block: save page offset gaps in cloned bio

block: save page offset gaps in cloned bio

The cloned bio needs to inherit the accumulated gaps between vectors so
that we can know if this bio can subscribe to the iova coalescing
optimization.

When cloning for a split, the gap only applies to the front bio since
that's as far as has been processed. The remaining bio can reset its
gaps to 0 since it advanced past the checked vectors, and will start its
accounting from there on the next split check.

Fixes: 2f6b2565d43c ("block: accumulate memory segment gaps per bio")
Reported-by: Eric Auger <eauger@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20260819154937.3903312-1-kbusch@meta.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>