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Subject[PATCH 19/62] Driver-Core: devtmpfs - remove EXPERIMENTAL and enable it by default
From: Kay Sievers <>

All major distros enable devtmpfs on recent systems, so remove
the EXPERIMENTAL flag, and enable it by default to reflect how it
is used today.

Signed-off-by: Kay Sievers <>
Signed-off-by: Greg Kroah-Hartman <>
drivers/base/Kconfig | 45 ++++++++++++++++++++++++++++-----------------
1 files changed, 28 insertions(+), 17 deletions(-)

diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
index ee37727..8497ce9 100644
--- a/drivers/base/Kconfig
+++ b/drivers/base/Kconfig
@@ -9,29 +9,40 @@ config UEVENT_HELPER_PATH
every uevent.

- bool "Create a kernel maintained /dev tmpfs (EXPERIMENTAL)"
+ bool "Maintain a devtmpfs filesystem to mount at /dev"
depends on HOTPLUG && SHMEM && TMPFS
+ default y
- This creates a tmpfs filesystem, and mounts it at bootup
- and mounts it at /dev. The kernel driver core creates device
- nodes for all registered devices in that filesystem. All device
- nodes are owned by root and have the default mode of 0600.
- Userspace can add and delete the nodes as needed. This is
- intended to simplify bootup, and make it possible to delay
- the initial coldplug at bootup done by udev in userspace.
- It should also provide a simpler way for rescue systems
- to bring up a kernel with dynamic major/minor numbers.
- Meaningful symlinks, permissions and device ownership must
- still be handled by userspace.
- If unsure, say N here.
+ This creates a tmpfs 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.
+ Userspace can modify the filesystem content as needed, add
+ symlinks, and apply needed permissions.
+ It provides a fully functional /dev directory, where usually
+ udev runs on top, managing permissions and adding meaningful
+ symlinks.
+ In very limited environments, it may provide a sufficient
+ functional /dev without any further help. It also allows simple
+ rescue systems, and reliably handles dynamic major/minor numbers.
+ If unsure, say Y here.

- bool "Automount devtmpfs at /dev"
+ bool "Automount devtmpfs at /dev, after the kernel mounted the rootfs"
depends on DEVTMPFS
+ default y
- This will mount devtmpfs at /dev if the kernel mounts the root
- filesystem. It will not affect initramfs based mounting.
- If unsure, say N here.
+ This will instruct the kernel to automatically mount the
+ devtmpfs filesystem at /dev, directly after the kernel has
+ mounted the root filesystem. The behavior can be overridden
+ with the commandline parameter: devtmpfs.mount=0|1.
+ This option does not affect initramfs based booting, here
+ the devtmpfs filesystem always needs to be mounted manually
+ after the roots is mounted.
+ With this option enabled, it allows to bring up a system in
+ rescue mode with init=/bin/sh, even when the /dev directory
+ on the rootfs is completely empty.
+ If unsure, say Y here.

bool "Select only drivers that don't need compile-time external firmware" if EXPERIMENTAL

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