migration/multifd: Allow receiving pages without packets

Currently multifd does not need to have knowledge of pages on the
receiving side because all the information needed is within the
packets that come in the stream.

We're about to add support to mapped-ram migration, which cannot use
packets because it expects the ramblock section in the migration file
to contain only the guest pages data.

Add a data structure to transfer pages between the ram migration code
and the multifd receiving threads.

We don't want to reuse MultiFDPages_t for two reasons:

a) multifd threads don't really need to know about the data they're
   receiving.

b) the receiving side has to be stopped to load the pages, which means
   we can experiment with larger granularities than page size when
   transferring data.

Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240229153017.2221-16-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/migration/multifd.h b/migration/multifd.h
index 6a54377cc1..1be985978e 100644
--- a/migration/multifd.h
+++ b/migration/multifd.h
@@ -13,6 +13,8 @@
 #ifndef QEMU_MIGRATION_MULTIFD_H
 #define QEMU_MIGRATION_MULTIFD_H
 
+typedef struct MultiFDRecvData MultiFDRecvData;
+
 bool multifd_send_setup(void);
 void multifd_send_shutdown(void);
 int multifd_recv_setup(Error **errp);
@@ -23,6 +25,8 @@ void multifd_recv_new_channel(QIOChannel *ioc, Error **errp);
 void multifd_recv_sync_main(void);
 int multifd_send_sync_main(void);
 bool multifd_queue_page(RAMBlock *block, ram_addr_t offset);
+bool multifd_recv(void);
+MultiFDRecvData *multifd_get_recv_data(void);
 
 /* Multifd Compression flags */
 #define MULTIFD_FLAG_SYNC (1 << 0)
@@ -63,6 +67,13 @@ typedef struct {
     RAMBlock *block;
 } MultiFDPages_t;
 
+struct MultiFDRecvData {
+    void *opaque;
+    size_t size;
+    /* for preadv */
+    off_t file_offset;
+};
+
 typedef struct {
     /* Fields are only written at creating/deletion time */
     /* No lock required for them, they are read only */
@@ -152,6 +163,8 @@ typedef struct {
 
     /* syncs main thread and channels */
     QemuSemaphore sem_sync;
+    /* sem where to wait for more work */
+    QemuSemaphore sem;
 
     /* this mutex protects the following parameters */
     QemuMutex mutex;
@@ -161,6 +174,8 @@ typedef struct {
     uint32_t flags;
     /* global number of generated multifd packets */
     uint64_t packet_num;
+    int pending_job;
+    MultiFDRecvData *data;
 
     /* thread local variables. No locking required */