linux-kernel - Re: [PATCH 4/3] squashfs: support reading fragments in readahead call

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Message-ID: <CAJMQK-hw-qURVaf-bSbtoS3OM_wV+gVr_zeVc-L+GV47yLg6Bw@mail.gmail.com>
Date:   Fri, 17 Jun 2022 16:29:03 +0800
From:   Hsin-Yi Wang <hsinyi@...omium.org>
To:     Phillip Lougher <phillip@...ashfs.org.uk>
Cc:     Xiongwei.Song@...driver.com, akpm@...ux-foundation.org,
        houtao1@...wei.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, m.szyprowski@...sung.com, miaoxie@...wei.com,
        squashfs-devel@...ts.sourceforge.net, willy@...radead.org,
        yi.zhang@...wei.com, zhengliang6@...wei.com
Subject: Re: [PATCH 4/3] squashfs: support reading fragments in readahead call

On Fri, Jun 17, 2022 at 11:04 AM Phillip Lougher
<phillip@...ashfs.org.uk> wrote:
>
> This patch adds a function which can be used to read fragments in the
> readahead call.
>
> This function is necessary because filesystems built with the -tailends
> (or -always-use-fragments) option may have fragments present which
> cannot be currently handled.
>
> Signed-off-by: Phillip Lougher <phillip@...ashfs.org.uk>
> ---
>  fs/squashfs/file.c | 35 +++++++++++++++++++++++++++++++++++
>  1 file changed, 35 insertions(+)
>
> diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c
> index f0c64ee272d5..3a4cce16d7da 100644
> --- a/fs/squashfs/file.c
> +++ b/fs/squashfs/file.c
> @@ -497,6 +497,41 @@ static int squashfs_read_folio(struct file *file, struct folio *folio)
>         return res;
>  }
>
> +static unsigned int squashfs_readahead_fragment(struct page **page,
hi Phillip,

Since the buffer->error is int, and also the variable to receive the
value is res, I modified it when sending it with the series, though it
won't affect the result.

> +       unsigned int pages, unsigned int expected)
> +{
> +       struct inode *inode = page[0]->mapping->host;
> +       struct squashfs_cache_entry *buffer = squashfs_get_fragment(inode->i_sb,
> +               squashfs_i(inode)->fragment_block,
> +               squashfs_i(inode)->fragment_size);
> +       struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
> +       unsigned int n, mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
> +
> +       if (buffer->error)
> +               goto out;
> +
> +       expected += squashfs_i(inode)->fragment_offset;
> +
> +       for (n = 0; n < pages; n++) {
> +               unsigned int base = (page[n]->index & mask) << PAGE_SHIFT;
> +               unsigned int offset = base + squashfs_i(inode)->fragment_offset;
> +
> +               if (expected > offset) {
> +                       unsigned int avail = min_t(unsigned int, expected -
> +                               offset, PAGE_SIZE);
> +
> +                       squashfs_fill_page(page[n], buffer, offset, avail);
> +               }
> +
> +               unlock_page(page[n]);
> +               put_page(page[n]);
> +       }
> +
> +out:
> +       squashfs_cache_put(buffer);
> +       return buffer->error;
> +}
> +
>  static void squashfs_readahead(struct readahead_control *ractl)
>  {
>         struct inode *inode = ractl->mapping->host;
> --
> 2.34.1
>