initmpfs: use initramfs if rootfstype= or root= specified

Command line option rootfstype=ramfs to obtain old initramfs behavior, and use ramfs instead of tmpfs for stub when root= defined (for cosmetic reasons). [[email protected]: coding-style fixes] Signed-off-by: Rob Landley <[email protected]> Cc: Jeff Layton <[email protected]> Cc: Jens Axboe <[email protected]> Cc: Stephen Warren <[email protected]> Cc: Rusty Russell <[email protected]> Cc: Jim Cromie <[email protected]> Cc: Sam Ravnborg <[email protected]> Cc: Greg Kroah-Hartman <[email protected]> Cc: "Eric W. Biederman" <[email protected]> Cc: Alexander Viro <[email protected]> Cc: "H. Peter Anvin" <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
rtvt123 · Sep 11, 2013 · 6e19ede · 6e19ede
1 parent 16203a7
commit 6e19ede
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Showing 2 changed files with 15 additions and 4 deletions.
diff --git a/Documentation/filesystems/ramfs-rootfs-initramfs.txt b/Documentation/filesystems/ramfs-rootfs-initramfs.txt
@@ -79,6 +79,10 @@ to just make sure certain lists can't become empty.
 Most systems just mount another filesystem over rootfs and ignore it.  The
 amount of space an empty instance of ramfs takes up is tiny.
 
+If CONFIG_TMPFS is enabled, rootfs will use tmpfs instead of ramfs by
+default.  To force ramfs, add "rootfstype=ramfs" to the kernel command
+line.
+
 What is initramfs?
 ------------------
 

diff --git a/init/do_mounts.c b/init/do_mounts.c
@@ -591,16 +591,20 @@ void __init prepare_namespace(void)
 	sys_chroot(".");
 }
 
+static bool is_tmpfs;
 static struct dentry *rootfs_mount(struct file_system_type *fs_type,
 	int flags, const char *dev_name, void *data)
 {
 	static unsigned long once;
+	void *fill = ramfs_fill_super;
 
 	if (test_and_set_bit(0, &once))
 		return ERR_PTR(-ENODEV);
 
-	return mount_nodev(fs_type, flags, data,
-		IS_ENABLED(CONFIG_TMPFS) ? shmem_fill_super : ramfs_fill_super);
+	if (IS_ENABLED(CONFIG_TMPFS) && is_tmpfs)
+		fill = shmem_fill_super;
+
+	return mount_nodev(fs_type, flags, data, fill);
 }
 
 static struct file_system_type rootfs_fs_type = {
@@ -616,10 +620,13 @@ int __init init_rootfs(void)
 	if (err)
 		return err;
 
-	if (IS_ENABLED(CONFIG_TMPFS))
+	if (IS_ENABLED(CONFIG_TMPFS) && !saved_root_name[0] &&
+		(!root_fs_names || strstr(root_fs_names, "tmpfs"))) {
 		err = shmem_init();
-	else
+		is_tmpfs = true;
+	} else {
 		err = init_ramfs_fs();
+	}
 
 	if (err)
 		unregister_filesystem(&rootfs_fs_type);