linux-kernel - Re: [PATCH v3] iomap: support tail packing inline read

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Date:   Mon, 19 Jul 2021 17:13:10 +0200
From:   Christoph Hellwig <hch@....de>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Gao Xiang <hsiangkao@...ux.alibaba.com>,
        linux-erofs@...ts.ozlabs.org, linux-fsdevel@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@....de>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Andreas Gruenbacher <andreas.gruenbacher@...il.com>
Subject: Re: [PATCH v3] iomap: support tail packing inline read

On Mon, Jul 19, 2021 at 04:02:30PM +0100, Matthew Wilcox wrote:
> > +	if (iomap->type == IOMAP_INLINE) {
> > +		iomap_read_inline_data(inode, page, iomap, pos);
> > +		plen = PAGE_SIZE - poff;
> > +		goto done;
> > +	}
> 
> This is going to break Andreas' case that he just patched to work.
> GFS2 needs for there to _not_ be an iop for inline data.  That's
> why I said we need to sort out when to create an iop before moving
> the IOMAP_INLINE case below the creation of the iop.
> 
> If we're not going to do that first, then I recommend leaving the
> IOMAP_INLINE case where it is and changing it to ...
> 
> 	if (iomap->type == IOMAP_INLINE)
> 		return iomap_read_inline_data(inode, page, iomap, pos);
> 
> ... and have iomap_read_inline_data() return the number of bytes that
> it copied + zeroed (ie PAGE_SIZE - poff).

Returning the bytes is much cleaner anyway.  But we still need to deal
with the sub-page uptodate status in one form or another.