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Date: Wed, 03 Oct 2012 17:50:08 +0200
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Subject: [Qemu-devel] O_DIRECT on glusterfs (was Re: [PATCH v9 4/4] block:
 Support GlusterFS as a QEMU block backend)
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To: bharata@linux.vnet.ibm.com
Cc: Kevin Wolf <kwolf@redhat.com>, Anthony Liguori <aliguori@us.ibm.com>, Anand Avati <aavati@redhat.com>, Vijay Bellur <vbellur@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>, Harsh Bora <harsh@linux.vnet.ibm.com>, Amar Tumballi <amarts@redhat.com>, qemu-devel@nongnu.org, "Richard W.M. Jones" <rjones@redhat.com>, Blue Swirl <blauwirbel@gmail.com>, Avi Kivity <avi@redhat.com>, Daniel Veillard <veillard@redhat.com>

Il 24/09/2012 11:13, Bharata B Rao ha scritto:
> +
> +    if ((bdrv_flags & BDRV_O_NOCACHE)) {
> +        open_flags |= O_DIRECT;
> +    }
> +

If I understand correctly what I was told, this prevents the brick
server from using its own buffer cache.  This is quite different from
what we do for example over NFS (where the host does no caching, but
nothing prevents it on the remote server).

I think these 3 lines should be removed.  We're bypassing the host
buffer cache just by virtue of using a userspace driver, and that's what
cache=none cares about.

Paolo