[OpenWrt-Devel] [PATCH v2] dnsmasq: allow using dnsmasq as the sole resolver

[Paul Oranje]

> Op 22 feb. 2019, om 03:05 heeft Yousong Zhou <yszhou4tech at gmail.com> het volgende geschreven:
> 
> On Tue, 19 Feb 2019 at 23:02, Paul Oranje <por at oranjevos.nl> wrote:
>> 
>> Op 18 feb. 2019, om 21:50 heeft Hans Dedecker <dedeckeh at gmail.com> het volgende geschreven:
>>> 
>>> On Mon, Feb 18, 2019 at 3:18 PM Yousong Zhou <yszhou4tech at gmail.com> wrote:
>>>> 
>>>> Currently it seems impossible to configure /etc/config/dhcp to achieve
>>>> the following use case
>>>> 
>>>> - run dnsmasq with no-resolv
>>>> - re-generate /etc/resolv.conf with "nameserver 127.0.0.1"
>>>> 
>>>> Before this change, we have to set resolvfile to /tmp/resolv.conf.auto
>>>> to achive the 2nd effect above, but setting resolvfile requires noresolv
>>>> being false.
>>>> 
>>>> A new boolean option "localuse" is added to indicate that we intend to
>>>> use dnsmasq as the local dns resolver.  It's false by default and to
>>>> align with old behaviour it will be true automatically if resolvfile is
>>>> set to /tmp/resolv.conf.auto
>>>> 
>>>> Signed-off-by: Yousong Zhou <yszhou4tech at gmail.com>
>>> Acked-by: Hans Dedecker <dedeckeh at gmail.com>
>>>> ---
>>>> v2 <- v1
>>>> 
>>>> - retain /tmp/resolv.conf.auto as the default value of resolvfile when
>>>>  doing config_get, i.e. 2nd patch in the 1st version is now dropped
>>>> - retain the old behavior of rewriting /tmp/resolv.conf when resolvfile
>>>>  is /tmp/resolv.conf.auto
>>>> 
>>>> .../services/dnsmasq/files/dnsmasq.init       | 30 +++++++++----------
>>>> 1 file changed, 15 insertions(+), 15 deletions(-)
>>>> 
>>>> diff --git a/package/network/services/dnsmasq/files/dnsmasq.init b/package/network/services/dnsmasq/files/dnsmasq.init
>>>> index f3066627d6..f65736e268 100644
>>>> --- a/package/network/services/dnsmasq/files/dnsmasq.init
>>>> +++ b/package/network/services/dnsmasq/files/dnsmasq.init
>>>> @@ -731,7 +731,9 @@ dhcp_relay_add() {
>>>> 
>>>> dnsmasq_start()
>>>> {
>>>> -       local cfg="$1" disabled resolvfile user_dhcpscript
>>>> +       local cfg="$1"
>>>> +       local disabled user_dhcpscript
>>>> +       local resolvfile localuse
>>>> 
>>>>       config_get_bool disabled "$cfg" disabled 0
>>>>       [ "$disabled" -gt 0 ] && return 0
>>>> @@ -882,14 +884,14 @@ dnsmasq_start()
>>>>       config_get_bool cachelocal "$cfg" cachelocal 1
>>>> 
>>>>       config_get_bool noresolv "$cfg" noresolv 0
>>>> +       config_get_bool localuse "$cfg" localuse 0
>>>>       if [ "$noresolv" != "1" ]; then
>>>> -               config_get resolvfile "$cfg" resolvfile "/tmp/resolv.conf.auto"
>>>> -               # So jail doesn't complain if file missing
>>>> -               [ -n "$resolvfile" -a \! -e "$resolvfile" ] && touch "$resolvfile"
>>>> +               config_get resolvfile "$cfg" resolvfile /tmp/resolv.conf.auto
>>>> +               [ -n "$resolvfile" -a ! -e "$resolvfile" ] && touch "$resolvfile"
>>>> +               xappend "--resolv-file=$resolvfile"
>>>> +               [ "$resolvfile" = "/tmp/resolv.conf.auto" ] && localuse=1
>>>>       fi
>>>> 
>>>> -       [ -n "$resolvfile" ] && xappend "--resolv-file=$resolvfile"
>>>> -
>>>>       config_get hostsfile "$cfg" dhcphostsfile
