Re: [Qemu-devel] [PATCH] increase BlockConf.min_io_size type from uint16_t to uint32_t

[Stefan Hajnoczi]

On Mon, Apr 30, 2012 at 4:52 PM, Michael Tokarev <address@hidden> 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 <address@hidden>
> ---
>  block.h |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

Which kernel<=>user interface?

Reviewed-by: Stefan Hajnoczi <address@hidden>