Messages in this thread | | | Date | Thu, 27 Apr 2017 17:11:21 +0200 | From | Petr Mladek <> | Subject | Re: [RFC PATCH] printk: Make functions of pr_<level> macros |
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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
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