Re: [PATCH v4 01/12] net: eth: Add a helper to pad a short Ethernet frame

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 3/16/21 1:04 PM, Bin Meng wrote:
> Add a helper to pad a short Ethernet frame to the minimum required
> length, which can be used by backend codes.

"backend codes" sounds odd but I'm not native English speaker.
I'd have used "backends' code" instead...

> Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
> 
> ---
> 
> Changes in v4:
> - change 'ethernet' to 'Ethernet'
> - do not inline the helper
> - check the padded buffer size to avoid buffer overflow
> 
> Changes in v3:
> - use 'without' instead of 'sans'
> - add a helper to pad short frames
> 
>  include/net/eth.h | 17 +++++++++++++++++
>  net/eth.c         | 17 +++++++++++++++++
>  2 files changed, 34 insertions(+)
> 
> diff --git a/include/net/eth.h b/include/net/eth.h
> index 0671be6916..6aabbdd0d3 100644
> --- a/include/net/eth.h
> +++ b/include/net/eth.h
> @@ -31,6 +31,7 @@
>  
>  #define ETH_ALEN 6
>  #define ETH_HLEN 14
> +#define ETH_ZLEN 60     /* Min. octets in frame without FCS */
>  
>  struct eth_header {
>      uint8_t  h_dest[ETH_ALEN];   /* destination eth addr */
> @@ -422,4 +423,20 @@ bool
>  eth_parse_ipv6_hdr(const struct iovec *pkt, int pkt_frags,
>                     size_t ip6hdr_off, eth_ip6_hdr_info *info);
>  
> +/**
> + * eth_pad_short_frame - pad a short frame to the minimum Ethernet frame length
> + *
> + * If the Ethernet frame size is shorter than 60 bytes, it will be padded to
> + * 60 bytes at the address @padded_pkt.
> + *
> + * @padded_pkt: buffer address to hold the padded frame
> + * @padded_buflen: buffer length of @padded_pkt. If the frame is padded, it is
> + *                 written to ETH_ZLEN, otherwise it remains unchanged.

 @padded_buflen: pointer holding length of @padded_pkt. If the frame is
                 padded, the length will be updated to the padded one.

Otherwise:
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

(since you describe frames, maybe s/pkt/frame/?)

> + * @pkt: address to hold the original Ethernet frame
> + * @pkt_size: size of the original Ethernet frame
> + * @return true if the frame is padded, otherwise false
> + */
> +bool eth_pad_short_frame(uint8_t *padded_pkt, size_t *padded_buflen,
> +                         const void *pkt, size_t pkt_size);
> +
>  #endif
> diff --git a/net/eth.c b/net/eth.c
> index 1e0821c5f8..f913e4396f 100644
> --- a/net/eth.c
> +++ b/net/eth.c
> @@ -548,3 +548,20 @@ bool eth_parse_ipv6_hdr(const struct iovec *pkt, int pkt_frags,
>      info->l4proto = ext_hdr.ip6r_nxt;
>      return true;
>  }
> +
> +bool eth_pad_short_frame(uint8_t *padded_pkt, size_t *padded_buflen,
> +                         const void *pkt, size_t pkt_size)
> +{
> +    assert(padded_buflen && *padded_buflen >= ETH_ZLEN);
> +
> +    if (pkt_size >= ETH_ZLEN) {
> +        return false;
> +    }
> +
> +    /* pad to minimum Ethernet frame length */
> +    memcpy(padded_pkt, pkt, pkt_size);
> +    memset(&padded_pkt[pkt_size], 0, ETH_ZLEN - pkt_size);
> +    *padded_buflen = ETH_ZLEN;
> +
> +    return true;
> +}
>