The prior use of the UID is uninteresting in general for consumers who
wants to learn things about _what_ the build is, not what is the UID of
the build user running it.
Achieving this with a place where a mapping between cgroup names and
build requests are maintained is non trivial because there's no "global"
daemon that keeps track of this information and such a daemon would
require a persistent location to track this.
Rather than solving that, we will just encode the derivation hash inside
the cgroup name. Userspace can simply pull this apart and query Nix to
obtain the original corresponding derivation for more information.
This provides userspace with a way to map cgroup names to pnames for
example. Going further, if you have a map between attribute paths and
derivation hashes, you can power a database of cgroup metrics per
attribute paths by combining all of that.
In addition to this rename, we adopt a systemd-ish convention for
template units (`@`).
As a result, userspace tooling that will scrape cgroup metrics will
discover a consistent path as long as they filter out the UID part,
especially in context of Id6c458aad30eaa08c3609ac8280a7dde8e8f3cf9
change.
This problem is tracked under #1073.
Change-Id: I238d0568a3e4b1ff3057781c0639528d666b4d37
Signed-off-by: Raito Bezarius <raito@lix.systems>
the cgroups experimental feature does not work properly without this
because we do not stop subdaemons when the main daemon is shut down.
systemd needs the assigned cgroups to be empty to restart the daemon
and thus cannot cleanly restart the daemon if any connections exist.
starting a fresh unit for each connection creates a new cgroup every
time instead of sharing any delegations and thus solves the problem.
fixes#1030
Change-Id: Id6c458aad30eaa08c3609ac8280a7dde8e8f3cf9
This bump nixpkgs input to 25.11 and fix the two warnings that were
coming with the update:
1. `pkgs.system` => `pkgs.stdenv.hostPlatform.system`
2. `runCommandNoCC` => `runCommand`
also:
1. remove cppnix 2.3 compat tests (cppnix 2.3 is officially dead now)
2. remove lowdown 1.3 compat tests (nixpkgs no longer carries it)
Co-authored-by: Tom Hubrecht <github@mail.hubrecht.ovh>
Change-Id: I78526b5d8992a6c63ecd7f0c7c1fa6346a6a6964
In the past, it tried direct access if it *could* [1] perform direct
access.
This solves a bunch of errors people had when they tried the cgroup
feature and their scripts did not pass NIX_REMOTE=daemon manually
(nixos-rebuild-ng, home-manager activation from a root systemd unit,
etc.)
To avoid looping infinitely while receiving daemon connections, we
forcibly change the store URI when forking for a subdaemon to do direct
access automatically, this doesn't break forward usecases where you
point a daemon to another socket because we only change NIX_REMOTE="",
NIX_REMOTE=daemon, NIX_REMOTE=auto to a local and direct access.
All these usecases would end up infinitely looping no matter what
settings are set, because we are also responsible for creating the
daemon socket.
[1]: this happened all the time if you were `root`.
Related: https://github.com/NixOS/nixpkgs/pull/415701
Change-Id: I783fc795a9c2ee25b3d9f44f453f8f94b063371f
Signed-off-by: Raito Bezarius <raito@lix.systems>
When Ctrl-C is sent to the workload, even across remote builds, the
whole process possess a global flag `_isInterrupted` which is checked in
certain filesystem operations, cancelling them, e.g. writeFile will
write nothing under interruption unwinding.
In addition, if any operation throws an exception before we `rmdir` the
cgroup, we may leave it hanging while we remove the state record.
Therefore, we put the final cleanup in a block.
In practice, reading statistics could lead to failures.
Control groups cleanups are critical though and should always be
performed.
Change-Id: I48fa87317b6a9f6663559bc8fa5f8a897f37011e
Signed-off-by: Raito Bezarius <raito@lix.systems>
We offer full cgroup delegation to our sandbox now, required for running
containers inside the sandbox.
To run systemd-nspawn or containers managers inside the sandbox, there
is a need for one extra ingredient now: control over your own cgroup
subtree inside the sandbox.
If, in addition, you need multiple UIDs, for e.g. rootless usecases, you
need to run with the `uid-range` system feature.
Therefore, when the daemon or Nix runs under the right condition, e.g.
systemd-style delegation of the cgroup subtree while placing the
nix-daemon in a supervisor sub-cgroup, we create a new sub-cgroup for
each build based on the build UID and delegate that sub-cgroup to the
builder's process.
Additionally, `uid-range` always request the `cgroups` feature now, as
`uid-range` builds would probably always benefit from having cgroups
delegated, but the converse is not true.
Inspired from https://github.com/NixOS/nix/pull/11412 with a different
design that does not use function-local statics to derive the root
cgroup.
Co-authored-by: Linus Heckemann <git@sphalerite.org>
Co-authored-by: Parker Hoyes <contact@parkerhoyes.com>
Change-Id: Ic8947c5adaf4b5bbd153386e05fad65a935274fa
Signed-off-by: Raito Bezarius <raito@lix.systems>
Raito Bezarius