[Qemu-devel] [PATCH v4 35/47] 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                   | 74 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 77 insertions(+)

diff --git a/include/migration/migration.h b/include/migration/migration.h
index cdd0e56..5e0d30d 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -45,6 +45,7 @@ enum mig_rpcomm_cmd {
     MIG_RPCOMM_INVALID = 0,  /* Must be 0 */
     MIG_RPCOMM_SHUT,         /* sibling will not send any more RP messages */
     MIG_RPCOMM_ACK,          /* data (seq: be32 ) */
+    MIG_RPCOMM_REQPAGES,     /* data (start: be64, len: be64) */
     MIG_RPCOMM_AFTERLASTVALID
 };
 
@@ -250,6 +251,8 @@ void migrate_send_rp_shut(MigrationIncomingState *mis,
                           uint32_t value);
 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 1731017..cfdaa52 100644
--- a/migration.c
+++ b/migration.c
@@ -144,6 +144,38 @@ 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;
@@ -784,6 +816,17 @@ 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);
+}
+
+/*
  * Handles messages sent on the return path towards the source VM
  *
  */
@@ -795,6 +838,8 @@ static void *source_return_path_thread(void *opaque)
     const int max_len = 512;
     uint8_t buf[max_len];
     uint32_t tmp32;
+    uint64_t tmp64a, tmp64b;
+    char *tmpstr;
     int res;
 
     DPRINTF("RP: %s entry", __func__);
@@ -810,6 +855,11 @@ static void *source_return_path_thread(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:
             error_report("RP: Received invalid cmd 0x%04x length 0x%04x",
                     header_com, header_len);
@@ -857,6 +907,30 @@ static void *source_return_path_thread(void *opaque)
             atomic_xchg(&ms->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) {
+                tmp64b -= 1; /* Remove the flag */
+                /* 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 (header_len != expected_len) {
+                error_report("RP: Received ReqPage with length %d expecting %d",
+                        header_len, expected_len);
+                source_return_path_bad(ms);
+            }
+            migrate_handle_rp_reqpages(ms, 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");
-- 
1.9.3