[U-Boot] [PATCH v2 1/2] cmd: nvedit: add whitelist option for env import

[Quentin Schulz]

On Mon, May 21, 2018 at 01:26:11PM +0100, Alex Kiernan wrote:
> On Mon, May 21, 2018 at 1:06 PM Quentin Schulz <quentin.schulz at bootlin.com>
> wrote:
> 
> > Hi Alex,
> 
> > On Mon, May 21, 2018 at 12:56:04PM +0100, Alex Kiernan wrote:
> > > On Mon, May 21, 2018 at 9:02 AM Quentin Schulz <
> quentin.schulz at bootlin.com>
> > > wrote:
> > >
> > > > Hi Stephen,
> > >
> > > > On Fri, May 18, 2018 at 10:00:27AM -0600, Stephen Warren wrote:
> > > > > On 05/18/2018 08:44 AM, Quentin Schulz wrote:
> > > > > > While the `env export` can take as parameters variables to be
> > > exported,
> > > > > > `env import` does not have such a mechanism of variable selection.
> > > > > >
> > > > > > Let's add a `-w` option that asks `env import` to look for the
> > > > > > `whitelisted_vars` env variable for a space-separated list of
> > > variables
> > > > > > that are whitelisted.
> > > > >
> > > > > Would it be better for the -w option to accept a variable name
> rather
> > > than
> > > > > hard-coding it as whitelisted_vars? That way, people could
> import/export
> > > > > different sets of variables at different times, and also could
> choose a
> > > more
> > > > > use-case-specific variable name than whitelisted_vars in order to
> > > describe
> > > > > why those variables are "whitelisted".
> > >
> > > > This has been raised in the previous version of the patch[1] (of which
> > > > you weren't in the mail recipients) and a similar patch[2] made by
> Alex
> > > > Kiernan (Cc of this patch series). I'd say it's an ongoing discussion,
> > > > though I should have mentioned it in the comments of the patch?
> > >
> > > > TL;DR:
> > > > Proposition 1: Have -w only which "hardcodedly" checks for
> > > > "whitelisting_vars",
> > > > +: straightforward implementation of the argument parsing,
> > > > -: implicit declaration of the list: you have to know to set
> > > >     whitelisted_vars in the environnement,
> > >
> > > > Proposition 2: Have -w followed by one string-word which is the name
> of
> > > > the env variable where to look for the list of whitelisted env
> > > > variables,
> > > > +: explicit var to check where whitelist is looked for,
> > > > -: a bit of complexity added to the parsing of the parameters of the
> env
> > > >     import function,
> > >
> > > > Proposition 3: Have -w followed by the list of whitelisted env
> variable,
> > > > +: explicit list
> > > > -: the list cannot be separated by comma (valid character for an env
> > > >     variable) or a space (would not be able to distinguish the last
> > > >     arguments of the commands which are address and size with size
> being
> > > >     optional => how to know if size was passed or not?), what char
> can be
> > > >     used to separate env variables in the list?
> > > >     how does it perform with a very long list of whitelisted
> variables?
> > >
> > >
> > > Two more thoughts, both of which delegate the separator problem to the
> > > caller (the second being the one I implemented as it's almost no code)
> > >
> > > - specify multiple -w options each specifying a whitelisted env variable
> 
> > You'll hit the maximum number of arguments/length of the command quickly
> > with this method. Quicker than with the other propositions.
> 
> > Moreover, this can make the command painfully long, painful to read and
> > thus cumbersome to find the small typo in your command.
> 
> > > - use the remaining arguments approach and eat all the trailing
> arguments
> > > as the names of env vars you import - needs a sentinel value for the
> size
> > > argument
> > >
> 
> > That can't work I think.
> 
> > How do you know if the size argument was passed or not? How'd you know
> > what string is addr, size or the whitelist (if there is even any)?
> 
> > env import foo1 foo2 foo3 foo4 addr size
> > env import foo1 foo2 foo3 addr
> > env import addr size
> > env import addr
> 
> 
> That's why you need a sentinel for the size:
> 
>   * env import [-d] [-t [-r] | -b | -c] addr [size] [var ...]
>   *      -d:     delete existing environment before importing;
>   *              otherwise overwrite / append to existing definitions
>   *      -t:     assume text format; either "size" must be given or the
>   *              text data must be '\0' terminated
>   *      -r:     handle CRLF like LF, that means exported variables with
>   *              a content which ends with \r won't get imported. Used
>   *              to import text files created with editors which are using
> CRLF
>   *              for line endings. Only effective in addition to -t.
>   *      -b:     assume binary format ('\0' separated, "\0\0" terminated)
>   *      -c:     assume checksum protected environment format
>   *      addr:   memory address to read from
>   *      size:   length of input data; if missing, proper '\0'
>   *              termination is mandatory. If not required and passing
>   *              variables to import use '-'
>   *      var...: List of variable names that get imported. Without arguments,
>   *              all variables are imported
> 
> Which for your examples translates to:
> 
> env import addr size foo1 foo2 foo3 foo4
> env import addr - foo1 foo2 foo3
> env import addr size
> env import addr
> 

Ah, I misunderstood the word sentinel then :)

Would have been an even better idea if we had some consistency between
env export and env import. For specifying the env export size, we have
to use the -s argument but it's a positional argument for env export. We
then have a list of variables to export, so it would make sense to have
the same for env import I guess?

Quentin
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