btrfs: don't rely on unchanging ->bi_bdev for zone append remaps

btrfs: don't rely on unchanging ->bi_bdev for zone append remaps

btrfs_record_physical_zoned relies on a bio->bi_bdev samples in the
bio_end_io handler to find the reverse map for remapping the zone append
write, but stacked block device drivers can and usually do change bi_bdev
when sending on the bio to a lower device.  This can happen e.g. with the
nvme-multipath driver when a NVMe SSD sets the shared namespace bit.

But there is no real need for the bdev in btrfs_record_physical_zoned,
as it is only passed to btrfs_rmap_block, which uses it to pick the
mapping to report if there are multiple reverse mappings.  As zone
writes can only do simple non-mirror writes right now, and anything
more complex will use the stripe tree there is no chance of the multiple
mappings case actually happening.

Instead open code the subset of btrfs_rmap_block in
btrfs_record_physical_zoned, which also removes a memory allocation and
remove the bdev field in the ordered extent.

Fixes: d8e3fb106f39 ("btrfs: zoned: use ZONE_APPEND write for zoned mode")
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David Sterba <dsterba@suse.com>