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Date: Wed, 18 Dec 2013 11:38:35 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCHv2] block: add native support for NFS
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To: Orit Wasserman <owasserm@redhat.com>
Cc: "kwolf@redhat.com" <kwolf@redhat.com>, "famz@redhat.com" <famz@redhat.com>, Peter Lieven <pl@kamp.de>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "stefanha@redhat.com" <stefanha@redhat.com>

Il 18/12/2013 11:24, Orit Wasserman ha scritto:
>>>
>>> For live migration we need the sync option (async ignores O_SYNC and
>>> O_DIRECT sadly),
>>> will it be supported? or will it be the default?
>>
>> Since this is bypassing the client kernel FS I/O layer question around
>> support of things like O_SYNC/O_DIRECT are not applicable.
>>
> 
> so no live migration support?

No, live migration just works.

O_SYNC is not used anymore in QEMU, we just issue a flush after every write.

And all protocol drivers except files/block devices _always_ bypass the
kernel page cache (libiscsi, NBD, ceph, and now libnfs) so they are
always behaving as if they had O_DIRECT.  For these protocols,
cache=writeback and cache=none are entirely the same.

Paolo