monitor: Add support for builtin pager functionality

Makefile.am

@@ -50,7 +50,8 @@ client_iwctl_LDADD = ell/libell-internal.la
 
 monitor_iwmon_SOURCES = monitor/main.c linux/nl80211.h \
 					monitor/nlmon.h monitor/nlmon.c \
-					monitor/pcap.h monitor/pcap.c
+					monitor/pcap.h monitor/pcap.c \
+					monitor/display.h monitor/display.c
 monitor_iwmon_LDADD = ell/libell-internal.la
 
 noinst_PROGRAMS = tools/hwsim

monitor/display.c

@@ -0,0 +1,171 @@
+/*
+ *
+ *  Wireless daemon for Linux
+ *
+ *  Copyright (C) 2013-2014  Intel Corporation. All rights reserved.
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, write to the Free Software
+ *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ */
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <stdio.h>
+#include <errno.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <string.h>
+#include <signal.h>
+#include <sys/wait.h>
+#include <sys/prctl.h>
+#include <sys/ioctl.h>
+#include <termios.h>
+
+#include "display.h"
+
+#define FALLBACK_TERMINAL_WIDTH 80
+
+static pid_t pager_pid = 0;
+
+bool use_color(void)
+{
+	static int cached_use_color = -1;
+
+	if (__builtin_expect(!!(cached_use_color < 0), 0))
+		cached_use_color = isatty(STDOUT_FILENO) > 0 || pager_pid > 0;
+
+	return !!cached_use_color;
+}
+
+unsigned int num_columns(void)
+{
+	static int cached_num_columns = -1;
+
+	if (__builtin_expect(!!(cached_num_columns < 0), 0)) {
+		struct winsize ws;
+
+		if (ioctl(STDOUT_FILENO, TIOCGWINSZ, &ws) < 0 ||
+								ws.ws_col == 0)
+			cached_num_columns = FALLBACK_TERMINAL_WIDTH;
+		else
+			cached_num_columns = ws.ws_col;
+	}
+
+	return cached_num_columns;
+}
+
+static void close_pipe(int p[])
+{
+	if (p[0] >= 0)
+		close(p[0]);
+	if (p[1] >= 0)
+		close(p[1]);
+}
+
+static void wait_for_terminate(pid_t pid)
+{
+	siginfo_t dummy;
+
+	for (;;) {
+		memset(&dummy, 0, sizeof(dummy));
+
+		if (waitid(P_PID, pid, &dummy, WEXITED) < 0) {
+			if (errno == EINTR)
+				continue;
+			return;
+		}
+
+		return;
+	}
+}
+
+void open_pager(void)
+{
+	const char *pager;
+	pid_t parent_pid;
+	int fd[2];
+
+	if (pager_pid > 0)
+		return;
+
+	pager = getenv("PAGER");
+	if (pager) {
+		if (!*pager || strcmp(pager, "cat") == 0)
+			return;
+	}
+
+	if (!(isatty(STDOUT_FILENO) > 0))
+		return;
+
+	num_columns();
+
+	if (pipe(fd) < 0) {
+		perror("Failed to create pager pipe");
+		return;
+	}
+
+	parent_pid = getpid();
+
+	pager_pid = fork();
+	if (pager_pid < 0) {
+		perror("Failed to fork pager");
+		close_pipe(fd);
+		return;
+	}
+
+	if (pager_pid == 0) {
+		dup2(fd[0], STDIN_FILENO);
+		close_pipe(fd);
+
+		setenv("LESS", "FRSX", 0);
+
+		if (prctl(PR_SET_PDEATHSIG, SIGTERM) < 0)
+			_exit(EXIT_FAILURE);
+
+		if (getppid() != parent_pid)
+			_exit(EXIT_SUCCESS);
+
+		if (pager) {
+			execlp(pager, pager, NULL);
+			execl("/bin/sh", "sh", "-c", pager, NULL);
+		}
+
+		execlp("pager", "pager", NULL);
+		execlp("less", "less", NULL);
+		execlp("more", "more", NULL);
+
+		_exit(EXIT_FAILURE);
+	}
+
+	if (dup2(fd[1], STDOUT_FILENO) < 0) {
+		perror("Failed to duplicate pager pipe");
+		return;
+	}
+
+	close_pipe(fd);
+}
+
+void close_pager(void)
+{
+	if (pager_pid <= 0)
+		return;
+
+	fclose(stdout);
+	kill(pager_pid, SIGCONT);
+	wait_for_terminate(pager_pid);
+	pager_pid = 0;
+}

monitor/display.h

@@ -0,0 +1,30 @@
+/*
+ *
+ *  Wireless daemon for Linux
+ *
+ *  Copyright (C) 2013-2014  Intel Corporation. All rights reserved.
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, write to the Free Software
+ *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ */
+
+#include <stdbool.h>
+
+bool use_color(void);
+
+unsigned int num_columns(void);
+
+void open_pager(void);
+void close_pager(void);

monitor/main.c

@@ -35,6 +35,7 @@
 #include "linux/nl80211.h"
 #include "monitor/nlmon.h"
 #include "monitor/pcap.h"
+#include "monitor/display.h"
 
 static struct nlmon *nlmon = NULL;
 
@@ -264,6 +265,8 @@ int main(int argc, char *argv[])
 	if (reader_path) {
 		struct pcap *pcap;
 
+		open_pager();
+
 		pcap = pcap_open(reader_path);
 		if (!pcap) {
 			exit_status = EXIT_FAILURE;
@@ -277,6 +280,8 @@ int main(int argc, char *argv[])
 			exit_status = process_pcap(pcap);
 
 		pcap_close(pcap);
+
+		close_pager();
 		goto done;
 	}