The image tag can be specified or generated from the output hash.
Previously, a generated tag could be recovered from the evaluated
image with some string operations.
However, with the introduction of streamLayeredImage, it's not
feasible to compute the generated tag yourself.
With this change, the imageTag attribute is set unconditionally,
for the buildImage, buildLayeredImage, streamLayeredImage functions.
In https://github.com/NixOS/nixpkgs/pull/58431 the authors ensured that
the resulting layer.tar would always list
/nix/
/nix/store/
first to fully comply to the tar spec. Various refactorings later it is only
ensured to create /nix/ but NOT /nix/store anymore. Instead tar transformed
them to /nix/nix and /nix/nix/store.
Calculating the tarsum after creating a layer is inefficient, since
we have to read the tarball we've just written from the disk.
This commit simultaneously calculates the tarsum while creating the
tarball.
Appending to an existing tar archive repeatedly seems to be a quadratic
operation, since tar seems to traverse the existing archive even using
the `-r, --append` flag. This commit avoids that by passing the list of
files to a single tar invocation.
This is useful when buildLayeredImage is called in a generic way
that should allow simple (base) images to be built, which may not
reference any store paths.
Fixes #78744
My previous change broke when there are more packages than the maximum
number of layers. I had assumed that the `store-path-to-layer.sh` was
only ever passed a single store path, but that is not the case if
there are multiple packages going into the final layer. To fix this, we
loop through the paths going into the final layer, appending them to the
tar file and making sure they end up at the right path.
Since a layer is reserved for "customization", the image can not
contains less than 2 layers.
The user gets the following message at evaluation:
nix-instantiate nixos/tests/docker-tools.nix
trace: the maxLayers argument of dockerTools.buildLayeredImage function must be greather than 1 (current value: 1)
Building a docker image with darwin binaries just yields a confusing
error when ran:
standard_init_linux.go:211: exec user process caused "exec format error"
This change prevents people from building such images in the first place
