On 18.03.2016 19:21, Kevin Wolf wrote: > This replaces the existing hack in the iscsi driver that sent the FUA > bit in writethrough mode and ignored the following flush in order to > optimise the number of roundtrips (see commit 73b5394e). > > Signed-off-by: Kevin Wolf <kw...@redhat.com> > --- > block/iscsi.c | 24 +++++++----------------- > 1 file changed, 7 insertions(+), 17 deletions(-) > > diff --git a/block/iscsi.c b/block/iscsi.c > index 3b54536..4f75204 100644 > --- a/block/iscsi.c > +++ b/block/iscsi.c
[...]
> @@ -1851,7 +1840,8 @@ static BlockDriver bdrv_iscsi = {
> .bdrv_co_discard = iscsi_co_discard,
> .bdrv_co_write_zeroes = iscsi_co_write_zeroes,
> .bdrv_co_readv = iscsi_co_readv,
> - .bdrv_co_writev = iscsi_co_writev,
> + .bdrv_co_writev_flags = iscsi_co_writev_flags,
> + .supported_write_flags = BDRV_REQ_FUA,
> .bdrv_co_flush_to_disk = iscsi_co_flush,
>
> #ifdef __linux__
>
Hm, wait, maybe not R-b. I can see three places in block/io.c which call
bdrv_co_writev(), and only one of them diverts to bdrv_co_writev_flags()
if that is available. Maybe we don't need to care about the
bounce-buffer case for write_zeroes, but I do think we need to care
about the COR case.
Of course bdrv_co_writev() can trivially be forwarded to
bdrv_co_writev_flags(), but I'm not sure who is supposed to do this
forwarding. I can imagine three ways:
(1) Keep a wrapper per block driver. Simple, but not so elegant.
(2) Make all bdrv_co_writev() callers call bdrv_co_writev_flags() if
the former is not available but the latter is.
(3) Introduce a generic function replacing every drv->bdrv_co_writev()
call which then decides which driver function to invoke.
Max
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