Comment # 20 on bug 1182227 from Thomas Blume

(In reply to Rub���n Torrero Marijnissen from comment #9)
> Converting the `ip=dhcp` line to wicked���s configuration format is still not
> supported by wicked. This is troublesome as it means that wicked needs to
> probe all interfaces for a valid DHCP offer and -for the sake of NFS root
> scenarios- chose the first valid offer which includes a root-path option. As
> said, we currently have no way of representing this in our configuration
> format but this should be supported in the future.
> 
> A workaround would be to use the alternative syntax of
> `ip=<interface>:dhcp`. But even with the workaround I haven���t been able to
> make the nfs root use case to work as it just configures the network and
> stops without attempting to mount the nfs root (seems that the nfsroot.sh is
> unaware that the network is up?)

Sorry that took a while.
Further tests turned out that wicked seems to be confused if both parameters:

ifname= and ip= 

contain the same interface name.
So the following command line fails:

-->
root=nfs4:192.168.57.254:/nfsroot:rw,relatime,vers=4.2,rsize=262144,wsize=262144,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=192.168.57.141,local_lock=none,addr=192.168.57.254
ifname=ens3:52:54:00:dc:43:b6 ip=ens3:dhcp rootfstype=nfs4
rootflags=rw,relatime,vers=4.2,rsize=262144,wsize=262144,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=192.168.57.141,local_lock=none,addr=192.168.57.254
initrd=initrd console=ttyS0
--<

removing the 'ifname=ens3:52:54:00:dc:43:b6' parameter results in the following
output from 'wicked show-config --ifconfig
dracut:cmdline:/home/tblume/Bugs/1180364/cmdline.17357.conf'

-->
<interface origin="dracut:cmdline">
  <name>ens3</name>
  <ethernet/>
  <link/>
  <ipv4>
    <enabled>true</enabled>
    <arp-verify>true</arp-verify>
  </ipv4>
  <ipv4:dhcp>
    <enabled>true</enabled>
    <update>default-route,dns,nis,ntp,nds,mtu,tz,boot</update>
    <defer-timeout>15</defer-timeout>
    <recover-lease>true</recover-lease>
    <release-lease>false</release-lease>
  </ipv4:dhcp>
</interface>
--<

That looks valid.
Renaming ip=ens3:dhcp to ip=eth0:dhcp outputs this xml file:

-->
<interface origin="dracut:cmdline">
  <name namespace="ethernet">
    <permanent-address>52:54:00:dc:43:b6</permanent-address>
  </name>
  <ethernet/>
  <link/>
</interface>
<interface origin="dracut:cmdline">
  <name>eth0</name>
  <ethernet/>
  <link/>
  <ipv4>
    <enabled>true</enabled>
    <arp-verify>true</arp-verify>
  </ipv4>
  <ipv4:dhcp>
    <enabled>true</enabled>
    <update>default-route,dns,nis,ntp,nds,mtu,tz,boot</update>
    <defer-timeout>15</defer-timeout>
    <recover-lease>true</recover-lease>
    <release-lease>false</release-lease>
  </ipv4:dhcp>
</interface>
--<

which also looks ok for eth0.
Removing ip=ens3 instead results in this most probably invalid config:

-->
<interface origin="dracut:cmdline">
  <name namespace="ethernet">
    <permanent-address>52:54:00:dc:43:b6</permanent-address>
  </name>
  <ethernet/>
  <link/>
</interface>
--<

So, maybe wicked just needs to ignore the ifname parameter (at least the name
from there)?
It doesn't seem to be necessary.