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Violators will be prosecuted for from ; Fri, 13 Nov 2015 08:26:34 -0000 Date: Fri, 13 Nov 2015 09:26:26 +0100 From: Greg Kurz Message-ID: <20151113092626.4ef6a434@bahia.local> In-Reply-To: <20151112185255.1bd6197b.cornelia.huck@de.ibm.com> References: <20151109172840.3075.48900.stgit@bahia.huguette.org> <20151109174021.3075.94401.stgit@bahia.huguette.org> <20151112185255.1bd6197b.cornelia.huck@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v2 1/2] virtio-net: use the backend cross-endian capabilities List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Cornelia Huck Cc: qemu-devel@nongnu.org, "Michael S. Tsirkin" On Thu, 12 Nov 2015 18:52:55 +0100 Cornelia Huck wrote: > On Mon, 09 Nov 2015 18:41:33 +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. If the backend cannot support the > > requested endiannes, we have to fall back on virtio_net_hdr_swap(): this > > is recorded in the needs_vnet_hdr_swap flag. > > > > The current vhost-net code also tries to configure net backends. This will > > be no more needed and will be addressed in a subsequent patch. > > > > Signed-off-by: Greg Kurz > > --- > > v2: - introduced virtio_net_needs_hdr_swap() to consolidate the logic in one > > place > > --- > > hw/net/virtio-net.c | 43 ++++++++++++++++++++++++++++++++++++++-- > > include/hw/virtio/virtio-net.h | 1 + > > 2 files changed, 42 insertions(+), 2 deletions(-) > > > > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c > > index a877614e3e7a..a10f7a0b4d28 100644 > > --- a/hw/net/virtio-net.c > > +++ b/hw/net/virtio-net.c > > @@ -152,6 +152,33 @@ static void virtio_net_vhost_status(VirtIONet *n, uint8_t status) > > } > > } > > > > +static int peer_has_vnet_hdr(VirtIONet *n); > > Hm, you do not seem to use this? > Oops I needed that in a earlier version of this patch and forgot to remove it... > > + > > +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; > > + > > + 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) && > > + !virtio_net_started(n, status)) { > > + 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 +186,7 @@ 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++) { > > @@ -949,6 +977,14 @@ static void work_around_broken_dhclient(struct virtio_net_hdr *hdr, > > } > > } > > > > +static bool virtio_net_needs_hdr_swap(VirtIONet *n) > > +{ > > + /* virtio_needs_swap() is constant for fixed endian targets: call it > > + * first to filter them out without penalty. > > What do you mean with 'constant' here? It still needs to retrieve the > feature bit from the device, no? > Yes the comment is inaccurate... With the "virtio: cross-endian helpers fixes" series, virtio_needs_swap() indeed resolves to { return 0; } for fixed little endian targets but we still need to check the feature bit when the target is big endian. If I drop the call to virtio_needs_swap(), all targets will have the same penalty. If I keep it, fixed little endian targets have no penalty but fixed big endian targets get an extra check and bi-endian targets get two extra checks... Not sure what to decide... > > + */ > > + return virtio_needs_swap(VIRTIO_DEVICE(n)) && n->needs_vnet_hdr_swap; > > +} > > + > > static void receive_header(VirtIONet *n, const struct iovec *iov, int iov_cnt, > > const void *buf, size_t size) > > { > > @@ -957,7 +993,10 @@ 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 (virtio_net_needs_hdr_swap(n)) { > > + 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 +1206,7 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q) > > error_report("virtio-net header incorrect"); > > exit(1); > > } > > - if (virtio_needs_swap(vdev)) { > > + if (virtio_net_needs_hdr_swap(n)) { > > virtio_net_hdr_swap(vdev, (void *) &mhdr); > > sg2[0].iov_base = &mhdr; > > sg2[0].iov_len = n->guest_hdr_len; > > diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h > > index f3cc25feca2b..27bc868fbc7d 100644 > > --- a/include/hw/virtio/virtio-net.h > > +++ b/include/hw/virtio/virtio-net.h > > @@ -94,6 +94,7 @@ typedef struct VirtIONet { > > uint64_t curr_guest_offloads; > > QEMUTimer *announce_timer; > > int announce_counter; > > + bool needs_vnet_hdr_swap; > > } VirtIONet; > > > > void virtio_net_set_netclient_name(VirtIONet *n, const char *name, > > > > >