[Qemu-devel] [PATCH 0/2]: convert device_del to the qapi

[Qemu-devel] [PATCH 0/2]: convert device_del to the qapi

[Luiz Capitulino]

Please, check individual patches for details.

 hmp-commands.hx      |    3 +--
 hmp.c                |    9 +++++++++
 hmp.h                |    1 +
 hw/pci-hotplug.c     |   15 ++++++++++++---
 hw/qdev-monitor.c    |   18 +++++++++++++-----
 hw/qdev.c            |    5 +++--
 hw/qdev.h            |    3 ++-
 hw/usb/dev-storage.c |    2 +-
 hw/xen_platform.c    |    4 ++--
 qapi-schema.json     |   20 ++++++++++++++++++++
 qmp-commands.hx      |    5 +----
 11 files changed, 65 insertions(+), 20 deletions(-)

[Qemu-devel] [PATCH 1/2] qdev: qdev_unplug(): Use error_set()

[Luiz Capitulino]

It currently uses qerror_report(), but next commits will convert
the drive_del command to the QAPI and this requires using
error_set().

One particularity of qerror_report() is that it knows when it's
running on monitor context or command-line context and prints the
error message accordingly. error_set() doesn't do this, so we
have to be careful not to drop error messages.

qdev_unplug() has three kinds of usages:

 1. It's called when hot adding a device fails, to undo anything
    that has been done before hitting the error

 2. It's called by function monitor functions like device_del(),
    to unplug a device

 3. It's used by xen_platform.c in a way that doesn't _seem_ to
    be in monitor context

Only item 2 can print an error message to the user, this commit
maintains that.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
---
 hw/pci-hotplug.c     |   15 ++++++++++++---
 hw/qdev-monitor.c    |   11 ++++++++++-
 hw/qdev.c            |    5 +++--
 hw/qdev.h            |    3 ++-
 hw/usb/dev-storage.c |    2 +-
 hw/xen_platform.c    |    4 ++--
 6 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/hw/pci-hotplug.c b/hw/pci-hotplug.c
index 5c6307f..a060917 100644
--- a/hw/pci-hotplug.c
+++ b/hw/pci-hotplug.c
@@ -32,6 +32,7 @@
 #include "virtio-blk.h"
 #include "qemu-config.h"
 #include "blockdev.h"
+#include "error.h"
 
 #if defined(TARGET_I386)
 static PCIDevice *qemu_pci_hot_add_nic(Monitor *mon,
@@ -191,7 +192,7 @@ static PCIDevice *qemu_pci_hot_add_storage(Monitor *mon,
             dev = NULL;
         if (dev && dinfo) {
             if (scsi_hot_add(mon, &dev->qdev, dinfo, 0) != 0) {
-                qdev_unplug(&dev->qdev);
+                qdev_unplug(&dev->qdev, NULL);
                 dev = NULL;
             }
         }
@@ -256,8 +257,9 @@ void pci_device_hot_add(Monitor *mon, const QDict *qdict)
 static int pci_device_hot_remove(Monitor *mon, const char *pci_addr)
 {
     PCIDevice *d;
-    int dom, bus;
+    int dom, bus, ret;
     unsigned slot;
+    Error *errp = NULL;
 
     if (pci_read_devaddr(mon, pci_addr, &dom, &bus, &slot)) {
         return -1;
@@ -268,7 +270,14 @@ static int pci_device_hot_remove(Monitor *mon, const char *pci_addr)
         monitor_printf(mon, "slot %d empty\n", slot);
         return -1;
     }
-    return qdev_unplug(&d->qdev);
+
+    ret = qdev_unplug(&d->qdev, &errp);
+    if (error_is_set(&errp)) {
+        monitor_printf(mon, "%s\n", error_get_pretty(errp));
+        error_free(errp);
+    }
+
+    return ret;
 }
 
