linux-kernel - Re: [PATCH 8/9] syslog_ns: implement ns_printk for specific syslog

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Date:	Mon, 29 Jul 2013 18:37:24 +0800
From:	Gu Zheng <guz.fnst@...fujitsu.com>
To:	Rui Xiang <rui.xiang@...wei.com>
CC:	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, serge.hallyn@...ntu.com,
	ebiederm@...ssion.com, akpm@...ux-foundation.org,
	gaofeng@...fujitsu.com, libo.chen@...wei.com
Subject: Re: [PATCH 8/9] syslog_ns: implement ns_printk for specific syslog_ns

Hi Rui,

On 07/29/2013 10:31 AM, Rui Xiang wrote:

> Add a new interface named ns_printk, and assign an
> patamater ns. Log which belong to a container can
> be printed by ns_printk.

One question, with the syslog_ns used, do the log we print by *printk* in the
host contains the log in each syslog_ns(print out with ns_printk) or not?

Thanks,
Gu

> 
> Signed-off-by: Rui Xiang <rui.xiang@...wei.com>
> ---
>  include/linux/printk.h |  4 ++++
>  kernel/printk.c        | 53 ++++++++++++++++++++++++++++++++++++++++++++++----
>  2 files changed, 53 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/printk.h b/include/linux/printk.h
> index 29e3f85..bf83ad9 100644
> --- a/include/linux/printk.h
> +++ b/include/linux/printk.h
> @@ -6,6 +6,7 @@
>  #include <linux/kern_levels.h>
>  #include <linux/linkage.h>
>  
> +struct syslog_namespace;
>  extern const char linux_banner[];
>  extern const char linux_proc_banner[];
>  
> @@ -123,6 +124,9 @@ asmlinkage int printk_emit(int facility, int level,
>  asmlinkage __printf(1, 2) __cold
>  int printk(const char *fmt, ...);
>  
> +asmlinkage __printf(2, 3) __cold
> +int ns_printk(struct syslog_namespace *ns, const char *fmt, ...);
> +
>  /*
>   * Special printk facility for scheduler use only, _DO_NOT_USE_ !
>   */
> diff --git a/kernel/printk.c b/kernel/printk.c
> index 6b561db..56a8b27 100644
> --- a/kernel/printk.c
> +++ b/kernel/printk.c
> @@ -1554,9 +1554,10 @@ static size_t cont_print_text(char *text, size_t size)
>  	return textlen;
>  }
>  
> -asmlinkage int vprintk_emit(int facility, int level,
> -			    const char *dict, size_t dictlen,
> -			    const char *fmt, va_list args)
> +static int ns_vprintk_emit(int facility, int level,
> +			const char *dict, size_t dictlen,
> +			const char *fmt, va_list args,
> +			struct syslog_namespace *ns)
>  {
>  	static int recursion_bug;
>  	static char textbuf[LOG_LINE_MAX];
> @@ -1566,7 +1567,6 @@ asmlinkage int vprintk_emit(int facility, int level,
>  	unsigned long flags;
>  	int this_cpu;
>  	int printed_len = 0;
> -	struct syslog_namespace *ns = &init_syslog_ns;
>  
>  	boot_delay_msec(level);
>  	printk_delay();
> @@ -1697,6 +1697,14 @@ out_restore_irqs:
>  
>  	return printed_len;
>  }
> +
> +asmlinkage int vprintk_emit(int facility, int level,
> +				const char *dict, size_t dictlen,
> +				const char *fmt, va_list args)
> +{
> +	return ns_vprintk_emit(facility, level, dict, dictlen, fmt, args,
> +				&init_syslog_ns);
> +}
>  EXPORT_SYMBOL(vprintk_emit);
>  
>  asmlinkage int vprintk(const char *fmt, va_list args)
> @@ -1762,6 +1770,43 @@ asmlinkage int printk(const char *fmt, ...)
>  }
>  EXPORT_SYMBOL(printk);
>  
> +/**
> + * ns_printk - print a kernel message in syslog_ns
> + * @ns: syslog namespace
> + * @fmt: format string
> + *
> + * This is ns_printk().
> + * It can be called from container context. We add a param
> + * ns to record current syslog namespace, because we need to
> + * print some log which are not generated by host, but contaner.
> + *
> + * See the vsnprintf() documentation for format string extensions over C99.
> + **/
> +asmlinkage int ns_printk(struct syslog_namespace *ns,
> +					const char *fmt, ...)
> +{
> +	va_list args;
> +	int r;
> +
> +	if (!ns)
> +		ns = current_user_ns()->syslog_ns;
> +
> +#ifdef CONFIG_KGDB_KDB
> +	if (unlikely(kdb_trap_printk)) {
> +		va_start(args, fmt);
> +		r = vkdb_printf(fmt, args);
> +		va_end(args);
> +		return r;
> +	}
> +#endif
> +	va_start(args, fmt);
> +	r = ns_vprintk_emit(0, -1, NULL, 0, fmt, args, ns);
> +	va_end(args);
> +
> +	return r;
> +}
> +EXPORT_SYMBOL(ns_printk);
> +

Here can we do some clean up to printk using ns_printk?

>  #else /* CONFIG_PRINTK */
>  
>  #define LOG_LINE_MAX		0


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