[Qemu-devel] [PATCH v6 22/47] MIG_CMD_PACKAGED: Send a packaged chunk of migration stream

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

MIG_CMD_PACKAGED is a migration command that wraps a chunk of migration
stream inside a package whose length can be determined purely by reading
its header.  The destination guarantees that the whole MIG_CMD_PACKAGED
is read off the stream prior to parsing the contents.

This is used by postcopy to load device state (from the package)
while leaving the main stream free to receive memory pages.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 include/sysemu/sysemu.h |  4 +++
 savevm.c                | 94 +++++++++++++++++++++++++++++++++++++++++++++++++
 trace-events            |  4 +++
 3 files changed, 102 insertions(+)

diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
index 6dd2382..0e3bf1e 100644
--- a/include/sysemu/sysemu.h
+++ b/include/sysemu/sysemu.h
@@ -87,6 +87,7 @@ enum qemu_vm_cmd {
     MIG_CMD_INVALID = 0,       /* Must be 0 */
     MIG_CMD_OPEN_RETURN_PATH,  /* Tell the dest to open the Return path */
     MIG_CMD_PING,              /* Request a PONG on the RP */
+    MIG_CMD_PACKAGED,          /* Send a wrapped stream within this stream */
 
     MIG_CMD_POSTCOPY_ADVISE = 20,  /* Prior to any page transfers, just
                                       warn we might want to do PC */
@@ -100,6 +101,8 @@ enum qemu_vm_cmd {
 
 };
 
+#define MAX_VM_CMD_PACKAGED_SIZE (1ul << 24)
+
 bool qemu_savevm_state_blocked(Error **errp);
 void qemu_savevm_state_begin(QEMUFile *f,
                              const MigrationParams *params);
@@ -112,6 +115,7 @@ void qemu_savevm_command_send(QEMUFile *f, enum qemu_vm_cmd command,
                               uint16_t len, uint8_t *data);
 void qemu_savevm_send_ping(QEMUFile *f, uint32_t value);
 void qemu_savevm_send_open_return_path(QEMUFile *f);
+int qemu_savevm_send_packaged(QEMUFile *f, const QEMUSizedBuffer *qsb);
 void qemu_savevm_send_postcopy_advise(QEMUFile *f);
 void qemu_savevm_send_postcopy_listen(QEMUFile *f);
 void qemu_savevm_send_postcopy_run(QEMUFile *f);
diff --git a/savevm.c b/savevm.c
index 8d2fe1f..1e940af 100644
--- a/savevm.c
+++ b/savevm.c
@@ -635,6 +635,50 @@ void qemu_savevm_send_open_return_path(QEMUFile *f)
     qemu_savevm_command_send(f, MIG_CMD_OPEN_RETURN_PATH, 0, NULL);
 }
 
+/* We have a buffer of data to send; we don't want that all to be loaded
+ * by the command itself, so the command contains just the length of the
+ * extra buffer that we then send straight after it.
+ * TODO: Must be a better way to organise that
+ *
+ * Returns:
+ *    0 on success
+ *    -ve on error
+ */
+int qemu_savevm_send_packaged(QEMUFile *f, const QEMUSizedBuffer *qsb)
+{
+    size_t cur_iov;
+    size_t len = qsb_get_length(qsb);
+    uint32_t tmp;
+
+    if (len > MAX_VM_CMD_PACKAGED_SIZE) {
+        error_report("%s: Unreasonably large packaged state: %zu",
+                     __func__, len);
+        return -1;
+    }
+
+    tmp = cpu_to_be32(len);
+
+    trace_qemu_savevm_send_packaged();
+    qemu_savevm_command_send(f, MIG_CMD_PACKAGED, 4, (uint8_t *)&tmp);
+
+    /* all the data follows (concatinating the iov's) */
+    for (cur_iov = 0; cur_iov < qsb->n_iov; cur_iov++) {
+        /* The iov entries are partially filled */
+        size_t towrite = (qsb->iov[cur_iov].iov_len > len) ?
+                              len :
+                              qsb->iov[cur_iov].iov_len;
+        len -= towrite;
+
+        if (!towrite) {
+            break;
+        }
+
+        qemu_put_buffer(f, qsb->iov[cur_iov].iov_base, towrite);
+    }
+
+    return 0;
+}
+
 /* Send prior to any postcopy transfer */
 void qemu_savevm_send_postcopy_advise(QEMUFile *f)
 {
@@ -1199,6 +1243,48 @@ static int loadvm_process_command_simple_lencheck(const char *name,
     return 0;
 }
 
