oci-sif: inefficent copies of oci (layout) and tarball images #2934
Description
Version of Singularity
Main / 4.1
Describe the bug
When creating an oci-sif image, we call ociimage.FetchToLayout.
For an oci: layout, this will copy the image into the cache, or a tmpDir if the cache is disabled. This is un-necessary.
For an oci-archive: this will extract the tar file into a directory, and then treat it as an oci: layout above.
There isn't really any benefit of bringing the layers into the cache when we are working with a layout that can be directly read from disk. It takes up cache space, and I/O.
We seem to do the copies as a result of the ggcr based code incrementally following the containers/image code, and not being reviewed with sufficient depth on completion... my fault :-)