On 07/16/2015 02:42 PM, Michael S. Tsirkin wrote: > On Wed, Jul 15, 2015 at 03:56:07PM +0800, Jason Wang wrote: >> Commit 032a74a1c0fcdd5fd1c69e56126b4c857ee36611 >> ("virtio-net: byteswap virtio-net header") breaks any layout by >> requiring out_sg[0].iov_len >= n->guest_hdr_len. Fixing this by >> copying header to temporary buffer if swap is needed, and then use >> this buffer as part of out_sg. >> >> Fixes 032a74a1c0fcdd5fd1c69e56126b4c857ee36611 >> ("virtio-net: byteswap virtio-net header") >> Cc: qemu-sta...@nongnu.org >> Cc: c...@fr.ibm.com >> Signed-off-by: Jason Wang <jasow...@redhat.com> >> --- >> Changes from V1: >> - avoid header copying if there's no need to do header swap >> - don't write the header back >> --- >> hw/net/virtio-net.c | 17 ++++++++++++++--- >> include/hw/virtio/virtio-access.h | 9 +++++++++ >> 2 files changed, 23 insertions(+), 3 deletions(-) >> >> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c >> index e3c2db3..12322bd 100644 >> --- a/hw/net/virtio-net.c >> +++ b/hw/net/virtio-net.c >> @@ -1142,7 +1142,8 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q) >> ssize_t ret, len; >> unsigned int out_num = elem.out_num; >> struct iovec *out_sg = &elem.out_sg[0]; >> - struct iovec sg[VIRTQUEUE_MAX_SIZE]; >> + struct iovec sg[VIRTQUEUE_MAX_SIZE], sg2[VIRTQUEUE_MAX_SIZE]; >> + struct virtio_net_hdr hdr; >> >> if (out_num < 1) { >> error_report("virtio-net header not in first element"); >> @@ -1150,11 +1151,21 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q) >> } >> >> if (n->has_vnet_hdr) { >> - if (out_sg[0].iov_len < n->guest_hdr_len) { >> + if (iov_size(out_sg, out_num) < n->guest_hdr_len) { >> error_report("virtio-net header incorrect"); >> exit(1); >> } > this scans the iov unnecessarily. How about checking return > code from iov_to_buf instead?
Looks ok since hdr is very short anyway. > >> - virtio_net_hdr_swap(vdev, (void *) out_sg[0].iov_base); >> + if (virtio_needs_swap(vdev)) { >> + iov_to_buf(out_sg, out_num, 0, &hdr, sizeof(hdr)); >> + virtio_net_hdr_swap(vdev, (void *) &hdr); >> + sg2[0].iov_base = &hdr; >> + sg2[0].iov_len = sizeof(hdr); >> + out_num = iov_copy(&sg2[1], ARRAY_SIZE(sg2) - 1, >> + out_sg, out_num, >> + sizeof(hdr), -1); > > This might truncate packet if it does not fit in 1024 anymore. > It might be better to just drop it. Ok, will do this in V3. > >> + out_num += 1; >> + out_sg = sg2; >> + } >> } >> >> /* >> diff --git a/include/hw/virtio/virtio-access.h >> b/include/hw/virtio/virtio-access.h >> index cee5dd7..1ec1dfd 100644 >> --- a/include/hw/virtio/virtio-access.h >> +++ b/include/hw/virtio/virtio-access.h >> @@ -143,6 +143,15 @@ static inline uint64_t virtio_ldq_p(VirtIODevice *vdev, >> const void *ptr) >> } >> } >> >> +static inline bool virtio_needs_swap(VirtIODevice *vdev) >> +{ >> +#ifdef HOST_WORDS_BIGENDIAN >> + return virtio_access_is_big_endian(vdev) ? false : true; >> +#else >> + return virtio_access_is_big_endian(vdev) ? true : false; >> +#endif >> +} >> + >> static inline uint16_t virtio_tswap16(VirtIODevice *vdev, uint16_t s) >> { >> #ifdef HOST_WORDS_BIGENDIAN >> -- >> 2.1.4