dmesg: implement backwardly compatible --raw for /dev/kmsg

.. and if you really want raw data from /dev/kmsg then use dd(1) ;-)

Signed-off-by: Karel Zak <kzak@redhat.com>

2 files changed, 25 insertions, 2 deletions

diff --git a/sys-utils/dmesg.1 b/sys-utils/dmesg.1
index ff149a9e3..c67cfa14a 100644
--- a/sys-utils/dmesg.1
+++ b/sys-utils/dmesg.1
@@ -98,12 +98,23 @@ will
 print or clear the kernel ring buffer.
 .IP "\fB\-r\fR, \fB\-\-raw\fR"
 Print the raw message buffer, i.e., do not strip the log level prefixes.
+
+Note that the real raw format depends on method how
+.BR dmesg (1)
+reads kernel messages. The /dev/kmsg uses different format than
+.BR syslog (2) .
+For backward compatibility
+.BR dmesg (1)
+returns data always in
+.BR syslog (2)
+format. The real raw data from /dev/kmsg is possible to read for example by
+command 'dd if=/dev/kmsg iflag=nonblock'.
 .IP "\fB\-S\fR, \fB\-\-syslog\fR"
 Force to use
-.BR syslog(2)
+.BR syslog (2)
 kernel interface to read kernel messages. The default is to use /dev/kmsg rather
 than
-.BR syslog(2)
+.BR syslog (2)
 since kernel 3.5.0.
 .IP "\fB\-s\fR, \fB\-\-buffer-size \fIsize\fR
 Use a buffer of
diff --git a/sys-utils/dmesg.c b/sys-utils/dmesg.c
index 70c0a2e71..65ace3e81 100644
--- a/sys-utils/dmesg.c
+++ b/sys-utils/dmesg.c
@@ -702,6 +702,16 @@ static void print_record(struct dmesg_control *ctl, struct dmesg_record *rec)
 		return;
 	}
 
+	if (ctl->raw) {
+		/* compose syslog(2) compatible output */
+		printf("<%d>[%5d.%06d] ",
+			LOG_MAKEPRI(rec->facility, rec->level),
+			(int) rec->tv.tv_sec,
+			(int) rec->tv.tv_usec);
+
+		goto mesg;
+	}
+
 	if (ctl->decode && rec->level >= 0 && rec->facility >= 0)
 		printf("%-6s:%-6s: ", facility_names[rec->facility].name,
 				      level_names[rec->level].name);
@@ -744,6 +754,7 @@ static void print_record(struct dmesg_control *ctl, struct dmesg_record *rec)
 	    !ctl->notime && !ctl->delta && !ctl->ctime)
 		printf("[%5d.%06d] ", (int) rec->tv.tv_sec, (int) rec->tv.tv_usec);
 
+mesg:
 	safe_fwrite(rec->mesg, rec->mesg_size, stdout);
 
 	if (*(rec->mesg + rec->mesg_size - 1) != '\n')
@@ -893,6 +904,7 @@ static int read_kmsg(struct dmesg_control *ctl)
 
 		if (parse_kmsg_record(ctl, &rec, buf, (size_t) sz) != 0)
 			continue;
+
 		print_record(ctl, &rec);
 	} while (1);