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. > > >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? > > Thanks, > Haozhong
