netdev - Re: hard_start_xmit struct sk

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Message-ID: <476CCFBA.2010305@garzik.org>
Date:	Sat, 22 Dec 2007 03:50:02 -0500
From:	Jeff Garzik <jeff@...zik.org>
To:	Matti Linnanvuori <mattilinnanvuori@...oo.com>
CC:	netdev@...r.kernel.org
Subject: Re: hard_start_xmit struct sk_buff read-only?

Matti Linnanvuori wrote:
> An old article about Linux's network drivers mentioned
> that the struct sk_buff whose pointer is passed to a
> driver's hard_start_xmit function is read-only to the
> function. Is that still so? If it is, there is no
> mention about it in the kernel tree as far as I know.

This begs the question, what are you trying to do?  ;-)

In terms of object lifetimes, control passes to the net driver when 
->hard_start_xmit() is called, but that does not mean you can freely 
scribble over things -- the skb may have been cloned, its destructor 
callback still needs to be called (via dev_kfree_skb), etc.

	Jeff



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