Re: [Qemu-devel] [PATCHv2] block: add native support for NFS

[Paolo Bonzini]

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