mirror of
https://github.com/AsahiLinux/u-boot
synced 2024-12-17 00:33:06 +00:00
52 lines
2.1 KiB
ReStructuredText
52 lines
2.1 KiB
ReStructuredText
|
.. SPDX-License-Identifier: GPL-2.0+
|
||
|
|
|
||
|
|
Environment implementation
|
||
|
|
==========================
|
||
|
|
|
||
|
|
See :doc:`../usage/environment` for usage information.
|
||
|
|
|
||
|
|
Callback functions for environment variables
|
||
|
|
--------------------------------------------
|
||
|
|
|
||
|
|
For some environment variables, the behavior of u-boot needs to change
|
||
|
|
when their values are changed. This functionality allows functions to
|
||
|
|
be associated with arbitrary variables. On creation, overwrite, or
|
||
|
|
deletion, the callback will provide the opportunity for some side
|
||
|
|
effect to happen or for the change to be rejected.
|
||
|
|
|
||
|
|
The callbacks are named and associated with a function using the
|
||
|
|
U_BOOT_ENV_CALLBACK macro in your board or driver code.
|
||
|
|
|
||
|
|
These callbacks are associated with variables in one of two ways. The
|
||
|
|
static list can be added to by defining CONFIG_ENV_CALLBACK_LIST_STATIC
|
||
|
|
in the board configuration to a string that defines a list of
|
||
|
|
associations. The list must be in the following format::
|
||
|
|
|
||
|
|
entry = variable_name[:callback_name]
|
||
|
|
list = entry[,list]
|
||
|
|
|
||
|
|
If the callback name is not specified, then the callback is deleted.
|
||
|
|
Spaces are also allowed anywhere in the list.
|
||
|
|
|
||
|
|
Callbacks can also be associated by defining the ".callbacks" variable
|
||
|
|
with the same list format above. Any association in ".callbacks" will
|
||
|
|
override any association in the static list. You can define
|
||
|
|
CONFIG_ENV_CALLBACK_LIST_DEFAULT to a list (string) to define the
|
||
|
|
".callbacks" environment variable in the default or embedded environment.
|
||
|
|
|
||
|
|
If CONFIG_REGEX is defined, the variable_name above is evaluated as a
|
||
|
|
regular expression. This allows multiple variables to be connected to
|
||
|
|
the same callback without explicitly listing them all out.
|
||
|
|
|
||
|
|
The signature of the callback functions is::
|
||
|
|
|
||
|
|
int callback(const char *name, const char *value, enum env_op op, int flags)
|
||
|
|
|
||
|
|
* name - changed environment variable
|
||
|
|
* value - new value of the environment variable
|
||
|
|
* op - operation (create, overwrite, or delete)
|
||
|
|
* flags - attributes of the environment variable change, see flags H_* in
|
||
|
|
include/search.h
|
||
|
|
|
||
|
|
The return value is 0 if the variable change is accepted and 1 otherwise.
|