Re: [PATCH v3 1/2] use HOST_NAME_MAX to size buffers for gethostname(2)

From: Junio C Hamano <gitster@pobox.com>
Date: Apr 19, 2017, 02:57 UTC
Message-ID: <xmqqzifdayuc.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <20170419012824.GA28740@aiede.svl.corp.google.com>

Jonathan Nieder <jrnieder@gmail.com> writes:

Show 22 quoted lines

>> @@ -274,7 +278,7 @@ static const char *lock_repo_for_gc(int force, pid_t* ret_pid)
>>  			 * running.
>>  			 */
>>  			time(NULL) - st.st_mtime <= 12 * 3600 &&
>> -			fscanf(fp, "%"SCNuMAX" %127c", &pid, locking_host) == 2 &&
>> +			fscanf(fp, scan_fmt, &pid, locking_host) == 2 &&
>
> I hoped this could be simplified since HOST_NAME_MAX is a numeric literal,
> using the double-expansion trick:
>
> #define STR_(s) # s
> #define STR(s) STR_(s)
>
> 			fscanf(fp, "%" SCNuMAX " %" STR(HOST_NAME_MAX) "c",
> 			       &pid, locking_host);
>
> Unfortunately, I don't think there's anything stopping a platform from
> defining
>
> 	#define HOST_NAME_MAX 0x100
>
> which would break that.

Yes, that was exactly why I went to the xstrfmt() route when I sent mine yesterday ;-).

> So this run-time calculation appears to be necessary.
>
> Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>

Thanks.