On 01.05.2012 12:27, Stefan Hajnoczi wrote: > On Mon, Apr 30, 2012 at 4:52 PM, Michael Tokarev <m...@tls.msk.ru> wrote: >> This value is used currently for virtio-blk only. It was defined >> as uint16_t before, which is the same as in kernel<=>user interface >> (in virtio_blk.h, struct virtio_blk_config). But the problem is >> that in kernel<=>user interface the units are sectors (which is >> usually 512 bytes or more), while in qemu it is in bytes. However, >> for, say, md raid5 arrays, it is typical to have actual min_io_size >> of a host device to be large. For example, for raid5 device of >> 3 drives with 64Kb chunk size, that value will be 128Kb, which does >> not fit in a uint16_t anymore. >> >> Increase the value size from 16bits to 32bits for now. >> >> But apparently, the kernel<=>user interface needs to be fixed too >> (while it is much more difficult due to compatibility issues), >> because even with 512byte units, the 16bit value there will overflow >> too with quite normal MD RAID configuration. >> >> Signed-off-by: Michael Tokarev <m...@tls.msk.ru> >> --- >> block.h | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) > > Which kernel<=>user interface?
struct virtio_blk_config in virtio_blk.h, which is used to pass information about block device from (qemu) userspace to guest kernel. Besides, it appears that at least minimum_io_size is not used anywhere in the kernel, -- so, for example, filesystems does not directly benefit from seeing this information. But mkfs.xfs do use it. > Reviewed-by: Stefan Hajnoczi <stefa...@linux.vnet.ibm.com> Thanks, /mjt
