Re: [PATCH resend] libxl, hotplug/Linux: default to phy backend for raw format file, take 2

[Ian Campbell <Ian.Campbell@citrix.com>]

On Mon, 2015-01-12 at 10:39 +0100, Fabio Fantoni wrote:
> Il 12/01/2015 10:31, Ian Campbell ha scritto:
> > On Mon, 2015-01-12 at 10:15 +0100, Fabio Fantoni wrote:
> >> In the meantime, I saw this:
> >> http://lists.xen.org/archives/html/xen-users/2015-01/msg00047.html
> >> Based on the post above seems that phy will have important risk of data
> >> loss if I understand good, from Ian Campbell post:
> >>> xl also uses qdisk for raw disk images instead of loop+blkback which
> >>> xend used, because there are concerns that the loop driver can lead to
> >>> data loss (by not implementing direct i/o the underlying device, and/or
> >>> not handling flushes correct, my memory is a bit fuzzy).
> > Stefano already corrected me on this in this very thread.
> >
> > Ian.
> >
> 
> Thanks for your reply.
> I saw other posts about and if I understand good when O_DIRECT patches 
> will be in upstream loop driver the data loss risk will be solved, right?

Stefano says that O_DIRECT is not needed, only correct barrier semantics
are and he believes those are correctly implemented.

O_DIRECT would be an additional layer of safety perhaps, but sounds to
be not strictly needed.

Ian.