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

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Date:   Mon, 19 Jul 2021 16:02:30 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Gao Xiang <hsiangkao@...ux.alibaba.com>
Cc:     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 10:47:47PM +0800, Gao Xiang wrote:
> @@ -246,18 +245,19 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
>  	unsigned poff, plen;
>  	sector_t sector;
>  
> -	if (iomap->type == IOMAP_INLINE) {
> -		WARN_ON_ONCE(pos);
> -		iomap_read_inline_data(inode, page, iomap);
> -		return PAGE_SIZE;
> -	}
> -
> -	/* zero post-eof blocks as the page may be mapped */
>  	iop = iomap_page_create(inode, page);
> +	/* needs to skip some leading uptodated blocks */
>  	iomap_adjust_read_range(inode, iop, &pos, length, &poff, &plen);
>  	if (plen == 0)
>  		goto done;
>  
> +	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).