[RFC PATCH v2 4/9] migration/multifd: Make MultiFDPages_t:offset a flexible array member

[Fabiano Rosas]

We're about to use MultiFDPages_t from inside the MultiFDSendData
payload union, which means we cannot have pointers to allocated data
inside the pages structure, otherwise we'd lose the reference to that
memory once another payload type touches the union. Move the offset
array into the end of the structure and turn it into a flexible array
member, so it is allocated along with the rest of MultiFDSendData in
the next patches.

Note that the ramblock pointer is still fine because the storage for
it is not owned by the migration code.

Signed-off-by: Fabiano Rosas <farosas@suse.de>
---
 migration/multifd.c | 21 ++++++---------------
 migration/multifd.h |  4 ++--
 2 files changed, 8 insertions(+), 17 deletions(-)

diff --git a/migration/multifd.c b/migration/multifd.c
index 20a767157e..440319b361 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -389,22 +389,10 @@ static int multifd_recv_initial_packet(QIOChannel *c, 
Error **errp)
     return msg.id;
 }
 
-static MultiFDPages_t *multifd_pages_init(uint32_t n)
-{
-    MultiFDPages_t *pages = g_new0(MultiFDPages_t, 1);
-
-    pages->allocated = n;
-    pages->offset = g_new0(ram_addr_t, n);
-
-    return pages;
-}
-
 static void multifd_pages_clear(MultiFDPages_t *pages)
 {
     multifd_pages_reset(pages);
     pages->allocated = 0;
-    g_free(pages->offset);
-    pages->offset = NULL;
     g_free(pages);
 }
 
@@ -1169,7 +1157,9 @@ bool multifd_send_setup(void)
     thread_count = migrate_multifd_channels();
     multifd_send_state = g_malloc0(sizeof(*multifd_send_state));
     multifd_send_state->params = g_new0(MultiFDSendParams, thread_count);
-    multifd_send_state->pages = multifd_pages_init(page_count);
+    multifd_send_state->pages = g_malloc0(sizeof(MultiFDPages_t) +
+                                          page_count * sizeof(ram_addr_t));
+    multifd_send_state->pages->allocated = page_count;
     qemu_sem_init(&multifd_send_state->channels_created, 0);
     qemu_sem_init(&multifd_send_state->channels_ready, 0);
     qatomic_set(&multifd_send_state->exiting, 0);
@@ -1181,8 +1171,9 @@ bool multifd_send_setup(void)
         qemu_sem_init(&p->sem, 0);
         qemu_sem_init(&p->sem_sync, 0);
         p->id = i;
-        p->pages = multifd_pages_init(page_count);
-
+        p->pages = g_malloc0(sizeof(MultiFDPages_t) +
+                             page_count * sizeof(ram_addr_t));
+        p->pages->allocated = page_count;
         if (use_packets) {
             p->packet_len = sizeof(MultiFDPacket_t)
                           + sizeof(uint64_t) * page_count;
diff --git a/migration/multifd.h b/migration/multifd.h
index c7b1ebe099..12d4247e23 100644
--- a/migration/multifd.h
+++ b/migration/multifd.h
@@ -78,9 +78,9 @@ typedef struct {
     uint32_t normal_num;
     /* number of allocated pages */
     uint32_t allocated;
+    RAMBlock *block;
     /* offset of each page */
-    ram_addr_t *offset;
-    RAMBlock *block;
+    ram_addr_t offset[];
 } MultiFDPages_t;
 
 struct MultiFDRecvData {
-- 
2.35.3