Re: [PATCH net v2 2/3] net: devmem: return EMSGSIZE on type mismatch

[Bobby Eshleman <bobbyeshleman@gmail.com>]

On Mon, Aug 03, 2026 at 05:14:40PM +0000, Mina Almasry wrote:
> When a devmem payload mixes with a standard page payload, return
> -EMSGSIZE instead of -EFAULT. This enables tcp_sendmsg to seamlessly
> fall back to creating a new segment instead of failing the socket send.
> 
> Fixes: bd61848900bff ("net: devmem: Implement TX path")
> Cc: Pavel Begunkov <asml.silence@gmail.com>
> Cc: Stanislav Fomichev <sdf@fomichev.me>
> Cc: Bobby Eshleman <bobbyeshleman@gmail.com>
> Signed-off-by: Mina Almasry <almasrymina@google.com>
> Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>  net/core/datagram.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/core/datagram.c b/net/core/datagram.c
> index 173b5d97bd409..6f8ffd61bcab4 100644
> --- a/net/core/datagram.c
> +++ b/net/core/datagram.c
> @@ -638,7 +638,7 @@ int zerocopy_fill_skb_from_iter(struct sk_buff *skb,
>  	int frag = skb_shinfo(skb)->nr_frags;
>  
>  	if (!skb_frags_readable(skb))
> -		return -EFAULT;
> +		return -EMSGSIZE;
>  
>  	while (length && iov_iter_count(from)) {
>  		struct page *head, *last_head = NULL;
> @@ -713,7 +713,7 @@ zerocopy_fill_skb_from_devmem(struct sk_buff *skb, struct iov_iter *from,
>  	struct net_iov *niov;
>  
>  	if (i && skb_frags_readable(skb))
> -		return -EFAULT;
> +		return -EMSGSIZE;
>  
>  	/* Devmem filling works by taking an IOVEC from the user where the
>  	 * iov_addrs are interpreted as an offset in bytes into the dma-buf to
> -- 
> 2.55.0.571.g244d577d93-goog
> 

Reviewed-by: Bobby Eshleman <bobbyeshleman@meta.com>