linux-kernel - Re: [PATCH] tools/lib/traceevent, perf tools: Handle %pU format correctly

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Date:   Wed, 16 Oct 2019 07:44:58 +0000
From:   Qu WenRuo <wqu@...e.com>
To:     Nikolay Borisov <nborisov@...e.com>,
        "linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-trace-devel@...r.kernel.org" 
        <linux-trace-devel@...r.kernel.org>
Subject: Re: [PATCH] tools/lib/traceevent, perf tools: Handle %pU format
 correctly



On 2019/10/16 下午3:39, Nikolay Borisov wrote:
> 
> 
> 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@...e.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"?

Oh, the original planned check is:
if (ptr[1] == 'b' || ptr[1] == 'B' ||
    ptr[1] == 'l' || ptr[1] == 'L')

Those options are finetunes for endian and upper/lower characters.

However I just choose to be lazy and use isalpha() to check them in one
line.
I will change the comment to make it more clear.

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