Re: [Qemu-devel] [PATCH v2 1/5] virtio-net: use the backend cross-endian capabilities
On Wed, 13 Jan 2016 10:53:11 +0100
Laurent Vivier wrote:
> On 13/01/2016 10:06, Greg Kurz wrote:
> > On Tue, 12 Jan 2016 18:24:28 +0100
> > Laurent Vivier wrote:
> >
> >> On 11/01/2016 17:12, Greg Kurz wrote:
> >>> When running a fully emulated device in cross-endian conditions, including
> >>> a virtio 1.0 device offered to a big endian guest, we need to fix the vnet
> >>> headers. This is currently handled by the virtio_net_hdr_swap() function
> >>> in the core virtio-net code but it should actually be handled by the net
> >>> backend.
> >>>
> >>> With this patch, virtio-net now tries to configure the backend to do the
> >>> endian fixing when the device starts (i.e. drivers sets the CONFIG_OK
> >>> bit).
> >>> If the backend cannot support the requested endiannes, we have to fallback
> >>> onto virtio_net_hdr_swap(): this is recorded in the needs_vnet_hdr_swap
> >>> flag,
> >>> to be used in the TX and RX paths.
> >>>
> >>> Note that we reset the backend to the default behaviour (guest native
> >>> endianness) when the device stops (i.e. device status had CONFIG_OK bit
> >>> and
> >>> driver unsets it). This is needed, with the linux tap backend at least,
> >>> otherwise the guest may loose network connectivity if rebooted into a
> >>> different endianness.
> >>>
> >>> The current vhost-net code also tries to configure net backends. This will
> >>> be no more needed and will be reverted in a subsequent patch.
> >>>
> >>> Signed-off-by: Greg Kurz
> >>> ---
> >>> v2:
> >>> - dropped useless check in the 'else if' branch in
> >>> virtio_net_vnet_status()
> >>> - merged virtio_net_vhost_status() change from patch 2
> >>> - use semicolon in "backend does no support..." error message
> >>> - merged patch 3 (drop the virtio_needs_swap() helper)
> >>> - provided some more details in changelog and comments
> >>> ---
> >>> hw/net/virtio-net.c | 49
> >>> +++--
> >>> include/hw/virtio/virtio-access.h |9 ---
> >>> include/hw/virtio/virtio-net.h|1 +
> >>> 3 files changed, 48 insertions(+), 11 deletions(-)
> >>>
> >>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> >>> index a877614e3e7a..497fb7119a08 100644
> >>> --- a/hw/net/virtio-net.c
> >>> +++ b/hw/net/virtio-net.c
> >>> @@ -128,6 +128,13 @@ static void virtio_net_vhost_status(VirtIONet *n,
> >>> uint8_t status)
> >>> if (!n->vhost_started) {
> >>> int r, i;
> >>>
> >>> +if (n->needs_vnet_hdr_swap) {
> >>> +error_report("backend does not support %s vnet headers; "
> >>> + "falling back on userspace virtio",
> >>> + virtio_is_big_endian(vdev) ? "BE" : "LE");
> >>> +return;
> >>> +}
> >>> +
> >>> /* Any packets outstanding? Purge them to avoid touching rings
> >>> * when vhost is running.
> >>> */
> >>> @@ -152,6 +159,40 @@ static void virtio_net_vhost_status(VirtIONet *n,
> >>> uint8_t status)
> >>> }
> >>> }
> >>>
> >>> +static void virtio_net_vnet_status(VirtIONet *n, uint8_t status)
> >>> +{
> >>> +VirtIODevice *vdev = VIRTIO_DEVICE(n);
> >>> +NetClientState *peer = qemu_get_queue(n->nic)->peer;
> >>> +
> >>> +if (virtio_net_started(n, status)) {
> >>> +int r;
> >>> +
> >>> +/* Before using the device, we tell the network backend about the
> >>> + * endianness to use when parsing vnet headers. If the backend
> >>> can't
> >>> + * do it, we fallback onto fixing the headers in the core
> >>> virtio-net
> >>> + * code.
