migration/multifd: multifd_send_prepare_header()

Introduce a helper multifd_send_prepare_header() to setup the header packet
for multifd sender.

It's fine to setup the IOV[0] _before_ send_prepare() because the packet
buffer is already ready, even if the content is to be filled in.

With this helper, we can already slightly clean up the zero copy path.

Note that I explicitly put it into multifd.h, because I want it inlined
directly into multifd*.c where necessary later.

Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240202102857.110210-13-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>

diff --git a/migration/multifd.c b/migration/multifd.c
index 44163e4e28982001237d287d15e60dd11c588579..cd4467aff4f54c28cd97084c06a9a6da9687a72c 100644 (file)
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -712,10 +712,14 @@ static void *multifd_send_thread(void *opaque)
         if (qatomic_read(&p->pending_job)) {
             MultiFDPages_t *pages = p->pages;
 
-            if (use_zero_copy_send) {
-                p->iovs_num = 0;
-            } else {
-                p->iovs_num = 1;
+            p->iovs_num = 0;
+
+            if (!use_zero_copy_send) {
+                /*
+                 * Only !zerocopy needs the header in IOV; zerocopy will
+                 * send it separately.
+                 */
+                multifd_send_prepare_header(p);
             }
 
             assert(pages->num);
@@ -735,10 +739,6 @@ static void *multifd_send_thread(void *opaque)
                 if (ret != 0) {
                     break;
                 }
-            } else {
-                /* Send header using the same writev call */
-                p->iov[0].iov_len = p->packet_len;
-                p->iov[0].iov_base = p->packet;
             }
 
             ret = qio_channel_writev_full_all(p->c, p->iov, p->iovs_num, NULL,

diff --git a/migration/multifd.h b/migration/multifd.h
index 2e4ad0dc56c1da59e042ec319121e994f593f831..4ec005f53f71649f353e1aa71435fd44f5a2f7b0 100644 (file)
--- a/migration/multifd.h
+++ b/migration/multifd.h
@@ -209,5 +209,13 @@ typedef struct {
 
 void multifd_register_ops(int method, MultiFDMethods *ops);
 
+static inline void multifd_send_prepare_header(MultiFDSendParams *p)
+{
+    p->iov[0].iov_len = p->packet_len;
+    p->iov[0].iov_base = p->packet;
+    p->iovs_num++;
+}
+
+
 #endif