We want to make the formats handle their own flushes autonomously, while keeping for guests the ability to use a writethrough cache. Since formats will write metadata via bs->file, bdrv_co_do_writev is the only place where we need to add a flush.
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com> Signed-off-by: Kevin Wolf <kw...@redhat.com> --- block.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/block.c b/block.c index 85ef6af..7538112 100644 --- a/block.c +++ b/block.c @@ -1758,8 +1758,8 @@ int bdrv_pwrite_sync(BlockDriverState *bs, int64_t offset, return ret; } - /* No flush needed for cache modes that use O_DSYNC */ - if ((bs->open_flags & BDRV_O_CACHE_WB) != 0) { + /* No flush needed for cache modes that already do it */ + if (bs->enable_write_cache) { bdrv_flush(bs); } @@ -1808,6 +1808,9 @@ static int coroutine_fn bdrv_co_do_copy_on_readv(BlockDriverState *bs, ret = bdrv_co_do_write_zeroes(bs, cluster_sector_num, cluster_nb_sectors); } else { + /* This does not change the data on the disk, it is not necessary + * to flush even in cache=writethrough mode. + */ ret = drv->bdrv_co_writev(bs, cluster_sector_num, cluster_nb_sectors, &bounce_qiov); } @@ -1977,6 +1980,10 @@ static int coroutine_fn bdrv_co_do_writev(BlockDriverState *bs, ret = drv->bdrv_co_writev(bs, sector_num, nb_sectors, qiov); } + if (ret == 0 && !bs->enable_write_cache) { + ret = bdrv_co_flush(bs); + } + if (bs->dirty_bitmap) { set_dirty_bitmap(bs, sector_num, nb_sectors, 1); } -- 1.7.10.1