tmpfs: depend on shmem

CONFIG_SHMEM off gives you (ramfs masquerading as) tmpfs, even when
CONFIG_TMPFS is off: that's a little anomalous, and I'd intended to make
more sense of it by removing CONFIG_TMPFS altogether, always enabling its
code when CONFIG_SHMEM; but so many defconfigs have CONFIG_SHMEM on
CONFIG_TMPFS off that we'd better leave that as is.

But there is no point in asking for CONFIG_TMPFS if CONFIG_SHMEM is off:
make TMPFS depend on SHMEM, which also prevents TMPFS_POSIX_ACL
shmem_acl.o being pointlessly built into the kernel when SHMEM is off.

And a selfish change, to prevent the world from being rebuilt when I
switch between CONFIG_SHMEM on and off: the only CONFIG_SHMEM in the
header files is mm.h shmem_lock() - give that a shmem.c stub instead.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/Kconfig

@@ -109,6 +109,7 @@ source "fs/sysfs/Kconfig"
 
 config TMPFS
 	bool "Virtual memory file system support (former shm fs)"
+	depends on SHMEM
 	help
 	  Tmpfs is a file system which keeps all files in virtual memory.
 

include/linux/mm.h

@@ -702,17 +702,8 @@ extern void pagefault_out_of_memory(void);
 
 extern void show_free_areas(void);
 
-#ifdef CONFIG_SHMEM
-extern int shmem_lock(struct file *file, int lock, struct user_struct *user);
-#else
-static inline int shmem_lock(struct file *file, int lock,
-			    struct user_struct *user)
-{
-	return 0;
-}
-#endif
+int shmem_lock(struct file *file, int lock, struct user_struct *user);
 struct file *shmem_file_setup(const char *name, loff_t size, unsigned long flags);
-
 int shmem_zero_setup(struct vm_area_struct *);
 
 #ifndef CONFIG_MMU

mm/shmem.c

@@ -2593,6 +2593,11 @@ int shmem_unuse(swp_entry_t entry, struct page *page)
 	return 0;
 }
 
+int shmem_lock(struct file *file, int lock, struct user_struct *user)
+{
+	return 0;
+}
+
 #define shmem_vm_ops				generic_file_vm_ops
 #define shmem_file_operations			ramfs_file_operations
 #define shmem_get_inode(sb, mode, dev, flags)	ramfs_get_inode(sb, mode, dev)