Commit e28fbd1c525d ("Revert "virtio-net: Copy received header to
buffer"") reverted commit 7987d2be5a8b, which attempted to remove the
need to patch the (const) input buffer.
Achieve the original goal by copying the header or the entire packet to
a writable buffer as necessary. Copy the virtio-net header when patching
it. Copy the entire packet when filling the UDP checksum as required by
net_checksum_calculate().
Signed-off-by: Akihiko Odaki <akihiko.od...@daynix.com>
---
Supersedes: <20250405-mtu-v1-1-08c5910fa...@daynix.com>
("[PATCH] virtio-net: Copy all for dhclient workaround")
This reapplies commit 7987d2be5a8b ("virtio-net: Copy all for dhclient
workaround"), which was reverted by commit e28fbd1c525d ("Revert
"virtio-net: Copy received header to buffer""), with a fix in the
superseded patch. It also renames identifiers according to the
discussion with Antoine Damhet.
---
Changes in v2:
- Rewrote the message avoiding archeology as suggested by
Michael S. Tsirkin.
- Link to v1:
https://lore.kernel.org/qemu-devel/20250423-reapply-v1-1-6f4fc3027...@daynix.com
---
hw/net/virtio-net.c | 91 ++++++++++++++++++++++++++++-------------------------
1 file changed, 48 insertions(+), 43 deletions(-)
diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index bd37651dabb0..f1688e0b2536 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -1687,6 +1687,11 @@ static void virtio_net_hdr_swap(VirtIODevice *vdev,
struct virtio_net_hdr *hdr)
virtio_tswap16s(vdev, &hdr->csum_offset);
}
+typedef struct PacketPrefix {
+ struct virtio_net_hdr_v1_hash virtio_net;
+ uint8_t payload[1500];
+} PacketPrefix;
+
/* dhclient uses AF_PACKET but doesn't pass auxdata to the kernel so
* it never finds out that the packets don't have valid checksums. This
* causes dhclient to get upset. Fedora's carried a patch for ages to
@@ -1701,42 +1706,46 @@ static void virtio_net_hdr_swap(VirtIODevice *vdev,
struct virtio_net_hdr *hdr)
* we should provide a mechanism to disable it to avoid polluting the host
* cache.
*/
-static void work_around_broken_dhclient(struct virtio_net_hdr *hdr,
- uint8_t *buf, size_t size)
+static void work_around_broken_dhclient(struct PacketPrefix *prefix,
+ size_t *prefix_len, const uint8_t *buf,
+ size_t buf_size, size_t *buf_offset)
{
size_t csum_size = ETH_HLEN + sizeof(struct ip_header) +
sizeof(struct udp_header);
+ uint8_t *payload = (uint8_t *)prefix + *prefix_len;
+
+ buf += *buf_offset;
+ buf_size -= *buf_offset;
- if ((hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) && /* missing csum */
- (size >= csum_size && size < 1500) && /* normal sized MTU */
+ if ((prefix->virtio_net.hdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) && /*
missing csum */
+ (buf_size >= csum_size && buf_size < sizeof(prefix->payload)) && /*
normal sized MTU */
(buf[12] == 0x08 && buf[13] == 0x00) && /* ethertype == IPv4 */
(buf[23] == 17) && /* ip.protocol == UDP */
(buf[34] == 0 && buf[35] == 67)) { /* udp.srcport == bootps */
- net_checksum_calculate(buf, size, CSUM_UDP);
- hdr->flags &= ~VIRTIO_NET_HDR_F_NEEDS_CSUM;
+ memcpy(payload, buf, buf_size);
+ net_checksum_calculate(payload, buf_size, CSUM_UDP);
+ prefix->virtio_net.hdr.flags &= ~VIRTIO_NET_HDR_F_NEEDS_CSUM;
+ *prefix_len += buf_size;
+ *buf_offset += buf_size;
}
}
-static void receive_header(VirtIONet *n, const struct iovec *iov, int iov_cnt,
