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

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Message-ID: <51F65D6F.40104@huawei.com>
Date:	Mon, 29 Jul 2013 20:17:51 +0800
From:	Rui Xiang <rui.xiang@...wei.com>
To:	Gu Zheng <guz.fnst@...fujitsu.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

On 2013/7/29 18:37, Gu Zheng wrote:
> 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?
> 

No. While using ns_printk, a parameter ns shouled be passed to identify syslog_ns.
If this ns has been created, it has a own log_buf to store logs. Otherwise this ns
comes from current->user_ns. When it is inis_syslog_ns the logs will be printed 
out in host.

> 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?
> 

ok, I will have a try to do it.:)

Thanks.


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