This patch adds the lcp-rtt-file configuration option, which instructs pppd to add a timestamp to the data section of each LCP echo request frame and then log their round trip time and any detected packet loss to a circular buffer in that file. Other programs then can asynchronously read the file and report statistics about the line. I am attaching as examples a simple program which dumps the content of the log file and a Prometheus exporter which can be run as a CGI. This feature was inspired by a similar one in a commercial PPP implementation, but I have never actually seen that and I do not know how it actually works or it was implemented. Signed-off-by: Marco d'Itri <md@xxxxxxxx> -- ciao, Marco
--- a/pppd/lcp.c
+++ b/pppd/lcp.c
@@ -47,6 +47,11 @@
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
+#include <fcntl.h>
+#include <string.h>
+#include <time.h>
+#include <arpa/inet.h>
+#include <sys/mman.h>
#include "pppd-private.h"
#include "options.h"
@@ -67,12 +72,18 @@
static void lcp_delayed_up(void *);
+#define LCP_RTT_MAGIC 0x19450425
+#define LCP_RTT_HEADER_LENGTH 4
+#define LCP_RTT_FILE_SIZE 8192
+#define LCP_RTT_ELEMENTS (LCP_RTT_FILE_SIZE / sizeof(u_int32_t) - LCP_RTT_HEADER_LENGTH) / 2
+
/*
* LCP-related command-line options.
*/
int lcp_echo_interval = 0; /* Interval between LCP echo-requests */
int lcp_echo_fails = 0; /* Tolerance to unanswered echo-requests */
bool lcp_echo_adaptive = 0; /* request echo only if the link was idle */
+char *lcp_rtt_file = NULL; /* measure the RTT of LCP echo-requests */
bool lax_recv = 0; /* accept control chars in asyncmap */
bool noendpoint = 0; /* don't send/accept endpoint discriminator */
@@ -152,6 +163,8 @@ static struct option lcp_option_list[] =
"Set time in seconds between LCP echo requests", OPT_PRIO },
{ "lcp-echo-adaptive", o_bool, &lcp_echo_adaptive,
"Suppress LCP echo requests if traffic was received", 1 },
+ { "lcp-rtt-file", o_string, &lcp_rtt_file,
+ "Write to this file the RTT of LCP echo requests", OPT_PRIO },
{ "lcp-restart", o_int, &lcp_fsm[0].timeouttime,
"Set time in seconds between LCP retransmissions", OPT_PRIO },
{ "lcp-max-terminate", o_int, &lcp_fsm[0].maxtermtransmits,
@@ -197,6 +210,8 @@ lcp_options lcp_hisoptions[NUM_PPP]; /*
static int lcp_echos_pending = 0; /* Number of outstanding echo msgs */
static int lcp_echo_number = 0; /* ID number of next echo frame */
static int lcp_echo_timer_running = 0; /* set if a timer is running */
+static int lcp_rtt_file_fd = 0; /* fd for the opened LCP RTT file */
+static volatile u_int32_t *lcp_rtt_buffer = NULL; /* the mmap'ed LCP RTT file */
static u_char nak_buffer[PPP_MRU]; /* where we construct a nak packet */
@@ -2226,6 +2241,61 @@ LcpEchoTimeout (void *arg)
}
/*
+ * lcp_rtt_update_buffer - log the RTT of the received LCP echo-request
+ *
+ * The header section at the beginning of lcp_rtt_file contains
+ * LCP_RTT_HEADER_LENGTH fields, each a u_int32_t in network byte order:
+ * [0] LCP_RTT_MAGIC