 void do_pci_device_hot_remove(Monitor *mon, const QDict *qdict)
diff --git a/hw/qdev-monitor.c b/hw/qdev-monitor.c
index a310cc7..58fa943 100644
--- a/hw/qdev-monitor.c
+++ b/hw/qdev-monitor.c
@@ -578,13 +578,22 @@ int do_device_del(Monitor *mon, const QDict *qdict, QObject **ret_data)
 {
     const char *id = qdict_get_str(qdict, "id");
     DeviceState *dev;
+    Error *local_err = NULL;
+    int ret;
 
     dev = qdev_find_recursive(sysbus_get_default(), id);
     if (NULL == dev) {
         qerror_report(QERR_DEVICE_NOT_FOUND, id);
         return -1;
     }
-    return qdev_unplug(dev);
+
+    ret = qdev_unplug(dev, &local_err);
+    if (error_is_set(&local_err)) {
+        qerror_report_err(local_err);
+        error_free(local_err);
+    }
+
+    return ret;
 }
 
 void qdev_machine_init(void)
diff --git a/hw/qdev.c b/hw/qdev.c
index ee21d90..cf2a9a9 100644
--- a/hw/qdev.c
+++ b/hw/qdev.c
@@ -28,6 +28,7 @@
 #include "net.h"
 #include "qdev.h"
 #include "sysemu.h"
+#include "error.h"
 
 int qdev_hotplug = 0;
 static bool qdev_hot_added = false;
@@ -172,12 +173,12 @@ void qdev_set_legacy_instance_id(DeviceState *dev, int alias_id,
     dev->alias_required_for_version = required_for_version;
 }
 
-int qdev_unplug(DeviceState *dev)
+int qdev_unplug(DeviceState *dev, Error **errp)
 {
     DeviceClass *dc = DEVICE_GET_CLASS(dev);
 
     if (!dev->parent_bus->allow_hotplug) {
-        qerror_report(QERR_BUS_NO_HOTPLUG, dev->parent_bus->name);
+        error_set(errp, QERR_BUS_NO_HOTPLUG, dev->parent_bus->name);
         return -1;
     }
     assert(dc->unplug != NULL);
diff --git a/hw/qdev.h b/hw/qdev.h
index 9cc3f98..22cf490 100644
--- a/hw/qdev.h
+++ b/hw/qdev.h
@@ -7,6 +7,7 @@
 #include "qemu-option.h"
 #include "qapi/qapi-visit-core.h"
 #include "qemu/object.h"
+#include "error.h"
 
 typedef struct Property Property;
 
@@ -148,7 +149,7 @@ int qdev_init(DeviceState *dev) QEMU_WARN_UNUSED_RESULT;
 void qdev_init_nofail(DeviceState *dev);
 void qdev_set_legacy_instance_id(DeviceState *dev, int alias_id,
                                  int required_for_version);
-int qdev_unplug(DeviceState *dev);
+int qdev_unplug(DeviceState *dev, Error **errp);
 void qdev_free(DeviceState *dev);
 int qdev_simple_unplug_cb(DeviceState *dev);
 void qdev_machine_creation_done(void);
diff --git a/hw/usb/dev-storage.c b/hw/usb/dev-storage.c
index bdbe7bd..d865a5e 100644
--- a/hw/usb/dev-storage.c
+++ b/hw/usb/dev-storage.c
@@ -499,7 +499,7 @@ static void usb_msd_password_cb(void *opaque, int err)
         err = usb_device_attach(&s->dev);
 
     if (err)
-        qdev_unplug(&s->dev.qdev);
+        qdev_unplug(&s->dev.qdev, NULL);
 }
 
 static const struct SCSIBusInfo usb_msd_scsi_info = {
diff --git a/hw/xen_platform.c b/hw/xen_platform.c
index 5a7c4cc..a9c52a6 100644
--- a/hw/xen_platform.c
+++ b/hw/xen_platform.c
@@ -87,7 +87,7 @@ static void unplug_nic(PCIBus *b, PCIDevice *d)
 {
     if (pci_get_word(d->config + PCI_CLASS_DEVICE) ==
             PCI_CLASS_NETWORK_ETHERNET) {
-        qdev_unplug(&(d->qdev));
+        qdev_unplug(&(d->qdev), NULL);
     }
 }
 
