[Qemu-devel] [PATCH 3/3] add live dumping capability

[Paolo Bonzini]

With the previous cleanups in place, it is easy to trigger
restart when the state machine goes from the COMPLETING to the
COMPLETED state.  Besides this, the patch is just simple
scaffolding for the monitor command and to migrate to a file
rather than a pipe (which is a bit simpler because we do not
need non-blocking I/O).

The patch reuses most of the code in migration-exec.c.  The
functions there were half named exec_* and the other half
named file_*.  I consistently adopted file_* for what can be used
for dumping, and exec_* when the function is different in the
two cases.
---
        Cancelling a dump will leave a half-created file.  I
        can fix this in a v2 or in a follow-up.  Right now,
        I would like to make sure that the idea is sound and
        agree on the name of the new monitor command (if
        anything).

 migration-exec.c |   48 +++++++++++++++++++++++++++++++++++++++++++-----
 migration.c      |   26 +++++++++++++++++++++++++-
 migration.h      |    7 +++++++
 qemu-monitor.hx  |    8 ++++++++
 4 files changed, 83 insertions(+), 6 deletions(-)

diff --git a/migration-exec.c b/migration-exec.c
index cfa1304..95642dc 100644
--- a/migration-exec.c
+++ b/migration-exec.c
@@ -36,14 +36,20 @@ static int file_errno(FdMigrationState *s)
     return errno;
 }
 
-static int file_write(FdMigrationState *s, const void * buf, size_t size)
+static int exec_write(FdMigrationState *s, const void * buf, size_t size)
 {
     return write(s->fd, buf, size);
 }
 
-static int exec_close(FdMigrationState *s)
+static int file_write(FdMigrationState *s, const void * buf, size_t size)
+{
+    qemu_put_buffer(s->opaque, buf, size);
+    return size;
+}
+
+static int file_close(FdMigrationState *s)
 {
-    dprintf("exec_close\n");
+    dprintf("file_close\n");
     if (s->opaque) {
         qemu_fclose(s->opaque);
         s->opaque = NULL;
@@ -80,9 +86,9 @@ MigrationState *exec_start_outgoing_migration(const char 
*command,
 
     s->opaque = qemu_popen(f, "w");
 
-    s->close = exec_close;
+    s->close = file_close;
     s->get_error = file_errno;
-    s->write = file_write;
+    s->write = exec_write;
 
     s->bandwidth_limit = bandwidth_limit;
 
@@ -138,3 +144,35 @@ int exec_start_incoming_migration(const char *command)
 
     return 0;
 }
+
+MigrationState *start_live_dump(const char *file,
+                                int64_t bandwidth_limit,
+                                int detach)
+{
+    FdMigrationState *s;
+    FILE *f;
+
+    s = qemu_mallocz(sizeof(*s));
+
+    s->opaque = qemu_fopen(file, "wb");
+    if (!s->opaque)
+        goto err_after_alloc;
+
+    s->close = file_close;
+    s->get_error = file_errno;
+    s->write = file_write;
+    s->bandwidth_limit = bandwidth_limit;
+
+    migrate_fd_init(s);
+    s->mig_state.restart_after = 1;
+    if (!detach)
+        migrate_monitor_suspend(&s->mig_state);
+
+    migrate_fd_connect(s);
+    return &s->mig_state;
+
+    pclose(f);
+err_after_alloc:
+    qemu_free(s);
+    return NULL;
+}
diff --git a/migration.c b/migration.c
index 96585dd..beed034 100644
--- a/migration.c
+++ b/migration.c
@@ -72,6 +72,29 @@ void do_migrate(Monitor *mon, int detach, const char *uri)
     }
 }
 
+void do_dump(Monitor *mon, int detach, const char *file)
+{
+    MigrationState *s;
+
+    if (current_migration) {
+        if (current_migration->state == MIG_STATE_ACTIVE) {
+            monitor_printf(mon, "migration in progress, cannot dump\n");
+            return;
+        }
+    }
+
+    s = start_live_dump(file, max_throttle, detach);
+
+    if (s == NULL)
+        monitor_printf(mon, "dump failed\n");
+    else {
+        if (current_migration)
+            current_migration->release(current_migration);
+
+        current_migration = s;
+    }
+}
+
 void do_migrate_cancel(Monitor *mon)
 {
     MigrationState *s = current_migration;
@@ -302,7 +325,8 @@ void migrate_set_state(MigrationState *s, int state)
        if (s->mon_resume)
             monitor_resume(s->mon_resume);
 
-        if (s->save_vm_running && state != MIG_STATE_COMPLETED)
+        if (s->save_vm_running &&
+           (state != MIG_STATE_COMPLETED || s->restart_after))
            vm_start();
         break;
     }
diff --git a/migration.h b/migration.h
index c44bd75..17dea30 100644
--- a/migration.h
+++ b/migration.h
@@ -28,6 +28,7 @@ struct MigrationState
 {
     Monitor *mon_resume;
     int state;
+    int restart_after;
     int save_vm_running;
 
     /* FIXME: add more accessors to print migration info */
@@ -52,6 +53,8 @@ struct FdMigrationState
 
 void qemu_start_incoming_migration(const char *uri);
 
+void do_dump(Monitor *mon, int detach, const char *file);
+
 void do_migrate(Monitor *mon, int detach, const char *uri);
 
 void do_migrate_cancel(Monitor *mon);
@@ -64,6 +67,10 @@ void do_migrate_set_downtime(Monitor *mon, const char 
*value);
 
 void do_info_migrate(Monitor *mon);
 
+MigrationState *start_live_dump(const char *file,
+                                int64_t bandwidth_limit,
+                                int detach);
+
 int exec_start_incoming_migration(const char *host_port);
 
 MigrationState *exec_start_outgoing_migration(const char *host_port,
diff --git a/qemu-monitor.hx b/qemu-monitor.hx
index dc10b75..86ec3a9 100644
--- a/qemu-monitor.hx
+++ b/qemu-monitor.hx
@@ -463,6 +463,14 @@ STEXI
 Inject an NMI on the given CPU (x86 only).
 ETEXI
 
+    { "dump", "-dF", do_dump,
+      "[-d] file", "dump the VM state to FILE (using -d to not wait for 
completion)" },
+STEXI
address@hidden dump [-d] @var{file}
+Dump the state of the running VM to @var{file} (using -d to not wait for
+completion).  Commands that act on migration can be used for dumps too.
+ETEXI
+
     { "migrate", "-ds", do_migrate,
       "[-d] uri", "migrate to URI (using -d to not wait for completion)" },
 STEXI
-- 
1.5.5.6