Re: [PATCH v2 1/2] tracing: Allow custom read/write processing in trace_min_max_{write,read}()

[Steven Rostedt <rostedt@goodmis.org>]

On Thu, 21 Nov 2024 10:18:22 +0800
Wei Li <liwei391@huawei.com> wrote:

> The 'trace_min_max_fops' implements a generic function to read/write
> u64 values from tracefs, add support of custom read/write processing
> to allow special requirements.


Instead of making a new parameter in trace_min_max_param, why not just
change the hwlat "width" file to have its own ops. Then you can make
the trace_min_max_read() non-static, reuse that, and then have the
hwlat use its own write function. It would make it much more straight
forward.

That could be done for a fix that would be tagged as stable, and it
would also be a single patch.

Really, for a clean up (after that is done), the trace_min_max_fops
should be replaced to get rid of the "lock" parameter. Perhaps have a
trace_min_max_lock_fops. But Linus hates conditional locking, and I
don't blame him. I'm trying to clean up this code with using guard()s
and that conditional locking makes that not possible.

-- Steve



> 
> Signed-off-by: Wei Li <liwei391@huawei.com>
> ---
>  kernel/trace/trace.c | 13 ++++++++++---
>  kernel/trace/trace.h |  2 ++
>  2 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 2b64b3ec67d9..ab5ea6d7148c 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -7689,8 +7689,12 @@ trace_min_max_write(struct file *filp, const
> char __user *ubuf, size_t cnt, loff if (param->max && val >
> *param->max) err = -EINVAL;
>  
> -	if (!err)
> -		*param->val = val;
> +	if (!err) {
> +		if (unlikely(param->write))
> +			param->write(param->val, val);
> +		else
> +			*param->val = val;
> +	}
>  
>  	if (param->lock)
>  		mutex_unlock(param->lock);
> @@ -7723,7 +7727,10 @@ trace_min_max_read(struct file *filp, char
> __user *ubuf, size_t cnt, loff_t *ppo if (!param)
>  		return -EFAULT;
>  
> -	val = *param->val;
> +	if (unlikely(param->read))
> +		val = param->read(param->val);
> +	else
> +		val = *param->val;
>  
>  	if (cnt > sizeof(buf))
>  		cnt = sizeof(buf);
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index c866991b9c78..2aaf3030c466 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -2159,6 +2159,8 @@ static inline void sanitize_event_name(char
> *name) struct trace_min_max_param {
>  	struct mutex	*lock;
>  	u64		*val;
> +	u64		(*read)(u64 *val);
> +	void		(*write)(u64 *val, u64 data);
>  	u64		*min;
>  	u64		*max;
>  };