linux-kernel - Re: [RFC PATCH] vsprintf: Add %pv extension replacement for print_vma

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Message-ID: <20200817114441.GK1891694@smile.fi.intel.com>
Date:   Mon, 17 Aug 2020 14:44:41 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Joe Perches <joe@...ches.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [RFC PATCH] vsprintf: Add %pv extension replacement for
 print_vma_addr

On Fri, Aug 14, 2020 at 10:53:03AM -0700, Joe Perches wrote:
> There is a print_vma_addr function used several places
> that requires KERN_CONT use.
> 
> Add a %pv mechanism to avoid the need for KERN_CONT.

I like the idea, but I would accent the selling point to make code
(in the user call sites) nicer.

> An example conversion is arch/x86/kernel/signal.c
> 
> from:
> 	if (show_unhandled_signals && printk_ratelimit()) {
> 		printk("%s"
> 		       "%s[%d] bad frame in %s frame:%p ip:%lx sp:%lx orax:%lx",
> 		       task_pid_nr(current) > 1 ? KERN_INFO : KERN_EMERG,
> 		       me->comm, me->pid, where, frame,
> 		       regs->ip, regs->sp, regs->orig_ax);
> 		print_vma_addr(KERN_CONT " in ", regs->ip);
> 		pr_cont("\n");
> to:
> 		printk("%s"
> 		       "%s[%d] bad frame in %s frame:%p ip:%lx sp:%lx orax:%lx in %pv\n",
> 		       task_pid_nr(current) > 1 ? KERN_INFO : KERN_EMERG,
> 		       me->comm, me->pid, where, frame,
> 		       regs->ip, regs->sp, regs->orig_ax, (void *)regs->ip);

...

> +#else
> +	buf = string_nocheck(buf, end, "CONFIG_MMU=n", default_str_spec);
> +#endif

Can we avoid this spammy message? Really it's quite long and fills valuable
space in kernel buffer. I would rather print the hashed pointer as it's done
for the rest of %pXXX.

-- 
With Best Regards,
Andy Shevchenko