> >>> + */
> >>> +if (virtio_is_big_endian(vdev)) {
> >>> +r = qemu_set_vnet_be(peer, true);
> >>> +} else {
> >>> +r = qemu_set_vnet_le(peer, true);
> >>> +}
> >>
> >> If endianess of the guest and the virtio device is the same, but r is <
> >> 0 (-ENOSYS or -EINVAL) you will badly swap header (and disable vhost).
> >>
> >
> > This can only happen if the endianness of the host is not the same as the
>
> OK, you're right, I was studying sources without commit:
>
> 052bd52 net: don't set native endianness
>
> Sorry for the noise...
>
No problem. Thank you again for your time !
> > endianness of the device. In this case (we usually call cross-endian) the
> > vnet headers must be byteswapped but the backend cannot handle it. This
> > has two consequences:
> > - vhost cannot be used since it requires the backend to support cross-endian
> > vnet headers, so we fallback onto full emulation in QEMU
> > - the emulation code must byteswap vnet headers
> >
> >> I think you need something like this to fall back to the old method:
> >>
> >> if (r < 0) {
> >> #ifdef HOST_WORDS_BIGENDIAN
> >> r = virtio_access_is_big_endian(vdev) ? false : true;
> >> #else
> >> r = virtio_access_is_big_endian(vdev) ? true : false;
> >> #endif
> >> }
> >>
> >>
> >> But...
> >>
> >
Re: [Qemu-devel] [PATCH v2 1/5] virtio-net: use the backend cross-endian capabilities
On 13/01/2016 10:06, Greg Kurz wrote:
> On Tue, 12 Jan 2016 18:24:28 +0100
> Laurent Vivier wrote:
>
>> On 11/01/2016 17:12, Greg Kurz wrote:
>>> When running a fully emulated device in cross-endian conditions, including
>>> a virtio 1.0 device offered to a big endian guest, we need to fix the vnet
>>> headers. This is currently handled by the virtio_net_hdr_swap() function
>>> in the core virtio-net code but it should actually be handled by the net
>>> backend.
>>>
>>> With this patch, virtio-net now tries to configure the backend to do the
>>> endian fixing when the device starts (i.e. drivers sets the CONFIG_OK bit).
>>> If the backend cannot support the requested endiannes, we have to fallback
>>> onto virtio_net_hdr_swap(): this is recorded in the needs_vnet_hdr_swap
>>> flag,
>>> to be used in the TX and RX paths.
>>>
>>> Note that we reset the backend to the default behaviour (guest native
>>> endianness) when the device stops (i.e. device status had CONFIG_OK bit and
>>> driver unsets it). This is needed, with the linux tap backend at least,
>>> otherwise the guest may loose network connectivity if rebooted into a
>>> different endianness.
>>>
>>> The current vhost-net code also tries to configure net backends. This will
>>> be no more needed and will be reverted in a subsequent patch.
>>>
>>> Signed-off-by: Greg Kurz
>>> ---
>>> v2:
>>> - dropped useless check in the 'else if' branch in virtio_net_vnet_status()
>>> - merged virtio_net_vhost_status() change from patch 2
>>> - use semicolon in "backend does no support..." error message
>>> - merged patch 3 (drop the virtio_needs_swap() helper)
>>> - provided some more details in changelog and comments
>>> ---
>>> hw/net/virtio-net.c | 49
>>> +++--
>>> include/hw/virtio/virtio-access.h |9 ---
>>> include/hw/virtio/virtio-net.h|1 +
>>> 3 files changed, 48 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
>>> index a877614e3e7a..497fb7119a08 100644
>>> --- a/hw/net/virtio-net.c
>>> +++ b/hw/net/virtio-net.c
>>> @@ -128,6 +128,13 @@ static void virtio_net_vhost_status(VirtIONet *n,
>>> uint8_t status)
>>> if (!n->vhost_started) {
>>> int r, i;
>>>
>>> +if (n->needs_vnet_hdr_swap) {
>>> +error_report("backend does not support %s vnet headers; "
>>> + "falling back on userspace virtio",
>>> + virtio_is_big_endian(vdev) ? "BE" : "LE");
>>> +return;
>>> +}
>>> +
>>> /* Any packets outstanding? Purge them to avoid touching rings
>>> * when vhost is running.
