On Wed, 18.01.12 09:47, Tejun Heo (tj@kernel.org) wrote:

Hello,

On Wed, Jan 18, 2012 at 04:27:18PM +0800, Li Zefan wrote:

quoted

Furthermore, I noticed tmpfs also implemented xattr support, and we
should be able to share most of the code, which makes the cost for
having this feature smaller.

Yes, maybe, but tmpfs doesn't have any special semantics attached to
files.  It's supposed to store opaque data from userland.  Regardless
of code complexity, I just don't think this is a good idea.  What if
we later want to attach certain config meaning to or export statistics
via xattrs?  That would be quite unusual and require strong rationale
but at least fall in the similar usage as with the rest of the fs.

If you plan to export kernel data to userspace via xattrs, then you
should probably place that in the system.xxx xattr namespace, not in
the user.xxx or trusted.xxx namespaces which are the only ones which can
be manipulated by userspace.

See attr(5) for more information about the four available xattr
namespaces.

In other words: kernel exported xattrs should never collide with xattrs
set by userspace.

Lennart

-- 
Lennart Poettering - Red Hat, Inc.