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Subject: Re: [virtio] Re: [virtio-comment] Problems with VIRTIO-4 and writeback only disks
Il 16/09/2013 03:34, Rusty Russell ha scritto: >> > The default WCE=0 semantics should be that the host ensures every write >> > reaches stable storage. > Here's the problem: I don't think anyone will really implement this. > > lguest certainly doesn't flush every write, not bhyve. Xen famously > didn't. I can't see where qemu does it either, but it could be buried > in the aio stuff? > It's here in block.c's bdrv_co_do_writev: if (ret < 0) { /* Do nothing, write notifier decided to fail this request */ } else if (flags & BDRV_REQ_ZERO_WRITE) { ret = bdrv_co_do_write_zeroes(bs, sector_num, nb_sectors); } else { ret = drv->bdrv_co_writev(bs, sector_num, nb_sectors, qiov); } if (ret == 0 && !bs->enable_write_cache) { ret = bdrv_co_flush(bs); } Paolo
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