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>
diff --git a/Documentation/ABI/testing/dev-kmsg b/Documentation/ABI/testing/dev-kmsg
index 281ecc5..7e7e07a 100644
--- a/Documentation/ABI/testing/dev-kmsg
+++ b/Documentation/ABI/testing/dev-kmsg
@@ -58,16 +58,18 @@
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 @@
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 @@
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
diff --git a/kernel/printk.c b/kernel/printk.c
index 6c3d5bf..a41106e 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -361,6 +361,7 @@
struct devkmsg_user {
u64 seq;
u32 idx;
+ enum log_flags prev;
struct mutex lock;
char buf[8192];
};
@@ -426,6 +427,7 @@
struct log *msg;
u64 ts_usec;
size_t i;
+ char cont = '-';
size_t len;
ssize_t ret;
@@ -463,8 +465,25 @@
msg = log_from_idx(user->idx);
ts_usec = msg->ts_nsec;
do_div(ts_usec, 1000);
- len = sprintf(user->buf, "%u,%llu,%llu;",
- (msg->facility << 3) | msg->level, user->seq, ts_usec);
+
+ /*
+ * If we couldn't merge continuation line fragments during the print,
+ * export the stored flags to allow an optional external merge of the
+ * records. Merging the records isn't always neccessarily correct, like
+ * when we hit a race during printing. In most cases though, it produces
+ * better readable output. 'c' in the record flags mark the first
+ * fragment of a line, '+' the following.
+ */
+ if (msg->flags & LOG_CONT && !(user->prev & LOG_CONT))
+ cont = 'c';
+ else if ((msg->flags & LOG_CONT) ||
+ ((user->prev & LOG_CONT) && !(msg->flags & LOG_PREFIX)))
+ cont = '+';
+
+ len = sprintf(user->buf, "%u,%llu,%llu,%c;",
+ (msg->facility << 3) | msg->level,
+ user->seq, ts_usec, cont);
+ user->prev = msg->flags;
/* escape non-printable characters */
for (i = 0; i < msg->text_len; i++) {