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SubjectRe: GCC nested functions?
On Wed, May 12, 2004 at 10:59:24AM -0700, Stephen Hemminger wrote:
> I used GCC nested functions in the (not released) bridge sysfs interface for 2.6.6.
> It seemed like a nice way to express the sysfs related interface without doing
> lots of code copying (or worse lots of macros).
>
> The code in question looks like:
> static ssize_t store_bridge_parm(struct class_device *cd,
> const char *buf, size_t len,
> void (*store)(struct net_bridge *, unsigned long))
> {
> struct net_bridge *br = to_bridge(cd);
> char *endp;
> unsigned long val;
>
> if (!capable(CAP_NET_ADMIN))
> return -EPERM;
>
> val = simple_strtoul(buf, &endp, 0);
> if (endp == buf)
> return -EINVAL;
>
> spin_lock_bh(&br->lock);
> store(br, val);
> spin_unlock_bh(&br->lock);
> return len;
> }
> ...
>
> static ssize_t store_forward_delay(struct class_device *cd, const char *buf,
> size_t len)
> {
> void store(struct net_bridge *br, unsigned long val)
> {
> unsigned long delay = clock_t_to_jiffies(val);
> br->forward_delay = delay;
> if (br_is_root_bridge(br))
> br->bridge_forward_delay = delay;
> }
>
> return store_bridge_parm(cd, buf, len, store);
> }
>
>
> This works fine for GCC 2.95 and 3.X for i386 and x86_64 architectures, but the ia64
> (cross compiler) pukes with:
>
> In function `store_forward_delay':
> : undefined reference to `__ia64_trampoline'
>
> Redoing it as separate functions is easy enough, but the questions are:
> - Are gcc nested functions allowed in the kernel? If not where should
> this restriction be put in Documentation? CodingStyles?

There is some kind of implicit prohibition in Documentation/CodingStyle
(Chapter3: Placing braces):

"Heretic people all over the world have claimed that this inconsistency
is ... well ... inconsistent, but all right-thinking people know that
(a) K&R are _right_ and (b) K&R are right. Besides, functions are
special anyway (you can't nest them in C)."
^^^^^^^^^^^^^^^^^^^^^^^^^^^
Maybe the way it is stated is too close so subliminal ;-) But I never found
a real need for them in C.

Gabriel
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