@@ -100,7 +100,7 @@ static void unplug_disks(PCIBus *b, PCIDevice *d)
 {
     if (pci_get_word(d->config + PCI_CLASS_DEVICE) ==
             PCI_CLASS_STORAGE_IDE) {
-        qdev_unplug(&(d->qdev));
+        qdev_unplug(&(d->qdev), NULL);
     }
 }
 
-- 
1.7.9.2.384.g4a92a

[Qemu-devel] [PATCH 2/2] qapi: convert device_del

[Luiz Capitulino]

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
---
 hmp-commands.hx   |    3 +--
 hmp.c             |    9 +++++++++
 hmp.h             |    1 +
 hw/qdev-monitor.c |   15 +++++++--------
 qapi-schema.json  |   20 ++++++++++++++++++++
 qmp-commands.hx   |    5 +----
 6 files changed, 39 insertions(+), 14 deletions(-)

diff --git a/hmp-commands.hx b/hmp-commands.hx
index bd35a3e..a6f5a84 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -622,8 +622,7 @@ ETEXI
         .args_type  = "id:s",
         .params     = "device",
         .help       = "remove device",
-        .user_print = monitor_user_noop,
-        .mhandler.cmd_new = do_device_del,
+        .mhandler.cmd = hmp_device_del,
     },
 
 STEXI
diff --git a/hmp.c b/hmp.c
index 9cf2d13..f3e5163 100644
--- a/hmp.c
+++ b/hmp.c
@@ -934,3 +934,12 @@ void hmp_migrate(Monitor *mon, const QDict *qdict)
         qemu_mod_timer(status->timer, qemu_get_clock_ms(rt_clock));
     }
 }
+
+void hmp_device_del(Monitor *mon, const QDict *qdict)
+{
+    const char *id = qdict_get_str(qdict, "id");
+    Error *err = NULL;
+
+    qmp_device_del(id, &err);
+    hmp_handle_error(mon, &err);
+}
diff --git a/hmp.h b/hmp.h
index 8807853..443b812 100644
--- a/hmp.h
+++ b/hmp.h
@@ -60,5 +60,6 @@ void hmp_block_stream(Monitor *mon, const QDict *qdict);
 void hmp_block_job_set_speed(Monitor *mon, const QDict *qdict);
 void hmp_block_job_cancel(Monitor *mon, const QDict *qdict);
 void hmp_migrate(Monitor *mon, const QDict *qdict);
+void hmp_device_del(Monitor *mon, const QDict *qdict);
 
 #endif
diff --git a/hw/qdev-monitor.c b/hw/qdev-monitor.c
index 58fa943..761ba90 100644
--- a/hw/qdev-monitor.c
+++ b/hw/qdev-monitor.c
@@ -19,6 +19,7 @@
 
 #include "qdev.h"
 #include "monitor.h"
+#include "qmp-commands.h"
 
 /*
  * Aliases were a bad idea from the start.  Let's keep them
@@ -574,26 +575,24 @@ int do_device_add(Monitor *mon, const QDict *qdict, QObject **ret_data)
     return 0;
 }
 
-int do_device_del(Monitor *mon, const QDict *qdict, QObject **ret_data)
+void qmp_device_del(const char *id, Error **errp)
 {
-    const char *id = qdict_get_str(qdict, "id");
     DeviceState *dev;
     Error *local_err = NULL;
     int ret;
 
     dev = qdev_find_recursive(sysbus_get_default(), id);
     if (NULL == dev) {
-        qerror_report(QERR_DEVICE_NOT_FOUND, id);
-        return -1;
+        error_set(errp, QERR_DEVICE_NOT_FOUND, id);
+        return;
     }
 