- const void *buf, size_t size)
+static size_t receive_prefix(VirtIONet *n, PacketPrefix *prefix,
+ const void *buf, size_t buf_size,
+ size_t *buf_offset)
{
- if (n->has_vnet_hdr) {
- /* FIXME this cast is evil */
- void *wbuf = (void *)buf;
- work_around_broken_dhclient(wbuf, wbuf + n->host_hdr_len,
- size - n->host_hdr_len);
+ size_t prefix_len = n->guest_hdr_len;
- 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 = {
- .flags = 0,
- .gso_type = VIRTIO_NET_HDR_GSO_NONE
- };
- iov_from_buf(iov, iov_cnt, 0, &hdr, sizeof hdr);
+ memcpy(prefix, buf, sizeof(struct virtio_net_hdr));
+
+ *buf_offset = n->host_hdr_len;
+ work_around_broken_dhclient(prefix, &prefix_len, buf, buf_size,
buf_offset);
+
+ if (n->needs_vnet_hdr_swap) {
+ virtio_net_hdr_swap(VIRTIO_DEVICE(n), (struct virtio_net_hdr *)prefix);
}
+
+ return prefix_len;
}
static int receive_filter(VirtIONet *n, const uint8_t *buf, int size)
@@ -1913,15 +1922,15 @@ static ssize_t virtio_net_receive_rcu(NetClientState
*nc, const uint8_t *buf,
VirtQueueElement *elems[VIRTQUEUE_MAX_SIZE];
size_t lens[VIRTQUEUE_MAX_SIZE];
struct iovec mhdr_sg[VIRTQUEUE_MAX_SIZE];
- struct virtio_net_hdr_v1_hash extra_hdr;
+ PacketPrefix prefix;
unsigned mhdr_cnt = 0;
size_t offset, i, guest_offset, j;
ssize_t err;
- memset(&extra_hdr, 0, sizeof(extra_hdr));
+ memset(&prefix.virtio_net, 0, sizeof(prefix.virtio_net));
if (n->rss_data.enabled && n->rss_data.enabled_software_rss) {
- int index = virtio_net_process_rss(nc, buf, size, &extra_hdr);
+ int index = virtio_net_process_rss(nc, buf, size, &prefix.virtio_net);
if (index >= 0) {
nc = qemu_get_subqueue(n->nic, index % n->curr_queue_pairs);
}
@@ -1986,23 +1995,19 @@ static ssize_t virtio_net_receive_rcu(NetClientState
*nc, const uint8_t *buf,
if (n->mergeable_rx_bufs) {
mhdr_cnt = iov_copy(mhdr_sg, ARRAY_SIZE(mhdr_sg),
sg, elem->in_num,
- offsetof(typeof(extra_hdr),
hdr.num_buffers),
- sizeof(extra_hdr.hdr.num_buffers));
+ offsetof(typeof(prefix),
+ virtio_net.hdr.num_buffers),
+ sizeof(prefix.virtio_net.hdr.num_buffers));
} else {
- extra_hdr.hdr.num_buffers = cpu_to_le16(1);
+ prefix.virtio_net.hdr.num_buffers = cpu_to_le16(1);
}
- receive_header(n, sg, elem->in_num, buf, size);
- if (n->rss_data.populate_hash) {
- offset = offsetof(typeof(extra_hdr), hash_value);
- iov_from_buf(sg, elem->in_num, offset,
- (char *)&extra_hdr + offset,
- sizeof(extra_hdr.hash_value) +
- sizeof(extra_hdr.hash_report));
- }
- offset = n->host_hdr_len;
- total += n->guest_hdr_len;
- guest_offset = n->guest_hdr_len;
+ guest_offset = n->has_vnet_hdr ?
+ receive_prefix(n, &prefix, buf, size, &offset) :
+ n->guest_hdr_len;
+
+ iov_from_buf(sg, elem->in_num, 0, &prefix, guest_offset);
+ total += guest_offset;
} else {
guest_offset = 0;
}
@@ -2028,11 +2033,11 @@ static ssize_t virtio_net_receive_rcu(NetClientState
*nc, const uint8_t *buf,
}
if (mhdr_cnt) {
- virtio_stw_p(vdev, &extra_hdr.hdr.num_buffers, i);
+ virtio_stw_p(vdev, &prefix.virtio_net.hdr.num_buffers, i);
iov_from_buf(mhdr_sg, mhdr_cnt,
0,
- &extra_hdr.hdr.num_buffers,
- sizeof extra_hdr.hdr.num_buffers);
+ &prefix.virtio_net.hdr.num_buffers,
+ sizeof prefix.virtio_net.hdr.num_buffers);
}
for (j = 0; j < i; j++) {
---
base-commit: 1da8f3a3c53b604edfe0d55e475102640490549e
change-id: 20250423-reapply-63176514d76d
Best regards,
--
Akihiko Odaki <akihiko.od...@daynix.com>
