Remove lxcbr0 lines from gitian-build.sh #11391

The gitian-build.sh script crashes with an error when I tried to use it, @kallewoof also had this same issue:

lxcbr0: ERROR while getting interface flags: No such device
SIOCSIFADDR: No such device
lxcbr0: ERROR while getting interface flags: No such device

And then:

lxc-execute: failed to find gateway addresses
lxc-execute: failed to spawn 'gitian'
./bin/gbuild:21:in `system!': failed to run make-clean-vm --suite trusty --arch amd64 (RuntimeError)

I believe it's because of the two lines which this PR removes, I tested it and seems to work as expected now. These lines are unique to this script and aren't mentioned in gitian-building.md or release-process.md. We discussed it on IRC, @achow101 agrees removing these lines would probably fix it: https://botbot.me/freenode/bitcoin-core-dev/2017-09-19/?msg=91299782&page=2

Has anyone successfully used this script as-is? Or does everyone else manually run the builds/write their own script like I have up til this point?

Has anyone successfully used this script as-is? Or does everyone else manually run the builds/write their own script like I have up til this point?

Yes, it's my script and there was a reason for those two lines there (it fixed some problems for me in the past). Removing those two lines doesn't effect my setup now (for some reason) so it should be fine to remove them.

Edit: Actually removing them does break my setup now. Normally I use kvm anyways so I don't notice it, but without those lines, things are broken.

Hmm how did you set up that bridge? It's not mentioned in any docs so maybe it's them that need amending not this. Do you also have a br0 bridge (the one configured here: https://github.com/bitcoin/bitcoin/blob/master/doc/gitian-building.md#setting-up-debian-for-gitian-building)? Or just lxcbr0?

I don't remember how that was all actually setup; I did it years ago. I believe it may be the same thing as the br0 setup in the gitian building guide but my setup probably had some weirdness to it or had br0 already taken by something else. I believe that it may have also been that lxc was defaulting to using lxcbr0 for me instead of br0. I'm not sure.

I think it makes more sense to have the script consistent with the VM set up in the docs, so it'd be good if at least one other person (ping @kallewoof ?) could confirm this fixes it like it does for me

Sorry for lack of response. I actually gave up trying to get this all to work as there are a few too many assumptions that I can't guess correctly. I believe the fix you suggest enables the --setup call. Even without this change I am able to run the --build variant, but I have no idea if the results are actually valid as I haven't verified or signed anything yet. Sorry, I will try to get back on this. For now, weak ACK from me.

Concept ACK. I don't think we should include workarounds that only work on a single dev's machine.

It's not mentioned in any docs

Indeed, this is causing confusion: https://github.com/bitcoin-core/docs/issues/3

Can this be added to v0.15.1?

@Sjors You can and should just copy the script out of the folder where you have the bitcoin source and use it from outside of that. There you can make any modifications that you want to it without said modifications being effected by the git tree changing.