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.
>
> A property 'notrunc' is added to memory-backend-file to allow users to
> control the truncation. If 'notrunc' is on, QEMU will not truncate the
> backend file and require the property 'size' is not larger than the file
> size. If 'notrunc' is off, QEMU will behave as before.
[...]
>
> #ifdef __linux__
> +static uint64_t get_file_size(const char *path, Error **errp)
Maybe QEMU laredy has an utility to do it that could be shared,
CCing block maintainers.
> +{
> + int fd;
> + struct stat st;
> + uint64_t size = 0;
> + Error *local_err = NULL;
> +
> + fd = qemu_open(path, O_RDONLY);
> + if (fd < 0) {
> + error_setg(&local_err, "cannot open file");
error_setg_errno
> + goto out;
> + }
> +
> + if (stat(path, &st)) {
fstat()
> + error_setg(&local_err, "cannot get file stat");
error_setg_errno
> + goto out_fclose;
> + }
> +
> + switch (st.st_mode & S_IFMT) {
> + case S_IFREG:
> + size = st.st_size;
> + break;
> +
> + case S_IFBLK:
> + if (ioctl(fd, BLKGETSIZE64, &size)) {
compilation might fail on platforms without BLKGETSIZE64,
> + error_setg(&local_err, "cannot get size of block device");
error_setg_errno
> + size = 0;
> + }
> + break;
> +
> + default:
> + error_setg(&local_err,
> + "only block device on Linux and regular file are
> supported");
what about huge page usecase, would it fall right here fail?
> + }
> +
> + out_fclose:
> + close(fd);
> + out:
> + error_propagate(errp, local_err);
> + return size;
> +}
> +
[...]
