[Additional Layer Store] Use TOCDigest as ID of each layer (patch for c/storage) #1924
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| // reference. Note that this hasn't been stored to this store yet: the actual creation of | ||
| // a usable layer is done by calling the returned object's PutAs() method. After creating | ||
| // a layer, the caller must then call the object's Release() method to free any temporary | ||
| // resources which were allocated for the object by this method or the object's PutAs() | ||
| // method. | ||
| // This API is experimental and can be changed without bumping the major version number. | ||
| LookupAdditionalLayer(d digest.Digest, imageref string) (AdditionalLayer, error) | ||
| LookupAdditionalLayer(tocDigest digest.Digest, imageref string) (AdditionalLayer, error) |
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In general, changing the semantics of a security-critical parameter in a caller-invisible way like this feels rather risky to me.
In this case, assuming there’s exactly the one caller in c/image, and because this breaks the API of AdditionalLayer, I suppose I can live with it.
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This does not, AFAICS, change the visible API. What is the migration path to ensure that c/storage and the FUSE backends are updated in lockstep? Or are there no real-world deployments at all, to worry about? |
Signed-off-by: Kohei Tokunaga <ktokunaga.mail@gmail.com>
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After this PR is merged, we'll merge containerd/stargz-snapshotter#1673 and release a new version as soon as possible. |
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/lgtm |
| // UncompressedDigest returns the uncompressed digest of this layer | ||
| UncompressedDigest() digest.Digest | ||
| // TOCDigest returns the digest of TOC of this layer. Returns "" if unknown. | ||
| TOCDigest() digest.Digest |
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Compare containers/image#2416 (comment) / containerd/stargz-snapshotter#1673 (comment) ; do we need this provided by the ALS backend at all?
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… we actually, sort of, do: if this returns "", we know the FUSE server is older than this PR expects, and interprets the digest as non-TOC compressed digest.
AFAICS the proposed stargz-snapshotter implementation never returns a different digest than the one we looked up, but at least the “supported/unsupported” bit seems valuable.
Needs: containers/image#2416
This commit changes the store implementation to use TOCDigset as the ID of each layer. This ensures the runtime to pass TOCDigest to the FUSE backend everytime requiring a layer.
This commit modifies c/storage's
LookupAdditionalLayerto receive a TOCDigest as one of the arguments. Then that TOCDigest is passed to Additional Layer Store as one of the path elements of the FUSE fs. For example, the extracted view of a layer diff contents is provided in the following path:Additional Layer Store implementation attempts lazy pulling of the layer that has the specified TOCDigest in the image.
If that image doesn't contain the layer matching to the TOCDigest, accessing to the layer directly results in an error.
Example draft implementation of Additional Layer Store is at containerd/stargz-snapshotter#1673