On Thu, Nov 29, 2012 at 05:32:14PM -0800, Hugh Dickins wrote: > Like you, I'm really hoping someone will join in and say they'd been > disadvantaged by lack of O_DIRECT on tmpfs: no strong feeling myself. Not disadvantaged as such, but we have had a workaround in libguestfs for a very long time. If you use certain qemu caching modes, then qemu will open the backing disk file using O_DIRECT. This breaks if the backing file happens to be on a tmpfs, which for libguestfs would not be unusual -- we often make or use temporary disk images for various reasons, and people sometimes have /tmp on a tmpfs. In 2009 I added code to libguestfs so that if the underlying filesystem doesn't support O_DIRECT, then we avoid the troublesome qemu caching modes. The code is here: https://github.com/libguestfs/libguestfs/blob/master/src/launch.c#L147 Since the workaround exists and has been in use for years, we don't need tmpfs to change. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones libguestfs lets you edit virtual machines. Supports shell scripting, bindings from many languages. http://libguestfs.org -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>