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    SubjectRe: [PATCH] aio: partial write should not return error code.
    Rusty Russell wrote:
    > When an AIO write gets an error after writing some data (eg. ENOSPC),
    > it should return the amount written already, not the error. Just like
    > write() is supposed to.

    Andrew, please don't queue this fix. I think the bug is valid but the
    patch is subtly dangerous.

    > diff -r 18802689361a fs/aio.c
    > --- a/fs/aio.c Thu Jan 03 15:22:24 2008 +1100
    > +++ b/fs/aio.c Thu Jan 03 18:05:25 2008 +1100
    > @@ -1346,6 +1350,13 @@ static ssize_t aio_rw_vect_retry(struct
    > /* This means we must have transferred all that we could */
    > /* No need to retry anymore */
    > if ((ret == 0) || (iocb->ki_left == 0))
    > + ret = iocb->ki_nbytes - iocb->ki_left;
    > +
    > + /* If we managed to write some out we return that, rather than
    > + * the eventual error. */
    > + if (opcode == IOCB_CMD_PWRITEV
    > + && ret < 0
    > + && iocb->ki_nbytes - iocb->ki_left)
    > ret = iocb->ki_nbytes - iocb->ki_left;

    This doesn't account for the (sigh) -EIOCB* error codes. They must be
    returned to the caller so that it can properly handle the iocb reference
    counting. Failure to do so can lead to oopses.

    To be fair, I think you'll have a really hard time finding an
    ->aio_write() implementation which would return partial progress and
    *then* one of the magical errnos. But the infrastructure does allow it.

    So maybe we could get a helper in aio.h that abstracts out the

    (ret < 0 && ret != -EIOCBQUEUED && ret != -EIOCBRETRY)

    condition. Then I think this patch would be fine.

    I assigned a bug to remind myself to revisit this if you aren't excited
    by continuing with the patch:

    http://bugzilla.kernel.org/show_bug.cgi?id=9681

    - z


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