Re: [PATCH linux-2.6.1-rc1-mm1] aiodio_fallback_bio_count.patch
From: Suparna Bhattacharya (suparna_at_in.ibm.com)
Date: 01/05/04
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Date: Mon, 5 Jan 2004 10:58:46 +0530 To: Andrew Morton <akpm@osdl.org>
On Sun, Jan 04, 2004 at 09:06:42PM -0800, Andrew Morton wrote:
> Suparna Bhattacharya <suparna@in.ibm.com> wrote:
> >
> > > What is the significance of `written > count' in there, and of `dio->result
> > > > dio->size' in finished_one_bio()? How can these states come about?
> > >
> >
> > Both of these are checks to determine whether all or only a part of
> > the request was serviced by DIO, leaving the rest to be serviced by
> > falling back to buffered I/O.
> >
> > Earlier, we would decide this based on whether dio->result == -ENOTBLK
> > and written == -ENOTBLK respectively. However, now that we also need the
> > result to indicate how much actually got written even in -ENOTBLK case,
> > so that we can issue buffered i/o only for the remaining part of the request,
> > dio->result and written had to be modified to reflect the number of bytes
> > transferred by DIO even for the fallback to buffered i/o case.
> > So we need checks like this to find out whether there is some i/o left
> > to be issued via buffered i/o.
>
> Sure. But the generic_file_aio_write_nolock() code is doing this:
>
> if (written >= count && !is_sync_kiocb(iocb))
> written = -EIOCBQUEUED;
> if (written < 0 || written >= count)
> goto out_status;
>
>
> Under what circumstances can `written' (the amount which was written) be
> greater than `count' (the amount to write)?
None. The '>' situation should never occur.
This is just being explicit about covering the "not less than" case
as a whole, and making sure we do not fall through to buffered i/o in
that case, i.e its the same as:
if (!(written < count) && !is_sync_kiocb(iocb))
Is that any less confusing ? Or would you rather just replace the '>=" by
"=='.
Regards
Suparna
-- Suparna Bhattacharya (suparna@in.ibm.com) Linux Technology Center IBM Software Lab, India - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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