On Thu, Oct 20, 2016 at 03:47:32PM +0200, Igor Mammedov wrote: > On Thu, 20 Oct 2016 21:33:53 +0800 > Haozhong Zhang <haozhong.zh...@intel.com> 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. > I'd avoid 0 sized backend files and enforce non 0 size value > with exact match to actual file size. i.e. let mgmt side take care of > proper backend file allocation.
This would break compatibility with existing setups that rely on the ftruncate() behavior. -- Eduardo
