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

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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>
This commit is contained in:
Kay Sievers 2012-07-16 18:35:30 -07:00 committed by Greg Kroah-Hartman
parent 96efedf149
commit d39f3d77c9
2 changed files with 41 additions and 11 deletions
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29
Documentation/ABI/testing/dev-kmsg
View File

@ -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

23
kernel/printk.c
View File

@ -361,6 +361,7 @@ static void log_store(int facility, int level,
struct devkmsg_user {
u64 seq;
u32 idx;
enum log_flags prev;
struct mutex lock;
char buf[8192];
};
@ -426,6 +427,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
struct log *msg;
u64 ts_usec;
size_t i;
char cont = '-';
size_t len;
ssize_t ret;
@ -463,8 +465,25 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
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++) {