Re: [PATCH 3/3] nbd: Add 'qemu-nbd -A' to expose allocation depth

[Vladimir Sementsov-Ogievskiy]

25.09.2020 23:32, Eric Blake wrote:
> 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 nbd-server-add.
>
> qemu as client can be hacked into viewing this new context by using
> the now-misnamed x-dirty-bitmap option when creating an NBD blockdev;

may be rename it to x-block-status ?

> although it is worth noting the decoding of how such context
> information will appear in 'qemu-img map --output=json':
>
> NBD_STATE_DEPTH_UNALLOC => "zero":false, "data":true
> NBD_STATE_DEPTH_LOCAL => "zero":false, "data":false
> NBD_STATE_DEPTH_BACKING => "zero":true, "data":true

It wouldn't be so simple if we decide to export exact depth number..


--
Best regards,
Vladimir