Re: xattr names for unprivileged stacking?

Matthew Wilcox
2020-08-16T23:09:23Z

On Mon, Aug 17, 2020 at 08:56:20AM +1000, Dave Chinner wrote:
> Indeed, most filesystems will not be able to implement ADS as
> xattrs. xattrs are implemented as atomicly journalled metadata on
> most filesytems, they cannot be used like a seekable file by
> userspace at all. If you want ADS to masquerade as an xattr, then
> you have to graft the entire file IO path onto filesytsem xattrs,
> and that just ain't gonna work without a -lot- of development in
> every filesystem that wants to support ADS.
>
> We've already got a perfectly good presentation layer for user data
> files that are accessed by file descriptors (i.e. directories
> containing files), so that should be the presentation layer you seek
> to extend.
>
> IOWs, trying to use abuse xattrs for ADS support is a non-starter.

One thing Dave didn't mention is that a directory can have xattrs,
forks and files (and acls). So your presentation layer needs to not
confuse one thing for another.

I don't understand why a fork would be permitted to have its own
permissions. That makes no sense. Silly Solaris.