From dbc7b01492371e4a54b92d2b6d968f9b863cc794 Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Tue, 27 Oct 2020 00:05:55 -0500 Subject: nbd: Add 'qemu-nbd -A' to expose allocation depth Allow the server to expose an additional metacontext to be requested by savvy clients. qemu-nbd adds a new option -A to expose the qemu:allocation-depth metacontext through NBD_CMD_BLOCK_STATUS; this can also be set via QMP when using block-export-add. qemu as client is hacked into viewing the key aspects of this new context by abusing the already-experimental x-dirty-bitmap option to collapse all depths greater than 2, which results in a tri-state value visible in the output of 'qemu-img map --output=json' (yes, that means x-dirty-bitmap is now a bit of a misnomer, but I didn't feel like renaming it as it would introduce a needless break of back-compat, even though we make no compat guarantees with x- members): unallocated (depth 0) => "zero":false, "data":true local (depth 1) => "zero":false, "data":false backing (depth 2+) => "zero":true, "data":true libnbd as client is probably a nicer way to get at the information without having to decipher such hacks in qemu as client. ;) Signed-off-by: Eric Blake Message-Id: <20201027050556.269064-11-eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy --- nbd/server.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'nbd') diff --git a/nbd/server.c b/nbd/server.c index ebbefcb6d3..d145e1a690 100644 --- a/nbd/server.c +++ b/nbd/server.c @@ -1641,6 +1641,8 @@ static int nbd_export_create(BlockExport *blk_exp, BlockExportOptions *exp_args, bdrv_dirty_bitmap_set_busy(exp->export_bitmaps[i], true); } + exp->allocation_depth = arg->allocation_depth; + blk_add_aio_context_notifier(blk, blk_aio_attached, blk_aio_detach, exp); QTAILQ_INSERT_TAIL(&exports, exp, next); -- cgit v1.2.3-55-g7522