On Wed, Feb 12, 2020 at 03:44:19PM -0600, Eric Blake wrote: > On 2/11/20 5:54 AM, Roman Kagan wrote: > > Devices (virtio-blk, scsi, etc.) and the block layer are happy to use > > 32-bit for logical_block_size, physical_block_size, and min_io_size. > > However, the properties in BlockConf are defined as uint16_t limiting > > the values to 32768. > > > > This appears unnecessary tight, and we've seen bigger block sizes handy > > at times. > > What larger sizes? I could see 64k or maybe even 1M block sizes,...
We played exactly with these two :) > > > > Make them 32 bit instead and lift the limitation. > > > > Signed-off-by: Roman Kagan <rvka...@yandex-team.ru> > > --- > > hw/core/qdev-properties.c | 21 ++++++++++++--------- > > include/hw/block/block.h | 8 ++++---- > > include/hw/qdev-properties.h | 2 +- > > 3 files changed, 17 insertions(+), 14 deletions(-) > > > > diff --git a/hw/core/qdev-properties.c b/hw/core/qdev-properties.c > > index 7f93bfeb88..5f84e4a3b8 100644 > > --- a/hw/core/qdev-properties.c > > +++ b/hw/core/qdev-properties.c > > @@ -716,30 +716,32 @@ const PropertyInfo qdev_prop_pci_devfn = { > > /* --- blocksize --- */ > > +#define MIN_BLOCK_SIZE 512 > > +#define MAX_BLOCK_SIZE 2147483648 > > ...but 2G block sizes are going to have tremendous performance problems. > > I'm not necessarily opposed to the widening to a 32-bit type, but think you > need more justification or a smaller number for the max block size, I thought any smaller value would just be arbitrary and hard to reason about, so I went ahead with the max value that fit in the type and could be made visibile to the guest. Besides this is a property that is set explicitly, so I don't see a problem leaving this up to the user. > particularly since qcow2 refuses to use cluster sizes larger than 2M and it > makes no sense to allow a block size larger than a cluster size. This still doesn't contradict passing a bigger value to the guest, for experimenting if nothing else. Thanks, Roman.