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Date:   Tue, 7 Jun 2022 03:09:43 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Damien Le Moal <damien.lemoal@opensource.wdc.com>
Cc:     Christoph Hellwig <hch@infradead.org>,
        linux-fsdevel@vger.kernel.org,
        Johannes Thumshirn <johannes.thumshirn@wdc.com>
Subject: Re: [PATCH 3/3] zonefs: fix zonefs_iomap_begin() for reads
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On Tue, Jun 07, 2022 at 03:53:35PM +0900, Damien Le Moal wrote:
> >> +	else if (offset < isize)
> >>  		length = min(length, isize - offset);
> > 
> > So you still report an IOMAP_UNWRITTEN extent for the whole size of
> > the requst past EOF?  Looking at XFS we do return the whole requested
> > length, but do return it as HOLE.  Maybe we need to clarify the behavior
> > here and document it.
> 
> Yes, I checked xfs and saw that. But in zonefs case, since the file blocks are
> always preallocated, blocks after the write pointer are indeed UNWRITTEN. I did
> check that iomap read processing treats UNWRITTEN and HOLE similarly, that is,
> ignore the value of length and stop issuing IOs when either type is seen. But I
> may have missed something.
> 
> Note that initially I wrote the patch below to fix the problem. But it is very
> large and should probably be a cleanup for the next cycle. It separates the
> begin op for read and write, which makes things easier to understand.

I much prefer this more extensive fix.