     ret = qdev_unplug(dev, &local_err);
     if (error_is_set(&local_err)) {
-        qerror_report_err(local_err);
-        error_free(local_err);
+        error_propagate(errp, local_err);
+    } else if (ret) {
+        error_set(errp, QERR_UNDEFINED_ERROR);
     }
-
-    return ret;
 }
 
 void qdev_machine_init(void)
diff --git a/qapi-schema.json b/qapi-schema.json
index 0d11d6e..ace55f3 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -1701,3 +1701,23 @@
 # Since: 1.1
 ##
 { 'command': 'xen-save-devices-state', 'data': {'filename': 'str'} }
+
+##
+# @device_del:
+#
+# Remove a device from a guest
+#
+# @id: the name of the device
+#
+# Returns: Nothing on success
+#          If @id is not a valid device, DeviceNotFound
+#          If the device does not support unplug, BusNoHotplug
+#
+# Notes: When this command completes, the device may not be removed from the
+#        guest.  Hot removal is an operation that requires guest cooperation.
+#        This command merely requests that the guest begin the hot removal
+#        process.
+#
+# Since: 0.14.0
+##
+{ 'command': 'device_del', 'data': {'id': 'str'} }
diff --git a/qmp-commands.hx b/qmp-commands.hx
index c626ba8..c878b54 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -314,10 +314,7 @@ EQMP
     {
         .name       = "device_del",
         .args_type  = "id:s",
-        .params     = "device",
-        .help       = "remove device",
-        .user_print = monitor_user_noop,
-        .mhandler.cmd_new = do_device_del,
+        .mhandler.cmd_new = qmp_marshal_input_device_del,
     },
 
 SQMP
-- 
1.7.9.2.384.g4a92a

Re: [Qemu-devel] [PATCH 1/2] qdev: qdev_unplug(): Use error_set()

[Stefan Hajnoczi]

On Wed, Mar 28, 2012 at 05:50:53PM -0300, Luiz Capitulino wrote:
> @@ -268,7 +270,14 @@ static int pci_device_hot_remove(Monitor *mon, const char *pci_addr)
>          monitor_printf(mon, "slot %d empty\n", slot);
>          return -1;
>      }
> -    return qdev_unplug(&d->qdev);
> +
> +    ret = qdev_unplug(&d->qdev, &errp);
> +    if (error_is_set(&errp)) {
> +        monitor_printf(mon, "%s\n", error_get_pretty(errp));
> +        error_free(errp);
> +    }

Minor thing if you respin: this if statement could be replaced with hmp_handle_error(mon, &errp).

Stefan

Re: [Qemu-devel] [PATCH 2/2] qapi: convert device_del

[Stefan Hajnoczi]

On Wed, Mar 28, 2012 at 05:50:54PM -0300, Luiz Capitulino wrote:
>      ret = qdev_unplug(dev, &local_err);
>      if (error_is_set(&local_err)) {
> -        qerror_report_err(local_err);
> -        error_free(local_err);
> +        error_propagate(errp, local_err);
> +    } else if (ret) {
> +        error_set(errp, QERR_UNDEFINED_ERROR);

Can we make qdev_unplug() void?  I can find no case in QEMU where we
return != 0 without setting error.  If we fix the function prototype
this invalid state can be eliminated forever.

(Other functions that take Error **errp are usually void.)

> diff --git a/qapi-schema.json b/qapi-schema.json
> index 0d11d6e..ace55f3 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -1701,3 +1701,23 @@
>  # Since: 1.1
>  ##
>  { 'command': 'xen-save-devices-state', 'data': {'filename': 'str'} }
> +
> +##
> +# @device_del:
> +#
> +# Remove a device from a guest
> +#
> +# @id: the name of the device
> +#
> +# Returns: Nothing on success
> +#          If @id is not a valid device, DeviceNotFound
> +#          If the device does not support unplug, BusNoHotplug
> +#
> +# Notes: When this command completes, the device may not be removed from the
> +#        guest.  Hot removal is an operation that requires guest cooperation.
> +#        This command merely requests that the guest begin the hot removal
> +#        process.

