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Fix the UDP recvmmsg support

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Previously, the netmgr/udp.c tried to detect the recvmmsg detection in
libuv with #ifdef UV_UDP_<foo> preprocessor macros.  However, because
the UV_UDP_<foo> are not preprocessor macros, but enum members, the
detection didn't work.  Because the detection didn't work, the code
didn't have access to the information when we received the final chunk
of the recvmmsg and tried to free the uvbuf every time.  Fortunately,
the isc__nm_free_uvbuf() had a kludge that detected attempt to free in
the middle of the receive buffer, so the code worked.

However, libuv 1.37.0 changed the way the recvmmsg was enabled from
implicit to explicit, and we checked for yet another enum member
presence with preprocessor macro, so in fact libuv recvmmsg support was
never enabled with libuv >= 1.37.0.

This commit changes to the preprocessor macros to autoconf checks for
declaration, so the detection now works again.  On top of that, it's now
possible to cleanup the alloc_cb and free_uvbuf functions because now,
the information whether we can or cannot free the buffer is available to
us.
This commit is contained in:
Ondřej Surý
2022-01-11 12:14:23 +01:00
parent abe466e5b3
commit 7370725008
7 changed files with 137 additions and 61 deletions
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50
lib/isc/netmgr/udp.c
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@@ -431,7 +431,7 @@ isc__nm_async_udplisten(isc__networker_t *worker, isc__netievent_t *ev0) {
REQUIRE(sock->parent != NULL);
REQUIRE(sock->tid == isc_nm_tid());
#ifdef UV_UDP_RECVMMSG
#if HAVE_DECL_UV_UDP_RECVMMSG
uv_init_flags |= UV_UDP_RECVMMSG;
#endif
r = uv_udp_init_ex(&worker->loop, &sock->uv_handle.udp, uv_init_flags);
@@ -556,7 +556,6 @@ udp_recv_cb(uv_udp_t *handle, ssize_t nrecv, const uv_buf_t *buf,
isc_nmsocket_t *sock = uv_handle_get_data((uv_handle_t *)handle);
isc__nm_uvreq_t *req = NULL;
uint32_t maxudp;
bool free_buf;
isc_result_t result;
isc_sockaddr_t sockaddr, *sa = NULL;
@@ -564,19 +563,22 @@ udp_recv_cb(uv_udp_t *handle, ssize_t nrecv, const uv_buf_t *buf,
REQUIRE(sock->tid == isc_nm_tid());
REQUIRE(atomic_load(&sock->reading));
#ifdef UV_UDP_MMSG_FREE
free_buf = ((flags & UV_UDP_MMSG_FREE) == UV_UDP_MMSG_FREE);
#elif UV_UDP_MMSG_CHUNK
free_buf = ((flags & UV_UDP_MMSG_CHUNK) == 0);
/*
* When using recvmmsg(2), if no errors occur, there will be a final
* callback with nrecv set to 0, addr set to NULL and the buffer
* pointing at the initially allocated data with the UV_UDP_MMSG_CHUNK
* flag cleared and the UV_UDP_MMSG_FREE flag set.
*/
#if HAVE_DECL_UV_UDP_MMSG_FREE
if ((flags & UV_UDP_MMSG_FREE) == UV_UDP_MMSG_FREE) {
INSIST(nrecv == 0);
INSIST(addr == NULL);
goto free;
}
#else
free_buf = true;
UNUSED(flags);
#endif
/*
* Four possible reasons to return now without processing:
*/
/*
* - If we're simulating a firewall blocking UDP packets
* bigger than 'maxudp' bytes for testing purposes.
@@ -640,9 +642,31 @@ udp_recv_cb(uv_udp_t *handle, ssize_t nrecv, const uv_buf_t *buf,
sock->processing = false;
free:
if (free_buf) {
isc__nm_free_uvbuf(sock, buf);
#if HAVE_DECL_UV_UDP_MMSG_CHUNK
/*
* When using recvmmsg(2), chunks will have the UV_UDP_MMSG_CHUNK flag
* set, those must not be freed.
*/
if ((flags & UV_UDP_MMSG_CHUNK) == UV_UDP_MMSG_CHUNK) {
return;
}
#endif
/*
* When using recvmmsg(2), if a UDP socket error occurs, nrecv will be <
* 0. In either scenario, the callee can now safely free the provided
* buffer.
*/
if (nrecv < 0) {
/*
* The buffer may be a null buffer on error.
*/
if (buf->base == NULL && buf->len == 0) {
return;
}
}
isc__nm_free_uvbuf(sock, buf);
}
/*