From ca716364f045da710ddef7fc6420bd6760e45b56 Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Thu, 10 Nov 2011 18:13:59 +0100 Subject: [PATCH] block: Make cache=unsafe flush to the OS cache=unsafe completely ignored bdrv_flush, because flushing the host disk costs a lot of performance. However, this means that qcow2 images (and potentially any other format) can lose data even after the guest has issued a flush if the qemu process crashes/is killed. In case of a host crash, data loss is certainly expected with cache=unsafe, but if just the qemu process dies this is a bit too unsafe. Now that we have two separate flush functions, we can choose to flush everythign to the OS, but don't enforce that it's physically written to the disk. Signed-off-by: Kevin Wolf --- block.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/block.c b/block.c index b1a462956f..86910b046c 100644 --- a/block.c +++ b/block.c @@ -2791,12 +2791,11 @@ int coroutine_fn bdrv_co_flush(BlockDriverState *bs) { int ret; - if (bs->open_flags & BDRV_O_NO_FLUSH) { - return 0; - } else if (!bs->drv) { + if (!bs->drv) { return 0; } + /* Write back cached data to the OS even with cache=unsafe */ if (bs->drv->bdrv_co_flush_to_os) { ret = bs->drv->bdrv_co_flush_to_os(bs); if (ret < 0) { @@ -2804,6 +2803,11 @@ int coroutine_fn bdrv_co_flush(BlockDriverState *bs) } } + /* But don't actually force it to the disk with cache=unsafe */ + if (bs->open_flags & BDRV_O_NO_FLUSH) { + return 0; + } + if (bs->drv->bdrv_co_flush_to_disk) { return bs->drv->bdrv_co_flush_to_disk(bs); } else if (bs->drv->bdrv_aio_flush) {