Configure out file locking features

This patch adds the CONFIG_FILE_LOCKING option which allows to remove
support for advisory locks. With this patch enabled, the flock()
system call, the F_GETLK, F_SETLK and F_SETLKW operations of fcntl()
and NFS support are disabled. These features are not necessarly needed
on embedded systems. It allows to save ~11 Kb of kernel code and data:

   text          data     bss     dec     hex filename
1125436        118764  212992 1457192  163c28 vmlinux.old
1114299        118564  212992 1445855  160fdf vmlinux
 -11137    -200       0  -11337   -2C49 +/-

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

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Matt Mackall <mpm@selenic.com>
Cc: matthew@wil.cx
Cc: linux-fsdevel@vger.kernel.org
Cc: mpm@selenic.com
Cc: akpm@linux-foundation.org
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

kernel/sysctl.c

@@ -97,7 +97,7 @@ static int sixty = 60;
 static int neg_one = -1;
 #endif
 
-#ifdef CONFIG_MMU
+#if defined(CONFIG_MMU) && defined(CONFIG_FILE_LOCKING)
 static int two = 2;
 #endif
 
@@ -1261,6 +1261,7 @@ static struct ctl_table fs_table[] = {
 		.extra1		= &minolduid,
 		.extra2		= &maxolduid,
 	},
+#ifdef CONFIG_FILE_LOCKING
 	{
 		.ctl_name	= FS_LEASES,
 		.procname	= "leases-enable",
@@ -1269,6 +1270,7 @@ static struct ctl_table fs_table[] = {
 		.mode		= 0644,
 		.proc_handler	= &proc_dointvec,
 	},
+#endif
 #ifdef CONFIG_DNOTIFY
 	{
 		.ctl_name	= FS_DIR_NOTIFY,
@@ -1280,6 +1282,7 @@ static struct ctl_table fs_table[] = {
 	},
 #endif
 #ifdef CONFIG_MMU
+#ifdef CONFIG_FILE_LOCKING
 	{
 		.ctl_name	= FS_LEASE_TIME,
 		.procname	= "lease-break-time",
@@ -1291,6 +1294,7 @@ static struct ctl_table fs_table[] = {
 		.extra1		= &zero,
 		.extra2		= &two,
 	},
+#endif
 	{
 		.procname	= "aio-nr",
 		.data		= &aio_nr,