diff mbox series

hw/virtio/vdpa-dev: Check returned value instead of dereferencing @errp

Message ID 20240715095939.72492-2-zhao1.liu@intel.com (mailing list archive)
State New, archived
Headers show
Series hw/virtio/vdpa-dev: Check returned value instead of dereferencing @errp | expand

Commit Message

Zhao Liu July 15, 2024, 9:59 a.m. UTC 
As the comment in qapi/error, dereferencing @errp requires
ERRP_GUARD():

* = Why, when and how to use ERRP_GUARD() =
*
* Without ERRP_GUARD(), use of the @errp parameter is restricted:
* - It must not be dereferenced, because it may be null.
...
* ERRP_GUARD() lifts these restrictions.
*
* To use ERRP_GUARD(), add it right at the beginning of the function.
* @errp can then be used without worrying about the argument being
* NULL or &error_fatal.
*
* Using it when it's not needed is safe, but please avoid cluttering
* the source with useless code.

Though vhost_vdpa_device_realize() is called at DeviceClass.realize()
context and won't get NULL @errp, it's still better to follow the
requirement to add the ERRP_GUARD().

But qemu_open() and vhost_vdpa_device_get_u32()'s return values can
distinguish between successful and unsuccessful calls, so check the
return values directly without dereferencing @errp, which eliminates
the need of ERRP_GUARD().

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: "Eugenio Pérez" <eperezma@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
---
 hw/virtio/vdpa-dev.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

Comments

Eugenio Perez Martin July 15, 2024, 9:01 p.m. UTC | #1 
On Mon, Jul 15, 2024 at 11:45 AM Zhao Liu <zhao1.liu@intel.com> wrote:
>
> As the comment in qapi/error, dereferencing @errp requires
> ERRP_GUARD():
>
> * = Why, when and how to use ERRP_GUARD() =
> *
> * Without ERRP_GUARD(), use of the @errp parameter is restricted:
> * - It must not be dereferenced, because it may be null.
> ...
> * ERRP_GUARD() lifts these restrictions.
> *
> * To use ERRP_GUARD(), add it right at the beginning of the function.
> * @errp can then be used without worrying about the argument being
> * NULL or &error_fatal.
> *
> * Using it when it's not needed is safe, but please avoid cluttering
> * the source with useless code.
>
> Though vhost_vdpa_device_realize() is called at DeviceClass.realize()
> context and won't get NULL @errp, it's still better to follow the
> requirement to add the ERRP_GUARD().
>
> But qemu_open() and vhost_vdpa_device_get_u32()'s return values can
> distinguish between successful and unsuccessful calls, so check the
> return values directly without dereferencing @errp, which eliminates
> the need of ERRP_GUARD().
>
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Cc: "Eugenio Pérez" <eperezma@redhat.com>
> Cc: Jason Wang <jasowang@redhat.com>
> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> ---
>  hw/virtio/vdpa-dev.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/hw/virtio/vdpa-dev.c b/hw/virtio/vdpa-dev.c
> index 64b96b226c39..7b439efdc1d3 100644
> --- a/hw/virtio/vdpa-dev.c
> +++ b/hw/virtio/vdpa-dev.c
> @@ -50,6 +50,7 @@ vhost_vdpa_device_get_u32(int fd, unsigned long int cmd, Error **errp)
>
>  static void vhost_vdpa_device_realize(DeviceState *dev, Error **errp)
>  {
> +    ERRP_GUARD();

Good catch, thank you! But removing the err dereferencing eliminates
the need for ERRP_GUARD(), doesn't it?

Thanks!

