[PATCH v8 4/8] env: Allow U-Boot scripts to be placed in a .env file

[Simon Glass]

Hi Tom,

On Tue, 19 Oct 2021 at 08:25, Tom Rini <trini at konsulko.com> wrote:
>
> On Tue, Oct 19, 2021 at 08:11:08AM -0600, Simon Glass wrote:
> > Hi Tom,
> >
> > On Tue, 19 Oct 2021 at 08:07, Tom Rini <trini at konsulko.com> wrote:
> > >
> > > On Mon, Oct 18, 2021 at 12:13:18PM -0600, Simon Glass wrote:
> > >
> > > > At present U-Boot environment variables, and thus scripts, are defined
> > > > by CONFIG_EXTRA_ENV_SETTINGS. It is painful to add large amounts of text
> > > > to this file and dealing with quoting and newlines is harder than it
> > > > should be. It would be better if we could just type the script into a
> > > > text file and have it included by U-Boot.
> > > >
> > > > Add a feature that brings in a .env file associated with the board
> > > > config, if present. To use it, create a file in a board/<vendor>
> > > > directory, typically called <board>.env and controlled by the
> > > > CONFIG_ENV_SOURCE_FILE option.
> > > >
> > > > The environment variables should be of the form "var=value". Values can
> > > > extend to multiple lines. See the README under 'Environment Variables:'
> > > > for more information and an example. Note that environment variables may
> > > > not end in + but can start with other strange characters, including
> > > > underscore, comma and slash.
> > > >
> > > > In many cases environment variables need access to the U-Boot CONFIG
> > > > variables to select different options. Enable this so that the environment
> > > > scripts can be as useful as the ones currently in the board config files.
> > > > This uses the C preprocessor, means that comments can be included in the
> > > > environment using /* ... */
> > > >
> > > > Also support += to allow variables to be appended to. This is needed when
> > > > using the preprocessor.
> > > >
> > > > Signed-off-by: Simon Glass <sjg at chromium.org>
> > >
> > > As much as I and others appreciate that you've written the parser here
> > > in a classic UNIX tool, awk, since a lot of the problems also seem to
> > > stem from having the parser be able to handle previously valid
> > > environment variables, if this was written in Python say, would we have
> > > this problem?
> >
> > Well ideally I'd like to avoid Python in this case as it is in the
> > compilation path. I am not sure yet what Wolfgang actually wants,
> > apart from variable names ending with + which I would like to
> > disallow.
> >
> > So if we can clearly understand the goal, then we might be able to do
> > it in awk, but, again, can we just disallow '+' in var names ?
>
> If we say that everything that's valid in the environment today needs to
> continue to be valid, so that includes '+' and only disallowing '=' and
> NUL as Wolfgang has said, can you update the awk parser to handle it?

But how do we handle this?

var+=fred

Is this appending to var or assigning to var+  ?

var++=fred

is unambiguous but very confusing. I think it would be better to disallow +

We can allow it in the middle of the var name if you like.

Regards,
Simon