>>>>       [ -e "$hostsfile" ] && xappend "--dhcp-hostsfile=$hostsfile"
>>>> 
>>>> @@ -1011,7 +1013,7 @@ dnsmasq_start()
>>>>       mv -f $CONFIGFILE_TMP $CONFIGFILE
>>>>       mv -f $HOSTFILE_TMP $HOSTFILE
>>>> 
>>>> -       [ "$resolvfile" = "/tmp/resolv.conf.auto" ] && {
>>>> +       [ "$localuse" -gt 0 ] && {
>>>>               rm -f /tmp/resolv.conf
>>>>               [ $ADD_LOCAL_DOMAIN -eq 1 ] && [ -n "$DOMAIN" ] && {
>>>>                       echo "search $DOMAIN" >> /tmp/resolv.conf
>>>> @@ -1037,17 +1039,15 @@ dnsmasq_start()
>>>> 
>>>> dnsmasq_stop()
>>>> {
>>>> -       local cfg="$1" resolvfile
>>>> +       local cfg="$1"
>>>> +       local noresolv resolvfile localuse
>>>> 
>>>> +       config_get_bool noresolv "$cfg" noresolv 0
>>>> +       config_get_bool localuse "$cfg" localuse 0
>>>>       config_get resolvfile "$cfg" "resolvfile"
>>>> 
>>>> -       #relink /tmp/resolve.conf only for main instance
>>>> -       [ "$resolvfile" = "/tmp/resolv.conf.auto" ] && {
>>>> -               [ -f /tmp/resolv.conf ] && {
>>>> -                       rm -f /tmp/resolv.conf
>>>> -                       ln -s "$resolvfile" /tmp/resolv.conf
>>>> -               }
>>>> -       }
>>>> +       [ "$noresolv" = 0 -a "$resolvfile" = "/tmp/resolv.conf.auto" ] && localuse=1
>>>> +       [ "$localuse" -gt 0 ] && ln -sf "/tmp/resolv.conf.auto" /tmp/resolv.conf
>>>> 
>>>>       rm -f ${BASEDHCPSTAMPFILE}.${cfg}.*.dhcp
>>>> }
>>> 
>> 
>> Hi,
>> 
>> In 2017 I submitted a patch to deal with having resolv.conf (used by the CLIB local resolver) being set correctly, see [1] and [2].
>> For the problem it sets out to solve (partially) an issue was opened [3].
>> The use-case concerned having Unbound as nameserver with dnsmasq handling DNS for the local lan domain and DHCP.
>> The patch was not merged since it was deemed that setting resolv.conf requires atomicity which would imply extending netifd with the functionality to handle this instead as my patch could not offer this atomic setting of resolv.conf.
>> 
>> Currently with the use-case (Unbound with "option dhcp_link 'dnsmasq'" set) still requires restarting Unbound manually after a restart of dnsmasq since dnsmasq.init will reset resol.conf to /etc/resolv.conf.auto.
>> 
>> I wonder, did you see that patch and could that patch still be relevant ?
>> 
>> [1] http://lists.openwrt.org/pipermail/openwrt-devel/2017-June/007923.html
>> [2] https://patchwork.ozlabs.org/patch/780353/
>> [3] https://bugs.openwrt.org/index.php?do=details&task_id=785
>> 
>> Regards,
>> Paul
> 
> Hi, Paul
> 
> I think scripting action by guessing users' intention is not a good
> approach here.  dnsmasq can be very flexible and OpenWrt/Linux is a
> highly-customizable system.  It's very hard to cover all cases to
> fulfill the original intention of the guess logic itself.  And the
> result of that is people may find the smart thing stand in their way
> when doing customizations.  That's my first impression on the "if
> dnsmasq listens on port 53 then touch /etc/resolv.conf"
> implementation.
> 
> Regards,
>                yousong
> 
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I agree, in the end "intelligent solutions" **alway** bite.
Paul
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