Re: [Qemu-devel] iSCSI support for QEMU, update

[Christoph Hellwig <hch@lst.de>]

On Fri, Apr 22, 2011 at 04:08:57PM +1000, ronnie sahlberg wrote:
> So I should set FUA when
> BDRV_O_CACHE_WB==0  or  BDRV_O_NOCACHE==1
> right?

At this point you need to set it if either the BDRV_O_CACHE_WB and
BDRV_O_NOCACHE flags are set.  And yes, the naming of the nocache
flag is rather confusing.

Take a look at block.c:bdrv_open_common():

    /*
     * Yes, BDRV_O_NOCACHE aka O_DIRECT means we have to present a
     * write cache to the guest.  We do need the fdatasync to flush
     * out transactions for block allocations, and we maybe have a
     * volatile write cache in our backing device to deal with.
     */
    if (flags & (BDRV_O_CACHE_WB|BDRV_O_NOCACHE))
        bs->enable_write_cache = 1;