static NetClientInfo net_tap_info = {
.type = NET_CLIENT_OPTIONS_KIND_TAP,
.size = sizeof(TAPState),
.receive = tap_receive,
.receive_raw = tap_receive_raw,
.receive_iov = tap_receive_iov,
.poll = tap_poll,
.cleanup = tap_cleanup,
};
finally all functions for network will call receive_raw or receive. as qemu_deliver_packet function.
ssize_t qemu_deliver_packet(NetClientState *sender,
unsigned flags,
const uint8_t *data,
size_t size,
void *opaque)
{
NetClientState *nc = opaque; // this is a peer's state.
ssize_t ret;
if (nc->link_down) {
return size;
}
if (nc->receive_disabled) {
return 0;
}
if (flags & QEMU_NET_PACKET_FLAG_RAW && nc->info->receive_raw) {
ret = nc->info->receive_raw(nc, data, size);
} else {
ret = nc->info->receive(nc, data, size);
}
if (ret == 0) {
nc->receive_disabled = 1;
};
return ret;
}
both tap_receive for receive and tap_receive_raw for receive_raw will call tap_write_packet function.
static ssize_t tap_receive_raw(NetClientState *nc, const uint8_t *buf, size_t size)
{
TAPState *s = DO_UPCAST(TAPState, nc, nc);
struct iovec iov[2];
int iovcnt = 0;
struct virtio_net_hdr_mrg_rxbuf hdr = { };
if (s->host_vnet_hdr_len) {
iov[iovcnt].iov_base = &hdr;
iov[iovcnt].iov_len = s->host_vnet_hdr_len;
iovcnt++;
}
iov[iovcnt].iov_base = (char *)buf;
iov[iovcnt].iov_len = size;
iovcnt++;
return tap_write_packet(s, iov, iovcnt);
}
static ssize_t tap_receive(NetClientState *nc, const uint8_t *buf, size_t size)
{
TAPState *s = DO_UPCAST(TAPState, nc, nc);
struct iovec iov[1];
if (s->host_vnet_hdr_len && !s->using_vnet_hdr) {
return tap_receive_raw(nc, buf, size);
}
iov[0].iov_base = (char *)buf;
iov[0].iov_len = size;
return tap_write_packet(s, iov, 1);
}
static ssize_t tap_write_packet(TAPState *s, const struct iovec *iov, int iovcnt)
{
ssize_t len;
do {
len = writev(s->fd, iov, iovcnt);
} while (len == -1 && errno == EINTR);
if (len == -1 && errno == EAGAIN) {
tap_write_poll(s, true);
return 0;
}
return len;
}
static ssize_t readv_writev(int fd, const struct iovec *iov, int iov_cnt, bool do_write)
{
unsigned i = 0;
ssize_t ret = 0;
while (i < iov_cnt) {
ssize_t r = do_write
? write(fd, iov[i].iov_base, iov[i].iov_len)
: read(fd, iov[i].iov_base, iov[i].iov_len);
if (r > 0) {
ret += r;
} else if (!r) {
break;
} else if (errno == EINTR) {
continue;
} else {
/* else it is some "other" error,
* only return if there was no data processed. */
if (ret == 0) {
ret = -1;
}
break;
}
i++;
}
return ret;
}
finally we found file descriptor network bridge use!!.
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