linux-kernel - Re: [RFC 3/8] kmsg: introduce additional kmsg devices support

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Date:	Wed, 8 Jul 2015 13:10:58 +0200
From:	Petr Mladek <pmladek@...e.com>
To:	Marcin Niesluchowski <m.niesluchow@...sung.com>
Cc:	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-api@...r.kernel.org, Jonathan Corbet <corbet@....net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Tejun Heo <tj@...nel.org>, Kay Sievers <kay@...y.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Joe Perches <joe@...ches.com>,
	Karol Lewandowski <k.lewandowsk@...sung.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [RFC 3/8] kmsg: introduce additional kmsg devices support

On Fri 2015-07-03 12:49:50, Marcin Niesluchowski wrote:
> kmsg device provides operations on cyclic logging buffer used mainly
> by kernel but also in userspace by privileged processes.
> 
> Additional kmsg devices keep the same log format but may be added
> dynamically with custom size.
> 
> Signed-off-by: Marcin Niesluchowski <m.niesluchow@...sung.com>

> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -234,29 +234,37 @@ struct printk_log {
>  	u8 level:3;		/* syslog level */
>  };

Just in case, this is accepted. If you already touch the API, I would
suggest to rename struct printk_log to printk_msg. The current name
is pretty misleading.

> +struct log_buffer {
> +#ifdef CONFIG_PRINTK
> +	struct list_head list;	/* kmsg as head of the list */
> +	char *buf;		/* cyclic log buffer */
> +	u32 len;		/* buffer length */
> +	wait_queue_head_t wait;	/* wait queue for kmsg buffer */
> +#endif
>  /*
> - * The logbuf_lock protects kmsg buffer, indices, counters.  This can be taken
> - * within the scheduler's rq lock. It must be released before calling
> - * console_unlock() or anything else that might wake up a process.
> + * The lock protects kmsg buffer, indices, counters. This can be taken within
> + * the scheduler's rq lock. It must be released before calling console_unlock()
> + * or anything else that might wake up a process.
>   */
> -static DEFINE_RAW_SPINLOCK(logbuf_lock);
> +	raw_spinlock_t lock;
> +	u64 first_seq;		/* sequence number of the first record stored */
> +	u32 first_idx;		/* index of the first record stored */
> +/* sequence number of the next record to store */
> +	u64 next_seq;
> +#ifdef CONFIG_PRINTK
> +	u32 next_idx;		/* index of the next record to store */
> +	int mode;		/* mode of device (kmsg_sys only) */
> +	int minor;		/* minor representing buffer device */
> +#endif
> +};


> @@ -1069,10 +1253,10 @@ const struct file_operations kmsg_fops = {
>   */
>  void log_buf_kexec_setup(void)
>  {
> -	VMCOREINFO_SYMBOL(log_buf);
> -	VMCOREINFO_SYMBOL(log_buf_len);
> -	VMCOREINFO_SYMBOL(log_first_idx);
> -	VMCOREINFO_SYMBOL(log_next_idx);
> +	VMCOREINFO_SYMBOL(log_buf.buf);
> +	VMCOREINFO_SYMBOL(log_buf.len);
> +	VMCOREINFO_SYMBOL(log_buf.first_idx);
> +	VMCOREINFO_SYMBOL(log_buf.next_idx);

Have you tried to use this in crash or some other utility, please?
I guess that it will need to be exported a similar way like
struct printk_log, something like:

	VMCOREINFO_SYMBOL(log_buf);
	VMCOREINFO_STRUCT_SIZE(log_buffer);
	VMCOREINFO_OFFSET(log_buffer, buf);
	VMCOREINFO_OFFSET(log_buffer, len);
	VMCOREINFO_OFFSET(log_buffer, first_idx);
	VMCOREINFO_OFFSET(log_buffer, next_idx);

Best Regards,
Petr
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