+ * [1] status (1: the file is open and is being written)
+ * [2] index of the most recently updated element
+ * [3] the value of the lcp-echo-interval parameter
+ *
+ * The header is followed by a ring buffer of LCP_RTT_ELEMENTS elements, each
+ * containing a pair of u_int32_t in network byte order with this content:
+ * [0] UNIX timestamp
+ * [1] bits 24-31: the number of lost LCP echo replies
+ * bits 0-23: the measured RTT in microseconds
+ *
+ * Consumers of lcp_rtt_file are expected to:
+ * - read the complete file of arbitrary lenght
+ * - check the magic number
+ * - process the data elements starting at the index
+ * - discard the last data element, i.e. the one preceding the element
+ * referenced by the index
+ * - ignore any elements with a timestamp of 0
+ */
+static void
+lcp_rtt_update_buffer (unsigned long rtt)
+{
+ volatile u_int32_t *const ring_buffer = lcp_rtt_buffer
+ + LCP_RTT_HEADER_LENGTH;
+ unsigned int next_entry, lost;
+
+ /* choose the next entry where the data will be stored */
+ if (ntohl(lcp_rtt_buffer[2]) >= (LCP_RTT_ELEMENTS - 1) * 2)
+ next_entry = 0; /* go back to the beginning */
+ else
+ next_entry = ntohl(lcp_rtt_buffer[2]) + 2; /* use the next one */
+
+ /* update the data element */
+ /* storing the timestamp in an *unsigned* long allows dates up to 2106 */
+ ring_buffer[next_entry] = htonl((u_int32_t) time(NULL));
+ lost = lcp_echos_pending - 1;
+ if (lost > 0xFF)
+ lost &= 0xFF; /* truncate the lost packets to 256 */
+ if (rtt > 0xFFFFFF)
+ rtt &= 0xFFFFFF; /* truncate the RTT to 16777216 */
+ /* use bits 24-31 for the lost packets and bits 0-23 for the RTT */
+ ring_buffer[next_entry + 1] = htonl((u_int32_t) ((lost << 24) + rtt));
+
+ /* update the pointer to the (just updated) most current data element */
+ lcp_rtt_buffer[2] = htonl(next_entry);
+
+ if (msync(lcp_rtt_buffer, LCP_RTT_FILE_SIZE, MS_ASYNC) < 0)
+ error("msync() for %s failed: %m", lcp_rtt_file);
+}
+
+/*
* LcpEchoReply - LCP has received a reply to the echo
*/
@@ -2246,6 +2316,30 @@ lcp_received_echo_reply (fsm *f, int id,
return;
}
+ if (lcp_rtt_file_fd && len >= 16) {
+ long lcp_rtt_magic;
+
+ /*
+ * If the magic word is found at the beginning of the data section
+ * of the frame then read the timestamp which follows and subtract
+ * it from the current time to compute the round trip time.
+ */
+ GETLONG(lcp_rtt_magic, inp);
+ if (lcp_rtt_magic == LCP_RTT_MAGIC) {
+ struct timespec ts;
+ unsigned long req_sec, req_nsec, rtt;
+
+ clock_gettime(CLOCK_MONOTONIC, &ts);
+ GETLONG(req_sec, inp);
+ GETLONG(req_nsec, inp);
+ /* compute the RTT in microseconds */
+ rtt = (ts.tv_sec - req_sec) * 1000000
+ + (ts.tv_nsec / 1000 - req_nsec / 1000);
+ /* log the RTT */
+ lcp_rtt_update_buffer(rtt);
+ }
+ }
+
/* Reset the number of outstanding echo frames */
lcp_echos_pending = 0;
}
@@ -2258,7 +2352,7 @@ static void
LcpSendEchoRequest (fsm *f)
{
u_int32_t lcp_magic;
- u_char pkt[4], *pktp;
+ u_char pkt[16], *pktp;
/*
* Detect the failure of the peer at this point.
