You can always use the MVS NFS server to do this with any release of Linux or OS/390 a.k.a z/OS, however there are some nice features appearing in the Linux world to make direct processing more appealing.
Hitachi Japan has released a new Linux filesystem that can read and (with appropriate coordination with OS/390 and z/OS) update QSAM data from VM. It still does not completely understand catalogs, but the basics are there. The code is still somewhat experimental -- ie, don't use it on the production payroll files just yet -- but it's promising work. The gist of it is to use the ability of VM to export fullpack minidisks as MWV volumes and have VM handle virtual reserve-release on the volumes to keep z/OS happy. I don't beleive any of the mainstream distributors have picked up this code yet and packaged it into RPM format, but there are Debian packages for it.
The details of the MFS (Mainframe File System) are available from http://linuxvm.org.
This was first published in December 2005