[U-Boot] [PATCH] fw_setenv: avoid writing environment when nothing has changed

[Alex Kiernan]

On Wed, Sep 5, 2018 at 8:23 PM Rasmus Villemoes
<rasmus.villemoes at prevas.dk> wrote:
>
> In the case where one deletes an already-non-existing variable, or sets
> a variable to the value it already has, there is no point in writing the
> environment back, thus reducing wear on the underlying storage
> device.
>
> Signed-off-by: Rasmus Villemoes <rasmus.villemoes at prevas.dk>

If you were running with a redundant env, and you were trying to sync
both copies, wouldn't you want a non-changing write to happen?

> ---
>  tools/env/fw_env.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/tools/env/fw_env.c b/tools/env/fw_env.c
> index a5d75958e1..87aaa15198 100644
> --- a/tools/env/fw_env.c
> +++ b/tools/env/fw_env.c
> @@ -110,6 +110,7 @@ struct environment {
>         unsigned char *flags;
>         char *data;
>         enum flag_scheme flag_scheme;
> +       int dirty;
>  };
>
>  static struct environment environment = {
> @@ -508,6 +509,9 @@ int fw_env_flush(struct env_opts *opts)
>         if (!opts)
>                 opts = &default_opts;
>
> +       if (!environment.dirty)
> +               return 0;
> +
>         /*
>          * Update CRC
>          */
> @@ -553,7 +557,8 @@ int fw_env_write(char *name, char *value)
>
>         deleting = (oldval && !(value && strlen(value)));
>         creating = (!oldval && (value && strlen(value)));
> -       overwriting = (oldval && (value && strlen(value)));
> +       overwriting = (oldval && (value && strlen(value) &&
> +                                 strcmp(oldval, value)));
>
>         /* check for permission */
>         if (deleting) {
> @@ -593,6 +598,7 @@ int fw_env_write(char *name, char *value)
>                 /* Nothing to do */
>                 return 0;
>
> +       environment.dirty = 1;
>         if (deleting || overwriting) {
>                 if (*++nxt == '\0') {
>                         *env = '\0';
> @@ -1441,6 +1447,7 @@ int fw_env_open(struct env_opts *opts)
>                                 "Warning: Bad CRC, using default environment\n");
>                         memcpy(environment.data, default_environment,
>                                sizeof(default_environment));
> +                       environment.dirty = 1;
>                 }
>         } else {
>                 flag0 = *environment.flags;
> @@ -1503,6 +1510,7 @@ int fw_env_open(struct env_opts *opts)
>                                 "Warning: Bad CRC, using default environment\n");
>                         memcpy(environment.data, default_environment,
>                                sizeof(default_environment));
> +                       environment.dirty = 1;
>                         dev_current = 0;
>                 } else {
>                         switch (environment.flag_scheme) {
> --
> 2.16.4
>
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-- 
Alex Kiernan