Re: [Qemu-devel] [PATCH 8/9] blockdev: add x-blockdev-set-iothread testing command

[Eric Blake <eblake@redhat.com>]

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On 12/05/2017 04:41 AM, Stefan Hajnoczi wrote:
> Currently there is no easy way for iotests to ensure that a BDS is bound
> to a particular IOThread.  Normally the virtio-blk device calls
> blk_set_aio_context() when dataplane is enabled during guest driver
> initialization.  This never happens in iotests since -machine
> accel=qtest means there is no guest activity (including device driver
> initialization).
> 
> This patch adds a QMP command to explicitly assign IOThreads in test
> cases.  See qapi/block-core.json for a description of the command.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---

> +##
> +# @x-blockdev-set-iothread:
> +#
> +# Move @node and its children into the @iothread.  If @iothread is empty then
> +# move @node and its children into the main loop.
> +#
> +# The node must not be attached to a BlockBackend.
> +#
> +# @node-name: the name of the block driver node
> +#
> +# @iothread: the name of the IOThread object
> +#

> +# 2. Move a node into the main loop
> +# -> { "execute": "x-blockdev-set-iothread",
> +#      "arguments": { "node-name": "disk1",
> +#                     "iothread": "" } }

Eww. Special casing of the empty string.  Would it be better design to
have iothread be optional, and to omit it to move a node into the main
loop?  Or use the StrOrNull type to allow JSON null instead of "" to
mean the main loop?

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


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