[Buildroot] [PATCH] pppd: Do not overwrite /etc/resolv.conf

[Arnout Vandecappelle]

On 11-09-17 09:58, Jeroen Roovers wrote:
> On 28 August 2017 at 22:28, Arnout Vandecappelle <arnout at mind.be> wrote:
> 
>>> pppd will overwrite any existing entries when /etc/resolv.conf is used instead, which is
>>> bad.
>>
>>  I agree that this is bad.
> 
> Thanks.
> 
>>  However, this is a regression.
> 
> 1. dnsmasq(8) mentions using /etc/dhcp/resolv.conf as well as
> /etc/ppp/resolv.conf.
> 2. On the greater Internet you can easily find plenty of examples of
> people getting confused because /etc/resolv.conf does not reflect what
> usepeerdns has written to the wrong file in /etc/ppp/
> 3. usepeerdns is not enable by default.
> 
>> People who currently have ppp as their only
>> interface, or who never have ppp and ethernet running at the same time
> 
> So it's a regression for what I can only assume must be a tiny
> minority of system builders who don't configure their own systems and
> are powerless but to rely on a second-guessed set of defaults that you
> would like to support.

 My point is: people who currently use pppd and another network interface
simultaneously either have something that doesn't really work (unlikely) or have
fixed it locally (more likely). However, people who currently have a working
ppp-only setup would no longer have a working setup after updating Buildroot.
That's something we prefer to avoid.

 If there is no way to avoid breaking existing configs, we probably indeed
should still accept this patch because as you say, it does fix things for a
(probably) more common use case. Well, except it doesn't really fix things,
because you still need an additional script to actually use the DNS information.

 Your point 1. is interesting. It suggests that a better solution would be to
not change pathnames.h at all, but instead symlink /etc/ppp/resolv.conf to
either /etc/resolv.conf (keeping the current behaviour) or /tmp/ppp-resolv.conf
(providing the behaviour you want).


 We recently added a "Migrating" section in the Buildroot manual. So what we
could do is:
1. ln -s ../../tmp/ppp-resolv.conf $(TARGET_DIR)/etc/ppp/resolv.conf
2. Add a paragraph to the Migrating section explaining that a configuration that
was using pppd with usepeerdns needs to either enable dnsmasq or to symlink
$(TARGET_DIR)/etc/ppp/resolv.conf to /tmp/resolv.conf or to create a
/etc/ppp/ip-up script.

 Does that sound reasonable?


> 
> Additionally, the current pppd.mk suggests /etc/ppp/resolv.conf is not
> writeable (in some configurations) but you say adding an ip-up script
> would solve the issue, when that ip-up script is then supposed to
> write to /etc/resolv.conf, which supposedly *is* writeable.

 Indeed, /etc/resolv.conf is a symlink to /tmp/resolv.conf.


 Regards,
 Arnout

> 
> Please enlighten me.
> 
> 
> Kind regards,
>      jer
> 

-- 
Arnout Vandecappelle                          arnout at mind be
Senior Embedded Software Architect            +32-16-286500
Essensium/Mind                                http://www.mind.be
G.Geenslaan 9, 3001 Leuven, Belgium           BE 872 984 063 RPR Leuven
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