Re: [PATCH] module-setup: Fix improper dns setup in kdump_setup_dns()

[Baoquan He]

Thanks, Leo.

Hi Daniel and NetworkManager team,

We are kdump team dev, now have question about DNS handling from
NetworkManager and those scripts in /etc/sysconfig/network-scripts.
Could you please help to have a look when it's convenient to you?

Thanks
Baoquan

On 04/25/16 at 05:47pm, Hangbin Liu wrote:
> cc Daniel and network manager development team. They are experts on NM.
>
> On Mon, Apr 25, 2016 at 04:45:23PM +0800, Baoquan He wrote:
> > Hi network experts,
> >
> > We got confusion on network DNS handling when we try to fix a kdump
> > bug. For better representation let's assume a network interface enp0s25
> > with static DNS setting in ifcfg-enp0s25 as "DNS1=8.8.8.8", and dhclient
> > privides 2 DNS server ip:
> >
> > 10.72.17.5
> >    10.68.5.26
> >
> > Now the confusion is:
> > In 1st kernel if NetworkManager take control of the network setup and
> >
> > PEERDNS=yes, the behaviour of DNS handling is that it adds dhclient's DNS
> > firstly then add static DNS from ifcfg-enp0s25. The result of
> > /etc/resolv.conf will be as follows:
> >        nameserver 10.72.17.5
> >        nameserver 10.68.5.26
> >        nameserver 8.8.8.8
> > But if we set PEERDNS=no, the result of /etc/resolv.conf is:
> >    nameserver 8.8.8.8
> > Apprently "PEERDNS=no" doesn't allow dhclient to add its DNS into
> > /etc/resolv.conf.
> > However in 1st kernel if NetworkManager is disabled, means scripts
> >
> > under /etc/sysconfig/network-scripts/ take control of network setup and
> > PEERDNS=yes, its behaviour is much different with NetworkManager. It
> > will firstly add dhclient's DNS, then replace the first entry, namely
> > "10.72.17.5" with the found static DNS from ifcfg-enp0s25. The result of
> > /etc/resolv.conf will be like:
> >        nameserver 8.8.8.8
> >        nameserver 10.68.5.26
> > If PEERDNS=no set in ifcfg-enp0s25
> > /etc/resolv.conf won't be changed at all.
> >
> > Using NetworkManager or not using it can bring us so different
> > behaviours and different /etc/resolv.conf. Could you give suggestion how
> > we can make decision to choose a reasonable one since kdump probablly
> > need to cope with both of them?
> >
> > In fact above cases are not problems we have since dracut have another
> > different rules then above, and we need handle it. But now we need to
> > clarify how DNS handling acts in 1st kernel. Your suggestions and ideas
> > are very precisous to us.
> >
> > Thanks
> > Baoquan
> >
> > On 04/25/16 at 03:29pm, Xunlei Pang wrote:
> > > ============= 3. Conclusion =============
> > > Dracut, network-manager, and "network-scripts" all have different hehavior
> > > in handling DNS.
> > >
> > > As a dhcp example:
> > > Suppose enp0s25, the dhcped DNSes are stable: 10.72.17.5 and 10.68.5.26
> > >
> > > In ifcfg-enp0s25:
> > > DNS1: 8.8.8.8
> > >
> > > For 1st kernel's network-manager, the final nameservers in /etc/resolv.conf
> > > -) If PEERDNS=yes(default is yes if PEERDNS doesn't exist) in ifcfg-enp0s25
> > >     nameserver 10.72.17.5
> > >     nameserver 10.68.5.26
> > >     nameserver 8.8.8.8
> > > -) If PEERDNS=no in ifcfg-enp0s25
> > >     nameserver 10.72.17.5
> > >     nameserver 10.68.5.26
> > >     nameserver 8.8.8.8
> > >
> > > For 1st kernel's scripts under /etc/sysconfig/network-scripts/ without network-manager
> > > -) If PEERDNS=yes in ifcfg-enp0s25
> > >     nameserver 8.8.8.8
> > >     nameserver 10.68.5.26
> > > -) If PEERDNS=no in ifcfg-enp0s25
> > >     Not touch /etc/resolv.conf
> > >     (i.e. /etc/resolv.conf is left unchanged as that before calling "ifup <config>")
> > >
> > > For dracut in latest fedora kexec-tools(1st kernel using network-manager)
> > > "${initdir}/etc/cmdline.d/42dns.conf" will contain:
> > >     nameserver=8.8.8.8
> > >     nameserver=10.72.17.5
> > >     nameserver=10.68.5.26
> > >     nameserver=8.8.8.8
> > >
