Configure out AIO support

This patchs adds the CONFIG_AIO option which allows to remove support
for asynchronous I/O operations, that are not necessarly used by
applications, particularly on embedded devices. As this is a
size-reduction option, it depends on CONFIG_EMBEDDED. It allows to
save ~7 kilobytes of kernel code/data:

   text	   data	    bss	    dec	    hex	filename
1115067	 119180	 217088	1451335	 162547	vmlinux
1108025	 119048	 217088	1444161	 160941	vmlinux.new
  -7042    -132       0   -7174   -1C06 +/-

This patch has been originally written by Matt Mackall
<mpm@selenic.com>, and is part of the Linux Tiny project.

[randy.dunlap@oracle.com: build fix]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: Zach Brown <zach.brown@oracle.com>
Signed-off-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/Makefile

@@ -8,7 +8,7 @@
 obj-y :=	open.o read_write.o file_table.o super.o \
 		char_dev.o stat.o exec.o pipe.o namei.o fcntl.o \
 		ioctl.o readdir.o select.o fifo.o dcache.o inode.o \
-		attr.o bad_inode.o file.o filesystems.o namespace.o aio.o \
+		attr.o bad_inode.o file.o filesystems.o namespace.o \
 		seq_file.o xattr.o libfs.o fs-writeback.o \
 		pnode.o drop_caches.o splice.o sync.o utimes.o \
 		stack.o
@@ -27,6 +27,7 @@ obj-$(CONFIG_ANON_INODES)	+= anon_inodes.o
 obj-$(CONFIG_SIGNALFD)		+= signalfd.o
 obj-$(CONFIG_TIMERFD)		+= timerfd.o
 obj-$(CONFIG_EVENTFD)		+= eventfd.o
+obj-$(CONFIG_AIO)               += aio.o
 obj-$(CONFIG_FILE_LOCKING)      += locks.o
 obj-$(CONFIG_COMPAT)		+= compat.o compat_ioctl.o
 

include/linux/aio.h

@@ -204,12 +204,21 @@ struct kioctx {
 /* prototypes */
 extern unsigned aio_max_size;
 
+#ifdef CONFIG_AIO
 extern ssize_t wait_on_sync_kiocb(struct kiocb *iocb);
 extern int aio_put_req(struct kiocb *iocb);
 extern void kick_iocb(struct kiocb *iocb);
 extern int aio_complete(struct kiocb *iocb, long res, long res2);
 struct mm_struct;
 extern void exit_aio(struct mm_struct *mm);
+#else
+static inline ssize_t wait_on_sync_kiocb(struct kiocb *iocb) { return 0; }
+static inline int aio_put_req(struct kiocb *iocb) { return 0; }
+static inline void kick_iocb(struct kiocb *iocb) { }
+static inline int aio_complete(struct kiocb *iocb, long res, long res2) { return 0; }
+struct mm_struct;
+static inline void exit_aio(struct mm_struct *mm) { }
+#endif /* CONFIG_AIO */
 
 #define io_wait_to_kiocb(wait) container_of(wait, struct kiocb, ki_wait)
 

init/Kconfig

@@ -713,6 +713,14 @@ config SHMEM
 	  option replaces shmem and tmpfs with the much simpler ramfs code,
 	  which may be appropriate on small systems without swap.
 
+config AIO
+	bool "Enable AIO support" if EMBEDDED
+	default y
+	help
+	  This option enables POSIX asynchronous I/O which may by used
+          by some high performance threaded applications. Disabling
+          this option saves about 7k.
+
 config VM_EVENT_COUNTERS
 	default y
 	bool "Enable VM event counters for /proc/vmstat" if EMBEDDED

kernel/sys_ni.c

@@ -126,6 +126,11 @@ cond_syscall(sys_vm86);
 cond_syscall(compat_sys_ipc);
 cond_syscall(compat_sys_sysctl);
 cond_syscall(sys_flock);
+cond_syscall(sys_io_setup);
+cond_syscall(sys_io_destroy);
+cond_syscall(sys_io_submit);
+cond_syscall(sys_io_cancel);
+cond_syscall(sys_io_getevents);
 
 /* arch-specific weak syscall entries */
 cond_syscall(sys_pciconfig_read);

kernel/sysctl.c

@@ -1281,6 +1281,7 @@ static struct ctl_table fs_table[] = {
 		.extra2		= &two,
 	},
 #endif
+#ifdef CONFIG_AIO
 	{
 		.procname	= "aio-nr",
 		.data		= &aio_nr,
@@ -1295,6 +1296,7 @@ static struct ctl_table fs_table[] = {
 		.mode		= 0644,
 		.proc_handler	= &proc_doulongvec_minmax,
 	},
+#endif /* CONFIG_AIO */
 #ifdef CONFIG_INOTIFY_USER
 	{
 		.ctl_name	= FS_INOTIFY,