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

[Alex Kiernan]

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

-- 
Alex Kiernan