On Thu, 2017-03-02 at 14:35 +0900, Sergey Senozhatsky wrote:
> Hello Joe,
>
> On (02/28/17 19:17), Joe Perches wrote:
> > Can save the space that the KERN_<LEVEL> headers require.
> >
> > The biggest negative here is the %pV use which needs
> > recursion and adds stack depth.
> >
> > $ size vmlinux.o* (defconfig, x86-64)
> > text data bss dec hex filename
> > 12586135 1909841 777528 15273504 e90e20 vmlinux.o.new
> > 12590348 1909841 777528 15277717 e91e95 vmlinux.o.old
>
> interesting. 4K.
Yeah, more when more calls are converted,
Maybe more like 12k, still the goal is to
create singletons for the pr_fmt prefixes
and whatever __func__ uses that are most
common via a SOH + flag and using
__builtin_return_address where possible and
appropriate. That could shrink another 10k
or so.
> [..]
> > +#define define_pr_func(func, level) \
> > +asmlinkage __visible int func(const char *fmt, ...) \
> > +{ \
> > + va_list args; \
> > + int r; \
> > + struct va_format vaf; \
> > + \
> > + va_start(args, fmt); \
> > + vaf.fmt = fmt; \
> > + vaf.va = &args; \
> > + \
> > + r = printk(level "%pV", &vaf); \
> > + \
> > + va_end(args); \
> > + \
> > + return r; \
> > +} \
>
> hm. that's really hacky (which is a compliment) and a bit complicated.
> my quick thought was to tweak vprintk_emit() for 'facility != 0' so it
> could get loglevel (and adjust lflags) from the passed level, not from
> the text, and then do something like this
> #define define_pr_func(func, level) asmlinkage __visible int func(const char
> *fmt, ...)
> {
> va_start(args, fmt);
> r = vprintk_emit(level[0], level[1], NULL, 0, fmt, args);
> va_end();
> }
>
> but this won't do the trick. because func()->vprintk_emit() shortcut
> disables the printk-safe mechanism:
> func()->printk()->vprintk_func()->this_cpu(printk_context)::print()
That was what I had done originally a while ago
https://lkml.org/lkml/2016/6/23/652
Now the with "safe" version, it's a bit more complicated.
[stack depth can be high, ~400 bytes per recursion]
> dunno, at the moment I'm not really comfortable with %pV recursion
> for every pr_foo() call
Me neither really. I'd much prefer a direct vprintk_emit.
