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>

fs/Kconfig

@@ -419,6 +419,14 @@ config FS_POSIX_ACL
 	bool
 	default n
 
+config FILE_LOCKING
+	bool "Enable POSIX file locking API" if EMBEDDED
+	default y
+	help
+	  This option enables standard file locking support, required
+          for filesystems like NFS and for the flock() system
+          call. Disabling this option saves about 11k.
+
 source "fs/xfs/Kconfig"
 source "fs/gfs2/Kconfig"
 

fs/Makefile

@@ -7,7 +7,7 @@
 
 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 locks.o dcache.o inode.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 \
 		seq_file.o xattr.o libfs.o fs-writeback.o \
 		pnode.o drop_caches.o splice.o sync.o utimes.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-$(CONFIG_FILE_LOCKING)      += locks.o
 obj-$(CONFIG_COMPAT)		+= compat.o compat_ioctl.o
 
 nfsd-$(CONFIG_NFSD)		:= nfsctl.o

fs/proc/proc_misc.c

@@ -684,6 +684,7 @@ static int cmdline_read_proc(char *page, char **start, off_t off,
 	return proc_calc_metrics(page, start, off, count, eof, len);
 }
 
+#ifdef CONFIG_FILE_LOCKING
 static int locks_open(struct inode *inode, struct file *filp)
 {
 	return seq_open(filp, &locks_seq_operations);
@@ -695,6 +696,7 @@ static const struct file_operations proc_locks_operations = {
 	.llseek		= seq_lseek,
 	.release	= seq_release,
 };
+#endif /* CONFIG_FILE_LOCKING */
 
 static int execdomains_read_proc(char *page, char **start, off_t off,
 				 int count, int *eof, void *data)
@@ -888,7 +890,9 @@ void __init proc_misc_init(void)
 #ifdef CONFIG_PRINTK
 	proc_create("kmsg", S_IRUSR, NULL, &proc_kmsg_operations);
 #endif
+#ifdef CONFIG_FILE_LOCKING
 	proc_create("locks", 0, NULL, &proc_locks_operations);
+#endif
 	proc_create("devices", 0, NULL, &proc_devinfo_operations);
 	proc_create("cpuinfo", 0, NULL, &proc_cpuinfo_operations);
 #ifdef CONFIG_BLOCK

include/linux/fs.h

@@ -983,6 +983,13 @@ struct file_lock {
 
 #include <linux/fcntl.h>
 
+extern void send_sigio(struct fown_struct *fown, int fd, int band);
+
+/* fs/sync.c */
+extern int do_sync_mapping_range(struct address_space *mapping, loff_t offset,
+			loff_t endbyte, unsigned int flags);
+
+#ifdef CONFIG_FILE_LOCKING
 extern int fcntl_getlk(struct file *, struct flock __user *);
 extern int fcntl_setlk(unsigned int, struct file *, unsigned int,
 			struct flock __user *);
@@ -993,14 +1000,9 @@ extern int fcntl_setlk64(unsigned int, struct file *, unsigned int,
 			struct flock64 __user *);
 #endif
 
-extern void send_sigio(struct fown_struct *fown, int fd, int band);
 extern int fcntl_setlease(unsigned int fd, struct file *filp, long arg);
 extern int fcntl_getlease(struct file *filp);
 