@@ -2293,11 +2387,68 @@ LcpSendEchoRequest (fsm *f)
lcp_magic = lcp_gotoptions[f->unit].magicnumber;
pktp = pkt;
PUTLONG(lcp_magic, pktp);
+
+ /* Put a timestamp in the data section of the frame */
+ if (lcp_rtt_file_fd) {
+ struct timespec ts;
+
+ PUTLONG(LCP_RTT_MAGIC, pktp);
+ clock_gettime(CLOCK_MONOTONIC, &ts);
+ PUTLONG((u_int32_t)ts.tv_sec, pktp);
+ PUTLONG((u_int32_t)ts.tv_nsec, pktp);
+ }
+
fsm_sdata(f, ECHOREQ, lcp_echo_number++ & 0xFF, pkt, pktp - pkt);
++lcp_echos_pending;
}
}
+static void
+lcp_rtt_open_file (void)
+{
+ if (!lcp_rtt_file)
+ return;
+
+ lcp_rtt_file_fd = open(lcp_rtt_file, O_RDWR | O_CREAT, 0644);
+ if (lcp_rtt_file_fd < 0) {
+ error("Can't open the RTT log file %s: %m", lcp_rtt_file);
+ lcp_rtt_file_fd = 0;
+ return;
+ }
+
+ if (ftruncate(lcp_rtt_file_fd, LCP_RTT_FILE_SIZE) < 0)
+ fatal("ftruncate() of %s failed: %m", lcp_rtt_file);
+ lcp_rtt_buffer = mmap(0, LCP_RTT_FILE_SIZE, PROT_READ | PROT_WRITE,
+ MAP_SHARED, lcp_rtt_file_fd, 0);
+ if (lcp_rtt_buffer == MAP_FAILED)
+ fatal("mmap() of %s failed: %m", lcp_rtt_file);
+
+ /* initialize the ring buffer */
+ if (lcp_rtt_buffer[0] != htonl(LCP_RTT_MAGIC)) {
+ memset(lcp_rtt_buffer, 0, LCP_RTT_FILE_SIZE);
+ lcp_rtt_buffer[0] = htonl(LCP_RTT_MAGIC);
+ }
+
+ lcp_rtt_buffer[3] = htonl(lcp_echo_interval);
+ lcp_rtt_buffer[1] = htonl(1); /* status: LCP up, file opened */
+}
+
+static void
+lcp_rtt_close_file (void)
+{
+ if (!lcp_rtt_file_fd)
+ return;
+
+ lcp_rtt_buffer[1] = htonl(0); /* status: LCP down, file closed */
+
+ if (munmap(lcp_rtt_buffer, LCP_RTT_FILE_SIZE) < 0)
+ error("munmap() of %s failed: %m", lcp_rtt_file);
+ if (close(lcp_rtt_file_fd) < 0)
+ error("close() of %s failed: %m", lcp_rtt_file);
+ lcp_rtt_buffer = NULL;
+ lcp_rtt_file_fd = 0;
+}
+
/*
* lcp_echo_lowerup - Start the timer for the LCP frame
*/
@@ -2311,6 +2462,9 @@ lcp_echo_lowerup (int unit)
lcp_echos_pending = 0;
lcp_echo_number = 0;
lcp_echo_timer_running = 0;
+
+ /* Open the file where the LCP RTT data will be logged */
+ lcp_rtt_open_file();
/* If a timeout interval is specified then start the timer */
if (lcp_echo_interval != 0)
@@ -2330,4 +2484,7 @@ lcp_echo_lowerdown (int unit)
UNTIMEOUT (LcpEchoTimeout, f);
lcp_echo_timer_running = 0;
}
+
+ /* Close the file containing the LCP RTT data */
+ lcp_rtt_close_file();
}
--- a/pppd/pppd.8
+++ b/pppd/pppd.8
@@ -637,6 +637,9 @@ Set the maximum number of LCP terminate-
Set the LCP restart interval (retransmission timeout) to \fIn\fR
seconds (default 3).
.TP
+.B lcp\-rtt\-file \fIfilename
+Sets the file where the RTT of LCP echo-request frames will be logged.
