[U-Boot] interaction between CONFIG_CMD_SAVEENV and CONFIG_BOOTCOMMAND

[Nicolas le bayon]

Dear Wolfgang,

Regarding your recommendations about U-Boot usage, I completely agree with
that. In fact, In my description, I wouldn't give too many details, but
your answer leads me to add some :-)

As I told you, this "old" u-boot is used only as primary bootloader, and
its main objective is just to "source" a script on an external device. Note
that this script is only a text file that can be modified by the user.

We propose different script examples to the user, the basic one will only
start the kernel (all images will be stored on the external device), but
the most used one will start a secondary bootloader, so a second u-boot
(this one is currently in rebasing phase, on 2016.09 release). And in this
second u-boot, there is no access restrictions, user will be able to custom.

Finally note that this is an intermediate step of our project. In final
release, this "primary u-boot" will be replaced by a "bootrom" (so no more
u-boot), and in that case, we will have only one "secondary" u-boot. Hope
this clarifies :-)

Back to our issue on our "primary" u-boot, we found an alternative. We
generate two binaries, the first one used only to flash the second. In that
case, we are able te disallow use of external env for the second and flash
access (define CONFIG_ENV_IS_NOWHERE and undef CONFIG_XXX_FLASH). It seems
functional after further tests.

So indeed, there is a bug, but on our side, not in u-boot. We need
"saveenv" to flash, our script was using the .elf (via gdb) to flash the
.bin. And this flash operation was using the saveenv. So by using two
differents binaries, we solve our issue, and u-boot is going well :-)

Thanks Wolfgang for tyour reactivity and your recommendations. Please note
that in our final product, we'll use u-boot with total respect of its
philosophy, and we'll be aligned on one of the latest releases :)

Best regards,
Nicolas




2016-09-14 20:38 GMT+02:00 Wolfgang Denk <wd at denx.de>:

> Dear Nicolas,
>
> In message <CAJZhe_jhWpQLgwquHZ2U5jHL7hvkBFc=Kz0j
> oyELDAM5vR+t7A at mail.gmail.com> you wrote:
> >
> > > Would that really be enough?  Please keep in mind that "env save" (or
> > > "saveenv") is only responsible for storing the current environment
> > > into persistant storage.  It does not modify the environment at all.
> > > To modify the environment, you can use quite a number of commands,
> > > including "env set", "env import" etc.  You would have to disable all
> > > of these to prevent modifications of the environment settings - and
> > > probably cripple U-Boot to a level where it becomes unusable.
> >
> > >> Our objective is just to avoid the user to modify the content in the
> > persistent storage. Indeed, we have to retrieve the original content at
> > each reboot.
> > If the user makes something wrong in its current environment, this is its
> > responsability, but after the reset, we have to gat back the original
> > content we stored once for all. In that case, saveenv would maybe be
> > enough, don't you think?
>
> It should work as you expect.
>
> But since you ask what I _think_ ... :-)  As a developer I really hate
> systems that attempt to lock me down into such a crippled environment.
> I still love and cherish the old quote:
>
> "UNIX was not designed to stop you from doing stupid things,  because
> that would also stop you from doing clever things."       - Doug Gwyn
>
> You plan to implement a policy that restricts the freedom of the user
> for a questionable (to me - I don't know your requirements) advantage.
> Would it not be possible to implement a more open design, where the
> user can actually save his changes to the persistent environment
> (so someone who knows what he is doing can use the full power of the
> software), and instead provide a way to perform a factory reset (using
> "env default -f" or similar) to your original settings?  That would
> feel much more U-Boot-like to me :-)
>
>
> > > Which exact version of U-Boot are you talking about?
> > >>  a quite old one, v2015.01 :-( And we do not plan to upgrade this
> > "primary bootloader" u-boot.
>
> Hm... this should still not show such behaviour.  Check your board
> config file thoroughly, especially your environment settings.  Check
> that environment definitions are explicitly terminated by NUL
> characters, and that all string quotes pair.  If you have any #ifdef
> magic there, check that, too.
>
>
> Best regards,
>
> Wolfgang Denk
>
> --
> DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
> HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
> Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
> All I ask is a chance to prove that money can't make me happy.
>