Composefs for integrity protection and data sharing

Posted Dec 8, 2022 10:27 UTC (Thu) by hsiangkao (guest, #123981)
In reply to: Composefs for integrity protection and data sharing by smcv
Parent article: Composefs for integrity protection and data sharing

EROFS over fscache can do all of them in kernel already since 5.19.

Composefs for integrity protection and data sharing

Posted Dec 10, 2022 18:15 UTC (Sat) by gscrivano (subscriber, #74830) [Link] (1 responses)

How does it _all_ happen in the kernel if fscache makes requests to userspace to retrieve data from the cache?

Using a FUSE filesystem as a secondary store, composefs would need a request to userspace only for files that are not available locally, and fully resolved within the kernel. EROFS ends up in request to userspace also for files that are already in the local cache but unknown to fscache.

Additionally composefs can use multiple sources transparently for each mount instead of forcing a single userspace handler for /dev/cachefiles.

Composefs for integrity protection and data sharing

Posted Dec 11, 2022 4:58 UTC (Sun) by hsiangkao (guest, #123981) [Link]

> Using a FUSE filesystem as a secondary store, composefs would need a request to userspace only for files that are not available locally, and fully resolved within the kernel. EROFS ends up in request to userspace also for files that are already in the local cache but unknown to fscache.

That is not the truth. EROFS only ends up in request to userspace for files that are _not_ in the local cache and unknown to fscache. If the files is already in the local cache, EROFS won't trigger into userspace anymore.

Please take a look at this: https://d7y.io/blog/2022/06/06/evolution-of-nydus/

> Additionally composefs can use multiple sources transparently for each mount instead of forcing a single userspace handler for /dev/cachefiles.

It's just a interface. Fscache itself also has multiple daemon and multiple directory plan.

In addition, as I said many times in this thread, if you want to directly access files and such overlay model is considered as _safe_ (which I don't think so), EROFS can support this mode in a few days as well.