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SubjectRe: [PATCH] printk: inject caller information into the body of message
Hi, Steven

On (09/12/18 12:05), Steven Rostedt wrote:
> > : Introduce a few helper functions for it:
> > :
> > : init_line_buffer(&buf);
> > : print_line(&buf, fmt, args);
> > : vprint_line(&buf, fmt, vararg);
> > : finish_line(&buf);
> > :
>
> This sounds like seq_buf to me.

Correct.

> > +struct pr_line {
> > + char *buffer;
> > + int size;
> > + int len;
> > + char *level;
> > +};
>
> Can you look at implementing this with using a seq_buf?

Certainly, attached.

It doesn't seem to save us that much code, tho. It looks smaller just
because I dropped "truncated" print out and didn't include !CONFIG_PRINTK
noise this time around. And the OK thing about previous version was that
it didn't introduce any new dependencies to printk.

Making pr_line available via printk.h -- #include seq_buf.h in printk.h - at
glance looks like some fun. printk.h is getting included very early, before
we have all the stuff that seq_buf.h wants - we can remove fs.h from
seq_buf.h and add a bunch of forward declarations for path and seq_file;
but all those BUG_ON/WARN_ON/etc is another story (unless we want every
pr_line user to include seq_buf.h).

... maybe I can change API. But I sort of like that implicit buffer case:

DEFINE_PR_LINE(KERN_ERR, pl);

pr_line(&pl, "Hello, ");
pr_line(&pl, "%s.\n", "Steven");

And, looking at potential users of pr_line, I'd say that we better
have DEFINE_PR_LINE_BUF, because some of them do print messages longer
than 80 chars.

===

From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Subject: [PATCH] lib/seq_buf: add pr_line buffering API

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
include/linux/seq_buf.h | 35 +++++++++++++++++++++++++++++++
lib/seq_buf.c | 46 +++++++++++++++++++++++++++++++++++++++++
2 files changed, 81 insertions(+)

diff --git a/include/linux/seq_buf.h b/include/linux/seq_buf.h
index aa5deb041c25..5e9a5ff9a440 100644
--- a/include/linux/seq_buf.h
+++ b/include/linux/seq_buf.h
@@ -23,6 +23,36 @@ struct seq_buf {
loff_t readpos;
};

+#define __SEQ_BUF_INITIALIZER(buf, length) { \
+ .buffer = (buf), \
+ .size = (length), \
+ .len = 0, \
+ .readpos = 0, }
+
+#ifdef CONFIG_PRINTK
+#define __PR_LINE_BUF_SZ 80
+#else
+#define __PR_LINE_BUF_SZ 0
+#endif
+
+struct pr_line {
+ struct seq_buf sb;
+ char *level;
+};
+
+#define DEFINE_PR_LINE(lev, name) \
+ char __line[__PR_LINE_BUF_SZ]; \
+ struct pr_line name = { \
+ .sb = __SEQ_BUF_INITIALIZER(__line, __PR_LINE_BUF_SZ), \
+ .level = lev, \
+ }
+
+#define DEFINE_PR_LINE_BUF(lev, name, buf, sz) \
+ struct pr_line name = { \
+ .sb = __SEQ_BUF_INITIALIZER(buf, (sz)), \
+ .level = lev, \
+ }
+
static inline void seq_buf_clear(struct seq_buf *s)
{
s->len = 0;
@@ -131,4 +161,9 @@ extern int
seq_buf_bprintf(struct seq_buf *s, const char *fmt, const u32 *binary);
#endif

+extern __printf(2, 0)
+int vpr_line(struct pr_line *pl, const char *fmt, va_list args);
+extern __printf(2, 3)
+int pr_line(struct pr_line *pl, const char *fmt, ...);
+extern void pr_line_flush(struct pr_line *pl);
#endif /* _LINUX_SEQ_BUF_H */
diff --git a/lib/seq_buf.c b/lib/seq_buf.c
index 11f2ae0f9099..29bc4f24b83e 100644
--- a/lib/seq_buf.c
+++ b/lib/seq_buf.c
@@ -324,3 +324,49 @@ int seq_buf_to_user(struct seq_buf *s, char __user *ubuf, int cnt)
s->readpos += cnt;
return cnt;
}
+
+int vpr_line(struct pr_line *pl, const char *fmt, va_list args)
+{
+ struct seq_buf *s = &pl->sb;
+ int ret, len;
+
+ if (fmt[0] == '\n') {
+ pr_line_flush(pl);
+ return 0;
+ }
+
+ ret = seq_buf_vprintf(s, fmt, args);
+
+ len = seq_buf_used(s);
+ if (len && s->buffer[len - 1] == '\n')
+ pr_line_flush(pl);
+
+ return ret;
+}
+EXPORT_SYMBOL(vpr_line);
+
+int pr_line(struct pr_line *pl, const char *fmt, ...)
+{
+ va_list ap;
+ int ret;
+
+ va_start(ap, fmt);
+ ret = vpr_line(pl, fmt, ap);
+ va_end(ap);
+
+ return ret;
+}
+EXPORT_SYMBOL(pr_line);
+
+void pr_line_flush(struct pr_line *pl)
+{
+ struct seq_buf *s = &pl->sb;
+ int len = seq_buf_used(s);
+
+ if (!len)
+ return;
+
+ printk("%s%.*s", pl->level, len, s->buffer);
+ seq_buf_clear(s);
+}
+EXPORT_SYMBOL(pr_line_flush);
--
2.19.0
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