Re: quick hack to support "option VIMAGE" on USB Ethernet

On Sun, Feb 16, 2014 at 2:20 AM, Hiroo Ono (小野寛生) <
hiroo.ono+freebsd_at_gmail.com> wrote:

> Hello,
>
> The problem of USB ethernet device with VIMAGE kernel still remains
> with 10.0-RELEASE and I think I have found the reason and a fix.
>
> I have filed a patch and backtrace as a followup to the PR
> http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/183835
>
> I will repeat the explanation here.
> The problem occur when ue_attach_post_task() (in
> sys/dev/usb/net/usb_ethernet.c) is called.
>
> ue_attach_post_task() calls if_alloc() (in sys/net/if.c)
> and ether_attach() (in sys/net/if_ethersubr.c), which finally refer
> V_if_index.
>
> The problem is that curvnet is NULL when ue_attach_post_task()
> is invoked, and with VIMAGE, V_if_index is defined to
>         VNET(if_index)  => VNET_VNET(curvnet, if_index)
>                         => (*VNET_VNET_PTR((curvnet), if_index))
>                         => (*_VNET_PTR((curvnet)->vnet_data_base,
> if_index))
>         and so on.
>
> For device attach, the following code in device_probe_and_attach()
> (in kern/subr_bus.c)
>
>         CURVNET_SET_QUIET(vnet0);
>         error = device_attach(dev);
>         CURVNET_RESTORE();
>
> should assign curvnet to vnet0, but it is not the case for ue device.
>
> As an example of USB ethernet device, with if_axe, device_attach(dev)
> is axe_attach() (in sys/dev/usb/net/if_axe.c).
> axe_attach() calls uether_ifattach() (in sys/dev/usb/net/usb_ethernet.c)
> (other USB ethernet devices' *_attach() also call this function),
> which *queues* (not calls) ue_attach_post_task().
> As ue_attach_post_task is called from usb_process (not from
> uther_ifattach),
> it is not assured that curvnet is properly assigned.
>


Well done!  Your analysis of the problem was very good!
I committed the patch, and will MFC in about a week.

--
Craig