vsprintf: Convert to printbuf

This converts vsnprintf() to printbufs: instead of passing around raw
char * pointers for current buf position and end of buf, we have a real
type!

This makes the calling convention for our existing pretty printers a lot
saner and less error prone, plus printbufs add some new helpers that
make the code smaller and more readable, with a lot less crazy pointer
arithmetic.

There are a lot more refactorings to be done: this patch tries to stick
to just converting the calling conventions, as that needs to be done all
at once in order to avoid introducing a ton of wrappers that will just
be deleted.

Thankfully we have good unit tests for printf, and they have been run
and are all passing with this patch.

We have two new exported functions with this patch:
 - prt_printf(), which is like snprintf but outputs to a printbuf
 - prt_vprintf, like vsnprintf

These are the actual core print routines now - vsnprintf() is a wrapper
around prt_vprintf().

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index fe6efb24d151..5c4f4b6d36ab 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -207,6 +207,10 @@ extern int num_to_str(char *buf, int size,
 
 /* lib/printf utilities */
 
+struct printbuf;
+extern __printf(2, 3) void prt_printf(struct printbuf *out, const char *fmt, ...);
+extern __printf(2, 0) void prt_vprintf(struct printbuf *out, const char *fmt, va_list);
+
 extern __printf(2, 3) int sprintf(char *buf, const char * fmt, ...);
 extern __printf(2, 0) int vsprintf(char *buf, const char *, va_list);
 extern __printf(3, 4)