Re: [Qemu-devel] [PATCH v2 1/1] Introduce "xen-load-devices-state"

[Dr. David Alan Gilbert]

* Changlong Xie (address@hidden) wrote:
> On 03/22/2016 08:22 PM, Dr. David Alan Gilbert wrote:
> >* Changlong Xie (address@hidden) wrote:
> >>From: Wen Congyang <address@hidden>
> >>
> >>Introduce a "xen-load-devices-state" QAPI command that can be used to
> >>load the state of all devices, but not the RAM or the block devices of
> >>the VM.
> >>
> >>We only have hmp commands savevm/loadvm, and qmp commands
> >>xen-save-devices-state.
> >
> >Can you explain on Xen how the RAM actually gets loaded?
> 
> Xen use xc(xen toolstack) to do RAM restore/save
> 
> >
> >>
> >>We use this new command for COLO:
> >>1. suspend both primary vm and secondary vm
> >>2. sync the state
> >>3. resume both primary vm and secondary vm
> >>
> >>In such case, we need to update all devices' state in any time.
> >>
> >>Signed-off-by: Wen Congyang <address@hidden>
> >>Signed-off-by: Changlong Xie <address@hidden>
> >>---
> >>  migration/savevm.c | 36 ++++++++++++++++++++++++++++++++++++
> >>  qapi-schema.json   | 14 ++++++++++++++
> >>  qmp-commands.hx    | 27 +++++++++++++++++++++++++++
> >>  3 files changed, 77 insertions(+)
> >>
> >>diff --git a/migration/savevm.c b/migration/savevm.c
> >>index 96e7db5..aaead12 100644
> >>--- a/migration/savevm.c
> >>+++ b/migration/savevm.c
> >>@@ -50,6 +50,7 @@
> >>  #include "qemu/iov.h"
> >>  #include "block/snapshot.h"
> >>  #include "block/qapi.h"
> >>+#include "hw/xen/xen.h"
> >>
> >>
> >>  #ifndef ETH_P_RARP
> >>@@ -1768,6 +1769,12 @@ qemu_loadvm_section_start_full(QEMUFile *f, 
> >>MigrationIncomingState *mis)
> >>          return -EINVAL;
> >>      }
> >>
> >>+    /* Validate if it is a device's state */
> >>+    if (xen_enabled() && se->is_ram) {
> >>+        error_report("loadvm: %s RAM loading not allowed on Xen", idstr);
> >>+        return -EINVAL;
> >>+    }
> >>+
> >>      /* Add entry */
> >>      le = g_malloc0(sizeof(*le));
> >>
> >>@@ -2077,6 +2084,35 @@ void qmp_xen_save_devices_state(const char 
> >>*filename, Error **errp)
> >>      }
> >>  }
> >>
> >>+void qmp_xen_load_devices_state(const char *filename, Error **errp)
> >>+{
> >>+    QEMUFile *f;
> >>+    int saved_vm_running;
> >>+    int ret;
> >>+
> >>+    saved_vm_running = runstate_is_running();
> >>+    vm_stop(RUN_STATE_RESTORE_VM);
> >>+
> >>+    f = qemu_fopen(filename, "rb");
> >>+    if (!f) {
> >>+        error_setg_file_open(errp, errno, filename);
> >>+        goto out;
> >>+    }
> >>+
> >>+    migration_incoming_state_new(f);
> >>+    ret = qemu_loadvm_state(f);
> >>+    qemu_fclose(f);
> >>+    migration_incoming_state_destroy();
> >>+    if (ret < 0) {
> >>+        error_setg(errp, QERR_IO_ERROR);
> >>+    }
> >>+
> >>+out:
> >>+    if (saved_vm_running) {
> >>+        vm_start();
> >>+    }
> >
> >Does it ever happen that you had it running immediately
> >before you did this command? Somehow you'd have to have loaded the RAM
> 
> No, we suspend vm before running this command in xen to make sure the
> condition that you discribed never happen.

OK, so then if the VM is suspended, what does the:

    if (saved_vm_running) {
        vm_start();
    }

at the end of your routine do?

Dave


> 
> Thanks
>       -Xie
> 
> >at just the right point, and I don't see how that would happen if the guest
> >was running.
> >
> >Dave
> >
> >>+}
> >>+
> >>  int load_vmstate(const char *name)
> >>  {
> >>      BlockDriverState *bs, *bs_vm_state;
> >>diff --git a/qapi-schema.json b/qapi-schema.json
> >>index 362c9d8..8cca59d 100644
> >>--- a/qapi-schema.json
> >>+++ b/qapi-schema.json
> >>@@ -4122,3 +4122,17 @@
> >>  ##
> >>  { 'enum': 'ReplayMode',
> >>    'data': [ 'none', 'record', 'play' ] }
> >>+
> >>+##
> >>+# @xen-load-devices-state:
> >>+#
> >>+# Load the state of all devices from file. The RAM and the block devices
> >>+# of the VM are not loaded by this command.
> >>+#
> >>+# @filename: the file to load the state of the devices from as binary
> >>+# data. See xen-save-devices-state.txt for a description of the binary
> >>+# format.
> >>+#
> >>+# Since: 2.7
> >>+##
> >>+{ 'command': 'xen-load-devices-state', 'data': {'filename': 'str'} }
> >>diff --git a/qmp-commands.hx b/qmp-commands.hx
> >>index b629673..4925702 100644
> >>--- a/qmp-commands.hx
> >>+++ b/qmp-commands.hx
> >>@@ -587,6 +587,33 @@ Example:
> >>  EQMP
> >>
> >>      {
> >>+        .name       = "xen-load-devices-state",
> >>+        .args_type  = "filename:F",
> >>+        .mhandler.cmd_new = qmp_marshal_xen_load_devices_state,
> >>+    },
> >>+
> >>+SQMP
> >>+xen-load-devices-state
> >>+----------------------
> >>+
> >>+Load the state of all devices from file. The RAM and the block devices
> >>+of the VM are not loaded by this command.
> >>+
> >>+Arguments:
> >>+
> >>+- "filename": the file to load the state of the devices from as binary
> >>+data. See xen-save-devices-state.txt for a description of the binary
> >>+format.
> >>+
> >>+Example:
> >>+
> >>+-> { "execute": "xen-load-devices-state",
> >>+     "arguments": { "filename": "/tmp/resume" } }
> >>+<- { "return": {} }
> >>+
> >>+EQMP
> >>+
> >>+    {
> >>          .name       = "xen-set-global-dirty-log",
> >>          .args_type  = "enable:b",
> >>          .mhandler.cmd_new = qmp_marshal_xen_set_global_dirty_log,
> >>--
> >>1.9.3
> >>
> >>
> >>
> >--
> >Dr. David Alan Gilbert / address@hidden / Manchester, UK
> >
> >
> >.
> >
> 
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK