> While the kernel driver has no problem with hot-removal, I see that if I
> "unregister" our UIO driver in response to the removal, then the mapping for
> the hardware's physical memory would become "invalid" (done by UIO on
> unregsiter). This could possibly cause the user-space process to crash due to
> illegal memory access.
You should just get 0xff on the memory reads, right? You can catch the
signal for invalid memory accesses.
Wouldn't I get an illegal memory access, as UIO would've removed the mappings that it setup when I registered the UIO driver? I saw the userspace process segfault after removal.
> Is there a "standard" way to handle this scenario, i.e for hotpluggable
> hardware using UIO?
Your kernel driver knows when the device is removed, so have it tell
userspace this. Or, just tie into libudev and have your userspace
program be notified when the device goes away.
Right. This is what I'm trying to do using a udev "remove" rule. Although the question still remains, what will happen if the device is being actively accessed _before_ the signal reaches the process. Is it safe to do "uio_unregister_device" while a userspace process is accessing the device?
I saw a patch for this very situation (UIO & hotplug) being discussed on LKML almost 4 yrs back, although I don't see it in my kernel version - 3.16.0 (Ubuntu 3.16.0-24-generic).
The LKML link:
Wouldn't this solve the issue? I wonder why it didn't make it into mainline?
Do you have a pointer to the source of your uio kernel driver anywhere?
Not yet, as this is still under active development (we don't have the h/w to test yet :/ ). Maybe once things stabilize a little, we'll probably open-source it along with the h/w too! :)
Thanks,
-mandeep
thanks,
greg k-h
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