Re: [Qemu-devel] [PATCH v4 1/1] Introduce "xen-load-devices-state"

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Amit Shah (amit.shah@redhat.com) wrote:
> Dave, can you take a look?

Yes, I think I'm happy with it;

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

I think people might try interesting non-Xen things with it; for
example I think if you backed QEMU's main RAM by a /tmp file
perhaps you could start a guest up even under KVM just
by loading the devices.

Dave

> 
> Thanks,
> 
> On (Mon) 11 Apr 2016 [11:56:02], Changlong Xie wrote:
> > From: Wen Congyang <wency@cn.fujitsu.com>
> > 
> > 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.
> > 
> > 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 <wency@cn.fujitsu.com>
> > Signed-off-by: Changlong Xie <xiecl.fnst@cn.fujitsu.com>
> > ---
> >  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 16ba443..d361a29 100644
> > --- a/migration/savevm.c
> > +++ b/migration/savevm.c
> > @@ -30,6 +30,7 @@
> >  #include "hw/boards.h"
> >  #include "hw/hw.h"
> >  #include "hw/qdev.h"
> > +#include "hw/xen/xen.h"
> >  #include "net/net.h"
> >  #include "monitor/monitor.h"
> >  #include "sysemu/sysemu.h"
> > @@ -1775,6 +1776,12 @@ 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));
> >  
> > @@ -2084,6 +2091,35 @@ 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 ret;
> > +
> > +    /* Guest must be paused before loading the device state; the RAM state
> > +     * will already have been loaded by xc
> > +     */
> > +    if (runstate_is_running()) {
> > +        error_setg(errp, "Cannot update device state while vm is running");
> > +        return;
> > +    }
> > +    vm_stop(RUN_STATE_RESTORE_VM);
> > +
> > +    f = qemu_fopen(filename, "rb");
> > +    if (!f) {
> > +        error_setg_file_open(errp, errno, filename);
> > +        return;
> > +    }
> > +
> > +    migration_incoming_state_new(f);
> > +    ret = qemu_loadvm_state(f);
> > +    qemu_fclose(f);
> > +    if (ret < 0) {
> > +        error_setg(errp, QERR_IO_ERROR);
> > +    }
> > +    migration_incoming_state_destroy();
> > +}
> > +
> >  int load_vmstate(const char *name)
> >  {
> >      BlockDriverState *bs, *bs_vm_state;
> > diff --git a/qapi-schema.json b/qapi-schema.json
> > index 54634c4..132264f 100644
> > --- a/qapi-schema.json
> > +++ b/qapi-schema.json
> > @@ -4144,6 +4144,20 @@
> >    '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'} }
> > +
> > +##
> >  # @GICCapability:
> >  #
> >  # The struct describes capability for a specific GIC (Generic
> > diff --git a/qmp-commands.hx b/qmp-commands.hx
> > index de896a5..68620f6 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
> > 
> > 
> > 
> 
> 		Amit
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK