Re: [Qemu-devel] [PATCH 1.2 3/7] block: always open protocol in writeback mode

[Paolo Bonzini]

Il 31/05/2012 13:33, Kevin Wolf ha scritto:
>> > diff --git a/block.c b/block.c
>> > index 7add33c..43b3de6 100644
>> > --- a/block.c
>> > +++ b/block.c
>> > @@ -661,7 +661,7 @@ static int bdrv_open_common(BlockDriverState *bs, 
>> > const char *filename,
>> >      if (drv->bdrv_file_open) {
>> >          ret = drv->bdrv_file_open(bs, filename, open_flags);
> Why don't you add the writeback flag here? Would the code is raw-posix
> that adds O_DSYNC be unused then. and can it still be used in other ways
> than format=file/host_* with this patch?

Because in this case there is no format over it, so the topmost BDS will
be open with BDRV_O_CACHE_WB and no one will call bdrv_flush.

We could indeed remove the BDRV_O_CACHE_WB handling in all the protocol
drivers (at least those where bdrv_flush_to_disk does something
sensible), and always open in writeback mode.  At that point this patch
could be reverted.

Paolo

>> >      } else {
>> > -        ret = bdrv_file_open(&bs->file, filename, open_flags);
>> > +        ret = bdrv_file_open(&bs->file, filename, open_flags | 
>> > BDRV_O_CACHE_WB);
>> >          if (ret >= 0) {
>> >              ret = drv->bdrv_open(bs, open_flags);
>> >          }