Re: [PATCH 1/2] lib/string_helpers: Introduce strsplit_u32()

[Péter Ujfalusi]

On 08/07/2022 15:30, Andy Shevchenko wrote:
> On Fri, Jul 08, 2022 at 02:13:14PM +0200, Cezary Rojewski wrote:
>> On 2022-07-08 1:46 PM, Andy Shevchenko wrote:
>>> On Fri, Jul 8, 2022 at 1:33 PM Cezary Rojewski
>>> <cezary.rojewski@xxxxxxxxx> wrote:
> 
> ...
> 
>>>> When I'd written the very first version of this function many months
>>>> ago, get_options() looked as it does not fulfill our needs. It seems to
>>>> be true even today: caller needs to know the number of elements in an
>>>> array upfront.
>>>
>>> Have you read a kernel doc for it? It does return the number of
>>> elements at the first pass.
>>
>> Yes, I've checked several parts of it. Perhaps I did miss something but
>> simple_strtoull() doc reads: use kstrtox() instead.
> 
> Doc was fixed to make clearer that in some cases it's okay to use
> simple_strtox(). And this was exactly due to obfuscation code with this
> recommendation. Yes, in general one supposed to use kstrtox(), but it's
> not 100% obligatory.
> 
>> Thus the strsplit_u32()
>> makes use of kstrtox().
> 
> Yeah...
> 
>>>> Also, kstrtox() takes into account '0x' and modifies the
>>>> base accordingly if that's the case. simple_strtoull() looks as not
>>>> capable of doing the same thing.
>>>
>>> How come?! It does parse all known prefixes: 0x, 0, +, -.
>>
>> Hmm.. doc says that it stops at the first non-digit character. Will
>> re-check.
> 
> Yes, but under non-digit implies the standard prefixes of digits.
> simple_strtox() and kstrotox() use the very same function for prefixes.
> 
>>>> The goal is to be able to parse input such as:
>>>>
>>>> 0x1000003,0,0,0x1000004,0,0
>>>>
>>>> into a sequence of 6 uints, filling the *tkns and *num_tkns for the caller.
>>>
>>> Yes. Have you checked the test cases for get_options()?
> 
> (1)
> 
> ...
> 
>>>> avs-driver, which is also part of the ASoC framework has very similar
>>>> debug-interface. I believe there's no need to duplicate the functions -
>>>> move them to common code instead.
>>>
>>> Taking the above into account, please try to use get_options() and
>>> then tell me what's not working with it. If so, we will add test cases
>>> to get_options() and fix it.
>>
>> There is a difference:
>>
>> 	// get_options
>> 	int ints[5];
>>
>> 	s = get_options(str, ARRAY_SIZE(ints), ints);
>>
>> 	// strsplit_u32()
>> 	u32 *tkns, num_tkns;
>>
>> 	ret = strsplit_u32(str, delim, &tkns, &num_tkns);
>>
>> Nothing has been told upfront for in the second case.
> 
> It seems you are missing the (1). The code has checks for the case where you
> can do get number upfront, it would just require two passes, but it's nothing
> in comparison of heave realloc().
> 
>   unsigned int *tokens;
>   char *p;
>   int num;
> 
>   p = get_options(str, 0, &num);
>   if (num == 0)
> 	// No numbers in the string!
> 
>   tokens = kcalloc(num + 1, sizeof(*tokens), GFP_KERNEL);
>   if (!tokens)
> 	return -ENOMEM;
> 
>   p = get_oprions(str, num, &tokens);
>   if (*p)
> 	// String was parsed only partially!
> 	// assuming it's not a fatal error
> 
>   return tokens;
> 

This diff is tested and works:
diff --git a/sound/soc/sof/sof-client-probes.c b/sound/soc/sof/sof-client-probes.c
index 60e4250fac87..48d405f78a83 100644
--- a/sound/soc/sof/sof-client-probes.c
+++ b/sound/soc/sof/sof-client-probes.c
@@ -410,61 +410,11 @@ static const struct snd_compress_ops sof_probes_compressed_ops = {
 	.copy = sof_probes_compr_copy,
 };
 
-/**
- * strsplit_u32 - Split string into sequence of u32 tokens
- * @buf:	String to split into tokens.
- * @delim:	String containing delimiter characters.
- * @tkns:	Returned u32 sequence pointer.
- * @num_tkns:	Returned number of tokens obtained.
- */
-static int strsplit_u32(char *buf, const char *delim, u32 **tkns, size_t *num_tkns)
-{
-	char *s;
-	u32 *data, *tmp;
-	size_t count = 0;
-	size_t cap = 32;
-	int ret = 0;
-
-	*tkns = NULL;
-	*num_tkns = 0;
-	data = kcalloc(cap, sizeof(*data), GFP_KERNEL);
-	if (!data)
-		return -ENOMEM;
-
-	while ((s = strsep(&buf, delim)) != NULL) {
-		ret = kstrtouint(s, 0, data + count);
-		if (ret)
-			goto exit;
-		if (++count >= cap) {
-			cap *= 2;
-			tmp = krealloc(data, cap * sizeof(*data), GFP_KERNEL);
-			if (!tmp) {
-				ret = -ENOMEM;
-				goto exit;
-			}
-			data = tmp;
-		}
-	}
-
-	if (!count)
-		goto exit;
-	*tkns = kmemdup(data, count * sizeof(*data), GFP_KERNEL);
-	if (!(*tkns)) {
-		ret = -ENOMEM;
-		goto exit;
-	}
-	*num_tkns = count;
-
-exit:
-	kfree(data);
-	return ret;
-}
-
 static int tokenize_input(const char __user *from, size_t count,
 			  loff_t *ppos, u32 **tkns, size_t *num_tkns)
 {
+	int ret, nints, i, *ints;
 	char *buf;
-	int ret;
 
 	buf = kmalloc(count + 1, GFP_KERNEL);
 	if (!buf)
@@ -473,12 +423,36 @@ static int tokenize_input(const char __user *from, size_t count,
 	ret = simple_write_to_buffer(buf, count, ppos, from, count);
 	if (ret != count) {
 		ret = ret >= 0 ? -EIO : ret;
-		goto exit;
+		goto free_buf;
 	}
 
 	buf[count] = '\0';
-	ret = strsplit_u32(buf, ",", tkns, num_tkns);
-exit:
+	get_options(buf, 0, &nints);
+	if (!nints) {
+		ret = -ENOENT;
+		goto free_buf;
+	}
+
+	ints = kcalloc(nints + 1, sizeof(*ints), GFP_KERNEL);
+	if (!ints) {
+		ret = -ENOMEM;
+		goto free_buf;
+	}
+
+	*tkns = kcalloc(nints, sizeof(u32), GFP_KERNEL);
+	if (!(*tkns)) {
+		ret = -ENOMEM;
+		goto free_ints;
+	}
+
+	get_options(buf, nints + 1, ints);
+	*num_tkns = nints;
+	for (i = 0; i < nints; i++)
+		(*tkns)[i] = ints[i + 1];
+	
+free_ints:
+	kfree(ints);
+free_buf:
 	kfree(buf);
 	return ret;
 }

Could be made nicer with some brain work put to it, we need strict u32 within the IPC message for the array...

-- 
Péter