>>> */
>>> @@ -152,6 +159,40 @@ static void virtio_net_vhost_status(VirtIONet *n,
>>> uint8_t status)
>>> }
>>> }
>>>
>>> +static void virtio_net_vnet_status(VirtIONet *n, uint8_t status)
>>> +{
>>> +VirtIODevice *vdev = VIRTIO_DEVICE(n);
>>> +NetClientState *peer = qemu_get_queue(n->nic)->peer;
>>> +
>>> +if (virtio_net_started(n, status)) {
>>> +int r;
>>> +
>>> +/* Before using the device, we tell the network backend about the
>>> + * endianness to use when parsing vnet headers. If the backend
>>> can't
>>> + * do it, we fallback onto fixing the headers in the core
>>> virtio-net
>>> + * code.
>>> + */
>>> +if (virtio_is_big_endian(vdev)) {
>>> +r = qemu_set_vnet_be(peer, true);
>>> +} else {
>>> +r = qemu_set_vnet_le(peer, true);
>>> +}
>>
>> If endianess of the guest and the virtio device is the same, but r is <
>> 0 (-ENOSYS or -EINVAL) you will badly swap header (and disable vhost).
>>
>
> This can only happen if the endianness of the host is not the same as the
OK, you're right, I was studying sources without commit:
052bd52 net: don't set native endianness
Sorry for the noise...
> endianness of the device. In this case (we usually call cross-endian) the
> vnet headers must be byteswapped but the backend cannot handle it. This
> has two consequences:
> - vhost cannot be used since it requires the backend to support cross-endian
> vnet headers, so we fallback onto full emulation in QEMU
> - the emulation code must byteswap vnet headers
>
>> I think you need something like this to fall back to the old method:
>>
>> if (r < 0) {
>> #ifdef HOST_WORDS_BIGENDIAN
>> r = virtio_access_is_big_endian(vdev) ? false : true;
>> #else
>> r = virtio_access_is_big_endian(vdev) ? true : false;
>> #endif
>> }
>>
>>
>> But...
>>
>>> +n->needs_vnet_hdr_swap = !!r;
>>> +} else if (virtio_net_started(n, vdev->status)) {
>>> +/* After using the device, we need to reset the network backend to
>>> + * the default (guest native endianness), otherwise the guest may
>>> + * loose network connectivity if it is rebooted into a different
>>> + * endianness.
>>> +
Re: [Qemu-devel] [PATCH v2 1/5] virtio-net: use the backend cross-endian capabilities
On Tue, 12 Jan 2016 18:24:28 +0100
Laurent Vivier wrote:
> On 11/01/2016 17:12, Greg Kurz wrote:
> > When running a fully emulated device in cross-endian conditions, including
> > a virtio 1.0 device offered to a big endian guest, we need to fix the vnet
> > headers. This is currently handled by the virtio_net_hdr_swap() function
> > in the core virtio-net code but it should actually be handled by the net
> > backend.
> >
> > With this patch, virtio-net now tries to configure the backend to do the
> > endian fixing when the device starts (i.e. drivers sets the CONFIG_OK bit).
> > If the backend cannot support the requested endiannes, we have to fallback
> > onto virtio_net_hdr_swap(): this is recorded in the needs_vnet_hdr_swap
> > flag,
> > to be used in the TX and RX paths.
> >
> > Note that we reset the backend to the default behaviour (guest native
> > endianness) when the device stops (i.e. device status had CONFIG_OK bit and
> > driver unsets it). This is needed, with the linux tap backend at least,
> > otherwise the guest may loose network connectivity if rebooted into a
> > different endianness.
> >
> > The current vhost-net code also tries to configure net backends. This will
> > be no more needed and will be reverted in a subsequent patch.
