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Subject: Re: [PATCH] tools/lib/traceevent, perf tools: Handle %pU format
 correctly
To:     Qu Wenruo <wqu@suse.com>, linux-btrfs@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-trace-devel@vger.kernel.org
References: <20191016063920.20791-1-wqu@suse.com>
From:   Nikolay Borisov <nborisov@suse.com>
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Message-ID: <fb568719-d0da-fcad-0069-2717fc0ff376@suse.com>
Date:   Wed, 16 Oct 2019 10:39:40 +0300
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On 16.10.19 г. 9:39 ч., Qu Wenruo wrote:
> [BUG]
> For btrfs related events, there is a field for fsid, but perf never
> parse it correctly.
> 
>  # perf trace -e btrfS:qgroup_meta_convert xfs_io -f -c "pwrite 0 4k" \
>    /mnt/btrfs/file1
>      0.000 xfs_io/77915 btrfs:qgroup_meta_reserve:(nil)U: refroot=5(FS_TREE) type=0x0 diff=2
>                                                   ^^^^^^ Not a correct UUID
>      ...
> 
> [CAUSE]
> The pretty_print() function doesn't handle the %pU format correctly.
> In fact it doesn't handle %pU as uuid at all.
> 
> [FIX]
> Add a new functiono, print_uuid_arg(), to handle %pU correctly.
> 
> Now perf trace can at least print fsid correctly:
>      0.000 xfs_io/79619 btrfs:qgroup_meta_reserve:23ad1511-dd83-47d4-a79c-e96625a15a6e refroot=5(FS_TREE) type=0x0 diff=2
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
> Please note in above case, the @type and @diff are not properly showed.
> That's another problem, will be addressed in later patches.
> ---
>  tools/lib/traceevent/event-parse.c | 38 ++++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
> 
> diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
> index d948475585ce..4f730ed527b0 100644
> --- a/tools/lib/traceevent/event-parse.c
> +++ b/tools/lib/traceevent/event-parse.c
> @@ -18,6 +18,7 @@
>  #include <errno.h>
>  #include <stdint.h>
>  #include <limits.h>
> +#include <linux/uuid.h>
>  #include <linux/time64.h>
>  
>  #include <netinet/in.h>
> @@ -4508,6 +4509,33 @@ get_bprint_format(void *data, int size __maybe_unused,
>  	return format;
>  }
>  
> +static void print_uuid_arg(struct trace_seq *s, void *data, int size,
> +			   struct tep_event *event, struct tep_print_arg *arg)
> +{
> +	const char *fmt;
> +	unsigned char *buf;
> +
> +	fmt = "%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x";
> +	if (arg->type != TEP_PRINT_FIELD) {
> +		trace_seq_printf(s, "ARG TYPE NOT FIELID but %d", arg->type);
> +		return;
> +	}
> +
> +	if (!arg->field.field) {
> +		arg->field.field = tep_find_any_field(event, arg->field.name);
> +		if (!arg->field.field) {
> +			do_warning("%s: field %s not found",
> +				   __func__, arg->field.name);
> +			return;
> +		}
> +	}
> +	buf = data + arg->field.field->offset;
> +
> +	trace_seq_printf(s, fmt, buf[0], buf[1], buf[2], buf[3], buf[4], buf[5],
> +		         buf[6], buf[7], buf[8], buf[9], buf[10], buf[11], buf[12],
> +			 buf[13], buf[14], buf[15]);
> +}
> +
>  static void print_mac_arg(struct trace_seq *s, int mac, void *data, int size,
>  			  struct tep_event *event, struct tep_print_arg *arg)
>  {
> @@ -5074,6 +5102,16 @@ static void pretty_print(struct trace_seq *s, void *data, int size, struct tep_e
>  						arg = arg->next;
>  						break;
>  					}
> +				} else if (*ptr == 'U') {
> +					/* Those finetunings are ignored for now */

I think this comment is cryptic. What do you mean by "finetunings"?

> +					if (isalpha(ptr[1]))
> +						ptr += 2;
> +					else
> +						ptr++;
> +
> +					print_uuid_arg(s, data, size, event, arg);
> +					arg = arg->next;
> +					break;
>  				}
>  
>  				/* fall through */
>