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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