Re: [PATCH v2 2/2] mingw: fix mingw_open_append to work with named pipes

From: Junio C Hamano <gitster@pobox.com>
Date: Sep 10, 2018, 22:00 UTC
Message-ID: <xmqqbm95rp27.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <a309396f-bb33-477d-5d92-a98699f5a856@kdbg.org>

Johannes Sixt <j6t@kdbg.org> writes:

>>   +#define IS_SBS(ch) (((ch) == '/') || ((ch) == '\\'))

I think you already have mingw_is_dir_sep() and its shorter alias is_dir_sep() available to you.

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>> +/*
>> + * Does the pathname map to the local named pipe filesystem?
>> + * That is, does it have a "//./pipe/" prefix?
>> + */
>> +static int mingw_is_local_named_pipe_path(const char *filename)

There is no need to prefix mingw_ to this function that is file local static. Isn't is_local_named_pipe() descriptive and unique enough?

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>> +{
>> +	return (IS_SBS(filename[0]) &&
>> +		IS_SBS(filename[1]) &&
>> +		filename[2] == '.'  &&
>> +		IS_SBS(filename[3]) &&
>> +		!strncasecmp(filename+4, "pipe", 4) &&
>> +		IS_SBS(filename[8]) &&
>> +		filename[9]);
>> +}
>> +#undef IS_SBS

It is kind-of surprising that there hasn't been any existing need for a helper function that would allow us to write this function like so:

	static int is_local_named_pipe(const char *path)
	{
		return path_is_in_directory(path, "//./pipe/");
	}

Not a suggestion to add such a thing; as long as we know there is no other codepath that would benefit from having one, a generalization like that can and should wait.

Show 18 quoted lines

>>   int mingw_open (const char *filename, int oflags, ...)
>>   {
>>   	typedef int (*open_fn_t)(wchar_t const *wfilename, int oflags, ...);
>> @@ -387,7 +419,7 @@ int mingw_open (const char *filename, int oflags, ...)
>>   	if (filename && !strcmp(filename, "/dev/null"))
>>   		filename = "nul";
>>   -	if (oflags & O_APPEND)
>> +	if ((oflags & O_APPEND) && !mingw_is_local_named_pipe_path(filename))
>>   		open_fn = mingw_open_append;
>>   	else
>>   		open_fn = _wopen;
>
> This looks reasonable.
>
> I wonder which part of the code uses local named pipes. Is it
> downstream in Git for Windows or one of the topics in flight?
>
> -- Hannes