The block layer has supported 64-bit block status from drivers since
commit 86a3d5c688 ("block: Add .bdrv_co_block_status() callback",
v2.12) and friends, with individual driver callbacks responsible for
capping things where necessary. Artificially capping things below 2G
in the qemu-io 'map' command, added in commit d6a644bbfe ("block: Make
bdrv_is_allocated() byte-based", v2.10) is thus no longer necessary.
One way to test this is with qemu-nbd as server on a raw file larger
than 4G (the entire file should show as allocated), plus 'qemu-io -f
raw -c map nbd://localhost --trace=nbd_\*' as client. Prior to this
patch, the NBD_CMD_BLOCK_STATUS requests are fragmented at 0x7ffffe00
distances; with this patch, the fragmenting changes to 0x7fffffff
(since the NBD protocol is currently still limited to 32-bit
transactions - see block/nbd.c:nbd_client_co_block_status). Then in
later patches, once I add an NBD extension for a 64-bit block status,
the same map command completes with just one NBD_CMD_BLOCK_STATUS.
Signed-off-by: Eric Blake<eblake@redhat.com>