[PATCH RFC] common: env: handle var="" not as var=NULL

[Sascha Hauer]

On Mon, Jun 13, 2016 at 12:51:52PM +0200, Alexander Aring wrote:
> This patch changes the behaviour which I think is used everywhere in
> barebox code. Currently var="" and var=NULL will end in the same
> behaviour.
> 
> New behaviour is:
> 
> setenv(name, "")	-> sets name to ""
> \-> getenv(name)	-> ""
> 
> setenv(name, NULL)	-> deletes env
> \-> getenv(name)	-> NULL
> 
> It seems that barebox code already wants such behaviour, by run
> 
> $ grep -r "\"\"" | grep setenv
> 
> it finds most all related code sections which use "".
> 
> I detected the issue while commenting #ip="foo" in my env. The code
> part:
> 
> net/ifup.c:	setenv("ip", "");
> 
> Sets at first "ip" to "" but will end in the old behaviour as "delete".
> The getenv("ip") in ifup.c will not check on the NULL value and has a
> general handling for unknown ip env.
> 
> Note:
> Also check commit e7ed69d5 ("setenv: be robust against setenv(<var>,
> NULL") which says that hush will handle "" and NULL as the same.
> 
> Another check would be:
> 
> $ grep -r "NULL" | grep setenv
> 
> which should show the behaviour in case of deleting env.
> 
> Signed-off-by: Alexander Aring <aar at pengutronix.de>
> ---
> I test the ip env stuff only that barebox will not crash anymore but I
> think it will break some other setenv/getenv behaviour.
> 
> The question is "Shall we keep that "" and NULL ends in same behaviour"
> and fix the code which use it wrong, e.g. setenv("ip", ""); getenv("ip").

I'm not sure at the moment if a var="" should delete a variable or just
set it to an empty string. In any case we should fix net/ifup.c.
getenv() can return NULL and the code should be prepared for that.

Sascha

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