Use static boot config params to acquire IP address, net mask and GW for xen unikernel

[julianchesterfield]

Following discussion during project meeting, we need a way to bootstrap a unikernel with a static assigned IP address from the xen config. There are some parameters that may be usable:

ip=x.x.x.x
netmask=255.x.x.x
gateway=x.x.x.x

also the vif=[] parameter allows assignment of IP address in the form:

vif=['bridge=br0,vifname=974f799d,mac=DE:AD:BE:EF:02:12,ip=10.200.2.12']

Longterm we should consider supporting Cloudinit to bootstrap VM info including passwords and ssh keys etc..

With the parameters provided above the cmdline variable in xenstore is populated as:

[root@192.168.1.20 tmp]# xenstore-read /vm/73f7b83b-61df-a521-0891-9b948acc5812/image/cmdline
ip=10.200.2.10:127.0.255.255:10.200.2.254:255.255.255.0::eth0:off

First approach to get things working is to grab the xenstore key at the start point and extract IP info if it is provided.

[avsm]

Confirmed that this doesn't work with XL, since it ignores the ip/netmask/gateway keys.

[avsm]

XL also doesn't update /vm/<uuid>/image/cmdline -- it's always blank.

However, by using the extra= key, the string is in the start_info page

[julianchesterfield]

Agreed, the 'extra' parameter should always work with all toolstacks. What format do you propose to pass in? Same as the kernel boot net info format such as:

ip=10.200.2.10:127.0.255.255:10.200.2.254:255.255.255.0::eth0:off

[avsm]

I made it simpler, so you can just add explicit ip/gateway/netmask entries. See:
https://github.com/mirage/mirage-skeleton/blob/master/xen/static_website%2Bip/README.md

Could you please try this out and see if it works for you? I explicitly built it out of Netif functors to control the IP assignment, and can fold it into the libraries later if this example works. Just cd xen/static_website+ip, and build it like the static website (contents in htdocs).

[samoht]

Should be improved by #360 (once completed)

[samoht]

This is now done.