Re: printk: what is going on with additional newlines?

Sergey Senozhatsky
2017-08-28T12:20:52Z

On (08/28/17 19:28), Sergey Senozhatsky wrote:
> On (08/28/17 11:05), Pavel Machek wrote:
> > Hi!
> >
> > In 4.13-rc, printk("foo"); printk("bar"); seems to produce
> > foo\nbar. That's... quite surprising/unwelcome. What is going on
> > there? Are timestamps responsible?
>
> well, one thing we know for sure it is not related to this patch set ;)
>
>
> does any of the below patches fix the problem for you?
>
> basically it sets up the rule -- if we don't have LOG_NEWLINE lflags
> then we enforce LOG_CONT.

[..]

> @@ -1670,7 +1670,9 @@ static size_t log_output(int facility, int level, enum log_flags lflags, const c
> * write from the same process, try to add it to the buffer.
> */
> if (cont.len) {
> if (cont.owner == current && (lflags & LOG_CONT)) {

on the other hand... I don't think I like that check at all.
so I *probably* want to change it to -- !LOG_NEWLINE messages of the
same loglevel AND from the same task are getting concatenated.
a message with LOG_NEWLINE flushes the cont buffer.

for example:

printk("foo"); printk("foo"); printk("bar\n");
printk("buz"); printk("buz"); printk("buz"); pr_info("INFO msg\n");
printk("buz"); printk("buz"); printk("buz"); pr_err("ERR msg\n");
printk(KERN_CONT"foo"); printk(KERN_CONT"foo"); printk(KERN_CONT"bar\n");
printk(KERN_CONT"foo"); printk(KERN_CONT"foo"); printk(KERN_ERR"bar\n");
printk(KERN_CONT"foo"); printk(KERN_ERR"foo err"); printk(KERN_ERR"bar err\n");

for instance,
printk(KERN_ERR"foo err"); printk(KERN_ERR"bar err\n");

should produce "foo errbar err\n". from the same task and of
the same loglevel, no new line. must be cont messages with a missing
KERN_CONT. right?

so, for the examples I posted above, I think, the output must be

foofoobar
buzbuzbuz
INFO msg
buzbuzbuz
ERR msg
foofoobar
foofoo
bar
foo
foo errbar err

how about something like this?

---

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index fc47863f629c..675febf84dc8 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1670,10 +1670,9 @@ static size_t log_output(int facility, int level, enum log_flags lflags, const c
* write from the same process, try to add it to the buffer.
*/
if (cont.len) {
- if (cont.owner == current && (lflags & LOG_CONT)) {
+ if (cont.owner == current && cont.level == level)
if (cont_add(facility, level, lflags, text, text_len))
return text_len;
- }
/* Otherwise, make sure it's flushed */
cont_flush();
}