+/* Immediately following this command is a blob of data containing an embedded
+ * chunk of migration stream; read it and load it.
+ */
+static int loadvm_handle_cmd_packaged(MigrationIncomingState *mis,
+                                      uint32_t length)
+{
+    int ret;
+    uint8_t *buffer;
+    QEMUSizedBuffer *qsb;
+
+    trace_loadvm_handle_cmd_packaged(length);
+
+    if (length > MAX_VM_CMD_PACKAGED_SIZE) {
+        error_report("Unreasonably large packaged state: %u", length);
+        return -1;
+    }
+    buffer = g_malloc0(length);
+    ret = qemu_get_buffer(mis->file, buffer, (int)length);
+    if (ret != length) {
+        g_free(buffer);
+        error_report("CMD_PACKAGED: Buffer receive fail ret=%d length=%d\n",
+                ret, length);
+        return (ret < 0) ? ret : -EAGAIN;
+    }
+    trace_loadvm_handle_cmd_packaged_received(ret);
+
+    /* Setup a dummy QEMUFile that actually reads from the buffer */
+    qsb = qsb_create(buffer, length);
+    g_free(buffer); /* Because qsb_create copies */
+    if (!qsb) {
+        error_report("Unable to create qsb");
+    }
+    QEMUFile *packf = qemu_bufopen("r", qsb);
+
+    ret = qemu_loadvm_state_main(packf, mis);
+    trace_loadvm_handle_cmd_packaged_main(ret);
+    qemu_fclose(packf);
+    qsb_free(qsb);
+
+    return ret;
+}
+
 /*
  * Process an incoming 'QEMU_VM_COMMAND'
  * 0           just a normal return
@@ -1249,6 +1335,14 @@ static int loadvm_process_command(QEMUFile *f)
         migrate_send_rp_pong(mis, tmp32);
         break;
 
+    case MIG_CMD_PACKAGED:
+        if (loadvm_process_command_simple_lencheck("CMD_POSTCOPY_PACKAGED",
+            len, 4)) {
+            return -1;
+         }
+        tmp32 = qemu_get_be32(f);
+        return loadvm_handle_cmd_packaged(mis, tmp32);
+
     case MIG_CMD_POSTCOPY_ADVISE:
         if (loadvm_process_command_simple_lencheck("CMD_POSTCOPY_ADVISE",
                                                    len, 16)) {
diff --git a/trace-events b/trace-events
index 26625be..4e53ad8 100644
--- a/trace-events
+++ b/trace-events
@@ -1175,6 +1175,10 @@ qemu_loadvm_state_main(void) ""
 qemu_loadvm_state_main_quit_parent(void) ""
 qemu_loadvm_state_post_main(int ret) "%d"
 qemu_loadvm_state_section_startfull(uint32_t section_id, const char *idstr, uint32_t instance_id, uint32_t version_id) "%u(%s) %u %u"
+qemu_savevm_send_packaged(void) ""
+loadvm_handle_cmd_packaged(unsigned int length) "%u"
+loadvm_handle_cmd_packaged_main(int ret) "%d"
+loadvm_handle_cmd_packaged_received(int ret) "%d"
 loadvm_postcopy_handle_advise(void) ""
 loadvm_postcopy_handle_listen(void) ""
 loadvm_postcopy_handle_run(void) ""
-- 
2.1.0