Re: [PATCH net-next v5 6/7] tap: Keep hdr_len in tap_get_user()

[Willem de Bruijn]

Akihiko Odaki wrote:
> hdr_len is repeatedly used so keep it in a local variable.
> 
> Signed-off-by: Akihiko Odaki <akihiko.odaki@xxxxxxxxxx>

> @@ -682,11 +683,8 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
>  	if (msg_control && sock_flag(&q->sk, SOCK_ZEROCOPY)) {
>  		struct iov_iter i;
>  
> -		copylen = vnet_hdr.hdr_len ?
> -			tap16_to_cpu(q, vnet_hdr.hdr_len) : GOODCOPY_LEN;
> -		if (copylen > good_linear)
> -			copylen = good_linear;
> -		else if (copylen < ETH_HLEN)
> +		copylen = min(hdr_len ? hdr_len : GOODCOPY_LEN, good_linear);
> +		if (copylen < ETH_HLEN)
>  			copylen = ETH_HLEN;

I forgot earlier: this can also use single line statement

    copylen = max(copylen, ETH_HLEN);

And perhaps easiest to follow is

    copylen = hdr_len ?: GOODCOPY_LEN;
    copylen = min(copylen, good_linear);
    copylen = max(copylen, ETH_HLEN);

>  		linear = copylen;
>  		i = *from;
> @@ -697,11 +695,9 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
>  
>  	if (!zerocopy) {
>  		copylen = len;
> -		linear = tap16_to_cpu(q, vnet_hdr.hdr_len);
> -		if (linear > good_linear)
> -			linear = good_linear;
> -		else if (linear < ETH_HLEN)
> -			linear = ETH_HLEN;
> +		linear = min(hdr_len, good_linear);
> +		if (copylen < ETH_HLEN)
> +			copylen = ETH_HLEN;

Same