Re: [USB-hacking] [PATCH] aio_run_iocb should always retry

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Thanks for the detailed reply, Zach!

On 9/24/07, Zach Brown  wrote:
> In any case, I don't think this is the right solution.  gadgetfs is
> pretty unusual in using one ki_retry to submit and then switching to
> another to copy the result to userspace and free.  The intent of
> ki_retry is to, well, retry.

I tried to trace the O_DIRECT AIO path to figure out how AIO was
intended to be implemented, and got hopelessly lost. At least the
approach of switching to a different ki_retry is simple and pretty easy
to understand.

> In the cases where sys_io_cancel() finds that it shouldn't call
> ki_cancel it could return EAGAIN.

EAGAIN never seems like the right answer to me for cancel, but you
understand this system better than I want to. :-) Shouldn't
sys_io_cancel block until it can either successfully cancel or report
that the iocb already completed?

> - ki_cancel will not be called after aio_complete() has been called
>
> Serializing ki_retry and ki_cancel calls will be easy because they're
> called from process context from fs/aio.c.  Serializing with
> aio_complete() will be harder as its called from interrupts from
> subsystems.

I don't understand why that makes it harder. Can't you pull it off with
a spinlock in the kiocb?

> If this sounds OK I could roll some patches.

Sounds good to me!

Jamey
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