Re: [Qemu-devel] [PATCH v1 4/4] vhost-user: Add new option to specify vhost-user backend features

[Eric Blake]

On 05/28/2015 10:42 PM, Tetsuya Mukawa wrote:
> This patch adds below '-net' options to let QEMU know which features
> vhost-user backend will support.

[meta-comment: when posting a new revision of a series, do it as a new
top-level thread rather than buried in-reply-to an earlier version]

> If above features are specified, QEMU assumes vhost-user backend supports
> the features, then QEMU can start without vhost-user backend connection.
> (While no connection, link status of virtio-net device will be down)
> 

> 
> When connection between QEMU and the backend is established, QEMU checkes 
> feature

s/checkes/checks/

> values of the backend to make sure the expected features are provided.
> If it doesn't, the connection will be closed by QEMU.
> 
> Signed-off-by: Tetsuya Mukawa <address@hidden>
> ---

> +++ b/qapi-schema.json
> @@ -2241,25 +2241,29 @@
>  #
>  # @vhostforce: #optional vhost on for non-MSIX virtio guests
>  #
> +# @backend_features: #optional feature flag to support vhost user backend
> +#                    (Since 2.4)
> +#

s/backend_features/backend-features/

(we document that qapi should prefer - over _ unless there is a
consistency issue with _ already used in the struct)


> @@ -2444,12 +2448,92 @@
>  #
>  # @vhostforce: #optional vhost on for non-MSIX virtio guests (default: 
> false).
>  #
> +# @backend_csum: #optional feature backend supports (default: false).
> +#                (Since 2.4)

Again, s/_/-/ throughout this struct.

> +#
> +# @backend_mq: #optional feature backend supports (default: false).
> +#              (Since 2.4)

A lot of identical descriptions. Might be worth more specific text to
each option; for example,
 @backend_mq: #optional: True if backend supports multiqueue feature
(default: false). (Since 2.4)


> +++ b/qemu-options.hx
> @@ -1467,6 +1467,15 @@ DEF("netdev", HAS_ARG, QEMU_OPTION_netdev,
>      "-netdev 
> tap,id=str[,fd=h][,fds=x:y:...:z][,ifname=name][,script=file][,downscript=dfile]\n"
>      "         
> [,helper=helper][,sndbuf=nbytes][,vnet_hdr=on|off][,vhost=on|off]\n"
>      "         
> [,vhostfd=h][,vhostfds=x:y:...:z][,vhostforce=on|off][,queues=n]\n"
> +    "         
> [,backend_csum=on|off][,backend_guest_csum=on|off][,backend_gso=on|off]\n"
> +    "         [,backend_guest_tso4=on|off][,backend_guest_tso6=on|off]\n"
> +    "         [,backend_guest_ecn=on|off][,backend_guest_ufo=on|off]\n"
> +    "         [,backend_guest_announce=on|off][,backend_host_tso4=on|off]\n"
> +    "         [,backend_host_tso6=on|off][,backend_host_ecn=on|off]\n"
> +    "         
> [,backend_host_ufo=on|off][,backend_mrg_rxbuf=on|off][,backend_status=on|off]\n"
> +    "         
> [,backend_ctrl_vq=on|off][,backend_ctrl_vx=on|off][,backend_ctrl_vlan=on|off]\n"
> +    "         
> [,backend_ctrl_rx_extra=on|off][,backend_ctrl_mac_addr=on|off]\n"
> +    "         [,backend_ctrl_guest_offloads=on|off][,backend_mq=on|off]\n"
>      "                configure a host TAP network backend with ID 'str'\n"
>      "                use network scripts 'file' (default=" 
> DEFAULT_NETWORK_SCRIPT ")\n"
>      "                to configure it and 'dfile' (default=" 
> DEFAULT_NETWORK_DOWN_SCRIPT ")\n"
> @@ -1486,6 +1495,7 @@ DEF("netdev", HAS_ARG, QEMU_OPTION_netdev,
>      "                use 'vhostfd=h' to connect to an already opened vhost 
> net device\n"
>      "                use 'vhostfds=x:y:...:z to connect to multiple already 
> opened vhost net devices\n"
>      "                use 'queues=n' to specify the number of queues to be 
> created for multiqueue TAP\n"
> +    "                use 'backend_*=on' to specify virtio-net feature that 
> vhost-user backend supports\n"

Bikeshedding: Rather than having a lot of booleans, I wonder if it would
be better to have an array of flag names.  That is, in QMP form, this
would select three features (and leave the others off)

'backend-features':[ 'csum', 'guest-csum', gso' ]

although I'm not sure on how that would best translate to the command line.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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