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Date: Sun, 4 Jan 2004 21:06:42 -0800
From: Andrew Morton <akpm@osdl.org>
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Subject: Re: [PATCH linux-2.6.1-rc1-mm1] aiodio_fallback_bio_count.patch
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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)?