• Kay Sievers's avatar
    Driver Core: devtmpfs - kernel-maintained tmpfs-based /dev · 2b2af54a
    Kay Sievers authored
    Devtmpfs lets the kernel create a tmpfs instance called devtmpfs
    very early at kernel initialization, before any driver-core device
    is registered. Every device with a major/minor will provide a
    device node in devtmpfs.
    Devtmpfs can be changed and altered by userspace at any time,
    and in any way needed - just like today's udev-mounted tmpfs.
    Unmodified udev versions will run just fine on top of it, and will
    recognize an already existing kernel-created device node and use it.
    The default node permissions are root:root 0600. Proper permissions
    and user/group ownership, meaningful symlinks, all other policy still
    needs to be applied by userspace.
    If a node is created by devtmps, devtmpfs will remove the device node
    when the device goes away. If the device node was created by
    userspace, or the devtmpfs created node was replaced by userspace, it
    will no longer be removed by devtmpfs.
    If it is requested to auto-mount it, it makes init=/bin/sh work
    without any further userspace support. /dev will be fully populated
    and dynamic, and always reflect the current device state of the kernel.
    With the commonly used dynamic device numbers, it solves the problem
    where static devices nodes may point to the wrong devices.
    It is intended to make the initial bootup logic simpler and more robust,
    by de-coupling the creation of the inital environment, to reliably run
    userspace processes, from a complex userspace bootstrap logic to provide
    a working /dev.
    Signed-off-by: default avatarKay Sievers <kay.sievers@vrfy.org>
    Signed-off-by: default avatarJan Blunck <jblunck@suse.de>
    Tested-By: default avatarHarald Hoyer <harald@redhat.com>
    Tested-By: default avatarScott James Remnant <scott@ubuntu.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
do_mounts.c 9.27 KB