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Re: [Qemu-trivial] [Qemu-devel] [RFC PATCH 4/4] qemu-options: Do not sho

From: Thomas Huth
Subject: Re: [Qemu-trivial] [Qemu-devel] [RFC PATCH 4/4] qemu-options: Do not show -enable-kvm and -enable-hax in the docs anymore
Date: Wed, 13 Jun 2018 17:11:51 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0

On 13.06.2018 15:44, Daniel P. Berrangé wrote:
> On Wed, Jun 13, 2018 at 02:38:40PM +0100, Stefan Hajnoczi wrote:
>> On Wed, Jun 13, 2018 at 07:05:21AM +0200, Thomas Huth wrote:
>>> We've got three ways of enabling an accelerator: -machine accel=xyz,
>>> -accel xyz and -enable-xyz. For new QEMU users, this must be very
>>> confusing ("Which one do I have to use? Is there a difference between
>>> the options?"). While -enable-kvm was useful in the past, there is no
>>> real good reason for using it anymore today ("-accel kvm" is even less
>>> to type than "-enable-kvm"), so let's decrease the confusing amount of
>>> options in our documenation a little bit by removing the -enable-xyz
>>> here. Note that the option itself is neither removed nor marked as
>>> deprecated - since -enable-kvm is likely used in a lot of scripts and
>>> since its code is easy to maintain, we should keep it around to avoid
>>> to break old setups.
>>> Signed-off-by: Thomas Huth <address@hidden>
>>> ---
>>>  PS: I guess Paolo won't like this patch ... let's try it anyway ;-)
>> It's widely used and we're removing the documentation for it?!  That is
>> likely to cause issues for new users who refer to the man page to
>> understand the QEMU command-lines they see online, in scripts, etc.
> Agreed, this is a very bad idea. Any option that is accepted by QEMU,
> but not documented is a bug that must be fixed. IOW removing docs
> is creating bugs.

Not documenting unliked options that are still kept for compatibility
was at least a common practice in the past (see -no-kvm for example, or
many of those deprecated options like -net channel that have been
removed in the past year).

> If we want to help users understand why we have -enable-kvm, just
> make the docs say that it is syntactic for '-machine accel=kvm'.
> Users can decide for themselves whether they want to switch to
> the more verbose way or not

Uh, well, in this case "-enable-kvm" is already the more verbose way:
"-accel kvm" is shorter :-)

It's just a big mess: We've got -enable-kvm, -enable-hax, but there is
no -enable-hvf, -enable-whpx or -enable-xen option. And to force TCG
mode, you've got to use -no-kvm ... honestly, if I were a new user, I'd
simply say: WTF!?!

But ok, since -enable-kvm has such a big tradition and is used in a lot
of examples out there, it's likely really better if we keep it in the
documentation. But we should either move it to a "obsolete option"
chapter, or update the current documentation with some words like
"obsolete" or "legacy" (to make it clear that nobody gets the idea of
introducing -enable-hvf or other similar options in the future).

And what about -enable-hax? That hardly has any tradtion. Should we
maybe even deprecate it?


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