Commit f9259be6 authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Al Viro
Browse files

init: allow mounting arbitrary non-blockdevice filesystems as root 



Currently the only non-blockdevice filesystems that can be used as the
initial root filesystem are NFS and CIFS, which use the magic
"root=/dev/nfs" and "root=/dev/cifs" syntax that requires the root
device file system details to come from filesystem specific kernel
command line options.

Add a little bit of new code that allows to just pass arbitrary
string mount options to any non-blockdevice filesystems so that it can
be mounted as the root file system.

For example a virtiofs root file system can be mounted using the
following syntax:

"root=myfs rootfstype=virtiofs rw"

Based on an earlier patch from Vivek Goyal <vgoyal@redhat.com>.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent e24d12b7

init/do_mounts.c

+43 −0
Original line number Diff line number Diff line
@@ -534,6 +534,45 @@ static int __init mount_cifs_root(void) 
}

#endif



static bool __init fs_is_nodev(char *fstype)

{

	struct file_system_type *fs = get_fs_type(fstype);

	bool ret = false;



	if (fs) {

		ret = !(fs->fs_flags & FS_REQUIRES_DEV);

		put_filesystem(fs);

	}



	return ret;

}



static int __init mount_nodev_root(void)

{

	char *fs_names, *fstype;

	int err = -EINVAL;



	fs_names = (void *)__get_free_page(GFP_KERNEL);

	if (!fs_names)

		return -EINVAL;

	split_fs_names(fs_names, root_fs_names);



	for (fstype = fs_names; *fstype; fstype += strlen(fstype) + 1) {

		if (!fs_is_nodev(fstype))

			continue;

		err = do_mount_root(root_device_name, fstype, root_mountflags,

				    root_mount_data);

		if (!err)

			break;

		if (err != -EACCES && err != -EINVAL)

			panic("VFS: Unable to mount root \"%s\" (%s), err=%d\n",

			      root_device_name, fstype, err);

	}



	free_page((unsigned long)fs_names);

	return err;

}



void __init mount_root(void)

{

#ifdef CONFIG_ROOT_NFS
@@ -550,6 +589,10 @@ void __init mount_root(void) 
		return;

	}

#endif

	if (ROOT_DEV == 0 && root_device_name && root_fs_names) {

		if (mount_nodev_root() == 0)

			return;

	}

#ifdef CONFIG_BLOCK

	{

		int err = create_dev("/dev/root", ROOT_DEV);