+.TP
.B linkname \fIname\fR
Sets the logical name of the link to \fIname\fR. Pppd will create a
file named \fBppp\-\fIname\fB.pid\fR in /var/run (or /etc/ppp on some
#!/usr/bin/perl
# vim: shiftwidth=4 tabstop=4
#
# This program dumps to standard output the content of the file written
# by pppd's lcp-rtt-file configuration option.
#
# Copyright (C) Marco d'Itri <md@xxxxxxxx>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
use v5.14;
use warnings;
use autodie;
use POSIX qw(strftime);
{
my $data = read_data($ARGV[0] || '/run/ppp-rtt.data');
die "The data file is invalid!\n" if not $data;
dump_data($data);
}
sub dump_data {
my ($s) = @_;
say "status: $s->{status}";
say "interval: $s->{echo_interval}";
say "position: $s->{position}";
say 'elements: ' . scalar(@{ $s->{data} });
say '';
foreach (my $i= 0; $i < @{ $s->{data} }; $i++) {
my $date = strftime('%F %T', localtime($s->{data}->[$i]->[0]));
print "$i\t$date\t$s->{data}->[$i]->[1]\t$s->{data}->[$i]->[2]\n";
}
}
sub read_data {
my ($file) = @_;
my $data;
open(my $fh, '<', $file);
binmode($fh);
my $bytes_read;
do {
$bytes_read = sysread($fh, $data, 8192, length($data));
} while ($bytes_read == 8192);
close($fh);
my ($magic, $status, $position, $echo_interval, $rest)
= unpack('NNNN a*', $data);
return undef if $magic != 0x19450425;
# the position is relative to the C array, not to the logical entries
$position /= 2;
my @rawdata = unpack('(N C a3)*', $rest);
my @data;
while (my ($time, $loss, $rtt) = splice(@rawdata, 0, 3)) {
push(@data, [ $time, unpack('N', "\000$rtt"), $loss ]);
}
if (0) {
# rearrange the list in chronological order
if ($position == $#data) {
@data = @data[1 .. $#data];
} elsif ($position == 0) {
@data = @data[0 .. $#data-1];
} else {
@data = (@data[$position+2 .. $#data], @data[0 .. $position]);
}
@data = grep { $_->[0] } @data;
}
return {
status => $status,
echo_interval => $echo_interval,
position => $position,
data => \@data,
};
}
#!/usr/bin/perl
# vim: shiftwidth=4 tabstop=4
#
# This CGI program is a Prometheus exporter for pppd's lcp-rtt-file feature.
#
# Copyright (C) Marco d'Itri <md@xxxxxxxx>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
use v5.14;
use warnings;
use autodie;
use List::Util qw(sum max min);
{
my $data = read_data('/run/ppp-rtt.data');
my $stats = compute_statistics($data, 60);
my $s = metrics($stats);
print "Content-type: text/plain\n\n$s";
exit;
}
sub metrics {
my ($stats) = @_;
my $s = <<END;
# TYPE lcp_rtt_status gauge
# HELP LCP RTT status
lcp_rtt_status $stats->{status}
END
foreach (qw(average min max loss)) {
next if not exists $stats->{$_};
$s .= <<END;
# TYPE lcp_rtt_$_ gauge
# HELP LCP RTT $_
lcp_rtt_$_ $stats->{$_}
END
}
return $s;
}
sub compute_statistics {
my ($data, $length) = @_;
my $cutoff = time() - $length;
my @e = grep { $_->[0] >= $cutoff } @{ $data->{data} };
return { status => -1 } if not @e; # no data
my $average = (sum map { $_->[1] } @e) / scalar(@e);
my $min = min map { $_->[1] } @e;
my $max = max map { $_->[1] } @e;
my $loss = sum map { $_->[2] } @e;
return {
status => $data->{status},
average => $average,
min => $min,
max => $max,
loss => $loss,
};
}
sub read_data {
my ($file) = @_;
my $data;
open(my $fh, '<', $file);
binmode($fh);
my $bytes_read;
do {
$bytes_read = sysread($fh, $data, 8192, length($data));
} while ($bytes_read == 8192);
close($fh);
my ($magic, $status, $position, $echo_interval, $rest)
= unpack('NNNN a*', $data);
return undef if $magic != 0x19450425;
# the position is relative to the C array, not to the logical entries
$position /= 2;
my @rawdata = unpack('(N C a3)*', $rest);
my @data;
while (my ($time, $loss, $rtt) = splice(@rawdata, 0, 3)) {
push(@data, [ $time, unpack('N', "\000$rtt"), $loss ]);
}
# rearrange the list in chronological order
if ($position == $#data) {
@data = @data[1 .. $#data];
} elsif ($position == 0) {
@data = @data[0 .. $#data-1];
} else {
@data = (@data[$position+2 .. $#data], @data[0 .. $position]);
}
@data = grep { $_->[0] } @data;
return {
status => $status,
echo_interval => $echo_interval,
position => $position,
data => \@data,
};
}
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