I have not peeked at the implementation in QEMU or libvirt, but is there
a QMP event for actual removal or would the user need to poll?  This bit
of information would be useful in the documentation.

Stefan

Re: [Qemu-devel] [PATCH 1/2] qdev: qdev_unplug(): Use error_set()

[Luiz Capitulino]

On Thu, 29 Mar 2012 08:00:15 +0100
Stefan Hajnoczi <stefanha@gmail.com> wrote:

> On Wed, Mar 28, 2012 at 05:50:53PM -0300, Luiz Capitulino wrote:
> > @@ -268,7 +270,14 @@ static int pci_device_hot_remove(Monitor *mon, const char *pci_addr)
> >          monitor_printf(mon, "slot %d empty\n", slot);
> >          return -1;
> >      }
> > -    return qdev_unplug(&d->qdev);
> > +
> > +    ret = qdev_unplug(&d->qdev, &errp);
> > +    if (error_is_set(&errp)) {
> > +        monitor_printf(mon, "%s\n", error_get_pretty(errp));
> > +        error_free(errp);
> > +    }
> 
> Minor thing if you respin: this if statement could be replaced with hmp_handle_error(mon, &errp).

I'm not sure I'd like to see hmp_handle_error() spread over the tree. It uses
the monitor object and I've added it just because having the same code
duplicated among HMP functions bothered me... I think it's better to
restrict it to hmp.c.

Re: [Qemu-devel] [PATCH 2/2] qapi: convert device_del

[Luiz Capitulino]

On Thu, 29 Mar 2012 08:08:51 +0100
Stefan Hajnoczi <stefanha@gmail.com> wrote:

> On Wed, Mar 28, 2012 at 05:50:54PM -0300, Luiz Capitulino wrote:
> >      ret = qdev_unplug(dev, &local_err);
> >      if (error_is_set(&local_err)) {
> > -        qerror_report_err(local_err);
> > -        error_free(local_err);
> > +        error_propagate(errp, local_err);
> > +    } else if (ret) {
> > +        error_set(errp, QERR_UNDEFINED_ERROR);
> 
> Can we make qdev_unplug() void?  I can find no case in QEMU where we
> return != 0 without setting error.  If we fix the function prototype
> this invalid state can be eliminated forever.

Good point, I'll change it.

> 
> (Other functions that take Error **errp are usually void.)
> 
> > diff --git a/qapi-schema.json b/qapi-schema.json
> > index 0d11d6e..ace55f3 100644
> > --- a/qapi-schema.json
> > +++ b/qapi-schema.json
> > @@ -1701,3 +1701,23 @@
> >  # Since: 1.1
> >  ##
> >  { 'command': 'xen-save-devices-state', 'data': {'filename': 'str'} }
> > +
> > +##
> > +# @device_del:
> > +#
> > +# Remove a device from a guest
> > +#
> > +# @id: the name of the device
> > +#
> > +# Returns: Nothing on success
> > +#          If @id is not a valid device, DeviceNotFound
> > +#          If the device does not support unplug, BusNoHotplug
> > +#
> > +# Notes: When this command completes, the device may not be removed from the
> > +#        guest.  Hot removal is an operation that requires guest cooperation.
> > +#        This command merely requests that the guest begin the hot removal
> > +#        process.
> 
> I have not peeked at the implementation in QEMU or libvirt, but is there
> a QMP event for actual removal or would the user need to poll?  This bit
> of information would be useful in the documentation.

There's no event, I'll document it. Is there any preferred method for
polling? query-pci?

