migration/multifd: Support incoming mapped-ram stream format

For the incoming mapped-ram migration we need to read the ramblock
headers, get the pages bitmap and send the host address of each
non-zero page to the multifd channel thread for writing.

Usage on HMP is:

(qemu) migrate_set_capability multifd on
(qemu) migrate_set_capability mapped-ram on
(qemu) migrate_incoming file:migfile

(the ram.h include needs to move because we've been previously relying
on it being included from migration.c. Now file.h will start including
multifd.h before migration.o is processed)

Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240229153017.2221-22-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>

migration/file.c

@@ -13,7 +13,6 @@
 #include "channel.h"
 #include "file.h"
 #include "migration.h"
-#include "multifd.h"
 #include "io/channel-file.h"
 #include "io/channel-util.h"
 #include "options.h"
@@ -204,3 +203,20 @@ int file_write_ramblock_iov(QIOChannel *ioc, const struct iovec *iov,
 
     return (ret < 0) ? ret : 0;
 }
+
+int multifd_file_recv_data(MultiFDRecvParams *p, Error **errp)
+{
+    MultiFDRecvData *data = p->data;
+    size_t ret;
+
+    ret = qio_channel_pread(p->c, (char *) data->opaque,
+                            data->size, data->file_offset, errp);
+    if (ret != data->size) {
+        error_prepend(errp,
+                      "multifd recv (%u): read 0x%zx, expected 0x%zx",
+                      p->id, ret, data->size);
+        return -1;
+    }
+
+    return 0;
+}

migration/file.h

@@ -11,6 +11,7 @@
 #include "qapi/qapi-types-migration.h"
 #include "io/task.h"
 #include "channel.h"
+#include "multifd.h"
 
 void file_start_incoming_migration(FileMigrationArgs *file_args, Error **errp);
 
@@ -21,4 +22,5 @@ void file_cleanup_outgoing_migration(void);
 bool file_send_channel_create(gpointer opaque, Error **errp);
 int file_write_ramblock_iov(QIOChannel *ioc, const struct iovec *iov,
                             int niov, RAMBlock *block, Error **errp);
+int multifd_file_recv_data(MultiFDRecvParams *p, Error **errp);
 #endif

migration/multifd.c

@@ -18,7 +18,6 @@
 #include "qemu/error-report.h"
 #include "qapi/error.h"
 #include "file.h"
-#include "ram.h"
 #include "migration.h"
 #include "migration-stats.h"
 #include "socket.h"
@@ -251,7 +250,7 @@ static int nocomp_recv(MultiFDRecvParams *p, Error **errp)
     uint32_t flags;
 
     if (!multifd_use_packets()) {
-        return 0;
+        return multifd_file_recv_data(p, errp);
     }
 
     flags = p->flags & MULTIFD_FLAG_COMPRESSION_MASK;
@@ -1331,22 +1330,48 @@ void multifd_recv_cleanup(void)
 void multifd_recv_sync_main(void)
 {
     int thread_count = migrate_multifd_channels();
+    bool file_based = !multifd_use_packets();
     int i;
 
-    if (!migrate_multifd() || !multifd_use_packets()) {
+    if (!migrate_multifd()) {
         return;
     }
 
+    /*
+     * File-based channels don't use packets and therefore need to
+     * wait for more work. Release them to start the sync.
+     */
+    if (file_based) {
+        for (i = 0; i < thread_count; i++) {
+            MultiFDRecvParams *p = &multifd_recv_state->params[i];
+
+            trace_multifd_recv_sync_main_signal(p->id);
+            qemu_sem_post(&p->sem);
+        }
+    }
+
     /*
      * Initiate the synchronization by waiting for all channels.
+     *
      * For socket-based migration this means each channel has received
      * the SYNC packet on the stream.
+     *
+     * For file-based migration this means each channel is done with
+     * the work (pending_job=false).
      */
     for (i = 0; i < thread_count; i++) {
         trace_multifd_recv_sync_main_wait(i);
         qemu_sem_wait(&multifd_recv_state->sem_sync);
     }
 
+    if (file_based) {
+        /*
+         * For file-based loading is done in one iteration. We're
+         * done.
+         */
+        return;
+    }
+
     /*
      * Sync done. Release the channels for the next iteration.
      */

migration/multifd.h

@@ -13,6 +13,8 @@
 #ifndef QEMU_MIGRATION_MULTIFD_H
 #define QEMU_MIGRATION_MULTIFD_H
 
+#include "ram.h"
+
 typedef struct MultiFDRecvData MultiFDRecvData;
 
 bool multifd_send_setup(void);

migration/ram.c

@@ -3952,6 +3952,22 @@ void colo_flush_ram_cache(void)
     trace_colo_flush_ram_cache_end();
 }
 
+static size_t ram_load_multifd_pages(void *host_addr, size_t size,
+                                     uint64_t offset)
+{
+    MultiFDRecvData *data = multifd_get_recv_data();
+
+    data->opaque = host_addr;
+    data->file_offset = offset;
+    data->size = size;
+
+    if (!multifd_recv()) {
+        return 0;
+    }
+
+    return size;
+}
+
 static bool read_ramblock_mapped_ram(QEMUFile *f, RAMBlock *block,
                                      long num_pages, unsigned long *bitmap,
                                      Error **errp)
@@ -3981,8 +3997,14 @@ static bool read_ramblock_mapped_ram(QEMUFile *f, RAMBlock *block,
 
             size = MIN(unread, MAPPED_RAM_LOAD_BUF_SIZE);
 
-            read = qemu_get_buffer_at(f, host, size,
-                                      block->pages_offset + offset);
+            if (migrate_multifd()) {
+                read = ram_load_multifd_pages(host, size,
+                                              block->pages_offset + offset);
+            } else {
+                read = qemu_get_buffer_at(f, host, size,
+                                          block->pages_offset + offset);
+            }
+
             if (!read) {
                 goto err;
             }