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