Re: [PATCH v4] qapi: net: deprecate vhostforce option

[Markus Armbruster <armbru@redhat.com>]

Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> writes:

> On 16.10.25 11:48, Markus Armbruster wrote:
>> Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> writes:
>> 
>>> This option for tap and vhost-user netdevs doesn't make sense
>>> since long ago (10 years!), starting from commits:
>>>
>>>   1e7398a140f7a6 ("vhost: enable vhost without without MSI-X")
>>>   24f938a682d934 ("vhost user:support vhost user nic for non msi guests")
>>>
>>> Prior these commits, to enable kernel vhost-net, or vhost-user-net for
>>> some specific kind of guests (that don't have MSI-X support), you should
>>> have set vhostforce=on.
>>>
>>> Now guest type doesn't matter, all guests are equal for these
>>> options logic.
>>>
>>> For tap the current logic is:
>>>    vhost=on / vhost=off : vhostforce ignored, doesn't make sense
>>>    vhost unset : vhostforce counts, enabling vhost
>>>
>>> So you may enable vhost for tap several ways:
>>> - vhost=on
>>> - vhostforce=on
>>> - vhost=on + vhostforce=on
>>> - and even vhost=on + vhostforce=off
>>>
>>> - they are all equal.
>>>
>>> For vhost-user we simply ignore the vhostforce option at all in the
>>> code.
>>>
>>> Let's finally deprecate the extra options.
>>>
>>> Also, fix @vhostforce documentation everywhere to show the real picture,
>>> and update vhost-user test to not use deprecated option.
>>>
>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>

[...]

>>> diff --git a/qemu-options.hx b/qemu-options.hx
>>> index 0223ceffeb..35a70096e8 100644
>>> --- a/qemu-options.hx
>>> +++ b/qemu-options.hx
>>> @@ -2882,7 +2882,7 @@ DEF("netdev", HAS_ARG, QEMU_OPTION_netdev,
>>>  #else
>>>      "-netdev tap,id=str[,fd=h][,fds=x:y:...:z][,ifname=name][,script=file][,downscript=dfile]\n"
>>>      "         [,br=bridge][,helper=helper][,sndbuf=nbytes][,vnet_hdr=on|off][,vhost=on|off]\n"
>>> -    "         [,vhostfd=h][,vhostfds=x:y:...:z][,vhostforce=on|off][,queues=n]\n"
>>> +    "         [,vhostfd=h][,vhostfds=x:y:...:z][,queues=n]\n"
>>>      "         [,poll-us=n]\n"
>>>      "                configure a host TAP network backend with ID 'str'\n"
>>>      "                connected to a bridge (default=" DEFAULT_BRIDGE_INTERFACE ")\n"
>>> @@ -2898,9 +2898,7 @@ DEF("netdev", HAS_ARG, QEMU_OPTION_netdev,
>>>      "                default is disabled 'sndbuf=0' to enable flow control set 'sndbuf=1048576')\n"
>>>      "                use vnet_hdr=off to avoid enabling the IFF_VNET_HDR tap flag\n"
>>>      "                use vnet_hdr=on to make the lack of IFF_VNET_HDR support an error condition\n"
>>> -    "                use vhost=on to enable experimental in kernel accelerator\n"
>>> -    "                    (only has effect for virtio guests which use MSIX)\n"
>>> -    "                use vhostforce=on to force vhost on for non-MSIX virtio guests\n"
>>> +    "                use vhost=on to enable in kernel accelerator\n"
>> 
>> So the kernel's accelerator is no longer experimental?
>
> Reading this, I heard the first time that vhost-net is experimental.
> It's about 15 years old, and used in production. I think "experimental"
> is inappropriate word here)

Just double-checking :)

The text you adjust is from 2010 (commit 82b0d80ef6a).  I guess the
accelerator was experimental back then.

Mention the correction in the commit message?

[...]