Re: [Qemu-devel] [PATCH] hostmem-file: add a property 'notrunc' to avoid data corruption

[Eduardo Habkost]

On Thu, Oct 20, 2016 at 02:34:12PM +0200, Igor Mammedov wrote:
> On Thu, 20 Oct 2016 14:13:01 +0800
> Haozhong Zhang <address@hidden> 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. But I agree we should: 1) make 'size' optional as
you suggested; 2) never truncate the file to a smaller size.

-- 
Eduardo