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The `manifests` option, as used for the `--tree` option on `docker image ls`
currently sorts manifests to put those that are present first. The intent was
to present "available" images at the top of each tree, followed by images that
were not pulled.
However, there's some limitations to this. First of all, the current approach
makes the output non-deterministic as the order in which variants are pulled
determines the order in which they're presented, i.e., the last pulled variant
is returned first (I omitted some variants in the example for brevity);
Here's the result of pulling `linux/riscv64`, then pulling `linux/arm64`;
docker pull --platform=linux/riscv64 alpine:latest
docker image ls -a --tree
IMAGE ID DISK USAGE CONTENT SIZE USED
alpine:latest beefdbd8a1da 10.6MB 3.37MB
├─ linux/riscv64 80cde017a105 10.6MB 3.37MB
├─ linux/amd64 33735bd63cf8 0B 0B
└─ linux/arm64/v8 9cee2b382fe2 0B 0B
docker pull --platform=linux/arm64 alpine:latest
docker image ls -a --tree
IMAGE ID DISK USAGE CONTENT SIZE USED
alpine:latest beefdbd8a1da 24.2MB 7.46MB
├─ linux/riscv64 80cde017a105 10.6MB 3.37MB
├─ linux/arm64/v8 9cee2b382fe2 13.6MB 4.09MB
└─ linux/amd64 33735bd63cf8 0B 0B
Repeating the steps but in reverse order results in the output to be reversed;
docker image rm alpine:latest
docker pull --platform=linux/arm64 alpine:latest
docker image ls -a --tree
IMAGE ID DISK USAGE CONTENT SIZE USED
alpine:latest beefdbd8a1da 13.6MB 4.09MB
├─ linux/arm64/v8 9cee2b382fe2 13.6MB 4.09MB
├─ linux/amd64 33735bd63cf8 0B 0B
└─ linux/riscv64 80cde017a105 0B 0B
docker image ls -a --tree
IMAGE ID DISK USAGE CONTENT SIZE USED
alpine:latest beefdbd8a1da 24.2MB 7.46MB
├─ linux/riscv64 80cde017a105 10.6MB 3.37MB
├─ linux/arm64/v8 9cee2b382fe2 13.6MB 4.09MB
└─ linux/amd64 33735bd63cf8 0B 0B
The second limitation is that order sometimes matters; when matching a
platform from a manifest-index, implementations may find multiple suitable
candidates. In most cases the _most_ suitable candidate can be selected
(e.g., prefer `linux/arm/v7` over `linux/arm/v6`), but manifest-indices do
allow multiple entries for the same platform, in which case implementations
match the first entry found.
While these situations will be less common (and usually due to incorect use
of tooling such as `docker manifest`), being able to observe the order in
which manifests appeared in the index can help debugging or help the user
understand why a specific variant was selected.
We should therefore not re-order these manifests, and return them in the
order in which they appeared. If we decide to present "present" variants
before "non-present" variants, we can do this ordering on the client side.
With this patch applied;
docker pull --quiet --platform=linux/riscv64 alpine:latest
docker pull --quiet --platform=linux/arm64 alpine:latest
docker image ls --tree alpine
IMAGE ID DISK USAGE CONTENT SIZE USED
alpine:latest beefdbd8a1da 24.2MB 7.46MB
├─ linux/amd64 33735bd63cf8 0B 0B
├─ linux/arm/v6 50f635c8b04d 0B 0B
├─ linux/arm/v7 f2f82d424957 0B 0B
├─ linux/arm64/v8 9cee2b382fe2 13.6MB 4.09MB
├─ linux/386 b3e87f642f5c 0B 0B
├─ linux/ppc64le c7a6800e3dc5 0B 0B
├─ linux/riscv64 80cde017a105 10.6MB 3.37MB
└─ linux/s390x 2b5b26e09ca2 0B 0B
Which matches the order of the manifests in the index:
docker buildx imagetools inspect --raw alpine:latest | jq -c .manifests[].platform
{"architecture":"amd64","os":"linux"}
{"architecture":"arm","os":"linux","variant":"v6"}
{"architecture":"arm","os":"linux","variant":"v7"}
{"architecture":"arm64","os":"linux","variant":"v8"}
{"architecture":"386","os":"linux"}
{"architecture":"ppc64le","os":"linux"}
{"architecture":"riscv64","os":"linux"}
{"architecture":"s390x","os":"linux"}
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>