savevm: Create a new continue flag to avoid resending block name

Allows us to compress the protocol a bit by setting a flag on the
offset which indicates we're still working within the same block
as last time.  That way we can avoid sending the block name for
every page.  Suggested by Anthony Liguori.
Signed-off-by: NAlex Williamson <alex.williamson@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

arch_init.c

@@ -87,6 +87,7 @@ const uint32_t arch_type = QEMU_ARCH;
 #define RAM_SAVE_FLAG_MEM_SIZE	0x04
 #define RAM_SAVE_FLAG_PAGE	0x08
 #define RAM_SAVE_FLAG_EOS	0x10
+#define RAM_SAVE_FLAG_CONTINUE	0x20
 
 static int is_dup_page(uint8_t *page, uint8_t ch)
 {
@@ -120,6 +121,7 @@ static int ram_save_block(QEMUFile *f)
     do {
         if (cpu_physical_memory_get_dirty(current_addr, MIGRATION_DIRTY_FLAG)) {
             uint8_t *p;
+            int cont = (block == last_block) ? RAM_SAVE_FLAG_CONTINUE : 0;
 
             cpu_physical_memory_reset_dirty(current_addr,
                                             current_addr + TARGET_PAGE_SIZE,
@@ -128,17 +130,21 @@ static int ram_save_block(QEMUFile *f)
             p = block->host + offset;
 
             if (is_dup_page(p, *p)) {
-                qemu_put_be64(f, offset | RAM_SAVE_FLAG_COMPRESS);
-                qemu_put_byte(f, strlen(block->idstr));
-                qemu_put_buffer(f, (uint8_t *)block->idstr,
-                                strlen(block->idstr));
+                qemu_put_be64(f, offset | cont | RAM_SAVE_FLAG_COMPRESS);
+                if (!cont) {
+                    qemu_put_byte(f, strlen(block->idstr));
+                    qemu_put_buffer(f, (uint8_t *)block->idstr,
+                                    strlen(block->idstr));
+                }
                 qemu_put_byte(f, *p);
                 bytes_sent = 1;
             } else {
-                qemu_put_be64(f, offset | RAM_SAVE_FLAG_PAGE);
-                qemu_put_byte(f, strlen(block->idstr));
-                qemu_put_buffer(f, (uint8_t *)block->idstr,
-                                strlen(block->idstr));
+                qemu_put_be64(f, offset | cont | RAM_SAVE_FLAG_PAGE);
+                if (!cont) {
+                    qemu_put_byte(f, strlen(block->idstr));
+                    qemu_put_buffer(f, (uint8_t *)block->idstr,
+                                    strlen(block->idstr));
+                }
                 qemu_put_buffer(f, p, TARGET_PAGE_SIZE);
                 bytes_sent = TARGET_PAGE_SIZE;
             }
@@ -289,6 +295,36 @@ int ram_save_live(Monitor *mon, QEMUFile *f, int stage, void *opaque)
     return (stage == 2) && (expected_time <= migrate_max_downtime());
 }
 
+static inline void *host_from_stream_offset(QEMUFile *f,
+                                            ram_addr_t offset,
+                                            int flags)
+{
+    static RAMBlock *block = NULL;
+    char id[256];
+    uint8_t len;
+
+    if (flags & RAM_SAVE_FLAG_CONTINUE) {
+        if (!block) {
+            fprintf(stderr, "Ack, bad migration stream!\n");
+            return NULL;
+        }
+
+        return block->host + offset;
+    }
+
+    len = qemu_get_byte(f);
+    qemu_get_buffer(f, (uint8_t *)id, len);
+    id[len] = 0;
+
+    QLIST_FOREACH(block, &ram_list.blocks, next) {
+        if (!strncmp(id, block->idstr, sizeof(id)))
+            return block->host + offset;
+    }
+
+    fprintf(stderr, "Can't find block %s!\n", id);
+    return NULL;
+}
+
 int ram_load(QEMUFile *f, void *opaque, int version_id)
 {
     ram_addr_t addr;
@@ -346,26 +382,11 @@ int ram_load(QEMUFile *f, void *opaque, int version_id)
             void *host;
             uint8_t ch;
 
-            if (version_id == 3) {
+            if (version_id == 3)
                 host = qemu_get_ram_ptr(addr);
-            } else {
-                RAMBlock *block;
-                char id[256];
-                uint8_t len;
-
-                len = qemu_get_byte(f);
-                qemu_get_buffer(f, (uint8_t *)id, len);
-                id[len] = 0;
+            else
+                host = host_from_stream_offset(f, addr, flags);
 
-                QLIST_FOREACH(block, &ram_list.blocks, next) {
-                    if (!strncmp(id, block->idstr, sizeof(id)))
-                        break;
-                }
-                if (!block)
-                    return -EINVAL;
-
-                host = block->host + addr;
-            }
             ch = qemu_get_byte(f);
             memset(host, ch, TARGET_PAGE_SIZE);
 #ifndef _WIN32
@@ -377,26 +398,11 @@ int ram_load(QEMUFile *f, void *opaque, int version_id)
         } else if (flags & RAM_SAVE_FLAG_PAGE) {
             void *host;
 
-            if (version_id == 3) {
+            if (version_id == 3)
                 host = qemu_get_ram_ptr(addr);
-            } else {
-                RAMBlock *block;
-                char id[256];
-                uint8_t len;
+            else
+                host = host_from_stream_offset(f, addr, flags);
 
-                len = qemu_get_byte(f);
-                qemu_get_buffer(f, (uint8_t *)id, len);
-                id[len] = 0;
-
-                QLIST_FOREACH(block, &ram_list.blocks, next) {
-                    if (!strncmp(id, block->idstr, sizeof(id)))
-                        break;
-                }
-                if (!block)
-                    return -EINVAL;
-
-                host = block->host + addr;
-            }
             qemu_get_buffer(f, host, TARGET_PAGE_SIZE);
         }
         if (qemu_file_has_error(f)) {