On Fri, Sep 25, 2020 at 03:32:49PM -0500, 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;
> 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
>
> libnbd as client is probably a nicer way to get at the information
> without having to decipher such hacks in qemu as client. ;)
I've been meaning to add extents information to nbdinfo, or
perhaps a new tool ("nbdmap").
Rich.
--
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