Re: [PATCH v8 18/20] erofs: implement fscache-based data read for inline layout

[Gao Xiang <xiang@kernel.org>]

On Wed, Apr 06, 2022 at 03:56:10PM +0800, Jeffle Xu wrote:
> Implement the data plane of reading data from data blobs over fscache
> for inline layout.
> 
> For the heading non-inline part, the data plane for non-inline layout is
> reused, while only the tail packing part needs special handling.
> 
> Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
> ---
>  fs/erofs/fscache.c | 40 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 40 insertions(+)
> 
> diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
> index 65de1c754e80..d32cb5840c6d 100644
> --- a/fs/erofs/fscache.c
> +++ b/fs/erofs/fscache.c
> @@ -60,6 +60,40 @@ static int erofs_fscache_meta_readpage(struct file *data, struct page *page)
>  	return ret;
>  }
>  
> +static int erofs_fscache_readpage_inline(struct folio *folio,
> +					 struct erofs_map_blocks *map)
> +{
> +	struct inode *inode = folio_file_mapping(folio)->host;
> +	struct super_block *sb = inode->i_sb;
> +	struct erofs_buf buf = __EROFS_BUF_INITIALIZER;
> +	erofs_blk_t blknr;
> +	size_t offset, len;
> +	void *src, *dst;
> +
> +	/*
> +	 * For inline (tail packing) layout, the offset may be non-zero, which
> +	 * can be calculated from corresponding physical address directly.
> +	 */
> +	offset = erofs_blkoff(map->m_pa);
> +	blknr = erofs_blknr(map->m_pa);
> +	len = map->m_llen;
> +
> +	src = erofs_read_metabuf(&buf, sb, blknr, EROFS_KMAP);
> +	if (IS_ERR(src))
> +		return PTR_ERR(src);
> +
> +	DBG_BUGON(folio_size(folio) != PAGE_SIZE);
> +
> +	dst = kmap(folio_page(folio, 0));

kmap_local_folio?

> +	memcpy(dst, src + offset, len);
> +	memset(dst + len, 0, PAGE_SIZE - len);
> +	kunmap(folio_page(folio, 0));
> +
> +	erofs_put_metabuf(&buf);
> +
> +	return 0;
> +}
> +
>  static int erofs_fscache_readpage(struct file *file, struct page *page)
>  {
>  	struct folio *folio = page_folio(page);
> @@ -85,6 +119,12 @@ static int erofs_fscache_readpage(struct file *file, struct page *page)
>  		goto out_uptodate;
>  	}
>  
> +	/* inline readpage */

I think the code below is self-explained.

> +	if (map.m_flags & EROFS_MAP_META) {
> +		ret = erofs_fscache_readpage_inline(folio, &map);
> +		goto out_uptodate;
> +	}
> +
>  	/* no-inline readpage */

Same here.

Thanks,
Gao Xiang

>  	mdev = (struct erofs_map_dev) {
>  		.m_deviceid = map.m_deviceid,
> -- 
> 2.27.0
>