This fixes a regression from 993baa587c which requires
networking.hostName to be a valid DNS label [0].
Unfortunately we missed the fact that the hostnames may also be empty,
if the user wants to obtain it from a DHCP server. This is even required
by a few modules/images (e.g. Amazon EC2, Azure, and Google Compute).
[0]: https://github.com/NixOS/nixpkgs/pull/76542#issuecomment-638138666
xchg is advertised as a bidirectional exchange dir, but file content
transfer from host to VM fails due to caching:
If a file is read in the VM and then modified on the host, subsequent
re-reads in the VM can yield old, cached data.
This is caused by the use of 9p's cache=loose mode that is explicitly
meant for read-only mounts.
9p doesn't provide any suitable cache modes, so fix this by disabling
caching.
Also, remove a now unnecessary sync in the test driver.
This effectively disables nscd's built-in hosts cache, which turns out
to be erratic in some cases.
We only use nscd these days as a more ABI-neutral NSS dispatcher
mechanism.
Local caching should still be possible with local resolvers in
/etc/resolv.conf (via the `dns` NSS module), or without local resolvers
via systemd-networkd (via the `resolve` nss module)
We don't set enable-cache to no due to
https://github.com/NixOS/nixpkgs/pull/50316#discussion_r241035226.
Refactor the systemd service definition for the haproxy reverse proxy,
using the upstream systemd service definition. This allows the service
to be reloaded on changes, preserving existing server state, and adds
some hardening options.
These syncs have the goal to transfer host filesystem changes to the VM,
but they have no effect because 1) syncing in the VM can't possibly pull
in host data and 2) 9p is accessing the host filesystem on the cached
layer anyways, so even syncing on the host would have no effect in the
VM.
The `networking.interfaces.<name?>.proxyARP` option previously mentioned it would also enable IPv6 forwarding and `proxy_ndp`.
However, the `proxy_ndp` option was never actually set (the non-existing `net.ipv6.conf.proxy_arp` sysctl was set
instead). In addition `proxy_ndp` also needs individual entries for each ip to proxy for.
Proxy ARP and Proxy NDP are two different concepts, and enabling the latter
should be a conscious decision.
This commit removes the broken NDP support, and disables explicitly
enabling IPv6 forwarding (which is the default in most cases anyways)
Fixes #62339.
