Re: [PATCH] block: add blockdev-attach QMP command

[Kevin Wolf <kwolf@redhat.com>]

Am 15.04.2026 um 19:39 hat mr-083 geschrieben:
> Add a blockdev-attach QMP command that attaches a block driver state
> tree to a device's block backend.  Unlike blockdev-insert-medium, this
> works for non-removable devices such as NVMe namespaces.
> 
> After drive_del removes a device's backing store, the BlockBackend
> remains attached to the guest device but has no BlockDriverState.
> blockdev-attach reconnects a block node (previously created with
> blockdev-add) to the device's BlockBackend via blk_insert_bs().
> 
> This separates the two concerns as recommended: blockdev-add creates
> the block node, blockdev-attach associates it with the device.
> 
> Example usage with NVMe namespace hot-swap:
>   drive_del drv0
>   blockdev-add node-name=node0 driver=qcow2 file.driver=file \
>                file.filename=disk.qcow2
>   blockdev-attach id=ns0 node-name=node0

Is the intended functionality the same as the following?

   blockdev-add node-name=node0 driver=qcow2 file.driver=file \
                file.filename=disk.qcow2
   qom-set path=ns0 property=drive value=node0
   drive-del drv0 / blockdev-del node-name=old-node

This seems cleaner because there is no window where the namespace
isn't backed by any block node.

If this does what you want, it's unclear to me if we want a separate QMP
command to do the same in a maybe more discoverable way. Markus, do we
have precedence for this?

> An HMP wrapper is included for convenience.

An HMP convenience command mapping to qom-set should still be possible
either way.

Kevin