Hi, Quoting Helmut Grohne (2024-05-24 14:12:38) > while working with debusine.debian.net, I ran into a rather crazier kind > of issue with the unshare backend. It seems like debusine.debian.net > creates a chroot.tar where resolv.conf is a symbolic link: > > | lrwxrwxrwx 0/0 0 2024-05-20 17:15 ./etc/resolv.conf -> > ../run/systemd/resolve/stub-resolv.conf > > Notably, /run/systemd/resolve does not exist inside the tar nor does > sbuild run systemd-resolved nor systemd-tmpfiles for creating this > location. When building, the unshare backend tries to bind mount > /etc/resolv.conf: > > | --: 13: cannot create /tmp/tmp.sbuild.OQ0pOU6LQg/etc/resolv.conf: Directory > nonexistent > https://debusine.debian.net/artifact/427489/hostname_3.23+nmu2_amd64-2024-05-24T10:06:30Z.build > > This fails, because mount attempts to dereference the symbolic link and > finds that an intermediate directory does not exist. As a result, this > fails and network generally does not work resulting in all sorts of > badness.
I'm not sure where you see bind-mounting /etc/resolv.conf being done in the
$network_setup code. If network is enabled, it reads:
[ -f /etc/resolv.conf ] && cat /etc/resolv.conf >
"$rootdir/etc/resolv.conf" || echo "nameserver 127.0.0.53" >
"$rootdir/etc/resolv.conf";
and when it's disabled:
ip link set lo up;> "$rootdir/etc/resolv.conf";
> Technically speaking, you can bind mount onto a symbolic link. You just
> cannot do so using the mount(2) API nor the mount(1) command. Unless you
> pass MOVE_MOUNT_T_SYMLINKS to move_mount(2), it will not dereference a
> symlink being pointed at. I'm not sure we want to go this extra mile
> though.
>
> On the debusine side, I think we want to work around this issue in some
> way to avoid imposing a high version constraint in sbuild. I am
> reporting it here as it kinda is a bug (up to your judgement) and it
> helps having the diagnosis written down.
in unshare mode, we are always working with an ephemeral chroot. Would there be
any downside to sbuild just first running "rm -f $rootdir/etc/resolv.conf" and
then re-creating it as a real file in the $network_setup snippet of
_get_exec_argv() in lib/Sbuild/ChrootUnshare.pm?
Thanks!
cheers, josch
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