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Impove cache behaviour for TCP connections.

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For ease of implementaion, dnsmasq has always forked a new process to
handle each incoming TCP connection. A side-effect of this is that any
DNS queries answered from TCP connections are not cached: when TCP
connections were rare, this was not a problem.  With the coming of
DNSSEC, it's now the case that some DNSSEC queries have answers which
spill to TCP, and if, for instance, this applies to the keys for the
root then those never get cached, and performance is very bad.  This
fix passes cache entries back from the TCP child process to the main
server process, and fixes the problem.
This commit is contained in:
Simon Kelley
2018-10-18 19:35:29 +01:00
parent 91421cb757
commit a799ca0c63
5 changed files with 291 additions and 19 deletions
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58
src/dnsmasq.c
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@@ -930,6 +930,10 @@ int main (int argc, char **argv)
check_servers();
pid = getpid();
daemon->pipe_to_parent = -1;
for (i = 0; i < MAX_PROCS; i++)
daemon->tcp_pipes[i] = -1;
#ifdef HAVE_INOTIFY
/* Using inotify, have to select a resolv file at startup */
@@ -1611,7 +1615,7 @@ static int set_dns_listeners(time_t now)
we don't need to explicitly arrange to wake up here */
if (listener->tcpfd != -1)
for (i = 0; i < MAX_PROCS; i++)
if (daemon->tcp_pids[i] == 0)
if (daemon->tcp_pids[i] == 0 && daemon->tcp_pipes[i] == -1)
{
poll_listen(listener->tcpfd, POLLIN);
break;
@@ -1624,6 +1628,13 @@ static int set_dns_listeners(time_t now)
}
#ifndef NO_FORK
if (!option_bool(OPT_DEBUG))
for (i = 0; i < MAX_PROCS; i++)
if (daemon->tcp_pipes[i] != -1)
poll_listen(daemon->tcp_pipes[i], POLLIN);
#endif
return wait;
}
@@ -1632,7 +1643,10 @@ static void check_dns_listeners(time_t now)
struct serverfd *serverfdp;
struct listener *listener;
int i;
#ifndef NO_FORK
int pipefd[2];
#endif
for (serverfdp = daemon->sfds; serverfdp; serverfdp = serverfdp->next)
if (poll_check(serverfdp->fd, POLLIN))
reply_query(serverfdp->fd, serverfdp->source_addr.sa.sa_family, now);
@@ -1642,7 +1656,26 @@ static void check_dns_listeners(time_t now)
if (daemon->randomsocks[i].refcount != 0 &&
poll_check(daemon->randomsocks[i].fd, POLLIN))
reply_query(daemon->randomsocks[i].fd, daemon->randomsocks[i].family, now);
#ifndef NO_FORK
/* Races. The child process can die before we read all of the data from the
pipe, or vice versa. Therefore send tcp_pids to zero when we wait() the
process, and tcp_pipes to -1 and close the FD when we read the last
of the data - indicated by cache_recv_insert returning zero.
The order of these events is indeterminate, and both are needed
to free the process slot. Once the child process has gone, poll()
returns POLLHUP, not POLLIN, so have to check for both here. */
if (!option_bool(OPT_DEBUG))
for (i = 0; i < MAX_PROCS; i++)
if (daemon->tcp_pipes[i] != -1 &&
poll_check(daemon->tcp_pipes[i], POLLIN | POLLHUP) &&
!cache_recv_insert(now, daemon->tcp_pipes[i]))
{
close(daemon->tcp_pipes[i]);
daemon->tcp_pipes[i] = -1;
}
#endif
for (listener = daemon->listeners; listener; listener = listener->next)
{
if (listener->fd != -1 && poll_check(listener->fd, POLLIN))
@@ -1736,15 +1769,20 @@ static void check_dns_listeners(time_t now)
while (retry_send(close(confd)));
}
#ifndef NO_FORK
else if (!option_bool(OPT_DEBUG) && (p = fork()) != 0)
else if (!option_bool(OPT_DEBUG) && pipe(pipefd) == 0 && (p = fork()) != 0)
{
if (p != -1)
close(pipefd[1]); /* parent needs read pipe end. */
if (p == -1)
close(pipefd[0]);
else
{
int i;
for (i = 0; i < MAX_PROCS; i++)
if (daemon->tcp_pids[i] == 0)
if (daemon->tcp_pids[i] == 0 && daemon->tcp_pipes[i] == -1)
{
daemon->tcp_pids[i] = p;
daemon->tcp_pipes[i] = pipefd[0];
break;
}
}
@@ -1761,7 +1799,7 @@ static void check_dns_listeners(time_t now)
int flags;
struct in_addr netmask;
int auth_dns;
if (iface)
{
netmask = iface->netmask;
@@ -1777,7 +1815,11 @@ static void check_dns_listeners(time_t now)
/* Arrange for SIGALRM after CHILD_LIFETIME seconds to
terminate the process. */
if (!option_bool(OPT_DEBUG))
alarm(CHILD_LIFETIME);
{
alarm(CHILD_LIFETIME);
close(pipefd[0]); /* close read end in child. */
daemon->pipe_to_parent = pipefd[1];
}
#endif
/* start with no upstream connections. */