linux-kernel - Re: [PATCH v1 2/5] relayfs: introduce dump of relayfs statistics function

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Message-Id: <20250513185810.3d57dfe2a0c05784ddf8f0a9@kernel.org>
Date: Tue, 13 May 2025 18:58:10 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Jason Xing <kerneljasonxing@...il.com>
Cc: axboe@...nel.dk, rostedt@...dmis.org, mathieu.desnoyers@...icios.com,
 akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
 linux-block@...r.kernel.org, linux-trace-kernel@...r.kernel.org, Jason Xing
 <kernelxing@...cent.com>, Yushan Zhou <katrinzhou@...cent.com>
Subject: Re: [PATCH v1 2/5] relayfs: introduce dump of relayfs statistics
 function

Hi Jason,

On Mon, 12 May 2025 10:49:32 +0800
Jason Xing <kerneljasonxing@...il.com> wrote:

> From: Jason Xing <kernelxing@...cent.com>
> 
> In this version, only support dumping the counter for buffer full and
> implement the framework of how it works. Users MUST pass a valid @buf
> with a valid @len that is required to be larger than RELAY_DUMP_BUF_MAX_LEN
> to acquire which information indicated by @flags to dump.
> 
> RELAY_DUMP_BUF_MAX_LEN shows the maximum len of the buffer if users
> choose to dump all the values.
> 
> Users can use this buffer to do whatever they expect in their own kernel
> module, say, print to console/dmesg or write them into the relay buffer.
> 
> Reviewed-by: Yushan Zhou <katrinzhou@...cent.com>
> Signed-off-by: Jason Xing <kernelxing@...cent.com>
> ---
>  include/linux/relay.h | 10 ++++++++++
>  kernel/relay.c        | 35 +++++++++++++++++++++++++++++++++++
>  2 files changed, 45 insertions(+)
> 
> diff --git a/include/linux/relay.h b/include/linux/relay.h
> index 022cf11e5a92..7a442c4cbead 100644
> --- a/include/linux/relay.h
> +++ b/include/linux/relay.h
> @@ -31,6 +31,15 @@
>  /*
>   * Relay buffer error statistics dump
>   */
> +enum {
> +	RELAY_DUMP_BUF_FULL = (1 << 0),
> +
> +	RELAY_DUMP_LAST = RELAY_DUMP_BUF_FULL,
> +	RELAY_DUMP_MASK = (RELAY_DUMP_LAST - 1) | RELAY_DUMP_LAST
> +};
> +
> +#define RELAY_DUMP_BUF_MAX_LEN 32
> +
>  struct rchan_buf_error_stats
>  {
>  	unsigned int full;		/* counter for buffer full */
> @@ -170,6 +179,7 @@ extern int relay_late_setup_files(struct rchan *chan,
>  				  struct dentry *parent);
>  extern void relay_close(struct rchan *chan);
>  extern void relay_flush(struct rchan *chan);
> +extern void relay_dump(struct rchan *chan, char *buf, int len, int flags);
>  extern void relay_subbufs_consumed(struct rchan *chan,
>  				   unsigned int cpu,
>  				   size_t consumed);
> diff --git a/kernel/relay.c b/kernel/relay.c
> index b5db4aa60da1..0e675a77285c 100644
> --- a/kernel/relay.c
> +++ b/kernel/relay.c
> @@ -810,6 +810,41 @@ void relay_flush(struct rchan *chan)
>  }
>  EXPORT_SYMBOL_GPL(relay_flush);
>  
> +/**
> + *	relay_dump - dump statistics of the specified channel buffer
> + *	@chan: the channel
> + *	@buf: buf to store statistics
> + *	@len: len of buf to check
> + *	@flags: select particular information to dump
> + */
> +void relay_dump(struct rchan *chan, char *buf, int len, int flags)
> +{
> +	unsigned int i, full_counter = 0;
> +	struct rchan_buf *rbuf;
> +	int offset = 0;
> +
> +	if (!chan || !buf || flags & ~RELAY_DUMP_MASK)
> +		return;
> +
> +	if (len < RELAY_DUMP_BUF_MAX_LEN)
> +		return;
> +
> +	if (chan->is_global) {
> +		rbuf = *per_cpu_ptr(chan->buf, 0);
> +		full_counter = rbuf->stats.full;
> +	} else {
> +		for_each_possible_cpu(i) {
> +			if ((rbuf = *per_cpu_ptr(chan->buf, i)))
> +				full_counter += rbuf->stats.full;
> +	}
> +
> +	if (flags & RELAY_DUMP_BUF_FULL)
> +		offset += snprintf(buf, sizeof(unsigned int), "%u", full_counter);
> +
> +	snprintf(buf + offset, 1, "\n");

Is there any reason to return the value as string?
If it returns a digit value and the caller makes it a string,
it could be more flexible for other use cases.

Thank you,

> +}
> +EXPORT_SYMBOL_GPL(relay_dump);
> +
>  /**
>   *	relay_file_open - open file op for relay files
>   *	@inode: the inode
> -- 
> 2.43.5
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>