Re: [PATCH V3] PR gdb/33747: gdb/ser-unix: modernize Linux custom baud rate support

[Sunil Kumar Dora <sunilkumar.dora@windriver.com>]

Thanks Kevin.

On 3/20/2026 4:14 AM, Kevin Buettner wrote:
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> On Thu, 12 Mar 2026 14:01:06 -0700
> sunilkumar.dora@windriver.com wrote:
>
>> diff --git a/gdb/ser-unix.c b/gdb/ser-unix.c
>> index c295a9c5ba1..a15f4cc2162 100644
>> --- a/gdb/ser-unix.c
>> +++ b/gdb/ser-unix.c
>> @@ -510,36 +510,59 @@ set_baudcode_baudrate (struct serial *scb, int
>> baud_code)
>>   #if HAVE_CUSTOM_BAUDRATE_SUPPORT && defined(BOTHER)
>>
>> -/* Set a custom baud rate using the termios BOTHER.  */
>> +/* Set a custom baud rate.
>> +
>> +   Prefer the POSIX cfsetispeed/cfsetospeed interface when it accepts
>> +   arbitrary baud rates.  Otherwise fall back to Linux-specific termios2
>> +   (BOTHER) or legacy termios interfaces.  */
>>
>>   static void
>>   set_custom_baudrate_linux (int fd, int rate)
>>   {
>> -#ifdef TCGETS2
>> -  struct termios2 tio;
>> -  const unsigned long req_get = TCGETS2;
>> -  const unsigned long req_set = TCSETS2;
>> -#else
>> +#if defined(HAVE_CFSETSPEED_ARBITRARY)
> Can you add a comment about how this code path is supported by glibc
> 2.42+ ?  You could also mention that this behavior is expected to be
> standardized by a future POSIX revision.
In V4:
   - set_custom_baudrate_posix() has a comment added as suggested,
     including the glibc 2.42+ support and future POSIX direction.
>
>>     struct termios tio;
>> -  const unsigned long req_get = TCGETS;
>> -  const unsigned long req_set = TCSETS;
>> -#endif
>> +  if (tcgetattr (fd, &tio) < 0)
>> +    perror_with_name (_("Cannot get current baud rate"));
>> +
>> +  cfsetispeed (&tio, rate);
>> +  cfsetospeed (&tio, rate);
> Return values for cfsetispeed and cfsetospeed should be checked.  If
> either call fails, it should either error out or try another way of
> setting the speed.
Return values of cfsetispeed() and cfsetospeed() are now checked, with 
perror_with_name()
called on failure in V4.

Thanks,
Sunil Dora
>
> Kevin
>