Re: [PATCH v3 1/7] lib: string: add functions to case-convert strings

[Markus Mayer]

On 9 July 2016 at 08:30, Markus Mayer <markus.mayer@xxxxxxxxxxxx> wrote:
> On 9 July 2016 at 05:04, Luis de Bethencourt <luisbg@xxxxxxxxxxxxxxx> wrote:
>> On 08/07/16 23:43, Markus Mayer wrote:
>>> Add a collection of generic functions to convert strings to lowercase
>>> or uppercase.
>>>
>>> Changing the case of a string (with or without copying it first) seems
>>> to be a recurring requirement in the kernel that is currently being
>>> solved by several duplicated implementations doing the same thing. This
>>> change aims at reducing this code duplication.
>>>
>>> The new functions are
>>>     void strlcpytoupper(char *dst, const char *src, size_t len);
>>>     void strlcpytolower(char *dst, const char *src, size_t len);
>>>     void strcpytoupper(char *dst, const char *src);
>>>     void strcpytolower(char *dst, const char *src);
>>>     void strtoupper(char *s);
>>>     void strtolower(char *s);
>>>
>>> The "str[l]cpyto*" versions of the function take a destination string
>>> and a source string as arguments. The "strlcpyto*" versions additionally
>>> take a length argument like strlcpy() itself. Lastly, the strto*
>>> functions take a single string argument and modify the passed-in string.
>>>
>>> Like strlcpy(), and unlike strncpy(), the functions guarantee NULL
>>> termination of the destination string.
>>>
>>> Signed-off-by: Markus Mayer <mmayer@xxxxxxxxxxxx>
>>> ---
>>>  include/linux/string.h | 40 ++++++++++++++++++++++++++++++++++++++++
>>>  lib/string.c           | 38 ++++++++++++++++++++++++++++++++++++++
>>>  2 files changed, 78 insertions(+)
>>>
>>> diff --git a/include/linux/string.h b/include/linux/string.h
>>> index 26b6f6a..36c9d14 100644
>>> --- a/include/linux/string.h
>>> +++ b/include/linux/string.h
>>> @@ -116,6 +116,8 @@ extern void * memchr(const void *,int,__kernel_size_t);
>>>  #endif
>>>  void *memchr_inv(const void *s, int c, size_t n);
>>>  char *strreplace(char *s, char old, char new);
>>> +extern void strlcpytoupper(char *dst, const char *src, size_t len);
>>> +extern void strlcpytolower(char *dst, const char *src, size_t len);
>>>
>>>  extern void kfree_const(const void *x);
>>>
>>> @@ -169,4 +171,42 @@ static inline const char *kbasename(const char *path)
>>>       return tail ? tail + 1 : path;
>>>  }
>>>
>>> +/**
>>> + * strcpytoupper - Copy string and convert to uppercase.
>>> + * @dst: The buffer to store the result.
>>> + * @src: The string to convert to uppercase.
>>> + */
>>> +static inline void strcpytoupper(char *dst, const char *src)
>>> +{
>>> +     strlcpytoupper(dst, src, -1);
>>> +}
>>> +
>>
>> Why not use SIZE_MAX instead of -1?
>
> Sure. I'll change all four of them. Thanks.

Turns out there's actually a circular dependency here. SIZE_MAX is
defined in linux/kernel.h. So, string.h would need to include
kernel.h. But kernel.h, by way of several other headers, includes
string.h.

Attempting to include kernel.h in string.h then leads to something like this:

  CHK     include/config/kernel.release
  CHK     include/generated/uapi/linux/version.h
  CHK     include/generated/utsrelease.h
  CC      scripts/mod/devicetable-offsets.s
  CHK     include/generated/timeconst.h
In file included from include/linux/printk.h:289:0,
                 from include/linux/kernel.h:13,
                 from include/linux/string.h:11,
                 from include/uapi/linux/uuid.h:21,
                 from include/linux/uuid.h:19,
                 from include/linux/mod_devicetable.h:12,
                 from scripts/mod/devicetable-offsets.c:2:
include/linux/dynamic_debug.h: In function âddebug_dyndbg_module_param_cbâ:
include/linux/dynamic_debug.h:122:2: error: implicit declaration of
function âstrstrâ [-Werror=implicit-function-declaration]
  if (strstr(param, "dyndbg")) {
  ^
include/linux/dynamic_debug.h:122:6: warning: incompatible implicit
declaration of built-in function âstrstrâ [enabled by default]
  if (strstr(param, "dyndbg")) {
      ^
Since kernel.h is referencing string.h (which is needed, but not
included a second time due to the include guards), this leads to
undeclared string functions, because we are still in the early stages
of including string.h itself and haven't gotten to the function
declarations yet.

>>> +/**
>>> + * strcpytolower - Copy string and convert to lowercase.
>>> + * @dst: The buffer to store the result.
>>> + * @src: The string to convert to lowercase.
>>> + */
>>> +static inline void strcpytolower(char *dst, const char *src)
>>> +{
>>> +     strlcpytolower(dst, src, -1);
>>> +}
>>> +
>>
>> Same here, and the 2 below :)
>>
>> Thanks Markus,
>> Luis
>>
>>> +/**
>>> + * strtoupper - Convert string to uppercase.
>>> + * @s: The string to operate on.
>>> + */
>>> +static inline void strtoupper(char *s)
>>> +{
>>> +     strlcpytoupper(s, s, -1);
>>> +}
>>> +
>>> +/**
>>> + * strtolower - Convert string to lowercase.
>>> + * @s: The string to operate on.
>>> + */
>>> +static inline void strtolower(char *s)
>>> +{
>>> +     strlcpytolower(s, s, -1);
>>> +}
>>> +
>>>  #endif /* _LINUX_STRING_H_ */
>>> diff --git a/lib/string.c b/lib/string.c
>>> index ed83562..fd8c427 100644
>>> --- a/lib/string.c
>>> +++ b/lib/string.c
>>> @@ -952,3 +952,41 @@ char *strreplace(char *s, char old, char new)
>>>       return s;
>>>  }
>>>  EXPORT_SYMBOL(strreplace);
>>> +
>>> +/**
>>> + * strlcpytoupper - Copy a length-limited string and convert to uppercase.
>>> + * @dst: The buffer to store the result.
>>> + * @src: The string to convert to uppercase.
>>> + * @len: Maximum string length. May be SIZE_MAX (-1) to set no limit.
>>> + */
>>> +void strlcpytoupper(char *dst, const char *src, size_t len)
>>> +{
>>> +     size_t i;
>>> +
>>> +     if (!len)
>>> +             return;
>>> +
>>> +     for (i = 0; i < len && src[i]; ++i)
>>> +             dst[i] = toupper(src[i]);
>>> +     dst[i < len ? i : i - 1] = '\0';
>>> +}
>>> +EXPORT_SYMBOL(strlcpytoupper);
>>> +
>>> +/**
>>> + * strlcpytolower - Copy a length-limited string and convert to lowercase.
>>> + * @dst: The buffer to store the result.
>>> + * @src: The string to convert to lowercase.
>>> + * @len: Maximum string length. May be SIZE_MAX (-1) to set no limit.
>>> + */
>>> +void strlcpytolower(char *dst, const char *src, size_t len)
>>> +{
>>> +     size_t i;
>>> +
>>> +     if (!len)
>>> +             return;
>>> +
>>> +     for (i = 0; i < len && src[i]; ++i)
>>> +             dst[i] = tolower(src[i]);
>>> +     dst[i < len ? i : i - 1] = '\0';
>>> +}
>>> +EXPORT_SYMBOL(strlcpytolower);
>>>
>>