[KJ] thread_info.h use kzalloc

[KJ] thread_info.h use kzalloc

[tom hisch]

[-- Attachment #1.1: Type: text/plain, Size: 878 bytes --]

hello,

i have some questions about the alloc_thread_info(tsk) macro in
asm-i386/thread_info.h


/* thread information allocation */
#ifdef CONFIG_DEBUG_STACK_USAGE
#define alloc_thread_info(tsk)                                  \
        ({                                                      \
                struct thread_info *ret;                        \
                                                                \
------>      ret = kmalloc(THREAD_SIZE, GFP_KERNEL);         \  //  what
about the use of kzalloc ??
                if (ret)                                        \
                        memset(ret, 0, THREAD_SIZE);            \
------>      ret;                                            \    // whats
the meaning of this instruction ??
        })
#else
#define alloc_thread_info(tsk) kmalloc(THREAD_SIZE, GFP_KERNEL)
#endif

thanks
tom hisch

[-- Attachment #1.2: Type: text/html, Size: 2728 bytes --]

[-- Attachment #2: Type: text/plain, Size: 168 bytes --]

_______________________________________________
Kernel-janitors mailing list
Kernel-janitors@lists.osdl.org
https://lists.osdl.org/mailman/listinfo/kernel-janitors

Re: [KJ] thread_info.h use kzalloc

[Nishanth Aravamudan]

On 11.07.2006 [18:47:14 +0200], tom hisch wrote:
> hello,
> 
> i have some questions about the alloc_thread_info(tsk) macro in
> asm-i386/thread_info.h
> 
> 
> /* thread information allocation */
> #ifdef CONFIG_DEBUG_STACK_USAGE
> #define alloc_thread_info(tsk)                                  \
>        ({                                                      \
>                struct thread_info *ret;                        \
>                                                                \
> ------>      ret = kmalloc(THREAD_SIZE, GFP_KERNEL);         \  //  what
> about the use of kzalloc ??
>                if (ret)                                        \
>                        memset(ret, 0, THREAD_SIZE);            \

Probably a reasonable change.

> ------>      ret;                                            \    // whats
> the meaning of this instruction ??
>        })

I think it's part of the magic of the ({ }) gcc'ism, which allows the
macro to effectively have a return value (that's how I think of it, at
least) without a return statement (in this case, the value of ret will
be stored in the corresponding lhs). I'm sure the real explanation can
be found in the gcc manual in the ({ }) section.

Thanks,
Nish

-- 
Nishanth Aravamudan <nacc@us.ibm.com>
IBM Linux Technology Center
_______________________________________________
Kernel-janitors mailing list
Kernel-janitors@lists.osdl.org
https://lists.osdl.org/mailman/listinfo/kernel-janitors

Re: [KJ] thread_info.h use kzalloc

[Alexey Dobriyan]

On Tue, Jul 11, 2006 at 06:47:14PM +0200, tom hisch wrote:
> i have some questions about the alloc_thread_info(tsk) macro in
> asm-i386/thread_info.h

> /* thread information allocation */
> #ifdef CONFIG_DEBUG_STACK_USAGE
> #define alloc_thread_info(tsk)                                  \
>        ({                                                      \
>                struct thread_info *ret;                        \
>                                                                \
> ------>      ret = kmalloc(THREAD_SIZE, GFP_KERNEL);         \  //  what
> about the use of kzalloc ??
>                if (ret)                                        \
>                        memset(ret, 0, THREAD_SIZE);            \

Indeed it should be kzalloc.

> ------>      ret;                                            \    // whats
> the meaning of this instruction ??
>        })

That's GNU extension meaning that value of this block equals to "ret" at
that point. It should be more or less equivalent to

static inline struct thread_info *alloc_thread_info(struct task_struct *task)
{
	return kzalloc(THREAD_SIZE, GFP_KERNEL);
}

> #else
> #define alloc_thread_info(tsk) kmalloc(THREAD_SIZE, GFP_KERNEL)
> #endif

_______________________________________________
Kernel-janitors mailing list
Kernel-janitors@lists.osdl.org
https://lists.osdl.org/mailman/listinfo/kernel-janitors