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udp: Move sending pasta tap frames to the end of udp_sock_handler()

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udp_sock_handler() has a surprising difference in flow between pasta and
passt mode: For pasta we send each frame to the tap interface as we prepare
it.  For passt, though, we prepare all the frames, then send them with a
single sendmmsg().

Alter the pasta path to also prepare all the frames, then send them at the
end.  We already have a suitable data structure for the passt case.  This
will make it easier to abstract out the tap backend difference in future.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
David Gibson 2023-01-05 15:26:18 +11:00 committed by Stefano Brivio
parent c196953f1e
commit a6e919a951
1 changed files with 42 additions and 19 deletions
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61
udp.c
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@ -783,6 +783,35 @@ static size_t udp_update_hdr6(const struct ctx *c, int n, in_port_t dstport,
return buf_len;
}
/**
* udp_tap_send_pasta() - Send datagrams to the pasta tap interface
* @c: Execution context
* @mmh: Array of message headers to send
* @n: Number of message headers to send
*
* #syscalls:pasta write
*/
static void udp_tap_send_pasta(const struct ctx *c, struct mmsghdr *mmh,
unsigned int n)
{
unsigned int i, j;
for (i = 0; i < n; i++) {
for (j = 0; j < mmh[i].msg_hdr.msg_iovlen; j++) {
struct iovec *iov = &mmh[i].msg_hdr.msg_iov[j];
/* We can't use writev() because the tap
* character device relies on the write()
* boundaries to discern frame boundaries
*/
if (write(c->fd_tap, iov->iov_base, iov->iov_len) < 0)
debug("tap write: %s", strerror(errno));
else
pcap(iov->iov_base, iov->iov_len);
}
}
}
/**
* udp_sock_handler() - Handle new data from socket
* @c: Execution context
@ -835,31 +864,25 @@ void udp_sock_handler(const struct ctx *c, union epoll_ref ref, uint32_t events,
else
buf_len = udp_update_hdr4(c, i, dstport, now);
if (c->mode == MODE_PASTA) {
void *frame = tap_iov[i].iov_base;
tap_iov[i].iov_len = buf_len;
if (write(c->fd_tap, frame, buf_len) < 0)
debug("tap write: %s", strerror(errno));
pcap(frame, buf_len);
} else {
tap_iov[i].iov_len = buf_len;
/* With bigger messages, qemu closes the connection. */
if (msg_bufs && msg_len + buf_len > SHRT_MAX) {
tap_mmh[msg_i].msg_hdr.msg_iovlen = msg_bufs;
msg_i++;
tap_mmh[msg_i].msg_hdr.msg_iov = &tap_iov[i];
msg_len = msg_bufs = 0;
}
msg_len += buf_len;
msg_bufs++;
/* With bigger messages, qemu closes the connection. */
if (c->mode == MODE_PASST && msg_bufs &&
msg_len + buf_len > SHRT_MAX) {
tap_mmh[msg_i].msg_hdr.msg_iovlen = msg_bufs;
msg_i++;
tap_mmh[msg_i].msg_hdr.msg_iov = &tap_iov[i];
msg_len = msg_bufs = 0;
}
msg_len += buf_len;
msg_bufs++;
}
tap_mmh[msg_i].msg_hdr.msg_iovlen = msg_bufs;
if (c->mode == MODE_PASTA)
if (c->mode == MODE_PASTA) {
udp_tap_send_pasta(c, tap_mmh, msg_i + 1);
return;
}
ret = sendmmsg(c->fd_tap, tap_mmh, msg_i + 1,
MSG_NOSIGNAL | MSG_DONTWAIT);