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Re: Question about debugging mac80211 without printk

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On 25 September 2014 18:54, Pink <pink@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> Hi,
>
> actually if have the following problem, if have a lot of debug messages
> using printk inside the mac layer but if there is a
> critical bug in the source code of the mac80211 module
> the system goes into kernel panic state during execution. Unfortunately so
> far i now, it isn't possible
> after a system restart to identify the rough position of the bug looking for
> the debug msg's written before the bug has occured in
> dmesg or syslog because the messages were not saved in follow of the crash.
>
> Now i thought user mode linux (uml) is maybe a potential solution to
> identify the bug, if the kernel running the mac layer
> is executed as virtual machine in uml. But i didn't found any kind of
> description how to forward the physical wireless card except using TAP/TUN
> device to the vm so
> that the kernel inside the vm can run its mac layer directly on the card.
>
> Now my question what tools are you use for the development and testing of
> the ath wireless driver
> as well as the complete wireless stack including mac80211. Is it user mode
> linux or something else?
> If user mode linux is used, is there any howto available to forward the
> atheros card to the vm.

You can try using KVM and pass through devices to a virtual machine.
Passing USB through has no extra requirements albeit from my
experience some USB controllers and USB devices have some issues
sometimes. PCI pass-through requires VT-d or AMD-v to be supported on
both CPU and motherboard.

I actually use this kind of setup (I'm using QEMU) myself. I can
attach gdb, emulate serial console, pass-through rootfs via 9p and
just boot a kernel in the VM omitting bootloader which is really
convenient. If it crashes I can get pretty much all info I need.


Michał
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