> >
> > Signed-off-by: Greg Kurz
> > ---
> > v2:
> > - dropped useless check in the 'else if' branch in virtio_net_vnet_status()
> > - merged virtio_net_vhost_status() change from patch 2
> > - use semicolon in "backend does no support..." error message
> > - merged patch 3 (drop the virtio_needs_swap() helper)
> > - provided some more details in changelog and comments
> > ---
> > hw/net/virtio-net.c | 49
> > +++--
> > include/hw/virtio/virtio-access.h |9 ---
> > include/hw/virtio/virtio-net.h|1 +
> > 3 files changed, 48 insertions(+), 11 deletions(-)
> >
> > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> > index a877614e3e7a..497fb7119a08 100644
> > --- a/hw/net/virtio-net.c
> > +++ b/hw/net/virtio-net.c
> > @@ -128,6 +128,13 @@ static void virtio_net_vhost_status(VirtIONet *n,
> > uint8_t status)
> > if (!n->vhost_started) {
> > int r, i;
> >
> > +if (n->needs_vnet_hdr_swap) {
> > +error_report("backend does not support %s vnet headers; "
> > + "falling back on userspace virtio",
> > + virtio_is_big_endian(vdev) ? "BE" : "LE");
> > +return;
> > +}
> > +
> > /* Any packets outstanding? Purge them to avoid touching rings
> > * when vhost is running.
> > */
> > @@ -152,6 +159,40 @@ static void virtio_net_vhost_status(VirtIONet *n,
> > uint8_t status)
> > }
> > }
> >
> > +static void virtio_net_vnet_status(VirtIONet *n, uint8_t status)
> > +{
> > +VirtIODevice *vdev = VIRTIO_DEVICE(n);
> > +NetClientState *peer = qemu_get_queue(n->nic)->peer;
> > +
> > +if (virtio_net_started(n, status)) {
> > +int r;
> > +
> > +/* Before using the device, we tell the network backend about the
> > + * endianness to use when parsing vnet headers. If the backend
> > can't
> > + * do it, we fallback onto fixing the headers in the core
> > virtio-net
> > + * code.
> > + */
> > +if (virtio_is_big_endian(vdev)) {
> > +r = qemu_set_vnet_be(peer, true);
> > +} else {
> > +r = qemu_set_vnet_le(peer, true);
> > +}
>
> If endianess of the guest and the virtio device is the same, but r is <
> 0 (-ENOSYS or -EINVAL) you will badly swap header (and disable vhost).
>
This can only happen if the endianness of the host is not the same as the
endianness of the device. In this case (we usually call cross-endian) the
vnet headers must be byteswapped but the backend cannot handle it. This
has two consequences:
- vhost cannot be used since it requires the backend to support cross-endian
vnet headers, so we fallback onto full emulation in QEMU
- the emulation code must byteswap vnet headers
> I think you need something like this to fall back to the old method:
>
> if (r < 0) {
> #ifdef HOST_WORDS_BIGENDIAN
> r = virtio_access_is_big_endian(vdev) ? false : true;
> #else
> r = virtio_access_is_big_endian(vdev) ? true : false;
> #endif
> }
>
>
> But...
>
> > +n->needs_vnet_hdr_swap = !!r;
> > +} else if (virtio_net_started(n, vdev->status)) {
> > +/* After using the device, we need to reset the network backend to
> > + * the default (guest native endianness), otherwise the guest may
> > + * loose network connectivity if it is rebooted into a different
> > + * endianness.
> > + */
> > +if (virtio_is_big_endian(vdev)) {
> > +qemu_set_vnet_be(peer, false);
> > +} else {
> > +qemu_set_vnet_le(peer, false);
> > +}
> > +}
>
Re: [Qemu-devel] [PATCH v2 1/5] virtio-net: use the backend cross-endian capabilities
On 11/01/2016 17:12, Greg Kurz wrote:
> When running a fully emulated device in cross-endian conditions, including
> a virtio 1.0 device offered to a big endian guest, we need to fix the vnet
> headers. This is currently handled by the virtio_net_hdr_swap() function
> in the core virtio-net code but it should actually be handled by the net
> backend.