-/* fs/sync.c */
-extern int do_sync_mapping_range(struct address_space *mapping, loff_t offset,
-			loff_t endbyte, unsigned int flags);
-
 /* fs/locks.c */
 extern void locks_init_lock(struct file_lock *);
 extern void locks_copy_lock(struct file_lock *, struct file_lock *);
@@ -1023,6 +1025,37 @@ extern int lease_modify(struct file_lock **, int);
 extern int lock_may_read(struct inode *, loff_t start, unsigned long count);
 extern int lock_may_write(struct inode *, loff_t start, unsigned long count);
 extern struct seq_operations locks_seq_operations;
+#else /* !CONFIG_FILE_LOCKING */
+#define fcntl_getlk(a, b) ({ -EINVAL; })
+#define fcntl_setlk(a, b, c, d) ({ -EACCES; })
+#if BITS_PER_LONG == 32
+#define fcntl_getlk64(a, b) ({ -EINVAL; })
+#define fcntl_setlk64(a, b, c, d) ({ -EACCES; })
+#endif
+#define fcntl_setlease(a, b, c) ({ 0; })
+#define fcntl_getlease(a) ({ 0; })
+#define locks_init_lock(a) ({ })
+#define __locks_copy_lock(a, b) ({ })
+#define locks_copy_lock(a, b) ({ })
+#define locks_remove_posix(a, b) ({ })
+#define locks_remove_flock(a) ({ })
+#define posix_test_lock(a, b) ({ 0; })
+#define posix_lock_file(a, b, c) ({ -ENOLCK; })
+#define posix_lock_file_wait(a, b) ({ -ENOLCK; })
+#define posix_unblock_lock(a, b) (-ENOENT)
+#define vfs_test_lock(a, b) ({ 0; })
+#define vfs_lock_file(a, b, c, d) (-ENOLCK)
+#define vfs_cancel_lock(a, b) ({ 0; })
+#define flock_lock_file_wait(a, b) ({ -ENOLCK; })
+#define __break_lease(a, b) ({ 0; })
+#define lease_get_mtime(a, b) ({ })
+#define generic_setlease(a, b, c) ({ -EINVAL; })
+#define vfs_setlease(a, b, c) ({ -EINVAL; })
+#define lease_modify(a, b) ({ -EINVAL; })
+#define lock_may_read(a, b, c) ({ 1; })
+#define lock_may_write(a, b, c) ({ 1; })
+#endif /* !CONFIG_FILE_LOCKING */
+
 
 struct fasync_struct {
 	int	magic;
@@ -1554,9 +1587,12 @@ extern int vfs_statfs(struct dentry *, struct kstatfs *);
 /* /sys/fs */
 extern struct kobject *fs_kobj;
 
+extern int rw_verify_area(int, struct file *, loff_t *, size_t);
+
 #define FLOCK_VERIFY_READ  1
 #define FLOCK_VERIFY_WRITE 2
 
+#ifdef CONFIG_FILE_LOCKING
 extern int locks_mandatory_locked(struct inode *);
 extern int locks_mandatory_area(int, struct inode *, struct file *, loff_t, size_t);
 
@@ -1587,8 +1623,6 @@ static inline int locks_verify_locked(struct inode *inode)
 	return 0;
 }
 
-extern int rw_verify_area(int, struct file *, loff_t *, size_t);
-
 static inline int locks_verify_truncate(struct inode *inode,
 				    struct file *filp,
 				    loff_t size)
@@ -1609,6 +1643,15 @@ static inline int break_lease(struct inode *inode, unsigned int mode)
 		return __break_lease(inode, mode);
 	return 0;
 }
+#else /* !CONFIG_FILE_LOCKING */
+#define locks_mandatory_locked(a) ({ 0; })
+#define locks_mandatory_area(a, b, c, d, e) ({ 0; })
+#define __mandatory_lock(a) ({ 0; })
+#define mandatory_lock(a) ({ 0; })
+#define locks_verify_locked(a) ({ 0; })
+#define locks_verify_truncate(a, b, c) ({ 0; })
+#define break_lease(a, b) ({ 0; })
+#endif /* CONFIG_FILE_LOCKING */
 
 /* fs/open.c */
 

kernel/sys_ni.c

@@ -125,6 +125,7 @@ cond_syscall(sys_vm86old);
 cond_syscall(sys_vm86);
 cond_syscall(compat_sys_ipc);
 cond_syscall(compat_sys_sysctl);
+cond_syscall(sys_flock);
 
 /* arch-specific weak syscall entries */
 cond_syscall(sys_pciconfig_read);

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,