Re: xattr names for unprivileged stacking?

Theodore Y. Ts'o
2020-09-01T14:52:44Z

On Tue, Sep 01, 2020 at 01:34:05PM +1000, Dave Chinner wrote:
>
> But, unlike your implication that this is -really complex and hard
> to do-, it's actually relatively trivial to do with the XFS
> implementation I mentioned as each ADS stream is a fully fledged
> inode that can point to shared data extents. If you can do data
> manipulation on a regular inode, you'll be able to do it on an ADS,
> and that includes copying ADS streams via reflink.

Is the reflink system call on a file with ADS's atomic, or not? What
if there are a million files is ADS hierarchy which is 100
subdirectories deep in some places, comprising several TB's worth of
data? Is that all going to fit in a single XFS transaction? What if
you crash in the middle of it? Is a partially reflinked copy of an
ADS file OK? Or a reflinked ADS file missing some portion of the
alternate data streams?

- Ted