[PATCH] CONFIG_FUTEX

From: Christopher Hoover <ch@murgatroid.com>

Not everyone needs futex support, so it should be optional.  This is needed
for small platforms.

include/linux/futex.h

@@ -14,4 +14,7 @@ asmlinkage long sys_futex(u32 __user *uaddr, int op, int val,
 			  struct timespec __user *utime, u32 __user *uaddr2);
 
 
+long do_futex(unsigned long uaddr, int op, int val,
+		unsigned long timeout, unsigned long uaddr2, int val2);
+
 #endif

init/Kconfig

@@ -108,7 +108,24 @@ config LOG_BUF_SHIFT
 		     13 =>  8 KB
 		     12 =>  4 KB
 
-endmenu
+
+menuconfig EMBEDDED
+	bool "Remove kernel features (for embedded systems)"
+	help
+	  This option allows certain base kernel features to be removed from
+	  the build.  This is for specialized environments which can tolerate
+	  a "non-standard" kernel.  Only use this if you really know what you
+	  are doing.
+
+config FUTEX
+	bool "Enable futex support" if EMBEDDED
+	default y
+	help
+	  Disabling this option will cause the kernel to be built without
+	  support for "fast userspace mutexes".  The resulting kernel may not
+	  run glibc-based applications correctly.
+
+endmenu		# General setup
 
 
 menu "Loadable module support"
@@ -181,4 +198,3 @@ config KMOD
 	  in <file:Documentation/kmod.txt>.
 
 endmenu
-

kernel/Makefile

@@ -5,9 +5,10 @@
 obj-y     = sched.o fork.o exec_domain.o panic.o printk.o profile.o \
 	    exit.o itimer.o time.o softirq.o resource.o \
 	    sysctl.o capability.o ptrace.o timer.o user.o \
-	    signal.o sys.o kmod.o workqueue.o futex.o pid.o \
+	    signal.o sys.o kmod.o workqueue.o pid.o \
 	    rcupdate.o intermodule.o extable.o params.o posix-timers.o
 
+obj-$(CONFIG_FUTEX) += futex.o
 obj-$(CONFIG_GENERIC_ISA_DMA) += dma.o
 obj-$(CONFIG_SMP) += cpu.o
 obj-$(CONFIG_UID16) += uid16.o

kernel/compat.c

@@ -18,6 +18,7 @@
 #include <linux/signal.h>
 #include <linux/sched.h>	/* for MAX_SCHEDULE_TIMEOUT */
 #include <linux/futex.h>	/* for FUTEX_WAIT */
+#include <linux/unistd.h>
 
 #include <asm/uaccess.h>
 
@@ -211,9 +212,7 @@ asmlinkage long compat_sys_sigprocmask(int how, compat_old_sigset_t *set,
 	return ret;
 }
 
-extern long do_futex(unsigned long uaddr, int op, int val,
-			unsigned long timeout, unsigned long uaddr2, int val2);
-
+#ifdef CONFIG_FUTEX
 asmlinkage long compat_sys_futex(u32 *uaddr, int op, int val,
 		struct compat_timespec *utime)
 {
@@ -231,6 +230,7 @@ asmlinkage long compat_sys_futex(u32 *uaddr, int op, int val,
 
 	return do_futex((unsigned long)uaddr, op, val, timeout, uaddr2, val2);
 }
+#endif
 
 asmlinkage long sys_setrlimit(unsigned int resource, struct rlimit *rlim);
 

kernel/sys.c

@@ -226,6 +226,8 @@ cond_syscall(sys_shutdown)
 cond_syscall(sys_sendmsg)
 cond_syscall(sys_recvmsg)
 cond_syscall(sys_socketcall)
+cond_syscall(sys_futex)
+cond_syscall(compat_sys_futex)
 
 static int set_one_prio(struct task_struct *p, int niceval, int error)
 {