Re: [PATCH bpf-next v1 4/7] bpf: Add bpf_dynptr_read and bpf_dynptr_write

["Toke Høiland-Jørgensen" <toke@redhat.com>]

Joanne Koong <joannekoong@fb.com> writes:

> From: Joanne Koong <joannelkoong@gmail.com>
>
> This patch adds two helper functions, bpf_dynptr_read and
> bpf_dynptr_write:
>
> long bpf_dynptr_read(void *dst, u32 len, struct bpf_dynptr *src, u32 offset);
>
> long bpf_dynptr_write(struct bpf_dynptr *dst, u32 offset, void *src, u32 len);
>
> The dynptr passed into these functions must be valid dynptrs that have
> been initialized.
>
> Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
> ---
>  include/linux/bpf.h            |  6 ++++
>  include/uapi/linux/bpf.h       | 18 +++++++++++
>  kernel/bpf/helpers.c           | 56 ++++++++++++++++++++++++++++++++++
>  tools/include/uapi/linux/bpf.h | 18 +++++++++++
>  4 files changed, 98 insertions(+)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index e0fcff9f2aee..cded9753fb7f 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -2426,6 +2426,12 @@ enum bpf_dynptr_type {
>  #define DYNPTR_MAX_SIZE	((1UL << 28) - 1)
>  #define DYNPTR_SIZE_MASK	0xFFFFFFF
>  #define DYNPTR_TYPE_SHIFT	29
> +#define DYNPTR_RDONLY_BIT	BIT(28)
> +
> +static inline bool bpf_dynptr_is_rdonly(struct bpf_dynptr_kern *ptr)
> +{
> +	return ptr->size & DYNPTR_RDONLY_BIT;
> +}
>  
>  static inline enum bpf_dynptr_type bpf_dynptr_get_type(struct bpf_dynptr_kern *ptr)
>  {
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 6a57d8a1b882..16a35e46be90 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -5175,6 +5175,22 @@ union bpf_attr {
>   *		After this operation, *ptr* will be an invalidated dynptr.
>   *	Return
>   *		Void.
> + *
> + * long bpf_dynptr_read(void *dst, u32 len, struct bpf_dynptr *src, u32 offset)
> + *	Description
> + *		Read *len* bytes from *src* into *dst*, starting from *offset*
> + *		into *dst*.

nit: this should be "starting from *offset* into *src*, no? (same below)

-Toke