[Qemu-devel] [PATCH v4 0/1] Introduce "xen-load-devices-state"

[Qemu-devel] [PATCH v4 0/1] Introduce "xen-load-devices-state"

[Changlong Xie]

Changelog
v4:
1. Rebased to the lastest code
v3:
1. Addressed on David's commets, fix a bug
v2:
1. Rebased to the lastest code
2. Addressed on Eric's comments, fixed coding style

Wen Congyang (1):
  Introduce "xen-load-devices-state"

 migration/savevm.c | 36 ++++++++++++++++++++++++++++++++++++
 qapi-schema.json   | 14 ++++++++++++++
 qmp-commands.hx    | 27 +++++++++++++++++++++++++++
 3 files changed, 77 insertions(+)

-- 
1.9.3

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

[Changlong Xie]

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

Re: [Qemu-devel] [PATCH v4 0/1] Introduce "xen-load-devices-state"

[Changlong Xie]

ping...

On 04/11/2016 11:56 AM, Changlong Xie wrote:
> Changelog
> v4:
> 1. Rebased to the lastest code
> v3:
> 1. Addressed on David's commets, fix a bug
> v2:
> 1. Rebased to the lastest code
> 2. Addressed on Eric's comments, fixed coding style
>
> Wen Congyang (1):
>    Introduce "xen-load-devices-state"
>
>   migration/savevm.c | 36 ++++++++++++++++++++++++++++++++++++
>   qapi-schema.json   | 14 ++++++++++++++
>   qmp-commands.hx    | 27 +++++++++++++++++++++++++++
>   3 files changed, 77 insertions(+)
>

Re: [Qemu-devel] [PATCH v4 0/1] Introduce "xen-load-devices-state"

[Changlong Xie]

On 04/11/2016 11:56 AM, Changlong Xie wrote:
> Changelog
> v4:
> 1. Rebased to the lastest code
> v3:
> 1. Addressed on David's commets, fix a bug
> v2:
> 1. Rebased to the lastest code
> 2. Addressed on Eric's comments, fixed coding style
>
> Wen Congyang (1):
>    Introduce "xen-load-devices-state"
>
>   migration/savevm.c | 36 ++++++++++++++++++++++++++++++++++++
>   qapi-schema.json   | 14 ++++++++++++++
>   qmp-commands.hx    | 27 +++++++++++++++++++++++++++
>   3 files changed, 77 insertions(+)
>

Hi Juan & Amit

	Would you please help to review this patch? We need this patch to xen 
colo. No respose over one month...

Thanks
	-Xie

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

[Anthony PERARD]

On Mon, Apr 11, 2016 at 11:56:02AM +0800, 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>

This patch looks good to me.

Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>

-- 
Anthony PERARD

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

[Amit Shah]

Dave, can you take a look?

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

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

[Stefano Stabellini]

On Fri, 27 May 2016, Anthony PERARD wrote:
> On Mon, Apr 11, 2016 at 11:56:02AM +0800, 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>
> 
> This patch looks good to me.
> 
> Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>

It would be nicer (and less problematic) to load the state from a file
descriptor, but given that we still saving the state to file, it would
be unfair to ask to use file descriptors here.

Acked-by: Stefano Stabellini <sstabellini@kernel.org>

Given that this is migration code, it still needs an ack from Juan or
Amit.

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

[Eric Blake]

[-- Attachment #1: Type: text/plain, Size: 1387 bytes --]

On 05/30/2016 09:17 AM, Stefano Stabellini wrote:
> On Fri, 27 May 2016, Anthony PERARD wrote:
>> On Mon, Apr 11, 2016 at 11:56:02AM +0800, 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>
>>
>> This patch looks good to me.
>>
>> Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
> 
> It would be nicer (and less problematic) to load the state from a file
> descriptor, but given that we still saving the state to file, it would
> be unfair to ask to use file descriptors here.

If you use qemu_open(), then you can pass the magic "/dev/fdset/1"
notation to use a file descriptor previously added to an fdset.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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

[Dr. David Alan Gilbert]

* 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

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

[Stefano Stabellini]

On Wed, 1 Jun 2016, Dr. David Alan Gilbert wrote:
> * 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.

I added this patch to the Xen queue.

Thanks,

Stefano

> > 
> > 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
> 

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

[Stefano Stabellini]

On Thu, 2 Jun 2016, Stefano Stabellini wrote:
> On Wed, 1 Jun 2016, Dr. David Alan Gilbert wrote:
> > * 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.
> 
> I added this patch to the Xen queue.

I spoke too quickly. I get:

/local/qemu/migration/savevm.c: In function 'qmp_xen_load_devices_state':
/local/qemu/migration/savevm.c:2089:5: error: implicit declaration of function 'qemu_fopen' [-Werror=implicit-function-declaration]
/local/qemu/migration/savevm.c:2089:5: error: nested extern declaration of 'qemu_fopen' [-Werror=nested-externs]
/local/qemu/migration/savevm.c:2089:7: error: assignment makes pointer from integer without a cast [-Werror]
  CC    i386-softmmu/hw/display/virtio-vga.o
cc1: all warnings being treated as errors

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

[Dr. David Alan Gilbert]

* Stefano Stabellini (sstabellini@kernel.org) wrote:
> On Thu, 2 Jun 2016, Stefano Stabellini wrote:
> > On Wed, 1 Jun 2016, Dr. David Alan Gilbert wrote:
> > > * 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.
> > 
> > I added this patch to the Xen queue.
> 
> I spoke too quickly. I get:
> 
> /local/qemu/migration/savevm.c: In function 'qmp_xen_load_devices_state':
> /local/qemu/migration/savevm.c:2089:5: error: implicit declaration of function 'qemu_fopen' [-Werror=implicit-function-declaration]
> /local/qemu/migration/savevm.c:2089:5: error: nested extern declaration of 'qemu_fopen' [-Werror=nested-externs]
> /local/qemu/migration/savevm.c:2089:7: error: assignment makes pointer from integer without a cast [-Werror]

Ah, yes, your problem is that Dan's crypto changes have probably just removed that;
see qmp_xen_save_devices_state and 8925839f  that changed it to use the new qio_channel_file_new_path.

Dave

>   CC    i386-softmmu/hw/display/virtio-vga.o
> cc1: all warnings being treated as errors
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

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

[Changlong Xie]

On 06/02/2016 06:16 PM, Dr. David Alan Gilbert wrote:
> * Stefano Stabellini (sstabellini@kernel.org) wrote:
>> On Thu, 2 Jun 2016, Stefano Stabellini wrote:
>>> On Wed, 1 Jun 2016, Dr. David Alan Gilbert wrote:
>>>> * 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.
>>>
>>> I added this patch to the Xen queue.
>>
>> I spoke too quickly. I get:
>>
>> /local/qemu/migration/savevm.c: In function 'qmp_xen_load_devices_state':
>> /local/qemu/migration/savevm.c:2089:5: error: implicit declaration of function 'qemu_fopen' [-Werror=implicit-function-declaration]
>> /local/qemu/migration/savevm.c:2089:5: error: nested extern declaration of 'qemu_fopen' [-Werror=nested-externs]
>> /local/qemu/migration/savevm.c:2089:7: error: assignment makes pointer from integer without a cast [-Werror]
>
> Ah, yes, your problem is that Dan's crypto changes have probably just removed that;
> see qmp_xen_save_devices_state and 8925839f  that changed it to use the new qio_channel_file_new_path.
>

Yes, i just send another patchset.

> Dave
>
>>    CC    i386-softmmu/hw/display/virtio-vga.o
>> cc1: all warnings being treated as errors
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>
>
> .
>