Extended error reporting to user space?

[Nikita V. Youshchenko]

Hi

I'm developing a device driver that, in it's ioctl()s, accepts a complex 
data structure. Before doing it's operation, it performs large number of 
checks if data is valid. If one of those checks fail, driver 
returns -EINVAL.

Unfortunately this -EINVAL is not really useful. E.g. if a developer, 
sitting in his IDE and debugging his code, will see ioctl() 
returning -EINVAL, and will have hard times finding what exactly is wrong.

Before inventing driver-specific extended error reporting, I'd like to ask 
if there is anything more or less generic for this.
I believe situation when -Exxx is too weak interface for error reporting is 
common.

Nikita
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