devtmpfs: support !CONFIG_TMPFS

Make devtmpfs available on (embedded) configurations without SHMEM/TMPFS,
using ramfs instead.

Saves ~15KB.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
Acked-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/base/Kconfig

@@ -18,9 +18,9 @@ config UEVENT_HELPER_PATH
 
 config DEVTMPFS
 	bool "Maintain a devtmpfs filesystem to mount at /dev"
-	depends on HOTPLUG && SHMEM && TMPFS
+	depends on HOTPLUG
 	help
-	  This creates a tmpfs filesystem instance early at bootup.
+	  This creates a tmpfs/ramfs filesystem instance early at bootup.
 	  In this filesystem, the kernel driver core maintains device
 	  nodes with their default names and permissions for all
 	  registered devices with an assigned major/minor number.
@@ -33,6 +33,9 @@ config DEVTMPFS
 	  functional /dev without any further help. It also allows simple
 	  rescue systems, and reliably handles dynamic major/minor numbers.
 
+	  Notice: if CONFIG_TMPFS isn't enabled, the simpler ramfs
+	  file system will be used instead.
+
 config DEVTMPFS_MOUNT
 	bool "Automount devtmpfs at /dev, after the kernel mounted the rootfs"
 	depends on DEVTMPFS

drivers/base/devtmpfs.c

@@ -20,6 +20,7 @@
 #include <linux/namei.h>
 #include <linux/fs.h>
 #include <linux/shmem_fs.h>
+#include <linux/ramfs.h>
 #include <linux/cred.h>
 #include <linux/sched.h>
 #include <linux/init_task.h>
@@ -45,7 +46,11 @@ __setup("devtmpfs.mount=", mount_param);
 static int dev_get_sb(struct file_system_type *fs_type, int flags,
 		      const char *dev_name, void *data, struct vfsmount *mnt)
 {
+#ifdef CONFIG_TMPFS
 	return get_sb_single(fs_type, flags, data, shmem_fill_super, mnt);
+#else
+	return get_sb_single(fs_type, flags, data, ramfs_fill_super, mnt);
+#endif
 }
 
 static struct file_system_type dev_fs_type = {

fs/ramfs/inode.c

@@ -214,7 +214,7 @@ static int ramfs_parse_options(char *data, struct ramfs_mount_opts *opts)
 	return 0;
 }
 
-static int ramfs_fill_super(struct super_block * sb, void * data, int silent)
+int ramfs_fill_super(struct super_block *sb, void *data, int silent)
 {
 	struct ramfs_fs_info *fsi;
 	struct inode *inode = NULL;

include/linux/ramfs.h

@@ -20,4 +20,6 @@ extern const struct file_operations ramfs_file_operations;
 extern const struct vm_operations_struct generic_file_vm_ops;
 extern int __init init_rootfs(void);
 
+int ramfs_fill_super(struct super_block *sb, void *data, int silent);
+
 #endif