Re: the printk problem

On Sat, Jul 5, 2008 at 3:24 PM, Jan Engelhardt [off-list ref] wrote:

On Saturday 2008-07-05 14:52, Vegard Nossum wrote:

quoted

quoted

On Saturday 2008-07-05 00:01, Andrew Morton wrote:

quoted

We don't know how much interest there would be in churning NIPQUAD from
the net guys.  Interestingly, there's also %C (wint_t) which is a
32-bit quantity.  So we could just go and say "%C prints an ipv4
address" and be done with it.  But there's no way of doing that for
ipv6 addresses so things would become asymmetrical there.

       struct in6_addr src;
       printk("Source address: %p{ipv6}\n", &src);

How about %p{feature}?

Something like this?

+static char *custom_format(char *buf, char *end,
+      const char *fmt, unsigned int fmtlen, void *arg)

I'd use const void *arg here, so nobody gets the idea
that you could modify the argument while printing :)

Oops, of course. Thanks.

quoted

+{
+      if (!strncmp(fmt, "sym", fmtlen)) {

...

quoted

+      }

And I assume it's then as simple as

       } else if (strncmp(fmt, "nip6", fmtlen) == 0) {
               snprintf(buf, end - buf (+1?), NIP6_FMT in expanded form,
                        NIP6 in expanded form(arg));
       }

Hm, that's going to get a big function when everyone adds their
fmttypes.

Yes. Luckily, the entry point is then fixed in a single place and it's
easy to convert it into something more dynamic :-)

A static array wouldn't help much because it still concentrates all
the names. But we could at least do a binary search on that and get
some speed improvements if it grows large.

I think the most elegant solution would be a macro similar to the
initcall macros, that adds the custom extensions to a table which is
defined by a special linker section. This allows complete
decentralization, but I don't think it's possible to do binary search
on the names anymore.

Dynamic registering/unregistering could be done too. Maybe this is a
good thing for modules...

Thoughts?

quoted

+
+      return buf;
+}
+
static char *number(char *buf, char *end, unsigned long long num, int base, int size, int precision, int type)
{
      /* we are called with base 8, 10 or 16, only, thus don't need "G..."  */

@@ -648,6 +673,25 @@ int vsnprintf(char *buf, size_t size, const char *fmt, va_list args)
                              continue;

                      case 'p':
+                              if (fmt[1] == '{') {
+                                      const char *cfmt;
+
+                                      /* Skip the '%{' */
+                                      ++fmt;
+                                      ++fmt;
+

Not this?

       /* Skip the '%p{' */
       fmt += 3;

Oops, the comment is wrong. It should say: "Skip the p{". But fmt += 3
is wrong. Since fmt[0] is at this point 'p', and fmt[1] is '{'. The %
and flags, etc. have already been skipped by the common code. So it
should be fmt += 2 :-)

Thanks!


Vegard

-- 
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
	-- E. W. Dijkstra, EWD1036