>      VirtIODevice *vdev = VIRTIO_DEVICE(dev);
>      VhostVdpaDevice *v = VHOST_VDPA_DEVICE(vdev);
>      struct vhost_vdpa_iova_range iova_range;
> @@ -63,19 +64,19 @@ static void vhost_vdpa_device_realize(DeviceState *dev, Error **errp)
>      }
>
>      v->vhostfd = qemu_open(v->vhostdev, O_RDWR, errp);
> -    if (*errp) {
> +    if (v->vhostfd < 0) {
>          return;
>      }
>
>      v->vdev_id = vhost_vdpa_device_get_u32(v->vhostfd,
>                                             VHOST_VDPA_GET_DEVICE_ID, errp);
> -    if (*errp) {
> +    if (v->vdev_id < 0) {
>          goto out;
>      }
>
>      max_queue_size = vhost_vdpa_device_get_u32(v->vhostfd,
>                                                 VHOST_VDPA_GET_VRING_NUM, errp);
> -    if (*errp) {
> +    if (max_queue_size < 0) {
>          goto out;
>      }
>
> @@ -89,7 +90,7 @@ static void vhost_vdpa_device_realize(DeviceState *dev, Error **errp)
>
>      v->num_queues = vhost_vdpa_device_get_u32(v->vhostfd,
>                                                VHOST_VDPA_GET_VQS_COUNT, errp);
> -    if (*errp) {
> +    if (v->num_queues < 0) {
>          goto out;
>      }
>
> @@ -127,7 +128,7 @@ static void vhost_vdpa_device_realize(DeviceState *dev, Error **errp)
>      v->config_size = vhost_vdpa_device_get_u32(v->vhostfd,
>                                                 VHOST_VDPA_GET_CONFIG_SIZE,
>                                                 errp);
> -    if (*errp) {
> +    if (v->config_size < 0) {
>          goto vhost_cleanup;
>      }
>
> --
> 2.34.1
>
Zhao Liu July 16, 2024, 3:21 a.m. UTC | #2 
On Mon, Jul 15, 2024 at 11:01:08PM +0200, Eugenio Perez Martin wrote:
> Date: Mon, 15 Jul 2024 23:01:08 +0200
> From: Eugenio Perez Martin <eperezma@redhat.com>
> Subject: Re: [PATCH] hw/virtio/vdpa-dev: Check returned value instead of
>  dereferencing @errp
> 
> On Mon, Jul 15, 2024 at 11:45 AM Zhao Liu <zhao1.liu@intel.com> wrote:
> >
> > As the comment in qapi/error, dereferencing @errp requires
> > ERRP_GUARD():
> >
> > * = Why, when and how to use ERRP_GUARD() =
> > *
> > * Without ERRP_GUARD(), use of the @errp parameter is restricted:
> > * - It must not be dereferenced, because it may be null.
> > ...
> > * ERRP_GUARD() lifts these restrictions.
> > *
> > * To use ERRP_GUARD(), add it right at the beginning of the function.
> > * @errp can then be used without worrying about the argument being
> > * NULL or &error_fatal.
> > *
> > * Using it when it's not needed is safe, but please avoid cluttering
> > * the source with useless code.
> >
> > Though vhost_vdpa_device_realize() is called at DeviceClass.realize()
> > context and won't get NULL @errp, it's still better to follow the
> > requirement to add the ERRP_GUARD().
> >
> > But qemu_open() and vhost_vdpa_device_get_u32()'s return values can
> > distinguish between successful and unsuccessful calls, so check the
> > return values directly without dereferencing @errp, which eliminates
> > the need of ERRP_GUARD().
> >
> > Cc: "Michael S. Tsirkin" <mst@redhat.com>
> > Cc: "Eugenio Pérez" <eperezma@redhat.com>
> > Cc: Jason Wang <jasowang@redhat.com>
> > Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> > ---
> >  hw/virtio/vdpa-dev.c | 11 ++++++-----
> >  1 file changed, 6 insertions(+), 5 deletions(-)
> >
> > diff --git a/hw/virtio/vdpa-dev.c b/hw/virtio/vdpa-dev.c
> > index 64b96b226c39..7b439efdc1d3 100644
> > --- a/hw/virtio/vdpa-dev.c
> > +++ b/hw/virtio/vdpa-dev.c
> > @@ -50,6 +50,7 @@ vhost_vdpa_device_get_u32(int fd, unsigned long int cmd, Error **errp)
> >
> >  static void vhost_vdpa_device_realize(DeviceState *dev, Error **errp)
> >  {
> > +    ERRP_GUARD();
> 
> Good catch, thank you! But removing the err dereferencing eliminates
> the need for ERRP_GUARD(), doesn't it?
>

