On Fri, Mar 3, 2023, at 12:37 PM, Gao Xiang wrote: > > Actually since you're container guys, I would like to mention > a way to directly reuse OCI tar data and not sure if you > have some interest as well, that is just to generate EROFS > metadata which could point to the tar blobs so that data itself > is still the original tar, but we could add fsverity + IMMUTABLE > to these blobs rather than the individual untared files. > - OCI layer diff IDs in the OCI spec [1] are guaranteed; The https://github.com/vbatts/tar-split approach addresses this problem domain adequately I think. Correct me if I'm wrong, but having erofs point to underlying tar wouldn't by default get us page cache sharing or even the "opportunistic" disk sharing that composefs brings, unless userspace did something like attempting to dedup files in the tar stream via hashing and using reflinks on the underlying fs. And then doing reflinks would require alignment inside the stream, right? The https://fedoraproject.org/wiki/Changes/RPMCoW change is very similar in that it's proposing a modification of the RPM format to 4k align files in the stream for this reason. But that's exactly it, then it's a new tweaked format and not identical to what came before, so the "compatibility" rationale is actually weakened a lot.