Re: [Qemu-devel] [PATCH 2/2] qapi: convert device_del

[Stefan Hajnoczi]

On Thu, Mar 29, 2012 at 2:17 PM, Luiz Capitulino <lcapitulino@redhat.com> wrote:
> On Thu, 29 Mar 2012 08:08:51 +0100
> Stefan Hajnoczi <stefanha@gmail.com> wrote:
>
>> On Wed, Mar 28, 2012 at 05:50:54PM -0300, Luiz Capitulino wrote:
>> >      ret = qdev_unplug(dev, &local_err);
>> >      if (error_is_set(&local_err)) {
>> > -        qerror_report_err(local_err);
>> > -        error_free(local_err);
>> > +        error_propagate(errp, local_err);
>> > +    } else if (ret) {
>> > +        error_set(errp, QERR_UNDEFINED_ERROR);
>>
>> Can we make qdev_unplug() void?  I can find no case in QEMU where we
>> return != 0 without setting error.  If we fix the function prototype
>> this invalid state can be eliminated forever.
>
> Good point, I'll change it.
>
>>
>> (Other functions that take Error **errp are usually void.)
>>
>> > diff --git a/qapi-schema.json b/qapi-schema.json
>> > index 0d11d6e..ace55f3 100644
>> > --- a/qapi-schema.json
>> > +++ b/qapi-schema.json
>> > @@ -1701,3 +1701,23 @@
>> >  # Since: 1.1
>> >  ##
>> >  { 'command': 'xen-save-devices-state', 'data': {'filename': 'str'} }
>> > +
>> > +##
>> > +# @device_del:
>> > +#
>> > +# Remove a device from a guest
>> > +#
>> > +# @id: the name of the device
>> > +#
>> > +# Returns: Nothing on success
>> > +#          If @id is not a valid device, DeviceNotFound
>> > +#          If the device does not support unplug, BusNoHotplug
>> > +#
>> > +# Notes: When this command completes, the device may not be removed from the
>> > +#        guest.  Hot removal is an operation that requires guest cooperation.
>> > +#        This command merely requests that the guest begin the hot removal
>> > +#        process.
>>
>> I have not peeked at the implementation in QEMU or libvirt, but is there
>> a QMP event for actual removal or would the user need to poll?  This bit
>> of information would be useful in the documentation.
>
> There's no event, I'll document it. Is there any preferred method for
> polling? query-pci?

I took a quick peek at libvirt and am none the wiser.  If we don't
know what the recommended approach is then let's leave it.

Stefan

Re: [Qemu-devel] [PATCH 1/2] qdev: qdev_unplug(): Use error_set()

[Stefan Hajnoczi]

On Thu, Mar 29, 2012 at 2:15 PM, Luiz Capitulino <lcapitulino@redhat.com> wrote:
> On Thu, 29 Mar 2012 08:00:15 +0100
> Stefan Hajnoczi <stefanha@gmail.com> wrote:
>
>> On Wed, Mar 28, 2012 at 05:50:53PM -0300, Luiz Capitulino wrote:
>> > @@ -268,7 +270,14 @@ static int pci_device_hot_remove(Monitor *mon, const char *pci_addr)
>> >          monitor_printf(mon, "slot %d empty\n", slot);
>> >          return -1;
>> >      }
>> > -    return qdev_unplug(&d->qdev);
>> > +
>> > +    ret = qdev_unplug(&d->qdev, &errp);
>> > +    if (error_is_set(&errp)) {
>> > +        monitor_printf(mon, "%s\n", error_get_pretty(errp));
>> > +        error_free(errp);
>> > +    }
>>
>> Minor thing if you respin: this if statement could be replaced with hmp_handle_error(mon, &errp).
>
> I'm not sure I'd like to see hmp_handle_error() spread over the tree. It uses
> the monitor object and I've added it just because having the same code
> duplicated among HMP functions bothered me... I think it's better to
> restrict it to hmp.c.

Okay.  I mentioned it because I noticed that there are several
different ways to do essentially the same thing.

Stefan

[Qemu-devel] [PATCH 1/2] qdev: qdev_unplug(): use error_set()

[Luiz Capitulino]

It currently uses qerror_report(), but next commit will convert
the drive_del command to the QAPI and this requires using
error_set().

