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

From: Jeff Moyer
Date: Mon Feb 19 2007 - 17:51:02 EST

==> On Mon, 19 Feb 2007 13:38:35 -0800 (PST), Zach Brown <zach.brown@xxxxxxxxxx> said:

Zach> This addresses an oops reported by Leonid Ananiev <leonid.i.ananiev@xxxxxxxxx>
Zach> as archived at
Zach> So this patch introduces a helper, aio_propogate_error(),

...which is spelled incorrectly: aio_propagate_error.

Zach> which queues post-submission errors in the iocb so that they are
Zach> given to the user completion event when aio_complete() is
Zach> finally called.

Ugly, but I can't think of a better way to do it, either.

> +
> + if (kiocbIsInserted(req))
> + aio_ring_insert_entry(ctx, req);
> +

This confused me at first reading. If it's inserted, then insert it.
Perhaps KIF_COMPLETED would be a better name?

> +/*
> + * This function is used to make sure that an error is communicated to
> + * userspace on iocb completion without stopping -EIOCBQUEUED from bubbling up
> + * to fs/aio.c from the place where it originated.
> + *
> + * If we have an existing -EIOCBQUEUED it must be returned all the way to
> + * fs/aio.c so that it doesn't double-complete the iocb along with whoever
> + * returned -EIOCBQUEUED.. In that case we put the new error in the iocb. It
> + * will be returned to userspace *intead of* the first result code given to
> + * aio_complete(). Use this only for errors which must overwrite whatever the
> + * return code might have been. The first non-zero new_err given to this
> + * function for a given iocb will be returned to userspace.
> + */
> +static inline int aio_propogate_error(struct kiocb *iocb, int existing_err,
> + int new_err)
> +{
> + if (existing_err != -EIOCBQUEUED)
> + return new_err;
> + if (!iocb->ki_pending_err)
> + iocb->ki_pending_err = new_err;
> + return -EIOCBQUEUED;
> +}
> +

I think that we would ideally cancel the I/Os in flight since we are
going to throw away the results. However, we don't exactly support
cancellation today. So, I have no objection to this less optimal

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