Re: [PATCH v8 13/20] erofs: add erofs_fscache_read_folios() helper

[Gao Xiang]

On Wed, Apr 06, 2022 at 03:56:05PM +0800, Jeffle Xu wrote:
> Add erofs_fscache_read_folios() helper reading from fscache. It supports
> on-demand read semantics. That is, it will make the backend prepare for
> the data when cache miss. Once data ready, it will reinitiate a read
> from the cache.
> 
> This helper can then be used to implement .readpage()/.readahead() of
> on-demand read semantics.
> 
> Signed-off-by: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx>

Reviewed-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>

Thanks,
Gao Xiang

> ---
>  fs/erofs/fscache.c | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
> 
> diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
> index 1c88614203d2..d38a6efc8e50 100644
> --- a/fs/erofs/fscache.c
> +++ b/fs/erofs/fscache.c
> @@ -5,6 +5,35 @@
>  #include <linux/fscache.h>
>  #include "internal.h"
>  
> +/*
> + * Read data from fscache and fill the read data into page cache described by
> + * @start/len, which shall be both aligned with PAGE_SIZE. @pstart describes
> + * the start physical address in the cache file.
> + */
> +static int erofs_fscache_read_folios(struct fscache_cookie *cookie,
> +				     struct address_space *mapping,
> +				     loff_t start, size_t len,
> +				     loff_t pstart)
> +{
> +	struct netfs_cache_resources cres;
> +	struct iov_iter iter;
> +	int ret;
> +
> +	memset(&cres, 0, sizeof(cres));
> +
> +	ret = fscache_begin_read_operation(&cres, cookie);
> +	if (ret)
> +		return ret;
> +
> +	iov_iter_xarray(&iter, READ, &mapping->i_pages, start, len);
> +
> +	ret = fscache_read(&cres, pstart, &iter,
> +			   NETFS_READ_HOLE_ONDEMAND, NULL, NULL);
> +
> +	fscache_end_operation(&cres);
> +	return ret;
> +}
> +
>  static const struct address_space_operations erofs_fscache_meta_aops = {
>  };
>  
> -- 
> 2.27.0
>