Re: [PATCH 2/2] aio: propogate post-EIOCBQUEUED errors to completion event

[Zach Brown <zach.brown@oracle.com>]

> This is an interesting trick, but I'd like to consider hard whether  
> the added
> complexity is worth it. Could you list the various other cases you  
> have in mind
> which would want to use it ?

I'm happy to report that the sync case and the  
invalidate_inode_pages2_range() case are the only two which try to  
rewrite 'ret'.  I audited all the call paths between aio_{read,write}  
and -EIOCBQUUEUED.

So, sure, maybe we can shuffle the house of cards a little in the  
direction away from having a fs/aio.c helper for the situation by  
simply removing the few current instances of the problem.  It won't  
scale as people add problems without knowing about the rule to not  
overwrite -EIOCBQUEUED, but hopefully that won't be a rule for much  
longer :) :).

For the O_SYNC case we could add another magical test to the is_async  
assignment which won't perform AIO on O_SYNC descriptors.

> For the invalidate_inode_pages2_range() case, I wonder if the right
> place to issue this is after the direct IO write has completed and  
> before
> aio_complete() is issued (somewhat like the way we do  
> bio_check_pages_dirty
> for DIO reads), rather than after submission when the IO may still  
> not have
> hit the disk. This would also make the behaviour uniform for  
> synchronous and
> async cases.

Hmm, I think I like that.  It solves the problem for the current sole  
user of -EIOCBQUEUED without too much disruption.

> BTW, am I right in interpreting that with your change aio_complete 
> () may
> trigger an io_getevents() wakeup, before the corresponding event is  
> placed
> on the ring buffer ?

Hmm, yeah, it looks like I goofed that.

I'll roll a patch which does the invalidation down in fs/direct-io.c.

- z
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