Running pmfs in VMs

[Matthew Wilcox]

On Tue, Jan 07, 2014 at 02:46:30PM +0000, Zuckerman, Boris wrote:
> Is it possible to run pmfs in VMs (any)? 
> How do I configure VMs to allow a correct mapping of physaddr (2 VMs can see the same physical range)?

Hi Boris,

You never got an answer to this, but I think it's worth discussing how
we can solve this problem in our brave new DAX-based future.  I suspect
ext2/ext4 can both mount the same block device simultaneously in read-only
mode, the same way that the s390 guys did originally with their XIP work.

For read-write mounts, ext4 doesn't support the shared-disc metaphor,
and I don't think XFS does either.  Linux does have two filesystems that
do support shared-discs; OCFS2 and GFS2.  Assuming we present the same
ranges to two VMs, and the block driver works, both of these filesystems
should do the right thing today.

We can improve them by adding DAX support, and a quick look makes it
seem like it would be relatively straightforward to do, the same way we
added support to ext4.

Would that address your use case?