Add support for 'dmesg -c' which clears the dmesg buffer after it has

been printed.  This provides compatibility with other *nix systems
(including Linux).

While here use stdbool booleans for 'all'.

PR:		bin/178295
Submitted by:	Levent Serinol <lserinol@gmail.com>
Reviewed by:	will

2 files changed, 18 insertions, 6 deletions

diff --git a/sbin/dmesg/dmesg.8 b/sbin/dmesg/dmesg.8
index 9d05e6c..b5004f5 100644
--- a/sbin/dmesg/dmesg.8
+++ b/sbin/dmesg/dmesg.8
@@ -36,7 +36,7 @@
 .Nd "display the system message buffer"
 .Sh SYNOPSIS
 .Nm
-.Op Fl a
+.Op Fl ac
 .Op Fl M Ar core Op Fl N Ar system
 .Sh DESCRIPTION
 The
@@ -59,6 +59,8 @@ Show all data in the message buffer.
 This includes any syslog records and
 .Pa /dev/console
 output.
+.It Fl c
+Clear the kernel buffer after printing.
 .It Fl M
 Extract values associated with the name list from the specified core.
 .It Fl N
diff --git a/sbin/dmesg/dmesg.c b/sbin/dmesg/dmesg.c
index 002732c..1d548a7 100644
--- a/sbin/dmesg/dmesg.c
+++ b/sbin/dmesg/dmesg.c
@@ -54,6 +54,7 @@ __FBSDID("$FreeBSD$");
 #include <locale.h>
 #include <nlist.h>
 #include <stdio.h>
+#include <stdbool.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
@@ -79,15 +80,20 @@ main(int argc, char *argv[])
 	kvm_t *kd;
 	size_t buflen, bufpos;
 	long pri;
-	int all, ch;
+	int ch, clear;
+	bool all;
 
-	all = 0;
+	all = false;
+	clear = false;
 	(void) setlocale(LC_CTYPE, "");
 	memf = nlistf = NULL;
-	while ((ch = getopt(argc, argv, "aM:N:")) != -1)
+	while ((ch = getopt(argc, argv, "acM:N:")) != -1)
 		switch(ch) {
 		case 'a':
-			all++;
+			all = true;
+			break;
+		case 'c':
+			clear = true;
 			break;
 		case 'M':
 			memf = optarg;
@@ -190,12 +196,16 @@ main(int argc, char *argv[])
 		(void)strvisx(visbp, p, nextp - p, 0);
 		(void)printf("%s", visbp);
 	}
+	if (clear)
+		if (sysctlbyname("kern.msgbuf_clear", NULL, NULL, &clear, sizeof(int)))
+			err(1, "sysctl kern.msgbuf_clear");
+
 	exit(0);
 }
 
 void
 usage(void)
 {
-	(void)fprintf(stderr, "usage: dmesg [-a] [-M core [-N system]]\n");
+	fprintf(stderr, "usage: dmesg [-ac] [-M core [-N system]]\n");
 	exit(1);
 }