>
> With this patch, virtio-net now tries to configure the backend to do the
> endian fixing when the device starts (i.e. drivers sets the CONFIG_OK bit).
> If the backend cannot support the requested endiannes, we have to fallback
> onto virtio_net_hdr_swap(): this is recorded in the needs_vnet_hdr_swap flag,
> to be used in the TX and RX paths.
>
> Note that we reset the backend to the default behaviour (guest native
> endianness) when the device stops (i.e. device status had CONFIG_OK bit and
> driver unsets it). This is needed, with the linux tap backend at least,
> otherwise the guest may loose network connectivity if rebooted into a
> different endianness.
>
> The current vhost-net code also tries to configure net backends. This will
> be no more needed and will be reverted in a subsequent patch.
>
> Signed-off-by: Greg Kurz
> ---
> v2:
> - dropped useless check in the 'else if' branch in virtio_net_vnet_status()
> - merged virtio_net_vhost_status() change from patch 2
> - use semicolon in "backend does no support..." error message
> - merged patch 3 (drop the virtio_needs_swap() helper)
> - provided some more details in changelog and comments
> ---
> hw/net/virtio-net.c | 49
> +++--
> include/hw/virtio/virtio-access.h |9 ---
> include/hw/virtio/virtio-net.h|1 +
> 3 files changed, 48 insertions(+), 11 deletions(-)
>
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index a877614e3e7a..497fb7119a08 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -128,6 +128,13 @@ static void virtio_net_vhost_status(VirtIONet *n,
> uint8_t status)
> if (!n->vhost_started) {
> int r, i;
>
> +if (n->needs_vnet_hdr_swap) {
> +error_report("backend does not support %s vnet headers; "
> + "falling back on userspace virtio",
> + virtio_is_big_endian(vdev) ? "BE" : "LE");
> +return;
> +}
> +
> /* Any packets outstanding? Purge them to avoid touching rings
> * when vhost is running.
> */
> @@ -152,6 +159,40 @@ static void virtio_net_vhost_status(VirtIONet *n,
> uint8_t status)
> }
> }
>
> +static void virtio_net_vnet_status(VirtIONet *n, uint8_t status)
> +{
> +VirtIODevice *vdev = VIRTIO_DEVICE(n);
> +NetClientState *peer = qemu_get_queue(n->nic)->peer;
> +
> +if (virtio_net_started(n, status)) {
> +int r;
> +
> +/* Before using the device, we tell the network backend about the
> + * endianness to use when parsing vnet headers. If the backend can't
> + * do it, we fallback onto fixing the headers in the core virtio-net
> + * code.
> + */
> +if (virtio_is_big_endian(vdev)) {
> +r = qemu_set_vnet_be(peer, true);
> +} else {
> +r = qemu_set_vnet_le(peer, true);
> +}
If endianess of the guest and the virtio device is the same, but r is <
0 (-ENOSYS or -EINVAL) you will badly swap header (and disable vhost).
I think you need something like this to fall back to the old method:
if (r < 0) {
#ifdef HOST_WORDS_BIGENDIAN
r = virtio_access_is_big_endian(vdev) ? false : true;
#else
r = virtio_access_is_big_endian(vdev) ? true : false;
#endif
}
But...
> +n->needs_vnet_hdr_swap = !!r;
> +} else if (virtio_net_started(n, vdev->status)) {
> +/* After using the device, we need to reset the network backend to
> + * the default (guest native endianness), otherwise the guest may
> + * loose network connectivity if it is rebooted into a different
> + * endianness.
