netdev - Re: Storing hardware timestamps - how about using the new skb's control block?

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Message-Id: <20081112.003927.153710640.davem@davemloft.net>
Date:	Wed, 12 Nov 2008 00:39:27 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	patrick.ohly@...el.com
Cc:	nanog@...5b20a518b8f6864949bd940457dc124746ddc.nosense.org,
	netdev@...r.kernel.org, opurdila@...acom.com
Subject: Re: Storing hardware timestamps - how about using the new skb's
 control block?

From: Patrick Ohly <patrick.ohly@...el.com>
Date: Wed, 12 Nov 2008 09:27:18 +0100

> My understanding of sk_buff->cb might be wrong, but isn't each layer
> allowed to overwrite it as the packet traverses the different queues?

Right.

> skb_share_check() is not mandatory:

And besides, skb_share_check() doesn't check if somebody "owns" the
skb->cb[]

And if you bump the reference count or something silly like that to
get skb_share_check() to copy the packet, every single locally
destined TCP packet will be copied.  That will effectively kill
performance.

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