On Wed 2017-03-01 21:58:54, Joe Perches wrote:
> 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
BTW: The above mentioned commit adds one argument to
vprintk_default(). But the symbol is exported. I am
not sure if we could break the API.
We might need to create alternative vprintk_* functions
(called vlprintk_* or so) that would have the extra parameter.
And call them from the existing vprintk_* ones. Sigh.
Also note that we might need to pass more information
via the extra parameter, for example, KERN_ERR + KERN_CONT.
> 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
Same here. We should avoid the recursion.
Best Regards,
Petr
