linux-kernel - Re: [PATCH 1/2] iomap: support tail packing inline read

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Date:   Fri, 16 Jul 2021 15:38:48 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Christoph Hellwig <hch@...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>,
        "Darrick J. Wong" <djwong@...nel.org>, Chao Yu <chao@...nel.org>,
        Liu Bo <bo.liu@...ux.alibaba.com>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        Liu Jiang <gerry@...ux.alibaba.com>,
        Andreas Gruenbacher <agruenba@...hat.com>
Subject: Re: [PATCH 1/2] iomap: support tail packing inline read

On Fri, Jul 16, 2021 at 02:47:35PM +0100, Matthew Wilcox wrote:
> I think it looks something like this ...
> 
> @@ -211,23 +211,18 @@ struct iomap_readpage_ctx {
>  };
> 
>  static void iomap_read_inline_data(struct inode *inode, struct folio *folio,
> -               struct iomap *iomap)
> +               struct iomap *iomap, loff_t pos, size_t size)
>  {
> -       size_t size = i_size_read(inode);
>         void *addr;
> +       size_t offset = offset_in_folio(folio, pos);
> 
> -       if (folio_test_uptodate(folio))
> -               return;
> +       BUG_ON(size != i_size_read(inode) - pos);
> 
> -       BUG_ON(folio->index);
> -       BUG_ON(folio_multi(folio));
> -       BUG_ON(size > PAGE_SIZE - offset_in_page(iomap->inline_data));
> -
> -       addr = kmap_local_folio(folio, 0);
> +       addr = kmap_local_folio(folio, offset);
>         memcpy(addr, iomap->inline_data, size);
>         memset(addr + size, 0, PAGE_SIZE - size);
>         kunmap_local(addr);
> -       folio_mark_uptodate(folio);
> +       iomap_set_range_uptodate(folio, to_iomap_page(folio), pos, size);

That should be s/size/PAGE_SIZE - offset/
(because this has just zeroed all the bytes in the page after end-of-file)