Re: [RFC PATCH v1 07/10] bpf: add kfuncs and helpers support for file dynptrs

[Eduard Zingerman <eddyz87@gmail.com>]

On Fri, 2025-10-03 at 17:04 +0100, Mykyta Yatsenko wrote:

[...]

> @@ -1702,6 +1733,25 @@ int bpf_dynptr_check_size(u64 size)
>  	return size > DYNPTR_MAX_SIZE ? -E2BIG : 0;
>  }
>  
> +static int bpf_file_fetch_bytes(struct bpf_dynptr_file_impl *df, u64 offset, void *buf, u64 len)
> +{
> +	const void *ptr;
> +
> +	if (!buf || len == 0)
> +		return -EINVAL;
> +
> +	df->freader.buf = buf;
> +	df->freader.buf_sz = len;
> +	ptr = freader_fetch(&df->freader, offset + df->offset, len);

What will happen, if file does not have enough data to read `len` bytes?
Will freader_fetch() return NULL?

> +	if (!ptr)
> +		return df->freader.err;
> +
> +	if (ptr != buf) /* Force copying into the buffer */
> +		memcpy(buf, ptr, len);
> +
> +	return 0;
> +}
> +
>  void bpf_dynptr_init(struct bpf_dynptr_kern *ptr, void *data,
>  		     enum bpf_dynptr_type type, u32 offset, u32 size)
>  {

[...]