[U-Boot] [PATCH 2/2] env: Fix saving environment to "bad CRC" location

[Simon Goldschmidt]

Am Fr., 18. Jan. 2019, 20:20 hat Sam Protsenko <semen.protsenko at linaro.org>
geschrieben:

> In case when the environment on some location is malformed (CRC isn't
> matching), there is a chance we won't be able to save the environment to
> that location. For example, consider the case when we only have the
> environment on eMMC, but it's zeroed out. In that case, we won't be able
> to "env save" to it, because of "bad CRC" error. That's happening
> because in env_load() function we consider malformed environment as
> incorrect one, and  defaulting to the location with highest (0)
> priority, which can be different from one we are dealing with right now
> (e.g., highest priority can be ENV_FAT on SD card, which is not
> inserted, but we want to use ENV_MMC on eMMC, where we were booted
> from).
>
> This issue began to reproduce after commit d30ba2315ae3 ("u-boot: remove
> driver lookup loop from env_save()") on BeagleBone Black, but that
> commit didn't introduce the wrong logic, it just changed the behavior
> for default location to use, merely revealing this issue.
>

In my opinion, this automatism of selecting a driver to save the env can
always produce a behaviour that is unexpected to the user.

I wonder if it wouldn't be better to either let the board define some
default env driver for saving or the user should specify the driver as
argument to 'env save'.

Note that this is not an objection to your oatches, I'm just not content
with the current auto-selection...

Regards,
Simon


> To fix that, let's implement next logic in env_load():
>   1. Try to find out correct environment; if found -- use it
>   2. If working environment wasn't found, but we found malformed one
>      (with bad CRC), let's use it for further "env save". But make sure
>      to use malformed environment location with highest priority.
>   3. If neither correct nor malformed environment was found, let's
>      default to environment location with highest priority (0)
>
> Steps to reproduce mentioned issue on BeagleBone Black (fixed in this
> patch):
>
> 1. Boot from SD card and erase eMMC in U-Boot shell:
>    => mmc dev 1
>    => mmc erase 0 100000
>    => gpt write mmc 1 $partitions
> 2. Write new SPL and U-Boot to eMMC; the rest of eMMC will stay filled
>    with zeroes
> 3. Boot from eMMC; try to do:
>    => env save
> 4. Observe the error (incorrect behavior). Correct behavior: environment
>    should be stored correctly on eMMC, in spite of it has "bad CRC"
>
> Fixes: d30ba2315ae3 ("u-boot: remove driver lookup loop from env_save()")
> Signed-off-by: Sam Protsenko <semen.protsenko at linaro.org>
> ---
>  env/env.c | 25 +++++++++++++++++++------
>  1 file changed, 19 insertions(+), 6 deletions(-)
>
> diff --git a/env/env.c b/env/env.c
> index 003509d342..4b417b90a2 100644
> --- a/env/env.c
> +++ b/env/env.c
> @@ -177,6 +177,7 @@ int env_get_char(int index)
>  int env_load(void)
>  {
>         struct env_driver *drv;
> +       int best_prio = -1;
>         int prio;
>
>         for (prio = 0; (drv = env_driver_lookup(ENVOP_LOAD, prio));
> prio++) {
> @@ -195,20 +196,32 @@ int env_load(void)
>                  * one message.
>                  */
>                 ret = drv->load();
> -               if (ret) {
> -                       debug("Failed (%d)\n", ret);
> -               } else {
> +               if (!ret) {
>                         printf("OK\n");
>                         return 0;
> +               } else if (ret == -ENOMSG) {
> +                       /* Handle "bad CRC" case */
> +                       if (best_prio == -1)
> +                               best_prio = prio;
> +               } else {
> +                       debug("Failed (%d)\n", ret);
>                 }
>         }
>
>         /*
>          * In case of invalid environment, we set the 'default' env
> location
> -        * to the highest priority. In this way, next calls to env_save()
> -        * will restore the environment at the right place.
> +        * to the best choice, i.e.:
> +        *   1. Environment location with bad CRC, if such location was
> found
> +        *   2. Otherwise use the location with highest priority
> +        *
> +        * This way, next calls to env_save() will restore the environment
> +        * at the right place.
>          */
> -       env_get_location(ENVOP_LOAD, 0);
> +       if (best_prio >= 0)
> +               debug("Selecting environment with bad CRC\n");
> +       else
> +               best_prio = 0;
> +       env_get_location(ENVOP_LOAD, best_prio);
>
>         return -ENODEV;
>  }
> --
> 2.20.1
>
> _______________________________________________
> U-Boot mailing list
> U-Boot at lists.denx.de
> https://lists.denx.de/listinfo/u-boot
>