> > > -) If "rd.peerdns=1"(default is "1" if "rd.peerdns" doesn't exist) is passed which is the default case
> > >     nameserver 8.8.8.8
> > >     nameserver 10.72.17.5
> > >     nameserver 10.68.5.26
> > >     nameserver 8.8.8.8
> > >     nameserver 10.72.17.5 // the last two are drauct' dhcp generated items
> > >     nameserver 10.68.5.26
> > > -) If "rd.peerdns=0" is passed
> > >     nameserver 8.8.8.8
> > >     nameserver 10.72.17.5
> > >     nameserver 10.68.5.26
> > >     nameserver 8.8.8.8
> > >
> > > Regards,
> > > Xunlei
> > > > > Regards,
> > > > > Xunlei
> > > > > > Regards,
> > > > > > Xunlei
> > > > > >
> > > > > > > Thanks
> > > > > > > Minfei
> > > > > > >
> > > > > > >> There are two issues by doing this:
> > > > > > >> 1) The dns sequence is different from that in 1st system.
> > > > > > >> 2) There are some duplicated items.
> > > > > > >>    NOTE: kdump_setup_dns() meant to avoid the duplication,
> > > > > > >>    but the original shell command is actually disfunctional:
> > > > > > >>    "[ ! $(cat $_dnsfile | grep -q $_dns) ]" (always true)
> > > > > > >>
> > > > > > >> Fix the issues by firstly parsing "/etc/resolv.conf", then
> > > > > > >> parsing ifcfg file, finally delete the duplicated items.
> > > > > > >>
> > > > > > >> Signed-off-by: Xunlei Pang 
> > > > > > >> ---
> > > > > > >>  dracut-module-setup.sh | 27 ++++++++++++++++-----------
> > > > > > >>  1 file changed, 16 insertions(+), 11 deletions(-)
> > > > > > >>
> > > > > > >> diff --git a/dracut-module-setup.sh b/dracut-module-setup.sh
> > > > > > >> index 350864e..b7763f7 100755
> > > > > > >> --- a/dracut-module-setup.sh
> > > > > > >> +++ b/dracut-module-setup.sh
> > > > > > >> @@ -68,14 +68,6 @@ kdump_setup_dns() {
> > > > > > >>      local _dnsfile=${initdir}/etc/cmdline.d/42dns.conf
> > > > > > >>      local ifcfg_file
> > > > > > >>  
> > > > > > >> -    ifcfg_file=$(get_ifcfg_filename $1)
> > > > > > >> -    if [ -f "${ifcfg_file}" ]; then
> > > > > > >> -        . ${ifcfg_file}
> > > > > > >> -    fi
> > > > > > >> -
> > > > > > >> -    [ -n "$DNS1" ] && echo "nameserver=$DNS1" > "$_dnsfile"
> > > > > > >> -    [ -n "$DNS2" ] && echo "nameserver=$DNS2" >> "$_dnsfile"
> > > > > > >> -
> > > > > > >>      while read content;
> > > > > > >>      do
> > > > > > >>          _nameserver=$(echo $content | grep ^nameserver)
> > > > > > >> @@ -84,10 +76,23 @@ kdump_setup_dns() {
> > > > > > >>          _dns=$(echo $_nameserver | cut -d' ' -f2)
> > > > > > >>          [ -z "$_dns" ] && continue
> > > > > > >>  
> > > > > > >> -        if [ ! -f $_dnsfile ] || [ ! $(cat $_dnsfile | grep -q $_dns) ]; then
> > > > > > >> -            echo "nameserver=$_dns" >> "$_dnsfile"
> > > > > > >> -        fi
> > > > > > >> +        echo "nameserver=$_dns" >> "$_dnsfile"
> > > > > > >>      done < "/etc/resolv.conf"
> > > > > > >> +
> > > > > > >> +    unset DNS1 DNS2
> > > > > > >> +    ifcfg_file=$(get_ifcfg_filename $1)
> > > > > > >> +    if [ -f "${ifcfg_file}" ]; then
> > > > > > >> +        . ${ifcfg_file}
> > > > > > >> +    fi
> > > > > > >> +
> > > > > > >> +    [ -n "$DNS1" ] && echo "nameserver=$DNS1" >> "$_dnsfile"
> > > > > > >> +    [ -n "$DNS2" ] && echo "nameserver=$DNS2" >> "$_dnsfile"
> > > > > > >> +
> > > > > > >> +    # Delete duplicated lines
> > > > > > >> +    if [ -f "$_dnsfile" ]; then
> > > > > > >> +        awk '!a[$0]++' $_dnsfile > $_dnsfile.tmp
> > > > > > >> +        mv -f $_dnsfile.tmp $_dnsfile
> > > > > > >> +    fi
> > > > > > >>  }
> > > > > > >>  
> > > > > > >>  #$1: netdev name
> > > > > > >> -- 
> > > > > > >> 1.8.3.1
> > > > > > >> _______________________________________________
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> > > > > > >> [e-mail]
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> > > > > > [e-mail]
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> > > > >
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>
> --
>
> Thanks & Best Regards
> Hangbin Liu 
> Leo on #kernel-qe, #kernel, #eng-china