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udp: Split sending to passt tap interface into separate function

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The last part of udp_sock_handler() does the actual sending of frames
to the tap interface.  For pasta that's just a call to
udp_tap_send_pasta() but for passt, it's moderately complex and open
coded.

For symmetry, move the passt send path into its own function,
udp_tap_send_passt().  This will make it easier to abstract the tap
interface in future (e.g. when we want to add vhost-user).

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 15:26:19 +11:00 committed by Stefano Brivio
parent a6e919a951
commit 09c00f1d2a
1 changed files with 72 additions and 58 deletions
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130
udp.c
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@ -812,6 +812,73 @@ static void udp_tap_send_pasta(const struct ctx *c, struct mmsghdr *mmh,
} }
} }
/**
* udp_tap_send_passt() - Send datagrams to the passt tap interface
* @c: Execution context
* @mmh: Array of message headers to send
* @n: Number of message headers to send
*
* #syscalls:passt sendmmsg sendmsg
*/
static void udp_tap_send_passt(const struct ctx *c, struct mmsghdr *mmh, int n)
{
struct msghdr *last_mh;
ssize_t missing = 0;
size_t msg_len = 0;
unsigned int i;
int ret;
ret = sendmmsg(c->fd_tap, mmh, n, MSG_NOSIGNAL | MSG_DONTWAIT);
if (ret <= 0)
return;
/* If we lose some messages to sendmmsg() here, fine, it's UDP. However,
* the last message needs to be delivered completely, otherwise qemu
* will fail to reassemble the next message and close the connection. Go
* through headers from the last sent message, counting bytes, and, if
* and as soon as we see more bytes than sendmmsg() sent, re-send the
* rest with a blocking call.
*
* In pictures, given this example:
*
* iov #0 iov #1 iov #2 iov #3
* tap_mmh[ret - 1].msg_hdr: .... ...... ..... ......
* tap_mmh[ret - 1].msg_len: 7 .... ...
*
* when 'msglen' reaches: 10 ^
* and 'missing' below is: 3 ---
*
* re-send everything from here: ^-- ----- ------
*/
last_mh = &mmh[ret - 1].msg_hdr;
for (i = 0; i < last_mh->msg_iovlen; i++) {
if (missing <= 0) {
msg_len += last_mh->msg_iov[i].iov_len;
missing = msg_len - mmh[ret - 1].msg_len;
}
if (missing > 0) {
uint8_t **iov_base;
int first_offset;
iov_base = (uint8_t **)&last_mh->msg_iov[i].iov_base;
first_offset = last_mh->msg_iov[i].iov_len - missing;
*iov_base += first_offset;
last_mh->msg_iov[i].iov_len = missing;
last_mh->msg_iov = &last_mh->msg_iov[i];
if (sendmsg(c->fd_tap, last_mh, MSG_NOSIGNAL) < 0)
debug("UDP: %li bytes to tap missing", missing);
*iov_base -= first_offset;
break;
}
}
pcapmm(mmh, ret);
}
/** /**
* udp_sock_handler() - Handle new data from socket * udp_sock_handler() - Handle new data from socket
* @c: Execution context * @c: Execution context
@ -820,16 +887,14 @@ static void udp_tap_send_pasta(const struct ctx *c, struct mmsghdr *mmh,
* @now: Current timestamp * @now: Current timestamp
* *
* #syscalls recvmmsg * #syscalls recvmmsg
* #syscalls:passt sendmmsg sendmsg
*/ */
void udp_sock_handler(const struct ctx *c, union epoll_ref ref, uint32_t events, void udp_sock_handler(const struct ctx *c, union epoll_ref ref, uint32_t events,
const struct timespec *now) const struct timespec *now)
{ {
in_port_t dstport = ref.r.p.udp.udp.port; in_port_t dstport = ref.r.p.udp.udp.port;
ssize_t n, msg_len = 0, missing = 0;
struct mmsghdr *tap_mmh, *sock_mmh; struct mmsghdr *tap_mmh, *sock_mmh;
int msg_bufs = 0, msg_i = 0, ret; int msg_bufs = 0, msg_i = 0;
struct msghdr *last_mh; ssize_t n, msg_len = 0;
struct iovec *tap_iov; struct iovec *tap_iov;
unsigned int i; unsigned int i;
@ -879,61 +944,10 @@ void udp_sock_handler(const struct ctx *c, union epoll_ref ref, uint32_t events,
} }
tap_mmh[msg_i].msg_hdr.msg_iovlen = 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); udp_tap_send_pasta(c, tap_mmh, msg_i + 1);
return; else
} udp_tap_send_passt(c, tap_mmh, msg_i + 1);
ret = sendmmsg(c->fd_tap, tap_mmh, msg_i + 1,
MSG_NOSIGNAL | MSG_DONTWAIT);
if (ret <= 0)
return;
/* If we lose some messages to sendmmsg() here, fine, it's UDP. However,
* the last message needs to be delivered completely, otherwise qemu
* will fail to reassemble the next message and close the connection. Go
* through headers from the last sent message, counting bytes, and, if
* and as soon as we see more bytes than sendmmsg() sent, re-send the
* rest with a blocking call.
*
* In pictures, given this example:
*
* iov #0 iov #1 iov #2 iov #3
* tap_mmh[ret - 1].msg_hdr: .... ...... ..... ......
* tap_mmh[ret - 1].msg_len: 7 .... ...
*
* when 'msglen' reaches: 10 ^
* and 'missing' below is: 3 ---
*
* re-send everything from here: ^-- ----- ------
*/
last_mh = &tap_mmh[ret - 1].msg_hdr;
for (i = 0, msg_len = 0; i < last_mh->msg_iovlen; i++) {
if (missing <= 0) {
msg_len += last_mh->msg_iov[i].iov_len;
missing = msg_len - tap_mmh[ret - 1].msg_len;
}
if (missing > 0) {
uint8_t **iov_base;
int first_offset;
iov_base = (uint8_t **)&last_mh->msg_iov[i].iov_base;
first_offset = last_mh->msg_iov[i].iov_len - missing;
*iov_base += first_offset;
last_mh->msg_iov[i].iov_len = missing;
last_mh->msg_iov = &last_mh->msg_iov[i];
if (sendmsg(c->fd_tap, last_mh, MSG_NOSIGNAL) < 0)
debug("UDP: %li bytes to tap missing", missing);
*iov_base -= first_offset;
break;
}
}
pcapmm(tap_mmh, ret);
} }
/** /**