xattrs are not preserved in final image

[dlech]

Docker uses xattrs for file linux capabilities. For example, ping has CAP_NET_RAW to enable non-root users to ping.

The tar command has the ability to preserve xattrs, but there is a bug in libguestfs that prevents the xattrs from being used by the tar-in command of guestfish.

Related:

• https://github.com/ev3dev/ev3dev/issues/766
• https://bugzilla.redhat.com/show_bug.cgi?id=1384241