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

Sergey Senozhatsky
2017-08-28T10:28:15Z

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.

---

@@ -1721,9 +1723,13 @@ asmlinkage int vprintk_emit(int facility, int level,
text_len = vscnprintf(text, sizeof(textbuf), fmt, args);

/* mark and strip a trailing newline */
- if (text_len && text[text_len-1] == '\n') {
- text_len--;
- lflags |= LOG_NEWLINE;
+ if (text_len) {
+ if (text[text_len-1] == '\n') {
+ text_len--;
+ lflags |= LOG_NEWLINE;
+ } else {
+ lflags |= LOG_CONT;
+ }
}

/* strip kernel syslog prefix and extract log level or control flags */

---

=== 8< === 8< ===

or... an alternative "solution"

---

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index fc47863f629c..5fd567abc5e6 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -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)) {
+ if (cont.owner == current &&
+ ((lflags & LOG_CONT) ||
+ !(lflags & LOG_NEWLINE))) {
if (cont_add(facility, level, lflags, text, text_len))
return text_len;
}

---

-ss