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From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Mathias Krause <minipli@googlemail.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 2/3] lib/string_helpers.c: Refactor string_escape_mem
Date: Thu, 29 Jan 2015 14:10:42 +0100	[thread overview]
Message-ID: <87sietbulp.fsf@rasmusvillemoes.dk> (raw)
In-Reply-To: <1422533541.31903.314.camel@linux.intel.com> (Andy Shevchenko's message of "Thu, 29 Jan 2015 14:12:21 +0200")

On Thu, Jan 29 2015, Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:

>>  
>> -static int escape_space(unsigned char c, char **dst, size_t *osz)
>> +static bool escape_space(unsigned char c, char **dst, char *end)
>>  {
>>  	char *out = *dst;
>>  	unsigned char to;
>>  
>> -	if (*osz < 2)
>> -		return -ENOMEM;
>> -
>>  	switch (c) {
>>  	case '\n':
>>  		to = 'n';
>> @@ -283,26 +275,23 @@ static int escape_space(unsigned char c, char **dst, size_t *osz)
>>  		to = 'f';
>>  		break;
>>  	default:
>> -		return 0;
>> +		return false;
>>  	}
>>  
>> -	*out++ = '\\';
>> -	*out++ = to;
>> +	if (out + 0 < end)
>> +		out[0] = '\\';
>> +	if (out + 1 < end)
>> +		out[1] = to;
>
> Could we do this in the same way like for hex_string, i.e.
>
> if (out < end)
>  *out = '\\';
> ++out;
>
> …
>
> *dst = out;
> return true;
>
> ?

We could, but I don't think either is more readable than the
other. Hence I chose the one requiring 2n+1 lines instead of 3n+1
lines. Had this been in vsprintf.c I would stick to the pattern you
suggest.


>> @@ -440,9 +424,10 @@ static int escape_hex(unsigned char c, char **dst, size_t *osz)
>>  int string_escape_mem(const char *src, size_t isz, char **dst, size_t osz,
>>  		      unsigned int flags, const char *esc)
>>  {
>> -	char *out = *dst, *p = out;
>> +	char *p = *dst;
>
> Leave 'out' here and…
>
>> +	char *end = p + osz;
>>  	bool is_dict = esc && *esc;
>> -	int ret = 0;
>> +	int ret;
>>  
>>  	while (isz--) {
>>  		unsigned char c = *src++;
>> @@ -462,55 +447,32 @@ int string_escape_mem(const char *src, size_t isz, char **dst, size_t osz,
>>  		    (is_dict && !strchr(esc, c))) {
>>  			/* do nothing */
>>  		} else {
>> -			if (flags & ESCAPE_SPACE) {
>> -				ret = escape_space(c, &p, &osz);
>> -				if (ret < 0)
>> -					break;
>> -				if (ret > 0)
>> -					continue;
>> -			}
>> -
>> -			if (flags & ESCAPE_SPECIAL) {
>> -				ret = escape_special(c, &p, &osz);
>> -				if (ret < 0)
>> -					break;
>> -				if (ret > 0)
>> -					continue;
>> -			}
>> -
>> -			if (flags & ESCAPE_NULL) {
>> -				ret = escape_null(c, &p, &osz);
>> -				if (ret < 0)
>> -					break;
>> -				if (ret > 0)
>> -					continue;
>> -			}
>> +			if (flags & ESCAPE_SPACE && escape_space(c, &p, end))
>> +				continue;
>> +
>> +			if (flags & ESCAPE_SPECIAL && escape_special(c, &p, end))
>> +				continue;
>> +
>> +			if (flags & ESCAPE_NULL && escape_null(c, &p, end))
>> +				continue;
>>  
>>  			/* ESCAPE_OCTAL and ESCAPE_HEX always go last */
>> -			if (flags & ESCAPE_OCTAL) {
>> -				ret = escape_octal(c, &p, &osz);
>> -				if (ret < 0)
>> -					break;
>> +			if (flags & ESCAPE_OCTAL && escape_octal(c, &p, end))
>>  				continue;
>> -			}
>> -			if (flags & ESCAPE_HEX) {
>> -				ret = escape_hex(c, &p, &osz);
>> -				if (ret < 0)
>> -					break;
>> +
>> +			if (flags & ESCAPE_HEX && escape_hex(c, &p, end))
>>  				continue;
>> -			}
>>  		}
>>  
>> -		ret = escape_passthrough(c, &p, &osz);
>> -		if (ret < 0)
>> -			break;
>> +		escape_passthrough(c, &p, end);
>> +	}
>
> + black line.
>
>> +	if (p > end) {
>> +		*dst = end;
>> +		return -ENOMEM;
>>  	}
>>  
>> +	ret = p - *dst;
>>  	*dst = p;
>> -
>> -	if (ret < 0)
>> -		return ret;
>> -
>> -	return p - out;
>
> …and do not change the logic right now. Just substitute if (ret < 0) by
> above if (p > end).
>

I'm not sure I follow. How does this change the logic? We return -ENOMEM
if and only if the entire output didn't fit, while still updating *dst
to point to one past the last output character. If the output did fit,
we return the size of the output.

