Ueventd manages /dev
, sets permissions for /sys
, and handles firmware uevents. It has default behavior described below, along with a scripting language that allows customizing this behavior, built on the same parser as init.
Ueventd has one generic customization parameter, the size of rcvbuf_size for the ueventd socket. It is customized by the uevent_socket_rcvbuf_size
parameter, which takes the format of
uevent_socket_rcvbuf_size <size>
For example
uevent_socket_rcvbuf_size 16M
Sets the uevent socket rcvbuf_size to 16 megabytes.
Ueventd reads /system/etc/ueventd.rc, all other files are imported via the import
command, which takes the format of
import <path>
This command parses an ueventd config file, extending the current configuration. If path is a directory, each file in the directory is parsed as a config file. It is not recursive, nested directories will not be parsed. Imported files are parsed after the current file has been parsed.
Ueventd listens to the kernel uevent sockets and creates/deletes nodes in /dev
based on the incoming add/remove uevents. It defaults to using 0600
mode and root
user/group. It always creates the nodes with the SELabel from the current loaded SEPolicy. It has three default behaviors for the node path:
/dev/block/<basename uevent DEVPATH>
. There are symlinks created to this node at /dev/block/<type>/<parent device>/<basename uevent DEVPATH>
, /dev/block/<type>/<parent device>/by-name/<uevent PARTNAME>
, and /dev/block/by-name/<uevent PARTNAME>
if the device is a boot device./dev/<uevent DEVNAME>
if DEVNAME
was specified for the uevent, otherwise as /dev/bus/usb/<bus_id>/<device_id>
where bus_id
is uevent MINOR / 128 + 1
and device_id
is uevent MINOR % 128 + 1
./dev/<basename uevent DEVPATH>
The permissions can be modified using a ueventd.rc script and a line that beings with /dev
. These lines take the format of
devname mode uid gid [options]
For example
/dev/null 0666 root root
When /dev/null
is created, its mode will be set to 0666
, its user to root
and its group to root
.
The path can be modified using a ueventd.rc script and a subsystem
section. There are three to set for a subsystem: the subsystem name, which device name to use, and which directory to place the device in. The section takes the below format of
subsystem <subsystem_name> devname uevent_devname|uevent_devpath [dirname <directory>]
subsystem_name
is used to match uevent SUBSYSTEM
value
devname
takes one of two options
uevent_devname
specifies that the name of the node will be the uevent DEVNAME
uevent_devpath
specified that the name of the node will be basename uevent DEVPATH
dirname
is an optional parameter that specifies a directory within /dev
where the node will be created.
For example
subsystem sound devname uevent_devpath dirname /dev/snd
Indicates that all uevents with SUBSYSTEM=sound
will create nodes as /dev/snd/<basename uevent DEVPATH>
.
Ueventd by default takes no action for /sys
, however it can be instructed to set permissions for certain files in /sys
when matching uevents are generated. This is done using a ueventd.rc script and a line that begins with /sys
. These lines take the format of
nodename attr mode uid gid [options]
For example
/sys/devices/system/cpu/cpu* cpufreq/scaling_max_freq 0664 system system
When a uevent that matches the pattern /sys/devices/system/cpu/cpu*
is sent, the matching sysfs attribute, cpufreq/scaling_max_freq
, will have its mode set to 0664
, its user to to system
and its group set to system
.
The path for a /dev
or /sys
entry can contain a *
anywhere in the path.
*
appears at the end of the string or if the options parameter is set to no_fnm_pathname
, ueventd matches the entry by fnmatch(entry_path, incoming_path, 0)
fnmatch(entry_path, incoming_path, FNM_PATHNAME)
See the man page for fnmatch for more details.
Ueventd by default serves firmware requests by searching through a list of firmware directories for a file matching the uevent FIRMWARE
. It then forks a process to serve this firmware to the kernel.
/apex/*/etc/firmware
is also searched after a list of firmware directories.
The list of firmware directories is customized by a firmware_directories
line in a ueventd.rc file. This line takes the format of
firmware_directories <firmware_directory> [ <firmware_directory> ]*
For example
firmware_directories /etc/firmware/ /odm/firmware/ /vendor/firmware/ /firmware/image/
Adds those 4 directories, in that order to the list of firmware directories that will be tried by ueventd. Note that this option always accumulates to the list; it is not possible to remove previous entries.
Ueventd will wait until after post-fs
in init, to keep retrying before believing the firmwares are not present.
The exact firmware file to be served can be customized by running an external program by a external_firmware_handler
line in a ueventd.rc file. This line takes the format of
external_firmware_handler <devpath> <user [group]> <path to external program>
The handler will be run as the given user, or if a group is provided, as the given user and group.
For example
external_firmware_handler /devices/leds/red/firmware/coeffs.bin system /vendor/bin/led_coeffs.bin
Will launch /vendor/bin/led_coeffs.bin
as the system user instead of serving the default firmware for /devices/leds/red/firmware/coeffs.bin
.
The devpath
argument may include asterisks (*
) to match multiple paths. For example, the string /dev/*/red
will match /dev/leds/red
as well as /dev/lights/red
. The pattern matching follows the rules of the fnmatch() function.
Ueventd will provide the uevent DEVPATH
and FIRMWARE
to this external program on the environment via environment variables with the same names. Ueventd will use the string written to stdout as the new name of the firmware to load. It will still look for the new firmware in the list of firmware directories stated above. It will also reject file names with ..
in them, to prevent leaving these directories. If stdout cannot be read, or the program returns with any exit code other than EXIT_SUCCESS
, or the program crashes, the default firmware from the uevent will be loaded.
Ueventd will additionally log all messages sent to stderr from the external program to the serial console after the external program has exited.
If the kernel command-line argument firmware_class.path
is set, this path will be used first by the kernel to search for the firmware files. If found, ueventd will not be called at all. See the kernel documentation for more details on this feature.
Ueventd must create devices in /dev
for all devices that have already sent their uevents before ueventd has started. To do so, when ueventd is started it does what it calls a ‘coldboot’ on /sys
, in which it writes ‘add’ to every ‘uevent’ file that it finds in /sys/class
, /sys/block
, and /sys/devices
. This causes the kernel to regenerate the uevents for these paths, and thus for ueventd to create the nodes.
For boot time purposes, this is done in parallel across a set of child processes. ueventd.cpp
in this directory contains documentation on how the parallelization is done.
There is an option to parallelize the restorecon function during cold boot as well. It is recommended that devices use genfscon for labeling sysfs nodes. However, some devices may benefit from enabling the parallelization option:
parallel_restorecon enabled
Do parallel restorecon to speed up boot process, subdirectories under /sys
can be sliced by ueventd.rc, and run on multiple process. parallel_restorecon_dir
For example parallel_restorecon_dir /sys parallel_restorecon_dir /sys/devices parallel_restorecon_dir /sys/devices/platform parallel_restorecon_dir /sys/devices/platform/soc