One particularity of qerror_report() is that it knows when it's
running on monitor context or command-line context and prints the
error message accordingly. error_set() doesn't do this, so we
have to be careful not to drop error messages.

qdev_unplug() has three kinds of usages:

 1. It's called when hot adding a device fails, to undo anything
    that has been done before hitting the error

 2. It's called by function monitor functions like device_del(),
    to unplug a device

 3. It's used by xen_platform.c in a way that doesn't _seem_ to
    be in monitor context

Only item 2 can print an error message to the user, this commit
maintains that.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
---
 hw/pci-hotplug.c     |   14 ++++++++++++--
 hw/qdev-monitor.c    |   11 ++++++++++-
 hw/qdev.c            |   12 ++++++++----
 hw/qdev.h            |    3 ++-
 hw/usb/dev-storage.c |    2 +-
 hw/xen_platform.c    |    4 ++--
 6 files changed, 35 insertions(+), 11 deletions(-)

diff --git a/hw/pci-hotplug.c b/hw/pci-hotplug.c
index 5c6307f..c55d8b9 100644
--- a/hw/pci-hotplug.c
+++ b/hw/pci-hotplug.c
@@ -32,6 +32,7 @@
 #include "virtio-blk.h"
 #include "qemu-config.h"
 #include "blockdev.h"
+#include "error.h"
 
 #if defined(TARGET_I386)
 static PCIDevice *qemu_pci_hot_add_nic(Monitor *mon,
@@ -191,7 +192,7 @@ static PCIDevice *qemu_pci_hot_add_storage(Monitor *mon,
             dev = NULL;
         if (dev && dinfo) {
             if (scsi_hot_add(mon, &dev->qdev, dinfo, 0) != 0) {
-                qdev_unplug(&dev->qdev);
+                qdev_unplug(&dev->qdev, NULL);
                 dev = NULL;
             }
         }
@@ -258,6 +259,7 @@ static int pci_device_hot_remove(Monitor *mon, const char *pci_addr)
     PCIDevice *d;
     int dom, bus;
     unsigned slot;
+    Error *local_err = NULL;
 
     if (pci_read_devaddr(mon, pci_addr, &dom, &bus, &slot)) {
         return -1;
@@ -268,7 +270,15 @@ static int pci_device_hot_remove(Monitor *mon, const char *pci_addr)
         monitor_printf(mon, "slot %d empty\n", slot);
         return -1;
     }
-    return qdev_unplug(&d->qdev);
+
+    qdev_unplug(&d->qdev, &local_err);
+    if (error_is_set(&local_err)) {
+        monitor_printf(mon, "%s\n", error_get_pretty(local_err));
+        error_free(local_err);
+        return -1;
+    }
+
+    return 0;
 }
 
 void do_pci_device_hot_remove(Monitor *mon, const QDict *qdict)
diff --git a/hw/qdev-monitor.c b/hw/qdev-monitor.c
index a310cc7..e952238 100644
--- a/hw/qdev-monitor.c
+++ b/hw/qdev-monitor.c
@@ -577,6 +577,7 @@ int do_device_add(Monitor *mon, const QDict *qdict, QObject **ret_data)
 int do_device_del(Monitor *mon, const QDict *qdict, QObject **ret_data)
 {
     const char *id = qdict_get_str(qdict, "id");
+    Error *local_err = NULL;
     DeviceState *dev;
 
     dev = qdev_find_recursive(sysbus_get_default(), id);
@@ -584,7 +585,15 @@ int do_device_del(Monitor *mon, const QDict *qdict, QObject **ret_data)
         qerror_report(QERR_DEVICE_NOT_FOUND, id);
         return -1;
     }
-    return qdev_unplug(dev);
+
+    qdev_unplug(dev, &local_err);
+    if (error_is_set(&local_err)) {
+        qerror_report_err(local_err);
+        error_free(local_err);
+        return -1;
+    }
+
+    return 0;
 }
 
 void qdev_machine_init(void)
diff --git a/hw/qdev.c b/hw/qdev.c
index ee21d90..8b0ad19 100644
--- a/hw/qdev.c
+++ b/hw/qdev.c
@@ -28,6 +28,7 @@
 #include "net.h"
 #include "qdev.h"
 #include "sysemu.h"
+#include "error.h"
 
 int qdev_hotplug = 0;
 static bool qdev_hot_added = false;
@@ -172,19 +173,22 @@ void qdev_set_legacy_instance_id(DeviceState *dev, int alias_id,
     dev->alias_required_for_version = required_for_version;
 }
 
