On Fri, 2015-11-13 at 12:33 +0300, Pavel Fedin wrote: > Hello! > > > > If we fix qemu, it will automatically start working with all > > > available kernels which are there in the wild. If we fix kernel, older > > > versions will still not work, however they can. > > > That's why i think that we should adapt qemu to what already exists. > > > But, well, you are The Boss, so you can just say "i don't care". So, > > > just let me now if you strongly disagree with this. > > > > I do care, in fact I care enough about the ABI that I'm suggesting what > > I think is the correct fix rather than taking the quick and dirty > > solution. It's an unfortunate bug, but it's not worth changing the ABI > > and removing the kernel's ability to indicate whether the pgsize bitmap > > field is valid IMO. > > Ok, i see your point... > But what about fix, which would work both with future kernels, which > do provide this flag, as well as would be compatible with already > existing kernels, which set flags == 0? > We could check for ((info.flags == 0) || (info.flags & > VFIO_IOMMU_INFO_PGSIZES)). This would conform to both behaviors: > a) All current kernels set flags = 0 and report page sizes. > b) Some future kernels could have set some flags, but not reported > page sizes and not set VFIO_IOMMI_PGSIZES > > What would you say about this? Yes, this would be a "workaround" > instead of "fix".
You haven't presented a compelling reason to do this. What is the case that you're thinking of that assuming PAGE_SIZE doesn't work or at least provide some degree of backwards compatibility? QEMU has been doing this all along. Thanks, Alex
