On Tue, Mar 09, 2021 at 12:37:35AM +0900, Akihiko Odaki wrote: > 2021年3月9日(火) 0:17 Stefan Hajnoczi <stefa...@redhat.com>: > > > > The live migration compatibility issue is still present. Migrating to > > another host might not work if the block limits are different. > > > > Here is an idea for solving it: > > > > Modify include/hw/block/block.h:DEFINE_BLOCK_PROPERTIES_BASE() to > > support a new value called "host". The default behavior remains > > unchanged for live migration compatibility but now you can use "host" if > > you know it's okay but don't care about migration compatibility. > > > > The downside to this approach is that users must explicitly say > > something like --drive ...,opt_io_size=host. But it's still better than > > the situation we have today where user must manually enter values for > > their disk. > > > > Does this sound okay to everyone? > > > > Stefan > > I wonder how that change affects other block drivers implementing > bdrv_probe_blocksizes. As far as I know, the values they report are > already used by default, which is contrary to the default not being > "host".
The behavior should remain unchanged for existing QEMU command-lines. The block drivers that report values by default should continue to do so: block/file-posix.c: only reports values for s390 DASD devices. block/nvme.c: reports the NVMe PCI adapter's values. block/raw-format.c: propagates its child's values unless the "offset" option is incompatible with them. These block drivers would default to logical_block_size=host and physical_block_size=host, while other block drivers would not. Stefan
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