On Thu, 20 Oct 2016 13:15:31 -0200 Eduardo Habkost <ehabk...@redhat.com> wrote:
> On Thu, Oct 20, 2016 at 04:17:35PM +0200, Igor Mammedov wrote: > > On Thu, 20 Oct 2016 11:47:18 -0200 > > Eduardo Habkost <ehabk...@redhat.com> wrote: > > > > > On Thu, Oct 20, 2016 at 09:33:53PM +0800, Haozhong Zhang wrote: > > > > On 10/20/16 11:21 -0200, Eduardo Habkost wrote: > > > > > On Thu, Oct 20, 2016 at 02:34:12PM +0200, Igor Mammedov wrote: > > > > > > On Thu, 20 Oct 2016 14:13:01 +0800 > > > > > > Haozhong Zhang <haozhong.zh...@intel.com> wrote: > > > > > > > > > > > > > If a file is used as the backend of memory-backend-file and its > > > > > > > size is > > > > > > > not identical to the property 'size', the file will be truncated. > > > > > > > For a > > > > > > > file used as the backend of vNVDIMM, its data is expected to be > > > > > > > persistent and the truncation may corrupt the existing data. > > > > > > I wonder if it's possible just skip 'size' property in your case > > > > > > instead > > > > > > 'notrunc' property. That way if size is not present one'd get > > > > > > actual size > > > > > > using get_file_size() and set 'size' to it? > > > > > > And if 'size' is provided and 'size' != file_size then error out. > > > > > > > > > > > > > > > > I think it is valid to start with a zero-size file and then let > > > > > QEMU extend it. > > > > > > > > For vNVDIMM, extending from zero-size file can be valid when a file is > > > > first used. However, it's not valid for the second and following use > > > > of the same file. > > > > > > > > > But I agree we should: 1) make 'size' optional as > > > > > you suggested; 2) never truncate the file to a smaller size. > > > > > > > > > > > > > I will add another patch for this. Is there any way in QEMU to decide > > > > whether a memory-backend-file object is used for vNVDIMM when the > > > > object is being created? Or 'size' can be optional for all kinds of > > > > usages? > > > > > > I believe 'size' can be optional for all usage, because at the > > > moment the memory allocation code asks the backend for a memory > > > region, it is supposed to know desired RAM size from the frontend > > > configuration (-numa, -m, or "size" property of pc-dimm). > > > > nope, currently the size propagates other way around > > from back-end to front-end and not backwards > > I'd say that this is a bug. Frontend size is guest ABI and > shouldn't be overridden by backend configuration if it's > explicitly set. frontend.size is always <= backend.size allocation specified when backend is created (-object/object_add) and front end size if needed/used is <= backend size so far code followed this design.
