libvirt users - Jun 2015 - Re: Recommended change for the networking page in wiki

On 06/08/2015 02:43 PM, Laine Stump wrote:
>> However, if I changed the destination address from "anywhere"
to the
>> IP of the host machine, the problem resolved. So I change the script
>> to as follows. (Changes are highlighted. For some reason the original
>> script didn't work using /bin/sh, but it did with /bin/bash, so I
>> changed that too).
> 
> I don't know for sure, but my guess is that this line:
> 
>   length=$(( ${#Host_port[@]} - 1 ))
Correct - that line is a bashism, and is not portable when /bin/sh is dash.
> 
> which was added by vgerris in order to support forwarding of multiple
> ports, could be what's causing the incompatibility (that wasn't in
the
> original, simpler version of the script, written by me.)
> 
>>
>> *#!/bin/bash*
>> # used some from advanced script to have multiple ports: use an equal
>> number of guest and host ports
>>
>> Guest_name=xxxxxxx
>> Guest_ipaddr=xxx.xxx.xxx.xx
>> *Host_ipaddr=xxx.xxx.xxx.xx*
>> Host_port=( '80' '443' )
>> Guest_port=( '80' '443' )
In fact, these two lines are also bashisms.  All the more reason to
require bash.
>> length=$(( ${#Host_port[@]} - 1 ))
>> if [ "${1}" = "${Guest_name}" ]; then
>>    if [ "${2}" = "stopped" -o "${2}" =
"reconnect" ]; then
test ... -o ... (also spelled [ ... -o ... ]) is not portable, even on
bash.  There are some expressions that are completely ambiguous on how
to be parsed, when -o is in the mix.  It is better to spell it: [ ... ]
|| [ ... ] (that is, use the shell's || instead of test's -o to do the
conjunction).
>>        for i in `seq 0 $length`; do
seq is not portable outside of GNU/Linux systems.
>> Lastly, I should note that I am using Ubuntu 14.04, both for the host
>> and guest. 
Yep, that's a system that uses dash for /bin/sh.
>>
>> I'm also curious as to why this is considered a hack method. It
states
>> in the wiki that "This method is a hack", but it doesn't
express why.
> 
> I consider it a hack because:
> 
> 1) It requires the IP address of the guest to be known before the guest
> is started, so either you need to guess the guest's IP (if the guest is
> getting its IP address via dhcp) or configured the guest IP address in
> multiple places.
Although recent work has been made to get libvirt to add an API that
queries the guest for its IP address, once the guest is running.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

So should I go ahead and make the changes to the script that I suggested?

Thanks,
BJ

On Mon, Jun 8, 2015 at 3:21 PM, Eric Blake <eblake@redhat.com> wrote:
> On 06/08/2015 02:43 PM, Laine Stump wrote:
> >> However, if I changed the destination address from
"anywhere" to the
> >> IP of the host machine, the problem resolved. So I change the
script
> >> to as follows. (Changes are highlighted. For some reason the
original
> >> script didn't work using /bin/sh, but it did with /bin/bash,
so I
> >> changed that too).
> >
> > I don't know for sure, but my guess is that this line:
> >
> >   length=$(( ${#Host_port[@]} - 1 ))
>
> Correct - that line is a bashism, and is not portable when /bin/sh is dash.
>
> >
> > which was added by vgerris in order to support forwarding of multiple
> > ports, could be what's causing the incompatibility (that
wasn't in the
> > original, simpler version of the script, written by me.)
> >
> >>
> >> *#!/bin/bash*
> >> # used some from advanced script to have multiple ports: use an
equal
> >> number of guest and host ports
> >>
> >> Guest_name=xxxxxxx
> >> Guest_ipaddr=xxx.xxx.xxx.xx
> >> *Host_ipaddr=xxx.xxx.xxx.xx*
> >> Host_port=( '80' '443' )
> >> Guest_port=( '80' '443' )
>
> In fact, these two lines are also bashisms.  All the more reason to
> require bash.
>
> >> length=$(( ${#Host_port[@]} - 1 ))
> >> if [ "${1}" = "${Guest_name}" ]; then
> >>    if [ "${2}" = "stopped" -o "${2}"
= "reconnect" ]; then
>
> test ... -o ... (also spelled [ ... -o ... ]) is not portable, even on
> bash.  There are some expressions that are completely ambiguous on how
> to be parsed, when -o is in the mix.  It is better to spell it: [ ... ]
> || [ ... ] (that is, use the shell's || instead of test's -o to do
the
> conjunction).
>
> >>        for i in `seq 0 $length`; do
>
> seq is not portable outside of GNU/Linux systems.
>
> >> Lastly, I should note that I am using Ubuntu 14.04, both for the
host
> >> and guest.
>
> Yep, that's a system that uses dash for /bin/sh.
>
> >>
> >> I'm also curious as to why this is considered a hack method.
It states
> >> in the wiki that "This method is a hack", but it
doesn't express why.
> >
> > I consider it a hack because:
> >
> > 1) It requires the IP address of the guest to be known before the
guest
> > is started, so either you need to guess the guest's IP (if the
guest is
> > getting its IP address via dhcp) or configured the guest IP address in
> > multiple places.
>
> Although recent work has been made to get libvirt to add an API that
> queries the guest for its IP address, once the guest is running.
>
> --
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>
>