[PATCH 2.6] 1/7 create kstrdup library function

[PATCH 2.6] 1/7 create kstrdup library function

[pmarques]

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This patch creates the kstrdup library function so that it doesn't have to be
reimplemented (or even EXPORT'ed) by every user that needs it.

Signed-off-by: Paulo Marques <pmarques@grupopie.com>

--
Paulo Marques - www.grupopie.com
 
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke (1729 - 1797)

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diff -buprN -X dontdiff vanilla-2.6.11-rc2-bk9/include/linux/string.h linux-2.6.11-rc2-bk9/include/linux/string.h
--- vanilla-2.6.11-rc2-bk9/include/linux/string.h	2004-12-24 21:34:31.000000000 +0000
+++ linux-2.6.11-rc2-bk9/include/linux/string.h	2005-01-31 19:31:12.000000000 +0000
@@ -88,6 +88,8 @@ extern int memcmp(const void *,const voi
 extern void * memchr(const void *,int,__kernel_size_t);
 #endif

+extern char *kstrdup(const char *s, int gfp);
+
 #ifdef __cplusplus
 }
 #endif
diff -buprN -X dontdiff vanilla-2.6.11-rc2-bk9/lib/string.c linux-2.6.11-rc2-bk9/lib/string.c
--- vanilla-2.6.11-rc2-bk9/lib/string.c	2005-01-31 20:05:37.000000000 +0000
+++ linux-2.6.11-rc2-bk9/lib/string.c	2005-01-31 20:00:31.000000000 +0000
@@ -599,3 +599,23 @@ void *memchr(const void *s, int c, size_
 }
 EXPORT_SYMBOL(memchr);
 #endif
+
+/*
+ * kstrdup - allocate space for and copy an existing string
+ *
+ * @s: the string to duplicate
+ * @gfp: the GFP mask used in the kmalloc() call when allocating memory
+ */
+char *kstrdup(const char *s, int gfp)
+{
+	int len;
+	char *buf;
+
+	if (!s) return NULL;
+
+	len = strlen(s) + 1;
+	buf = kmalloc(len, gfp);
+	if (buf)
+		memcpy(buf, s, len);
+	return buf;
+}
+
+EXPORT_SYMBOL(kstrdup);

Re: [PATCH 2.6] 1/7 create kstrdup library function

[Pekka Enberg]

Hi,

On Tue,  1 Feb 2005 03:28:21 +0000, pmarques@grupopie.com
<pmarques@grupopie.com> wrote:
> 
> This patch creates the kstrdup library function so that it doesn't have to be
> reimplemented (or even EXPORT'ed) by every user that needs it.
> 
> Signed-off-by: Paulo Marques <pmarques@grupopie.com>
> 
> diff -buprN -X dontdiff vanilla-2.6.11-rc2-bk9/lib/string.c linux-2.6.11-rc2-bk9/lib/string.c
> --- vanilla-2.6.11-rc2-bk9/lib/string.c 2005-01-31 20:05:37.000000000 +0000
> +++ linux-2.6.11-rc2-bk9/lib/string.c   2005-01-31 20:00:31.000000000 +0000
> @@ -599,3 +599,23 @@ void *memchr(const void *s, int c, size_
>  }
>  EXPORT_SYMBOL(memchr);
>  #endif
> +
> +/*
> + * kstrdup - allocate space for and copy an existing string
> + *
> + * @s: the string to duplicate
> + * @gfp: the GFP mask used in the kmalloc() call when allocating memory
> + */
> +char *kstrdup(const char *s, int gfp)
> +{
> +       int len;
> +       char *buf;
> +
> +       if (!s) return NULL;
> +
> +       len = strlen(s) + 1;
> +       buf = kmalloc(len, gfp);
> +       if (buf)
> +               memcpy(buf, s, len);
> +       return buf;
> +}
> +
> +EXPORT_SYMBOL(kstrdup);

kstrdup() is a special-case _memory allocator_ (not so much a string
operation) so I think it should go into mm/slab.c where we currently
have kcalloc().

P.S. Please inline patches to your email as per
Documentation/SubmittingPatches. I, for one, have trouble with
attachments.

                                   Pekka

Re: [PATCH 2.6] 1/7 create kstrdup library function

[Paulo Marques]

Pekka Enberg wrote:
> [...]
> 
> kstrdup() is a special-case _memory allocator_ (not so much a string
> operation) so I think it should go into mm/slab.c where we currently
> have kcalloc().

I was following Rusty Russell's approach. Also, I believe this is more 
intuitive because the standard libc strdup function is declared in string.h.

However, I really don't have strong feelings either way, so if the 
majority agrees that this should be in mm/slab, its fine by me.

