[Haifux] Telling the kernel business is closed (my weekly riddle)

Eli Billauer eli at billauer.co.il
Mon Jun 27 12:31:48 MSD 2011

Shachar Shemesh wrote:

> Nobody expects ENODEV on an already opened device. I'd go for EIO, 
> myself.
And so shall I. Thanks.

As for how to handle the disaster event, my question was if there's a 
standard way to handle it. Checking if the device is OK all the time 
will make the code uglier.

And the truth is that I don't care about recovering from such an error. 
If it ever happens, I want the user to trash the hardware or change the 
kernel configuration to avoid ASPM (a form of power management). The 
chip sometimes fails to wake up correctly from short power downs, and 
data is lost. It's basically as severe as discovering that the RAM may 
not perform writes every now and then. Not something I want to work around.
>> So here comes my question: Is there a convention for how a device 
>> driver can tell the kernel that certain devices (as in 
>> /dev/something) have turned unusable, in particular when some of them 
>> are already open? I guess this is related to hotpluggable devices, 
>> but in the latter case I suppose it's the kernel informing the device 
>> driver about the event, and not vice versa.
> I don't think you need to do anything beyond that, unless the 
> situation is recoverable without a reboot (say - by sending a reset to 
> the chip). If that's the case, I'd reset the chip, return EIO to any 
> connection opened before the reset, and treat new connection like I 
> always would. Of course, if there is a way for you to make the old 
> connections still function, even better.
> Shachar

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