This substituter basically cannot work reliably since we switched to
SQLite, since SQLite databases may need write access to open them even
just for reading (and in WAL mode they always do).
For instance, it's pointless to keep copy-from-other-stores running if
there are no other stores, or download-using-manifests if there are no
manifests. This also speeds things up because we don't send queries
to those substituters.
Before calling dumpPath(), we have to make sure the files are owned by
the build user. Otherwise, the build could contain a hard link to
(say) /etc/shadow, which would then be read by the daemon and
rewritten as a world-readable file.
This only affects systems that don't have hard link restrictions
enabled.
The assertion in canonicalisePathMetaData() failed because the
ownership of the path already changed due to the hash rewriting. The
solution is not to check the ownership of rewritten paths.
Issue #122.
Otherwise subsequent invocations of "--repair" will keep rebuilding
the path. This only happens if the path content differs between
builds (e.g. due to timestamps).
Previously, if a binary cache is hanging/unreachable/slow,
download-from-binary-cache.pl would also hang without any indication
to the user. Now, if fetching a URL takes more than 5 seconds, it
will print a message to that effect.
Amazon S3 returns HTTP status code 403 if a file doesn't exist and the
user has no permission to list the contents of the bucket. So treat
it as 404 (meaning it's cached in the NARExistence table).
The "$UID != 0" makes no sense: if the local side has write access to
the Nix store (which is always the case) then it doesn't matter if
we're root - we can import unsigned paths either way.
Functions in Nix are anonymous, but if they're assigned to a
variable/attribute, we can use the variable/attribute name in error
messages, e.g.
while evaluating `concatMapStrings' at `/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs/pkgs/lib/strings.nix:18:25':
...
Otherwise it will set the parent's stdin to non-blocking mode, causing
the subsequent read of the set of inputs/outputs to fail randomly.
That's insane.
Before selecting a machine, build-remote.pl will try to run the
command "nix-builds-inhibited" on the machine. If this command exists
and returns a 0 exit code, then the machine won't be used. It's up to
the user to provide this command, but it would typically be a script
that checks whether there is enough disk space and whether the load is
not too high.
Don't pass --timeout / --max-silent-time to the remote builder.
Instead, let the local Nix process terminate the build if it exceeds a
timeout. The remote builder will be killed as a side-effect. This
gives better error reporting (since the timeout message from the
remote side wasn't properly propagated) and handles non-Nix problems
like SSH hangs.
This allows providing additional binary caches, useful in scripts like
Hydra's build reproduction scripts, in particular because untrusted
caches are ignored.