> P.S. Please inline patches to your email as per
> Documentation/SubmittingPatches. I, for one, have trouble with
> attachments.

Unfortunately my email client messes up inline patches and wordwraps / 
mangles white space, so I resort to attaching them until I have time to 
look into fixing that :(

-- 
Paulo Marques - www.grupopie.com

All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke (1729 - 1797)

Re: [PATCH 2.6] 1/7 create kstrdup library function

[Pekka Enberg]

At some point in time, I wrote:
> > kstrdup() is a special-case _memory allocator_ (not so much a string
> > operation) so I think it should go into mm/slab.c where we currently
> > have kcalloc().

On Tue, 01 Feb 2005 17:00:17 +0000, Paulo Marques <pmarques@grupopie.com> wrote:
> I was following Rusty Russell's approach. Also, I believe this is more
> intuitive because the standard libc strdup function is declared in string.h.
> 
> However, I really don't have strong feelings either way, so if the
> majority agrees that this should be in mm/slab, its fine by me.

Intuitive, perhaps, but I think it's wrong. I don't like it because it
makes string operations depend on slab. Furthermore, kstrdup() is not
a string operation. It is about memory allocation, really, just like
kcalloc().

One possible way to clean this up would be to extract the
standard-like allocators (kmalloc, kcalloc, and kstrdup) from
mm/slab.c and move them into a separate file.

                          Pekka

Re: [PATCH 2.6] 1/7 create kstrdup library function

[Paulo Marques]

Pekka Enberg wrote:
> At some point in time, I wrote:
> 
>>>kstrdup() is a special-case _memory allocator_ (not so much a string
>>>operation) so I think it should go into mm/slab.c where we currently
>>>have kcalloc().
> 
> 
> On Tue, 01 Feb 2005 17:00:17 +0000, Paulo Marques <pmarques@grupopie.com> wrote:
> 
>>I was following Rusty Russell's approach. Also, I believe this is more
>>intuitive because the standard libc strdup function is declared in string.h.
>>
>>However, I really don't have strong feelings either way, so if the
>>majority agrees that this should be in mm/slab, its fine by me.
> 
> 
> Intuitive, perhaps, but I think it's wrong. I don't like it because it
> makes string operations depend on slab. Furthermore, kstrdup() is not
> a string operation. It is about memory allocation, really, just like
> kcalloc().

I agree with the "is like kcalloc" argument in the sense that it does an 
allocation + something else. But in this case the "something else" is in 
fact a string operation, so this just seem to be in the middle.

> One possible way to clean this up would be to extract the
> standard-like allocators (kmalloc, kcalloc, and kstrdup) from
> mm/slab.c and move them into a separate file.

I don't like this approach. From a quick grep you get 4972 kmalloc's in 
.c files in the kernel tree and only 35 kstrdup's. Moving kstrdup around 
is still just 7 patches, kmalloc is a much bigger problem.

Anyway, as I said before, if more people believe that moving kstrdup 
into mm/slab.c is the way to go, then its fine by me. The problem I was 
trying to solve was having several versions of strdup-like functions all 
around the kernel, and this problem gets fixed either way. Right now, 
the poll goes something like this:

string.c: me, Rusty Russell
slab.c: Pekka Enberg

I think we need more votes :)

-- 
Paulo Marques - www.grupopie.com

All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke (1729 - 1797)

Re: 1/7 create kstrdup library function

[Pekka J Enberg]

Paulo Marques writes:
> I agree with the "is like kcalloc" argument in the sense that it does an 
> allocation + something else. But in this case the "something else" is in 
> fact a string operation, so this just seem to be in the middle.

Sure, but now you're forcing all users of <string.h> to depend on the slab 
as well. Conceptually, kstrdup() is an initializing memory allocator, not a 
string operation, which is why I think it should go into slab.c. 

Paulo Marques writes:
> I don't like this approach. From a quick grep you get 4972 kmalloc's in .c 
> files in the kernel tree and only 35 kstrdup's. Moving kstrdup around is 
> still just 7 patches, kmalloc is a much bigger problem.

Hmm? Yes, moving the declaration from slab.h to some other header is 
painful. I only talked about moving the definition from slab.c. 

Paulo Marques writes:
> Anyway, as I said before, if more people believe that moving kstrdup into 
> mm/slab.c is the way to go, then its fine by me. The problem I was trying 
> to solve was having several versions of strdup-like functions all around 
> the kernel, and this problem gets fixed either way. Right now, the poll 
> goes something like this: 
> 
> string.c: me, Rusty Russell
> slab.c: Pekka Enberg 
> 
> I think we need more votes :)

Could we also get Rusty's confirmation on this? 

       Pekka