> + */
> +if (virtio_is_big_endian(vdev)) {
> +qemu_set_vnet_be(peer, false);
> +} else {
> +qemu_set_vnet_le(peer, false);
> +}
> +}
> +}
> +
> static void virtio_net_set_status(struct VirtIODevice *vdev, uint8_t status)
> {
> VirtIONet *n = VIRTIO_NET(vdev);
> @@ -159,6 +200,7 @@ static void virtio_net_set_status(struct VirtIODevice
> *vdev, uint8_t status)
> int i;
> uint8_t queue_status;
>
> +virtio_net_vnet_status(n, status);
> virtio_net_vhost_status(n, status);
>
> for (i = 0; i < n->max_queues; i++) {
> @@ -957,7 +999,10 @@ static void receive_header(VirtIONet *n, const struct
> iovec *iov, int iov_cnt,
> void *wbuf = (void *)buf;
> work_around_broken_dhclient(wbuf, wbuf + n->host_hdr_len,
> size - n->host_hdr_len);
> -virtio_net_hdr_swa
Re: [Qemu-devel] [PATCH v2 1/5] virtio-net: use the backend cross-endian capabilities
On 11/01/2016 17:12, Greg Kurz wrote:
> When running a fully emulated device in cross-endian conditions, including
> a virtio 1.0 device offered to a big endian guest, we need to fix the vnet
> headers. This is currently handled by the virtio_net_hdr_swap() function
> in the core virtio-net code but it should actually be handled by the net
> backend.
>
> With this patch, virtio-net now tries to configure the backend to do the
> endian fixing when the device starts (i.e. drivers sets the CONFIG_OK bit).
> If the backend cannot support the requested endiannes, we have to fallback
> onto virtio_net_hdr_swap(): this is recorded in the needs_vnet_hdr_swap flag,
> to be used in the TX and RX paths.
>
> Note that we reset the backend to the default behaviour (guest native
> endianness) when the device stops (i.e. device status had CONFIG_OK bit and
> driver unsets it). This is needed, with the linux tap backend at least,
> otherwise the guest may loose network connectivity if rebooted into a
> different endianness.
>
> The current vhost-net code also tries to configure net backends. This will
> be no more needed and will be reverted in a subsequent patch.
>
> Signed-off-by: Greg Kurz
> ---
> v2:
> - dropped useless check in the 'else if' branch in virtio_net_vnet_status()
> - merged virtio_net_vhost_status() change from patch 2
> - use semicolon in "backend does no support..." error message
> - merged patch 3 (drop the virtio_needs_swap() helper)
> - provided some more details in changelog and comments
> ---
> hw/net/virtio-net.c | 49
> +++--
> include/hw/virtio/virtio-access.h |9 ---
> include/hw/virtio/virtio-net.h|1 +
> 3 files changed, 48 insertions(+), 11 deletions(-)
>
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index a877614e3e7a..497fb7119a08 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -128,6 +128,13 @@ static void virtio_net_vhost_status(VirtIONet *n,
> uint8_t status)
> if (!n->vhost_started) {
> int r, i;
>
> +if (n->needs_vnet_hdr_swap) {
> +error_report("backend does not support %s vnet headers; "
> + "falling back on userspace virtio",
> + virtio_is_big_endian(vdev) ? "BE" : "LE");
> +return;
> +}
> +
> /* Any packets outstanding? Purge them to avoid touching rings
> * when vhost is running.
> */
> @@ -152,6 +159,40 @@ static void virtio_net_vhost_status(VirtIONet *n,
> uint8_t status)
> }
> }
>
> +static void virtio_net_vnet_status(VirtIONet *n, uint8_t status)
> +{
> +VirtIODevice *vdev = VIRTIO_DEVICE(n);
> +NetClientState *peer = qemu_get_queue(n->nic)->peer;
> +
> +if (virtio_net_started(n, status)) {
> +int r;
> +
> +/* Before using the device, we tell the network backend about the
> + * endianness to use when parsing vnet headers. If the backend can't
> + * do it, we fallback onto fixing the headers in the core virtio-net
> + * code.
> + */
> +if (virtio_is_big_endian(vdev)) {
> +r = qemu_set_vnet_be(peer, true);
> +} else {
> +r = qemu_set_vnet_le(peer, true);
> +}
> +
> +n->needs_vnet_hdr_swap = !!r;
> +} else if (virtio_net_started(n, vdev->status)) {
> +/* After using the device, we need to reset the network backend to
> + * the default (guest native endianness), otherwise the guest may
> + * loose network connectivity if it is rebooted into a different
> + * endianness.
