linux-kernel - Re: [RFC PATCH] printk: Make functions of pr

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Message-ID: <1493309301.18659.47.camel@perches.com>
Date:   Thu, 27 Apr 2017 09:08:21 -0700
From:   Joe Perches <joe@...ches.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [RFC PATCH] printk: Make functions of pr_<level> macros

On Thu, 2017-04-27 at 17:11 +0200, Petr Mladek wrote:
> On Wed 2017-03-01 21:58:54, Joe Perches wrote:
> > On Thu, 2017-03-02 at 14:35 +0900, Sergey Senozhatsky wrote:
> > > 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.
[]
> > 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_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.

I believe EXPORT_SYMBOL functions have been modified
in the past, but don't have an example at hand.

> 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.

That might work.

> 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.
> 
> :-(

Yeah, that too.