new helper: get_signal()

On success get_signal_to_deliver() fills k_sigaction and siginfo.
_All_ users pass it addresses of the local variables sitting in
the same function.  Then they proceed to pass those addresses
pretty much in tandem to a bunch of helper functions; again, all
callers of those helpers are passing them such a pair, and one that
had been through get_signal_to_deliver() at that.

The obvious cleanup: introduce a new type that would contain a
<k_sigaction,siginfo> pair (struct ksignal) and begin switching to
using it.  Turns out that it's convenient to store the signal number
in the same object.

New helper, taking that sucker is a wrapper for get_signal_to_deliver();
takes struct ksignal * and returns bool.  On success fills ksignal
with the information for signal handler to be invoked.

For now it's a macro (to avoid header ordering headache), but eventually
it'll be a function in kernel/signal.c, with get_signal_to_deliver()
folded into it.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/signal.h

@@ -279,10 +279,28 @@ struct old_sigaction {
 };
 #endif
 
+struct ksignal {
+	struct k_sigaction ka;
+	siginfo_t info;
+	int sig;
+};
+
 extern int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka, struct pt_regs *regs, void *cookie);
 extern void signal_delivered(int sig, siginfo_t *info, struct k_sigaction *ka, struct pt_regs *regs, int stepping);
 extern void exit_signals(struct task_struct *tsk);
 
+/*
+ * Eventually that'll replace get_signal_to_deliver(); macro for now,
+ * to avoid nastiness with include order.
+ */
+#define get_signal(ksig)					\
+({								\
+	struct ksignal *p = (ksig);				\
+	p->sig = get_signal_to_deliver(&p->info, &p->ka,	\
+					signal_pt_regs(), NULL);\
+	p->sig > 0;						\
+})
+
 extern struct kmem_cache *sighand_cachep;
 
 int unhandled_signal(struct task_struct *tsk, int sig);