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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: Kay Sievers <kay.sievers@vrfy.org> Signed-off-by: Jan Blunck <jblunck@suse.de> Tested-By: Harald Hoyer <harald@redhat.com> Tested-By: Scott James Remnant <scott@ubuntu.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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menu "Generic Driver Options"
config UEVENT_HELPER_PATH string "path to uevent helper" depends on HOTPLUG default "/sbin/hotplug" help Path to uevent helper program forked by the kernel for every uevent.
config DEVTMPFS bool "Create a kernel maintained /dev tmpfs (EXPERIMENTAL)" depends on HOTPLUG && SHMEM && TMPFS help 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.
config DEVTMPFS_MOUNT bool "Automount devtmpfs at /dev" depends on DEVTMPFS help 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.
config STANDALONE bool "Select only drivers that don't need compile-time external firmware" if EXPERIMENTAL default y help Select this option if you don't have magic firmware for drivers that need it.
If unsure, say Y.
config PREVENT_FIRMWARE_BUILD bool "Prevent firmware from being built" default y help Say yes to avoid building firmware. Firmware is usually shipped with the driver, and only when updating the firmware a rebuild should be made. If unsure say Y here.
config FW_LOADER tristate "Userspace firmware loading support" if EMBEDDED depends on HOTPLUG default y ---help--- This option is provided for the case where no in-kernel-tree modules require userspace firmware loading support, but a module built outside the kernel tree does.
config FIRMWARE_IN_KERNEL bool "Include in-kernel firmware blobs in kernel binary" depends on FW_LOADER default y help The kernel source tree includes a number of firmware 'blobs' which are used by various drivers. The recommended way to use these is to run "make firmware_install" and to copy the resulting binary files created in usr/lib/firmware directory of the kernel tree to the /lib/firmware on your system so that they can be loaded by userspace helpers on request.
Enabling this option will build each required firmware blob
into the kernel directly, where request_firmware() will find
them without having to call out to userspace. This may be
useful if your root file system requires a device which uses
such firmware, and do not wish to use an initrd.
This single option controls the inclusion of firmware for
every driver which uses request_firmware() and ships its
firmware in the kernel source tree, to avoid a proliferation
of 'Include firmware for xxx device' options.
Say 'N' and let firmware be loaded from userspace.
config EXTRA_FIRMWARE string "External firmware blobs to build into the kernel binary" depends on FW_LOADER help This option allows firmware to be built into the kernel, for the cases where the user either cannot or doesn't want to provide it from userspace at runtime (for example, when the firmware in question is required for accessing the boot device, and the user doesn't want to use an initrd).
This option is a string, and takes the (space-separated) names of the
firmware files -- the same names which appear in MODULE_FIRMWARE()
and request_firmware() in the source. These files should exist under
the directory specified by the EXTRA_FIRMWARE_DIR option, which is
by default the firmware/ subdirectory of the kernel source tree.
So, for example, you might set CONFIG_EXTRA_FIRMWARE="usb8388.bin",
copy the usb8388.bin file into the firmware/ directory, and build the
kernel. Then any request_firmware("usb8388.bin") will be
satisfied internally without needing to call out to userspace.
WARNING: If you include additional firmware files into your binary
kernel image which are not available under the terms of the GPL,
then it may be a violation of the GPL to distribute the resulting
image -- since it combines both GPL and non-GPL work. You should
consult a lawyer of your own before distributing such an image.
config EXTRA_FIRMWARE_DIR string "Firmware blobs root directory" depends on EXTRA_FIRMWARE != "" default "firmware" help This option controls the directory in which the kernel build system looks for the firmware files listed in the EXTRA_FIRMWARE option. The default is the firmware/ directory in the kernel source tree, but by changing this option you can point it elsewhere, such as the /lib/firmware/ directory or another separate directory containing firmware files.
config DEBUG_DRIVER bool "Driver Core verbose debug messages" depends on DEBUG_KERNEL help Say Y here if you want the Driver core to produce a bunch of debug messages to the system log. Select this if you are having a problem with the driver core and want to see more of what is going on.
If you are unsure about this, say N here.
config DEBUG_DEVRES bool "Managed device resources verbose debug messages" depends on DEBUG_KERNEL help This option enables kernel parameter devres.log. If set to non-zero, devres debug messages are printed. Select this if you are having a problem with devres or want to debug resource management for a managed device. devres.log can be switched on and off from sysfs node.
If you are unsure about this, Say N here.
config SYS_HYPERVISOR bool default n
endmenu