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Date:   Thu, 17 Oct 2019 13:52:09 +0200
From:   David Sterba <dsterba@suse.cz>
To:     Qu Wenruo <wqu@suse.com>
Cc:     linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-trace-devel@vger.kernel.org
Subject: Re: [PATCH v2] tools/lib/traceevent, perf tools: Handle %pU format
 correctly
Message-ID: <20191017115209.GG2751@twin.jikos.cz>
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        linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-trace-devel@vger.kernel.org
References: <20191017022800.31866-1-wqu@suse.com>
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On Thu, Oct 17, 2019 at 10:28:00AM +0800, 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 function, 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>
> ---
> Changelog:
> v2:
> - Use more comment explaining the finetunings we skipped for %pU*
> - Use more elegant way to output uuid string
> ---
>  tools/lib/traceevent/event-parse.c | 56 ++++++++++++++++++++++++++++++
>  1 file changed, 56 insertions(+)
> 
> diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
> index d948475585ce..3c9473f46efe 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 +4509,45 @@ 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)
> +{
> +	unsigned char *buf;
> +	int i;
> +
> +	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;
> +		}
> +	}
> +	if (arg->field.field->size < 16) {
> +		trace_seq_printf(s, "INVALID UUID: size have %u expect 16",
> +				arg->field.field->size);
> +		return;
> +	}

So if there's an interest for very compact printing loop, something like
this produces the same output:

	for (i = 0; i < 8; i++) {
		printf("%02X", buf[i]);
		printf("%02X", buf[i]);
		if (1 <= i && i <= 4)
			putchar('-');
	}

"23ad 1511 - dd83 - 47d4 - a79c - e966 25a1 5a6e"
 0    1      2      3      4      5    6    7

IOW, split into pairs and print dash after a few of them.