Error **errp)
     p->packet_num = be64_to_cpu(packet->packet_num);
     p->packets_recved++;
 
-    ret = multifd_ram_unfill_packet(p, errp);
+    if (p->flags & MULTIFD_FLAG_SYNC) {
+        p->normal_num = 0;
+        p->zero_num = 0;
+    } else {
+        ret = multifd_ram_unfill_packet(p, errp);
+    }
 
     trace_multifd_recv(p->id, p->packet_num, p->normal_num, p->zero_num,
                        p->flags, p->next_packet_size);
-- 
2.35.3