[Qemu-devel] [PATCH 34/46] Page request: Add MIG_RPCOMM_REQPAGES reverse command

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

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

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

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 include/migration/migration.h |  3 ++
 migration.c                   | 75 ++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 77 insertions(+), 1 deletion(-)

diff --git a/include/migration/migration.h b/include/migration/migration.h
index 67e5528..f53add7 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -45,6 +45,7 @@ struct MigrationParams {
 enum mig_rpcomm_cmd {
     MIG_RPCOMM_INVALID = 0,  /* Must be 0 */
     MIG_RPCOMM_ACK,          /* data (seq: be32 ) */
+    MIG_RPCOMM_REQPAGES,     /* data (start: be64, len: be64) */
     MIG_RPCOMM_AFTERLASTVALID
 };
 
@@ -234,6 +235,8 @@ void migrate_send_rp_message(MigrationIncomingState *mis,
                              uint16_t len, uint8_t *data);
 void migrate_send_rp_ack(MigrationIncomingState *mis,
                          uint32_t value);
+void migrate_send_rp_reqpages(MigrationIncomingState *mis, const char* rbname,
+                              ram_addr_t start, ram_addr_t len);
 
 
 void ram_control_before_iterate(QEMUFile *f, uint64_t flags);
diff --git a/migration.c b/migration.c
index c7ba6a1..efad18f 100644
--- a/migration.c
+++ b/migration.c
@@ -105,6 +105,38 @@ void migrate_send_rp_ack(MigrationIncomingState *mis,
     migrate_send_rp_message(mis, MIG_RPCOMM_ACK, 4, (uint8_t *)&buf);
 }
 
+/* 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_reqpages(MigrationIncomingState *mis, const char *rbname,
+                              ram_addr_t start, ram_addr_t len)
+{
+    uint8_t bufc[16+1+255]; /* start (8 byte), len (8 byte), rbname upto 256 */
+    uint64_t *buf64 = (uint64_t *)bufc;
+    size_t msglen = 16; /* start + len */
+
+    assert(!(len & 1));
+    if (rbname) {
+        int rbname_len = strlen(rbname);
+        assert(rbname_len < 256);
+
+        len |= 1; /* Flag to say we've got a name */
+        bufc[msglen++] = rbname_len;
+        memcpy(bufc + msglen, rbname, rbname_len);
+        msglen += rbname_len;
+    }
+
+    buf64[0] = (uint64_t)start;
+    buf64[0] = cpu_to_be64(buf64[0]);
+    buf64[1] = (uint64_t)len;
+    buf64[1] = cpu_to_be64(buf64[1]);
+    migrate_send_rp_message(mis, MIG_RPCOMM_REQPAGES, msglen, bufc);
+}
+
 void qemu_start_incoming_migration(const char *uri, Error **errp)
 {
     const char *p;
@@ -776,6 +808,17 @@ static void source_return_path_bad(MigrationState *s)
 }
 
 /*
+ * 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_reqpages(MigrationState *ms, const char* rbname,
+                                       ram_addr_t start, ram_addr_t len)
+{
+    DPRINTF("migrate_handle_rp_reqpages: at %zx for len %zx", start, len);
+}
+
+/*
  * 'can read handler' for the fd callback
  * stops the data handler being called if it's gone into
  * error.
@@ -799,9 +842,12 @@ static void source_return_path_handler(void *opaque)
 {
     MigrationState *s = opaque;
     QEMUFile *rp = qemu_file_get_return_path(s->file);
+    uint16_t expected_len;
     const int max_len = 512;
     uint8_t buf[max_len];
     uint32_t tmp32;
+    uint64_t tmp64a, tmp64b;
+    char *tmpstr;
     int res;
 
     DPRINTF("RP: Receive\n");
@@ -811,7 +857,6 @@ static void source_return_path_handler(void *opaque)
     }
 
     if (s->rp_state.header_com == MIG_RPCOMM_INVALID) {
-        uint16_t expected_len;
 
         /* No command stored, so we're expecting a new header */
         res = qemu_peek_buffer(rp, buf, 4, 0);
@@ -832,6 +877,11 @@ static void source_return_path_handler(void *opaque)
             expected_len = 4;
             break;
 
+        case MIG_RPCOMM_REQPAGES:
+            /* 16 byte start/len _possibly_ plus an id str */
+            expected_len = 16 + 256;
+            break;
+
         default:
             DPRINTF("RP: Received invalid cmd 0x%04x length 0x%04x\n",
                     s->rp_state.header_com, s->rp_state.header_len);
@@ -866,6 +916,29 @@ static void source_return_path_handler(void *opaque)
         atomic_xchg(&s->rp_state.latest_ack, tmp32);
         break;
 
+    case MIG_RPCOMM_REQPAGES:
+        tmp64a = be64_to_cpup((uint64_t *)buf);  /* Start */
+        tmp64b = be64_to_cpup(((uint64_t *)buf)+1); /* Len */
+        tmpstr = NULL;
+        if (tmp64b & 1) {
+            /* Now we expect an idstr */
+            tmp32 = buf[16]; /* Length of the following idstr */
+            tmpstr = (char *)&buf[17];
+            buf[17+tmp32] = '\0';
+            expected_len = 16+1+tmp32;
+        } else {
+            expected_len = 16;
+        }
+        if (s->rp_state.header_len != expected_len) {
+            error_report("RP: Received ReqPage with length %d expecting %d",
+                    s->rp_state.header_len, expected_len);
+            source_return_path_bad(s);
+        }
+        migrate_handle_rp_reqpages(s, tmpstr,
+                                      (ram_addr_t)tmp64a,
+                                      (ram_addr_t)tmp64b);
+        break;
+
     default:
         /* This shouldn't happen because we should catch this above */
         DPRINTF("RP: Bad header_com in dispatch\n");
-- 
1.9.3