From d39f3d77c9b1fe7cc33a14beb4a4849af0a4ac22 Mon Sep 17 00:00:00 2001 From: Kay Sievers Date: Mon, 16 Jul 2012 18:35:30 -0700 Subject: 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 Signed-off-by: Greg Kroah-Hartman --- Documentation/ABI/testing/dev-kmsg | 29 ++++++++++++++++++++--------- kernel/printk.c | 23 +++++++++++++++++++++-- 2 files changed, 41 insertions(+), 11 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 diff --git a/kernel/printk.c b/kernel/printk.c index 6c3d5bf14da2..a41106e19077 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -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++) { -- cgit v1.2.3