[dpdk-dev] [RFC] kernel paramters like DPDK CLI options

[Yuanhan Liu]

Hi all,

I guess we (maybe just me :) have stated few times something like
"hey, this kind of stuff is good to have, but you are trying to
add an EAL CLI option for a specific subsystem/driver, which is
wrong".

One recent example that is still fresh in my mind is the one from
Christian [0], that he made a proposal to introduce two new EAL
options, --vhost-owner and --vhost-perm, to configure the vhost
user socket file permission.

    [0]: http://dpdk.org/ml/archives/dev/2016-April/037948.html

Another example is the one I met while enabling virtio 1.0 support.
QEMU has the ability to support both virtio 0.95 (legacy) and 1.0
(modern) at the same time for one virtio device, therefore, we
could either use legacy driver or modern driver to operate the
device. However, the current logic is we try with modern driver
first, and then legacy driver if it failed. In above case, we will
never hit the legacy driver. But sometimes, it's nice to let it
force back to the legacy driver, say, for debug or compare purpose.

Apparently, adding a new EAL option like "--force-legacy" looks
wrong.

The generic yet elegant solution I just thought of while having
lunch is to add a new EAL option, say, --extra-options, where we
could specify driver/subsystem specific options. As you see, it's
nothing big deal, it just looks like Linux kernel parameters.

Take above two cases as example, it could be:

    --extra-options "vhost-owner=kvm:kvm force-legacy"

Note that those options could also be delimited by comma.

DPDK EAL then will provide some generic helper functions to get
and parse those options, and let the specific driver/subsystem
to invoke them to do the actual parse and do the proper action
when some option is specified, say, virtio PMD driver will force
back to legacy driver when "force-legacy" is given.

Comments? Makes sense to you guys, or something nice to have?

	--yliu