-int qdev_unplug(DeviceState *dev)
+void qdev_unplug(DeviceState *dev, Error **errp)
 {
     DeviceClass *dc = DEVICE_GET_CLASS(dev);
 
     if (!dev->parent_bus->allow_hotplug) {
-        qerror_report(QERR_BUS_NO_HOTPLUG, dev->parent_bus->name);
-        return -1;
+        error_set(errp, QERR_BUS_NO_HOTPLUG, dev->parent_bus->name);
+        return;
     }
     assert(dc->unplug != NULL);
 
     qdev_hot_removed = true;
 
-    return dc->unplug(dev);
+    if (dc->unplug(dev) < 0) {
+        error_set(errp, QERR_UNDEFINED_ERROR);
+        return;
+    }
 }
 
 static int qdev_reset_one(DeviceState *dev, void *opaque)
diff --git a/hw/qdev.h b/hw/qdev.h
index 9cc3f98..11f77cf 100644
--- a/hw/qdev.h
+++ b/hw/qdev.h
@@ -7,6 +7,7 @@
 #include "qemu-option.h"
 #include "qapi/qapi-visit-core.h"
 #include "qemu/object.h"
+#include "error.h"
 
 typedef struct Property Property;
 
@@ -148,7 +149,7 @@ int qdev_init(DeviceState *dev) QEMU_WARN_UNUSED_RESULT;
 void qdev_init_nofail(DeviceState *dev);
 void qdev_set_legacy_instance_id(DeviceState *dev, int alias_id,
                                  int required_for_version);
-int qdev_unplug(DeviceState *dev);
+void qdev_unplug(DeviceState *dev, Error **errp);
 void qdev_free(DeviceState *dev);
 int qdev_simple_unplug_cb(DeviceState *dev);
 void qdev_machine_creation_done(void);
diff --git a/hw/usb/dev-storage.c b/hw/usb/dev-storage.c
index bdbe7bd..d865a5e 100644
--- a/hw/usb/dev-storage.c
+++ b/hw/usb/dev-storage.c
@@ -499,7 +499,7 @@ static void usb_msd_password_cb(void *opaque, int err)
         err = usb_device_attach(&s->dev);
 
     if (err)
-        qdev_unplug(&s->dev.qdev);
+        qdev_unplug(&s->dev.qdev, NULL);
 }
 
 static const struct SCSIBusInfo usb_msd_scsi_info = {
diff --git a/hw/xen_platform.c b/hw/xen_platform.c
index 5a7c4cc..a9c52a6 100644
--- a/hw/xen_platform.c
+++ b/hw/xen_platform.c
@@ -87,7 +87,7 @@ static void unplug_nic(PCIBus *b, PCIDevice *d)
 {
     if (pci_get_word(d->config + PCI_CLASS_DEVICE) ==
             PCI_CLASS_NETWORK_ETHERNET) {
-        qdev_unplug(&(d->qdev));
+        qdev_unplug(&(d->qdev), NULL);
     }
 }
 
@@ -100,7 +100,7 @@ static void unplug_disks(PCIBus *b, PCIDevice *d)
 {
     if (pci_get_word(d->config + PCI_CLASS_DEVICE) ==
             PCI_CLASS_STORAGE_IDE) {
-        qdev_unplug(&(d->qdev));
+        qdev_unplug(&(d->qdev), NULL);
     }
 }
 
-- 
1.7.9.2.384.g4a92a