why is copying required twice during buildah commit？

[lddlww]

reference follow codes：
1: write to /var/tmp/buildahxxx

buildah/image.go

Line 1110 in e0e108c

size, err := io.Copy(writer, rc)

2: copy blob, write to /var/tmp/container_storagexxx

buildah/vendor/go.podman.io/image/v5/storage/storage_dest.go

Line 295 in e0e108c

_, err = io.Copy(diffID.Hash(), decompressed)

if first one exe io.Copy why second code used Copy too，does it instead of os.Rename?

above what would lead poor performance , or am i missing something?

[nalind]

io.Copy() doesn't manipulate the filesystem. https://pkg.go.dev/io#Copy describes its behavior.

[lddlww]

does storage_dest.go putBlobToPendingFile func could add extra parameter which is /var/tmp/buildahxxx/sha256xxxx, so that , putBlobToPendingFile func need not do io.Copy and digest?

storage_dest.go putBlobToPendingFile func do io.Copy only if /var/tmp/buildahxxx/sha256xxxx not exists

[nalind]

That logic is maintained in the https://github.com/containers/container-libs repository, and tbh it's been some time since I last looked at the details of it. If there's an optimization to be made there, that's where the pull request would be filed.

[github-actions]

A friendly reminder that this issue had no activity for 30 days.