[uml-user] sharing a filesystem between several guests

[Nicolas B. <nic...@ec...>]

Hi,

I've been willing to share an OCFS2 filesystem between several UML
guests. For what it's worth, the host's device givent to uml is an iSCSI
disc, seen by several hosts.

If I run the 2 guests on the same host, with no special option, it just
fails because of a lock.
If I use the 'c' (as "cluster"?) option to the ubd setup, still with the
2 guests on the same host, then it works fine. But running the 2 guests
on the same host is not so good, as far as high-availablility is
concerned. ;-)

If I run the 2 guests on 2 different hosts, then each guest thinks it is
the only one to access the filesystem.

My guess is that OCFS2 uses some location in the file system for a
heartbeat, and that because of some read caches on the host, each guest
does not see the other guest's heartbeat...

Then, if my guess is correct, opening the device with O_DIRECT would fix
the problem, as it would avoid read caches. Do you think it would be
worthy to add an option to the ubd setup to open the file/device with
O_DIRECT?


Cheers,

Nicolas Boullis