netdev - Re: [PATCH net v2] tun: fix return value when the number of iovs exceeds MAX_SKB

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Message-ID: <20201227044010-mutt-send-email-mst@kernel.org>
Date:   Sun, 27 Dec 2020 04:40:17 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     wangyunjian <wangyunjian@...wei.com>
Cc:     netdev@...r.kernel.org, jasowang@...hat.com,
        willemdebruijn.kernel@...il.com,
        virtualization@...ts.linux-foundation.org,
        jerry.lilijun@...wei.com, chenchanghu@...wei.com,
        xudingke@...wei.com, brian.huangbin@...wei.com
Subject: Re: [PATCH net v2] tun: fix return value when the number of iovs
 exceeds MAX_SKB_FRAGS

On Fri, Dec 25, 2020 at 10:52:16AM +0800, wangyunjian wrote:
> From: Yunjian Wang <wangyunjian@...wei.com>
> 
> Currently the tun_napi_alloc_frags() function returns -ENOMEM when the
> number of iovs exceeds MAX_SKB_FRAGS + 1. However this is inappropriate,
> we should use -EMSGSIZE instead of -ENOMEM.
> 
> The following distinctions are matters:
> 1. the caller need to drop the bad packet when -EMSGSIZE is returned,
>    which means meeting a persistent failure.
> 2. the caller can try again when -ENOMEM is returned, which means
>    meeting a transient failure.
> 
> Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver")
> Signed-off-by: Yunjian Wang <wangyunjian@...wei.com>
> Acked-by: Willem de Bruijn <willemb@...gle.com>

Acked-by: Michael S. Tsirkin <mst@...hat.com>

> ---
> v2:
>   * update commit log suggested by Willem de Bruijn
> ---
>  drivers/net/tun.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 2dc1988a8973..15c6dd7fb04c 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1365,7 +1365,7 @@ static struct sk_buff *tun_napi_alloc_frags(struct tun_file *tfile,
>  	int i;
>  
>  	if (it->nr_segs > MAX_SKB_FRAGS + 1)
> -		return ERR_PTR(-ENOMEM);
> +		return ERR_PTR(-EMSGSIZE);
>  
>  	local_bh_disable();
>  	skb = napi_get_frags(&tfile->napi);
> -- 
> 2.23.0