netdev - Re: [PATCH net-next v2 2/3] tipc: message reassembly using fragment chain

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Date:	Mon, 04 Nov 2013 16:12:54 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	erik.hugne@...csson.com
Cc:	netdev@...r.kernel.org, jon.maloy@...csson.com, maloy@...jonn.com,
	paul.gortmaker@...driver.com, ying.xue@...driver.com
Subject: Re: [PATCH net-next v2 2/3] tipc: message reassembly using
 fragment chain

From: <erik.hugne@...csson.com>
Date: Thu, 31 Oct 2013 09:40:13 +0100

> +	skb_pull(frag, msg_hdr_sz(msg));
> +	if (fragid == FIRST_FRAGMENT) {
> +		if (*head)
> +			goto out_free;
> +		*head = frag;
> +		skb_frag_list_init(*head);
>  		return 0;
> +	} else {
> +		if (!*head)
> +			goto out_free;
> +		if (!skb_has_frag_list(*head))
> +			skb_shinfo(*head)->frag_list = frag;
> +		else
> +			(*tail)->next = frag;
> +		*tail = frag;
> +		(*head)->truesize += frag->truesize;
> +	}
> +	if (fragid == LAST_FRAGMENT) {
> +		*fbuf = *head;
> +		*tail = *head = NULL;
> +		return LINK_REASM_COMPLETE;
>  	}

Please use skb_try_coalese(), and only use frag lists if that does not
succeed.

Also you must be certain to unclone the SKB if you are going to modify
it in this kind of way.

For a good example of how to attend to all of these things, see
ip_frag_reasm() in net/ipv4/ip_fragment.c
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