This patch series is based on this[1] patch series from Maxime.
This is an RFC. It's been only tested in a specific use case on a custom i.MX6 board. It's known to break compilation on a few boards.
I have a use case where we want some variables from a first environment to be overriden by variables from a second environment. For example, we want to load variables from the default env (ENV_IS_NOWHERE) and then load only a handful of other variables from, e.g., NAND.
In our use case, we basically can be sure that the default env in the U-Boot binary is secure but we want only a few variables to be modified, thus keeping control over the overall behaviour of U-Boot in secure mode.
It works in that way: - from highest to lowest priority, the first environment that can be loaded (that has successfully init and whose load function has returned no errors) will be the main environment, - then, all the following environment that could be successfully loaded (same conditions as the main environment) are secondary environment. The env variables that are defined both in CONFIG_ENV_VAR_WHITELIST_LIST and in the secondary environments override the ones in the main environment, - for saving, we save the whole environment to all environments available, be they main or secondary (it does not matter to save the whole environment on secondary environments as only the whitelisted variables will be overriden in the loading process,
I have also a few questions that could help me to get the whole thing to work.
1) I can't really get my head around the use of gd->env_addr, what is it used for? It is set in a bunch of different places but only once is it explicitly used (basically to alternate the env_addr between the one associated to main and redundant environment (in NAND for example)).
2) Why do we consider ENV_IS_NOWHERE an invalid environment? The only place I found a use for it was to just say that if the environment is invalid, we should set to default environment (in env_relocate in env/common.c). With my patch series I guess that we could remove this fallback and force ENV_IS_NOWHERE to be always there.
3) There are a few (20) boards that set gd->env_addr and gd->env_valid in their board file. What is the reason to do such a thing? Isn't those overriden anyway by the environment driver?
I'm looking forward to getting your feedback on this patch series.
Thanks, Quentin
[1] https://patchwork.ozlabs.org/cover/842057/
Quentin Schulz (11): env: fix ret not being set and fails when no env could have been init lib: hashtable: support whitelisting env variables env: add support for whitelisting variables from secondary environments env: make nowhere an env medium like the others cmd: saveenv: enable the saveenv command when ENV_IS_NOWHERE is defined but another env medium is enabled too env: add env_driver to env_driver functions' arguments env: gd flags without ENV_READY is enough to discriminate in env_get_default env: add env_driver parameter to env_import_redund env: make env_locations a global variable env: introducing env_info struct for storing info per env env: store information about each environment in gd
board/sunxi/board.c | 2 +- cmd/nvedit.c | 16 ++- common/board_r.c | 8 +- env/Kconfig | 29 +++--- env/common.c | 45 ++++++---- env/eeprom.c | 40 ++++----- env/env.c | 142 +++++++++++++++++++++++++------ env/ext4.c | 4 +- env/fat.c | 4 +- env/flash.c | 58 ++++++------- env/mmc.c | 14 +-- env/nand.c | 46 +++++----- env/nowhere.c | 12 ++- env/nvram.c | 18 ++-- env/onenand.c | 6 +- env/remote.c | 10 +- env/sata.c | 4 +- env/sf.c | 34 +++---- env/ubi.c | 14 +-- include/asm-generic/global_data.h | 5 +- include/environment.h | 59 ++++++++----- include/search.h | 2 +- lib/hashtable.c | 17 +++- 23 files changed, 379 insertions(+), 210 deletions(-)
base-commit: 5d41e28058e7b378c9fa5c61ecc074a682ba2db4