linux-kernel - Re: [PATCH v3 1/2] vsprintf: Add %p[mM]U for uppercase MAC address

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Date:   Thu, 27 Apr 2023 16:26:05 +0200
From:   Konrad Gräfe <k.graefe@...eware.de>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Quentin Schulz <quentin.schulz@...obroma-systems.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Andrzej Pietrasiewicz <andrzej.p@...labora.com>,
        Felipe Balbi <balbi@...com>
Cc:     stable@...r.kernel.org
Subject: Re: [PATCH v3 1/2] vsprintf: Add %p[mM]U for uppercase MAC address


On 27.04.23 14:35, Rasmus Villemoes wrote:
> On 27/04/2023 13.51, Konrad Gräfe wrote:
>> The CDC-ECM specification requires an USB gadget to send the host MAC
>> address as uppercase hex string. This change adds the appropriate
>> modifier.
>>
>> Cc: stable@...r.kernel.org
> 
> Why cc stable?

I believe the second patch matches the criteria but it uses this one.

> 
>> Signed-off-by: Konrad Gräfe <k.graefe@...eware.de>
>> ---
>> Added in v3
>>
>>   lib/vsprintf.c | 18 +++++++++++++++---
>>   1 file changed, 15 insertions(+), 3 deletions(-)
> 
> The diffstat here, or for some other patch in the same series,
> definitely ought to mention lib/test_printf.c.
> 
>> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
>> index be71a03c936a..8aee1caabd9e 100644
>> --- a/lib/vsprintf.c
>> +++ b/lib/vsprintf.c
>> @@ -1269,9 +1269,10 @@ char *mac_address_string(char *buf, char *end, u8 *addr,
>>   {
>>   	char mac_addr[sizeof("xx:xx:xx:xx:xx:xx")];
>>   	char *p = mac_addr;
>> -	int i;
>> +	int i, pos;
>>   	char separator;
>>   	bool reversed = false;
>> +	bool uppercase = false;
>>   
>>   	if (check_pointer(&buf, end, addr, spec))
>>   		return buf;
>> @@ -1281,6 +1282,10 @@ char *mac_address_string(char *buf, char *end, u8 *addr,
>>   		separator = '-';
>>   		break;
>>   
>> +	case 'U':
>> +		uppercase = true;
>> +		break;
>> +
>>   	case 'R':
>>   		reversed = true;
>>   		fallthrough;
> 
> This seems broken, and I'm surprised the compiler doesn't warn about
> separator possibly being uninitialized further down. I'm also surprised
> your testing hasn't caught this. For reference, the full switch
> statement is currently
> 
>          switch (fmt[1]) {
>          case 'F':
>                  separator = '-';
>                  break;
> 
>          case 'R':
>                  reversed = true;
>                  fallthrough;
> 
>          default:
>                  separator = ':';
>                  break;
>          }
> 
>> @@ -1292,9 +1297,14 @@ char *mac_address_string(char *buf, char *end, u8 *addr,
>>   
>>   	for (i = 0; i < 6; i++) {
>>   		if (reversed)
>> -			p = hex_byte_pack(p, addr[5 - i]);
>> +			pos = 5 - i;
>> +		else
>> +			pos = i;
>> +
>> +		if (uppercase)
>> +			p = hex_byte_pack_upper(p, addr[pos]);
>>   		else
>> -			p = hex_byte_pack(p, addr[i]);
>> +			p = hex_byte_pack(p, addr[pos]);
> 
> I think this becomes quite hard to follow. We have string_upper() in
> linux/string_helpers.h, so I'd rather just leave this loop alone and do
> 
>    if (uppercase)
>      string_upper(mac_addr, mac_addr);
> 
> after the nul-termination.
> 
> Rasmus
>