> + */
> +if (virtio_is_big_endian(vdev)) {
> +qemu_set_vnet_be(peer, false);
> +} else {
> +qemu_set_vnet_le(peer, false);
> +}
> +}
> +}
> +
> static void virtio_net_set_status(struct VirtIODevice *vdev, uint8_t status)
> {
> VirtIONet *n = VIRTIO_NET(vdev);
> @@ -159,6 +200,7 @@ static void virtio_net_set_status(struct VirtIODevice
> *vdev, uint8_t status)
> int i;
> uint8_t queue_status;
>
> +virtio_net_vnet_status(n, status);
> virtio_net_vhost_status(n, status);
>
> for (i = 0; i < n->max_queues; i++) {
> @@ -957,7 +999,10 @@ static void receive_header(VirtIONet *n, const struct
> iovec *iov, int iov_cnt,
> void *wbuf = (void *)buf;
> work_around_broken_dhclient(wbuf, wbuf + n->host_hdr_len,
> size - n->host_hdr_len);
> -virtio_net_hdr_swap(VIRTIO_DEVICE(n), wbuf);
> +
> +if (n->needs_vnet_hdr_swap) {
> +virtio_net_hdr_swap(VIRTIO_DEVICE(n), wbuf);
> +}
> iov_from_buf(iov, iov_cnt, 0, buf, sizeof(struct virtio_net_hdr));
> } else {
> struct virtio_net_hdr hdr = {
> @@ -1167,7 +1212,7 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
> error_report("virtio-net header incorrect");
>
Re: [Qemu-devel] [PATCH v2 1/5] virtio-net: use the backend cross-endian capabilities
On Mon, 11 Jan 2016 17:12:21 +0100
Greg Kurz wrote:
> When running a fully emulated device in cross-endian conditions, including
> a virtio 1.0 device offered to a big endian guest, we need to fix the vnet
> headers. This is currently handled by the virtio_net_hdr_swap() function
> in the core virtio-net code but it should actually be handled by the net
> backend.
>
> With this patch, virtio-net now tries to configure the backend to do the
> endian fixing when the device starts (i.e. drivers sets the CONFIG_OK bit).
> If the backend cannot support the requested endiannes, we have to fallback
> onto virtio_net_hdr_swap(): this is recorded in the needs_vnet_hdr_swap flag,
> to be used in the TX and RX paths.
>
> Note that we reset the backend to the default behaviour (guest native
> endianness) when the device stops (i.e. device status had CONFIG_OK bit and
> driver unsets it). This is needed, with the linux tap backend at least,
> otherwise the guest may loose network connectivity if rebooted into a
s/loose/lose/
> different endianness.
>
> The current vhost-net code also tries to configure net backends. This will
> be no more needed and will be reverted in a subsequent patch.
>
> Signed-off-by: Greg Kurz
(...)
> +static void virtio_net_vnet_status(VirtIONet *n, uint8_t status)
> +{
> +VirtIODevice *vdev = VIRTIO_DEVICE(n);
> +NetClientState *peer = qemu_get_queue(n->nic)->peer;
> +
> +if (virtio_net_started(n, status)) {
> +int r;
> +
> +/* Before using the device, we tell the network backend about the
> + * endianness to use when parsing vnet headers. If the backend can't
> + * do it, we fallback onto fixing the headers in the core virtio-net
> + * code.
> + */
> +if (virtio_is_big_endian(vdev)) {
> +r = qemu_set_vnet_be(peer, true);
> +} else {
> +r = qemu_set_vnet_le(peer, true);
> +}
> +
> +n->needs_vnet_hdr_swap = !!r;
> +} else if (virtio_net_started(n, vdev->status)) {
> +/* After using the device, we need to reset the network backend to
> + * the default (guest native endianness), otherwise the guest may
> + * loose network connectivity if it is rebooted into a different
here again
> + * endianness.
> + */
> +if (virtio_is_big_endian(vdev)) {
> +qemu_set_vnet_be(peer, false);
> +} else {
> +qemu_set_vnet_le(peer, false);
> +}
> +}
> +}
> +
Reviewed-by: Cornelia Huck
