Re: [RFC][PATCH 00/25] Network fs helper library & fscache kiocb API

David Howells
2021-01-21T19:19:53Z

J. Bruce Fields <bfields@fieldses.org> wrote:

> > Fixing this requires a much bigger overhaul of cachefiles than this patchset
> > performs.
>
> That sounds like "sometimes you may get file corruption and there's
> nothing you can do about it". But I know people actually use fscache,
> so it must be reliable at least for some use cases.

Yes. That's true for the upstream code because that uses bmap. I'm switching
to use SEEK_HOLE/SEEK_DATA to get rid of the bmap usage, but it doesn't change
the issue.

> Is it that those "bridging" blocks only show up in certain corner cases
> that users can arrange to avoid? Or that it's OK as long as you use
> certain specific file systems whose behavior goes beyond what's
> technically required by the bamp or seek interfaces?

That's a question for the xfs, ext4 and btrfs maintainers, and may vary
between kernel versions and fsck or filesystem packing utility versions.

David