Messages in this thread Patch in this message | | | From | Alex Elder <> | Subject | [PATCH 3/4] printk: honor LOG_PREFIX in msg_print_text() | Date | Wed, 16 Jul 2014 12:26:59 -0500 |
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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
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