Messages in this thread | | | Date | Thu, 03 Jan 2008 12:04:30 -0800 | From | Zach Brown <> | Subject | Re: [PATCH] aio: partial write should not return error code. |
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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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