One thing that only occured to me now is that we may now leave a partial
escape sequence at the end of the buffer. I can't see how this can
reasonably be avoided while still doing a meaningful refactorization
preparing it for the next patch.

Rasmus

  reply	other threads:[~2015-01-29 13:11 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-28 13:25 [PATCH 0/2] Two printf fixes Rasmus Villemoes
2015-01-28 13:25 ` [PATCH 1/2] lib/vsprintf.c: Fix potential NULL deref in hex_string Rasmus Villemoes
2015-01-28 14:53   ` Andy Shevchenko
2015-01-28 15:49     ` Rasmus Villemoes
2015-01-28 16:43       ` Andy Shevchenko
2015-01-28 13:25 ` [PATCH 2/2] string_helpers: Change semantics of string_escape_mem Rasmus Villemoes
2015-01-28 15:05   ` Andy Shevchenko
2015-01-29 10:03 ` [PATCH v2 0/3] Two printf fixes Rasmus Villemoes
2015-01-29 10:03   ` [PATCH v2 1/3] lib/vsprintf.c: Fix potential NULL deref in hex_string Rasmus Villemoes
2015-01-29 10:43     ` Andy Shevchenko
2015-01-29 10:03   ` [PATCH v2 2/3] lib/string_helpers.c: Refactor string_escape_mem Rasmus Villemoes
2015-01-29 12:12     ` Andy Shevchenko
2015-01-29 13:10       ` Rasmus Villemoes [this message]
2015-01-29 13:37         ` Andy Shevchenko
2015-01-29 19:33           ` Jeff Epler
2015-01-30 10:14             ` Andy Shevchenko
2015-01-29 10:03   ` [PATCH v2 3/3] lib/string_helpers.c: Change semantics of string_escape_mem Rasmus Villemoes
2015-01-29 13:29     ` Andy Shevchenko
2015-01-29 14:29       ` Rasmus Villemoes
2015-01-30 10:27         ` Andy Shevchenko
2015-01-30 23:39           ` Rasmus Villemoes
2015-01-30 23:39             ` Rasmus Villemoes
2015-02-02 10:56             ` Andy Shevchenko
2015-02-09 23:44   ` [PATCH v3 0/3] Two printf fixes Rasmus Villemoes
2015-02-09 23:44     ` Rasmus Villemoes
2015-02-09 23:44     ` [PATCH v3 1/3] lib/vsprintf.c: Fix potential NULL deref in hex_string Rasmus Villemoes
2015-02-09 23:44     ` [PATCH v3 2/3] lib/string_helpers.c: Refactor string_escape_mem Rasmus Villemoes
2015-02-10 12:16       ` Andy Shevchenko
2015-02-09 23:44     ` [PATCH v3 3/3] lib/string_helpers.c: Change semantics of string_escape_mem Rasmus Villemoes
2015-02-09 23:44       ` Rasmus Villemoes
2015-02-10 12:32       ` Andy Shevchenko
2015-02-10 12:32         ` Andy Shevchenko
2015-02-10 13:02         ` Rasmus Villemoes
2015-02-10 14:22           ` Andy Shevchenko
2015-02-10 14:22             ` Andy Shevchenko
2015-02-21  1:35             ` Rasmus Villemoes
2015-02-23 12:50               ` Andy Shevchenko
2015-02-23 12:50                 ` Andy Shevchenko
2015-02-23 22:55                 ` Rasmus Villemoes
2015-02-23 22:55                   ` Rasmus Villemoes
2015-03-02 12:37                   ` Andy Shevchenko
2015-03-02 12:37                     ` Andy Shevchenko
2015-03-02 23:03                     ` Rasmus Villemoes
2015-03-03 10:26                       ` Andy Shevchenko
2015-03-03 10:26                         ` Andy Shevchenko
2015-03-03 23:20     ` [PATCH v4 0/3] Two printf fixes Rasmus Villemoes
2015-03-03 23:20       ` [PATCH v4 1/3] lib/vsprintf.c: Fix potential NULL deref in hex_string Rasmus Villemoes
2015-03-03 23:20       ` [PATCH v4 2/3] lib/string_helpers.c: Refactor string_escape_mem Rasmus Villemoes
2015-03-04 10:51         ` Andy Shevchenko
2015-03-03 23:20       ` [PATCH v4 3/3] lib/string_helpers.c: Change semantics of string_escape_mem Rasmus Villemoes
2015-03-04 11:49         ` Andy Shevchenko
2015-03-04 11:49           ` Andy Shevchenko

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