[Qemu-devel] [PULL 40/57] Page request: Add MIG_RP_MSG_REQ_PAGES reverse command

[Juan Quintela <quintela@redhat.com>]

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

Add MIG_RP_MSG_REQ_PAGES command on Return path for the postcopy
destination to request a page from the source.

Two versions exist:
   MIG_RP_MSG_REQ_PAGES_ID that includes a RAMBlock name and start/len
   MIG_RP_MSG_REQ_PAGES that just has start/len for use with the same
                        RAMBlock as a previous MIG_RP_MSG_REQ_PAGES_ID

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
---
 include/migration/migration.h |  5 ++++
 migration/migration.c         | 70 +++++++++++++++++++++++++++++++++++++++++++
 trace-events                  |  1 +
 3 files changed, 76 insertions(+)

diff --git a/include/migration/migration.h b/include/migration/migration.h
index ff13ff2..1046d4e 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -49,6 +49,9 @@ enum mig_rp_message_type {
     MIG_RP_MSG_SHUT,         /* sibling will not send any more RP messages */
     MIG_RP_MSG_PONG,         /* Response to a PING; data (seq: be32 ) */

+    MIG_RP_MSG_REQ_PAGES_ID, /* data (start: be64, len: be32, id: string) */
+    MIG_RP_MSG_REQ_PAGES,    /* data (start: be64, len: be32) */
+
     MIG_RP_MSG_MAX
 };

@@ -256,6 +259,8 @@ void migrate_send_rp_shut(MigrationIncomingState *mis,
                           uint32_t value);
 void migrate_send_rp_pong(MigrationIncomingState *mis,
                           uint32_t value);
+void migrate_send_rp_req_pages(MigrationIncomingState *mis, const char* rbname,
+                              ram_addr_t start, size_t len);

 void ram_control_before_iterate(QEMUFile *f, uint64_t flags);
 void ram_control_after_iterate(QEMUFile *f, uint64_t flags);
diff --git a/migration/migration.c b/migration/migration.c
index b860777..ba0da4f 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -259,6 +259,35 @@ static void deferred_incoming_migration(Error **errp)
     deferred_incoming = true;
 }

+/* Request a range of pages from the source VM at the given
+ * start address.
+ *   rbname: Name of the RAMBlock to request the page in, if NULL it's the same
+ *           as the last request (a name must have been given previously)
+ *   Start: Address offset within the RB
+ *   Len: Length in bytes required - must be a multiple of pagesize
+ */
+void migrate_send_rp_req_pages(MigrationIncomingState *mis, const char *rbname,
+                               ram_addr_t start, size_t len)
+{
+    uint8_t bufc[12 + 1 + 255]; /* start (8), len (4), rbname upto 256 */
+    size_t msglen = 12; /* start + len */
+
+    *(uint64_t *)bufc = cpu_to_be64((uint64_t)start);
+    *(uint32_t *)(bufc + 8) = cpu_to_be32((uint32_t)len);
+
+    if (rbname) {
+        int rbname_len = strlen(rbname);
+        assert(rbname_len < 256);
+
+        bufc[msglen++] = rbname_len;
+        memcpy(bufc + msglen, rbname, rbname_len);
+        msglen += rbname_len;
+        migrate_send_rp_message(mis, MIG_RP_MSG_REQ_PAGES_ID, msglen, bufc);
+    } else {
+        migrate_send_rp_message(mis, MIG_RP_MSG_REQ_PAGES, msglen, bufc);
+    }
+}
+
 void qemu_start_incoming_migration(const char *uri, Error **errp)
 {
     const char *p;
@@ -1151,10 +1180,23 @@ static struct rp_cmd_args {
     [MIG_RP_MSG_INVALID]        = { .len = -1, .name = "INVALID" },
     [MIG_RP_MSG_SHUT]           = { .len =  4, .name = "SHUT" },
     [MIG_RP_MSG_PONG]           = { .len =  4, .name = "PONG" },
+    [MIG_RP_MSG_REQ_PAGES]      = { .len = 12, .name = "REQ_PAGES" },
+    [MIG_RP_MSG_REQ_PAGES_ID]   = { .len = -1, .name = "REQ_PAGES_ID" },
     [MIG_RP_MSG_MAX]            = { .len = -1, .name = "MAX" },
 };

 /*
+ * Process a request for pages received on the return path,
+ * We're allowed to send more than requested (e.g. to round to our page size)
+ * and we don't need to send pages that have already been sent.
+ */
+static void migrate_handle_rp_req_pages(MigrationState *ms, const char* rbname,
+                                       ram_addr_t start, size_t len)
+{
+    trace_migrate_handle_rp_req_pages(rbname, start, len);
+}
+
+/*
  * Handles messages sent on the return path towards the source VM
  *
  */
@@ -1166,6 +1208,8 @@ static void *source_return_path_thread(void *opaque)
     const int max_len = 512;
     uint8_t buf[max_len];
     uint32_t tmp32, sibling_error;
+    ram_addr_t start = 0; /* =0 to silence warning */
+    size_t  len = 0, expected_len;
     int res;

     trace_source_return_path_thread_entry();
@@ -1225,6 +1269,32 @@ static void *source_return_path_thread(void *opaque)
             trace_source_return_path_thread_pong(tmp32);
             break;

+        case MIG_RP_MSG_REQ_PAGES:
+            start = be64_to_cpup((uint64_t *)buf);
+            len = be32_to_cpup((uint32_t *)(buf + 8));
+            migrate_handle_rp_req_pages(ms, NULL, start, len);
+            break;
+
+        case MIG_RP_MSG_REQ_PAGES_ID:
+            expected_len = 12 + 1; /* header + termination */
+
+            if (header_len >= expected_len) {
+                start = be64_to_cpup((uint64_t *)buf);
+                len = be32_to_cpup((uint32_t *)(buf + 8));
+                /* Now we expect an idstr */
+                tmp32 = buf[12]; /* Length of the following idstr */
+                buf[13 + tmp32] = '\0';
+                expected_len += tmp32;
+            }
+            if (header_len != expected_len) {
+                error_report("RP: Req_Page_id with length %d expecting %zd",
+                        header_len, expected_len);
+                mark_source_rp_bad(ms);
+                goto out;
+            }
+            migrate_handle_rp_req_pages(ms, (char *)&buf[13], start, len);
+            break;
+
         default:
             break;
         }
diff --git a/trace-events b/trace-events
index 401d4c3..2bafa12 100644
--- a/trace-events
+++ b/trace-events
@@ -1451,6 +1451,7 @@ migrate_set_state(int new_state) "new state %d"
 migrate_fd_cleanup(void) ""
 migrate_fd_error(void) ""
 migrate_fd_cancel(void) ""
+migrate_handle_rp_req_pages(const char *rbname, size_t start, size_t len) "in %s at %zx len %zx"
 migrate_pending(uint64_t size, uint64_t max, uint64_t post, uint64_t nonpost) "pending size %" PRIu64 " max %" PRIu64 " (post=%" PRIu64 " nonpost=%" PRIu64 ")"
 migrate_send_rp_message(int msg_type, uint16_t len) "%d: len %d"
 migration_completion_file_err(void) ""
-- 
2.5.0