kmsg - export "continuation record" flag to /dev/kmsg

In some cases we are forced to store individual records for a continuation
line print.

Export a flag to allow the external re-construction of the line. The flag
allows us to apply a similar logic externally which is used internally when
the console, /proc/kmsg or the syslog() output is printed.

  $ cat /dev/kmsg
  4,165,0,-;Free swap  = 0kB
  4,166,0,-;Total swap = 0kB
  6,167,0,c;[
  4,168,0,+;0
  4,169,0,+;1
  4,170,0,+;2
  4,171,0,+;3
  4,172,0,+;]
  6,173,0,-;[0 1 2 3 ]
  6,174,0,-;Console: colour VGA+ 80x25
  6,175,0,-;console [tty0] enabled

Signed-off-by: Kay Sievers <kay@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 20 insertions, 9 deletions

diff --git a/Documentation/ABI/testing/dev-kmsg b/Documentation/ABI/testing/dev-kmsg
index 281ecc5f9709..7e7e07a82e0e 100644
--- a/Documentation/ABI/testing/dev-kmsg
+++ b/Documentation/ABI/testing/dev-kmsg
@@ -58,16 +58,18 @@ Description:	The /dev/kmsg character device node provides userspace access
 
 		The output format consists of a prefix carrying the syslog
 		prefix including priority and facility, the 64 bit message
-		sequence number and the monotonic timestamp in microseconds.
-		The values are separated by a ','. Future extensions might
-		add more comma separated values before the terminating ';'.
-		Unknown values should be gracefully ignored.
+		sequence number and the monotonic timestamp in microseconds,
+		and a flag field. All fields are separated by a ','.
+
+		Future extensions might add more comma separated values before
+		the terminating ';'. Unknown fields and values should be
+		gracefully ignored.
 
 		The human readable text string starts directly after the ';'
 		and is terminated by a '\n'. Untrusted values derived from
 		hardware or other facilities are printed, therefore
-		all non-printable characters in the log message are escaped
-		by "\x00" C-style hex encoding.
+		all non-printable characters and '\' itself in the log message
+		are escaped by "\x00" C-style hex encoding.
 
 		A line starting with ' ', is a continuation line, adding
 		key/value pairs to the log message, which provide the machine
@@ -75,11 +77,11 @@ Description:	The /dev/kmsg character device node provides userspace access
 		userspace.
 
 		Example:
-		7,160,424069;pci_root PNP0A03:00: host bridge window [io  0x0000-0x0cf7] (ignored)
+		7,160,424069,-;pci_root PNP0A03:00: host bridge window [io  0x0000-0x0cf7] (ignored)
 		 SUBSYSTEM=acpi
 		 DEVICE=+acpi:PNP0A03:00
-		6,339,5140900;NET: Registered protocol family 10
-		30,340,5690716;udevd[80]: starting version 181
+		6,339,5140900,-;NET: Registered protocol family 10
+		30,340,5690716,-;udevd[80]: starting version 181
 
 		The DEVICE= key uniquely identifies devices the following way:
 		  b12:8        - block dev_t
@@ -87,4 +89,13 @@ Description:	The /dev/kmsg character device node provides userspace access
 		  n8           - netdev ifindex
 		  +sound:card0 - subsystem:devname
 
+		The flags field carries '-' by default. A 'c' indicates a
+		fragment of a line. All following fragments are flagged with
+		'+'. Note, that these hints about continuation lines are not
+		neccessarily correct, and the stream could be interleaved with
+		unrelated messages, but merging the lines in the output
+		usually produces better human readable results. A similar
+		logic is used internally when messages are printed to the
+		console, /proc/kmsg or the syslog() syscall.
+
 Users:		dmesg(1), userspace kernel log consumers