Detecting RWF_NOWAIT support

[Avi Kivity]

I'm looking to add support for RWF_NOWAIT within a linux-aio iocb. 
Naturally, I need to detect at runtime whether the kernel support 
RWF_NOWAIT or not.


The only method I could find was to issue an I/O with RWF_NOWAIT set, 
and look for errors. This is somewhat less than perfect:

Â- from the error, I can't tell whether RWF_NOWAIT was the problem, or 
something else. If I enable a number of new features, I have to run 
through all combinations to figure out which ones are supported and 
which are not.

Â- RWF_NOWAIT support is per-filesystem, so I can't just remember not 
to enable RWF_NOWAIT globally, I have to track it per file.


Did I miss another method of detecting RWF_NOWAIT?