On 12/7/2010 9:20 AM, Greg KH wrote:
> On Mon, Dec 06, 2010 at 06:32:30PM -0800, pkondeti@xxxxxxxxxxxxxx wrote:
>> Hi Greg,
>>
>>> On Mon, Dec 06, 2010 at 06:07:50PM +0530, Pavankumar Kondeti wrote:
>>>> OTG specification mandates no silent failures and all errors should
>>>> be reported to the user. The spec itself does not give the exact
>>>> error description. But recommends the error message to be self
>>>> explanatory. Provide otg_notify_error() utility for USB core and
>>>> OTG driver to send the error codes to user space. All the error
>>>> code values are described in include/linux/usb/ch9.h. The user space
>>>> application can listen to netlink socket and parse the buffer for
>>>> "MODULE=OTG" and "ERROR=n", where 'n' contains the error code.
>>>
>>> How are you going to listen to the netlink socket that is already
>>> grabbed by libudev?
>>>
>> Sorry. I never worked with udev. But I read udev documentation.
>> I thought an external script can be invoked by adding a udev rule
>> when MODULE=OTG is matched and ERROR value can be accessed
>> in the script via env variable.
>
> So, you created a new kernel/user ABI and never even tried it out to see
> how someone would even use it?
>
> {sigh}
>
> I'm afraid to ask if you actually tested this code, let alone compiled
> the thing...
>
I have tested this patch with a sample program @
http://www.kernel.org/doc/pending/hotplug.txt on busybox environment
where udevd is not running. After seeing your comments, I ran the same
program concurrently
with udev on Linux box.
>>> Please, if you really want to do this, create your own netlink socket,
>>> don't create new uevent messages that will just confused the existing
>>> tools out there, that's ripe for big problems.
>>>
>> I have seen examples in drivers sending uevents for notifying docking
>> station status (drivers/acpi/dock.c)
>
> That is when the hardware configuration of the system changes.
>
>> and when backlight brightness changes
>> (drivers/video/backlight/backlight.c).
>
> Again, hardware configuration status changed.
>
Documentation/filesystems/gfs2-uevents.txt says OFFLINE uevent is sent
upon file system errors.
>> So I have taken this approach.
>
> Please don't, this is NOT the way to get errors from the kernel back out
> to userspace, because, as you have noted, this is not how any other
> subsystem does it.
>
Thanks for your feedback. Is there any other way kernel can send errors
to user space asynchronously? is /dev/ interface acceptable?
--
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
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