Re: [PATCH v4 3/7] trace-cmd: Fix tracecmd_read_page_record() to read more than one event

[Slavomir Kaslev <kaslevs@vmware.com>]

On Fri, Feb 22, 2019 at 04:28:32PM +0200, Tzvetomir Stoyanov wrote:
> The kbuffer_next_event() will return the next event on the sub buffer.
> If we pass in the last_record to tracecmd_read_page_record(), it
> initializes the sub buffer, and by calling kbuffer_next_event()
> (instead of kbuffer_read_event()), the second event on the sub buffer
> is returned. This causes the match of the last_record not to match if
> the last_record happens to be the first event on the sub buffer.
> 
> Signed-off-by: Tzvetomir Stoyanov <tstoyanov@vmware.com>
> ---
>  lib/trace-cmd/trace-input.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/lib/trace-cmd/trace-input.c b/lib/trace-cmd/trace-input.c
> index be6720c..0a6e820 100644
> --- a/lib/trace-cmd/trace-input.c
> +++ b/lib/trace-cmd/trace-input.c
> @@ -1679,18 +1679,22 @@ tracecmd_read_page_record(struct tep_handle *pevent, void *page, int size,
>  			goto out_free;
>  		}
>  
> -		do {
> +		ptr = kbuffer_read_event(kbuf, &ts);
> +		while (ptr < last_record->data) {
>  			ptr = kbuffer_next_event(kbuf, NULL);
>  			if (!ptr)
>  				break;
> -		} while (ptr < last_record->data);

Looks good to me with a nit: the following check is not necessary

> +			if (ptr == last_record->data)
> +				break;

since the `while ()` condition above will be already false if this holds. Or am
I missing something here?

Thank you,

-- Slavi

> +		}
>  		if (ptr != last_record->data) {
>  			warning("tracecmd_read_page_record: could not find last_record");
>  			goto out_free;
>  		}
> -	}
> +		ptr = kbuffer_next_event(kbuf, &ts);
> +	} else
> +		ptr = kbuffer_read_event(kbuf, &ts);
>  
> -	ptr = kbuffer_read_event(kbuf, &ts);
>  	if (!ptr)
>  		goto out_free;
>  
> -- 
> 2.20.1
>