Thanks Eugenio! You're right and I forgot to delete it. I'll post a new
version.
Eugenio Perez Martin July 16, 2024, 4:02 p.m. UTC | #3 
On Tue, Jul 16, 2024 at 5:05 AM Zhao Liu <zhao1.liu@intel.com> wrote:
>
> On Mon, Jul 15, 2024 at 11:01:08PM +0200, Eugenio Perez Martin wrote:
> > Date: Mon, 15 Jul 2024 23:01:08 +0200
> > From: Eugenio Perez Martin <eperezma@redhat.com>
> > Subject: Re: [PATCH] hw/virtio/vdpa-dev: Check returned value instead of
> >  dereferencing @errp
> >
> > On Mon, Jul 15, 2024 at 11:45 AM Zhao Liu <zhao1.liu@intel.com> wrote:
> > >
> > > As the comment in qapi/error, dereferencing @errp requires
> > > ERRP_GUARD():
> > >
> > > * = Why, when and how to use ERRP_GUARD() =
> > > *
> > > * Without ERRP_GUARD(), use of the @errp parameter is restricted:
> > > * - It must not be dereferenced, because it may be null.
> > > ...
> > > * ERRP_GUARD() lifts these restrictions.
> > > *
> > > * To use ERRP_GUARD(), add it right at the beginning of the function.
> > > * @errp can then be used without worrying about the argument being
> > > * NULL or &error_fatal.
> > > *
> > > * Using it when it's not needed is safe, but please avoid cluttering
> > > * the source with useless code.
> > >
> > > Though vhost_vdpa_device_realize() is called at DeviceClass.realize()
> > > context and won't get NULL @errp, it's still better to follow the
> > > requirement to add the ERRP_GUARD().
> > >
> > > But qemu_open() and vhost_vdpa_device_get_u32()'s return values can
> > > distinguish between successful and unsuccessful calls, so check the
> > > return values directly without dereferencing @errp, which eliminates
> > > the need of ERRP_GUARD().
> > >
> > > Cc: "Michael S. Tsirkin" <mst@redhat.com>
> > > Cc: "Eugenio Pérez" <eperezma@redhat.com>
> > > Cc: Jason Wang <jasowang@redhat.com>
> > > Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> > > ---
> > >  hw/virtio/vdpa-dev.c | 11 ++++++-----
> > >  1 file changed, 6 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/hw/virtio/vdpa-dev.c b/hw/virtio/vdpa-dev.c
> > > index 64b96b226c39..7b439efdc1d3 100644
> > > --- a/hw/virtio/vdpa-dev.c
> > > +++ b/hw/virtio/vdpa-dev.c
> > > @@ -50,6 +50,7 @@ vhost_vdpa_device_get_u32(int fd, unsigned long int cmd, Error **errp)
> > >
> > >  static void vhost_vdpa_device_realize(DeviceState *dev, Error **errp)
> > >  {
> > > +    ERRP_GUARD();
> >
> > Good catch, thank you! But removing the err dereferencing eliminates
> > the need for ERRP_GUARD(), doesn't it?
> >
>
> Thanks Eugenio! You're right and I forgot to delete it. I'll post a new
> version.
>
>

Good! With that removed,

Acked-by: Eugenio Pérez <eperezma@redhat.com>

Thanks!
diff mbox series

Patch

diff --git a/hw/virtio/vdpa-dev.c b/hw/virtio/vdpa-dev.c
index 64b96b226c39..7b439efdc1d3 100644
--- a/hw/virtio/vdpa-dev.c
+++ b/hw/virtio/vdpa-dev.c
@@ -50,6 +50,7 @@  vhost_vdpa_device_get_u32(int fd, unsigned long int cmd, Error **errp)
 
 static void vhost_vdpa_device_realize(DeviceState *dev, Error **errp)
 {
+    ERRP_GUARD();
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
     VhostVdpaDevice *v = VHOST_VDPA_DEVICE(vdev);
     struct vhost_vdpa_iova_range iova_range;
@@ -63,19 +64,19 @@  static void vhost_vdpa_device_realize(DeviceState *dev, Error **errp)
     }
 
     v->vhostfd = qemu_open(v->vhostdev, O_RDWR, errp);
-    if (*errp) {
+    if (v->vhostfd < 0) {
         return;
     }
 
     v->vdev_id = vhost_vdpa_device_get_u32(v->vhostfd,
                                            VHOST_VDPA_GET_DEVICE_ID, errp);
-    if (*errp) {
+    if (v->vdev_id < 0) {
         goto out;
     }
 
     max_queue_size = vhost_vdpa_device_get_u32(v->vhostfd,
                                                VHOST_VDPA_GET_VRING_NUM, errp);
-    if (*errp) {
+    if (max_queue_size < 0) {
         goto out;
     }
 
@@ -89,7 +90,7 @@  static void vhost_vdpa_device_realize(DeviceState *dev, Error **errp)
 
     v->num_queues = vhost_vdpa_device_get_u32(v->vhostfd,
                                               VHOST_VDPA_GET_VQS_COUNT, errp);
-    if (*errp) {
+    if (v->num_queues < 0) {
         goto out;
     }
 
@@ -127,7 +128,7 @@  static void vhost_vdpa_device_realize(DeviceState *dev, Error **errp)
     v->config_size = vhost_vdpa_device_get_u32(v->vhostfd,
                                                VHOST_VDPA_GET_CONFIG_SIZE,
                                                errp);
-    if (*errp) {
+    if (v->config_size < 0) {
         goto vhost_cleanup;
     }