question regarding SYSCALL macros

[Dave Hylands]

Hi Sudheer,

On Thu, Apr 28, 2011 at 3:16 AM, Sudheer Divakaran
<inbox1.sudheer at gmail.com> wrote:
> Hi,
>  I was going through the file kernel/time.c and found the definition
> of 'gettimeofday' system call as follows.
>
> SYSCALL_DEFINE2(gettimeofday, struct timeval __user *, tv,
>                struct timezone __user *, tz)   <--- NOTE THE COMMA between variable
> types and names.
>
> In syscalls.h I could find the needed macros for expanding the
> definition to its final form i.e.,
>
> asmlinkage long sys_gettimeofday(struct timeval __user * tv, struct
> timezone __user *tz)
>
>
> [syscalls.h macros]
>
> #define SYSCALL_DEFINE2(name, ...) SYSCALL_DEFINEx(2, _##name, __VA_ARGS__)
>
>
> #define SYSCALL_DEFINEx(x, sname, ...)  \
>        __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
>
>
> #define __SYSCALL_DEFINEx(x, name, ...) \
>        asmlinkage long sys##name(__SC_DECL##x(__VA_ARGS__))
>
>
> #define __SC_DECL1(t1, a1)      t1 a1
> #define __SC_DECL2(t2, a2, ...) t2 a2, __SC_DECL1(__VA_ARGS__)
>
>
> [Question]
> Note the comma between the variable types and names in the original
> definition  (e.g., "struct timeval __user *, tv" instead of "struct
> timeval __user *tv").
>
> What is is the reason behind separating variable types and variable
> names using 'comma' and latter removing the comma character using
> _SC_DECLx macros?

Some of the other macros, like SC_CAST1

#define __SC_CAST1(t1, a1)	(t1) a1

need the type to be separated from the argument.

-- 
Dave Hylands
Shuswap, BC, Canada
http://www.davehylands.com