On 13.08.20 18:29, Kevin Wolf wrote:
> Instead of implementing qemu-nbd --offset in the NBD code, just put a
> raw block node with the requested offset on top of the user image and
> rely on that doing the job.
> 
> This does not only simplify the nbd_export_new() interface and bring it
> closer to the set of options that the nbd-server-add QMP command offers,
> but in fact it also eliminates a potential source for bugs in the NBD
> code which previously had to add the offset manually in all relevant
> places.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  include/block/nbd.h |  4 ++--
>  blockdev-nbd.c      |  9 +--------
>  nbd/server.c        | 34 +++++++++++++++++-----------------
>  qemu-nbd.c          | 27 ++++++++++++---------------
>  4 files changed, 32 insertions(+), 42 deletions(-)

[...]

> diff --git a/nbd/server.c b/nbd/server.c
> index 774325dbe5..92360d1f08 100644
> --- a/nbd/server.c
> +++ b/nbd/server.c

[...]

> @@ -1569,7 +1574,7 @@ NBDExport *nbd_export_new(BlockDriverState *bs, uint64_t dev_offset,
>          exp->nbdflags |= (NBD_FLAG_SEND_TRIM | NBD_FLAG_SEND_WRITE_ZEROES |
>                            NBD_FLAG_SEND_FAST_ZERO);
>      }
> -    assert(size <= INT64_MAX - dev_offset);
> +    assert(size <= INT64_MAX);

Forgot to note: I think we can drop this assertion altogether now.

Max