lkml.org 
[lkml]   [2014]   [Jul]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 3/4] printk: honor LOG_PREFIX in msg_print_text()
Date
This patch fixes a problem similar to what was addressed in the
previous patch.

All paths that read and format log records (for consoles, and for
reading via syslog and /dev/kmsg) go through msg_print_text(). That
function starts with some logic to determine whether the given log
record when formatted should begin with a "prefix" string, and
whether it should end with a newline. That logic has a bug.

The LOG_PREFIX flag in a log record indicates that when it's
formatted, a log record should include a prefix. This is used to
force a record to begin a new line--even if its preceding log record
contained LOG_CONT (indicating its content should be combined with
the next record).

Like the previous patch, the problem occurs when these flags are
all set:
prev & LOG_CONT
msg->flags & LOG_PREFIX
msg->flags & LOG_CONT
In that case, "prefix" should be true but it is not.

The fix involves checking LOG_PREFIX when a message has its LOG_CONT
flag set, and in that case allowing "prefix" to become false only
if LOG_PREFIX is not set. I.e., the logic for "prefix" would become:

if (prev & LOG_CONT && !(msg->flags & LOG_PREFIX))
prefix = false;
if (msg->flags & LOG_CONT)
if (prev & LOG_CONT && !(msg->flags & LOG_PREFIX))
prefix = false;

However, note that this makes the (msg->flags & LOG_CONT) block
redunant--it's handled by the test just above it. The result
becomes quite a bit simpler than before.

The following table concisely defines the problem:

prev | msg | msg ||
CONT |PREFIX| CONT ||prefix
------+------+------++------
clear| clear| clear|| true
clear| clear| set || true
clear| set | clear|| true
clear| set | set || true
set | clear| clear||false
set | set | set ||false
set | set | clear|| true
set | set | set ||false <-- should be true

Signed-off-by: Alex Elder <elder@linaro.org>
---
kernel/printk/printk.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 9e9cf93..3f15d95 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1003,14 +1003,11 @@ static size_t msg_print_text(const struct printk_log *msg, enum log_flags prev,
bool newline = true;
size_t len = 0;

- if ((prev & LOG_CONT) && !(msg->flags & LOG_PREFIX))
+ if (prev & LOG_CONT && !(msg->flags & LOG_PREFIX))
prefix = false;

- if (msg->flags & LOG_CONT) {
- if (prev & LOG_CONT)
- prefix = false;
+ if (msg->flags & LOG_CONT)
newline = false;
- }

do {
const char *next = memchr(text, '\n', text_size);
--
1.9.1


\
 
 \ /
  Last update: 2014-07-16 20:21    [W:0.127 / U:0.588 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site