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

[Dr. David Alan Gilbert]

* Wen Congyang (address@hidden) wrote:
> On 03/23/2016 04:56 PM, Dr. David Alan Gilbert wrote:
> > * 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?
> 
> +    saved_vm_running = runstate_is_running();
> +    vm_stop(RUN_STATE_RESTORE_VM);
> 
> It is copied from the other codes in qemu.
> I think we should return failure if the vm is running:
> if (runstate_is_running()) {
>     error_setg(xxx);
>     return;
> }

OK, yes; and add a comment to explain.

Dave

> 
> Thanks
> Wen Congyang
> 
> > 
> > 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
> > 
> > 
> > .
> > 
> 
> 
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK