netdev - Re: [PATCH net] netlink: mmap: fix status setting in skb destructor

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Message-ID: <20150828073750.GA685@gmail.com>
Date:	Fri, 28 Aug 2015 16:37:50 +0900
From:	Ken-ichirou MATSUZAWA <chamaken@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, daniel@...earbox.net, fw@...len.de
Subject: Re: [PATCH net] netlink: mmap: fix status setting in skb destructor

On Tue, Aug 25, 2015 at 08:22:03PM -0700, David Miller wrote:
> From: Ken-ichirou MATSUZAWA <chamaken@...il.com>
> > I don't know the intension of setting VALID status in the skb
> > destructor. But I think it need to be set UNUSED status in case of
> 
> I think the idea is to have the user process this "zero length" frame
> and advance the status itself.
> 
> I think it is probably racy and problematic to have the kernel set a
> frame's state to UNUSED.  It is not a valid state transition for the
> kernel side of RX ring processing.
> 
> Only the user can safely release ring entries back to the kernel.

I will just update the frame status to UNUSED and advance ring
position in user space in case of nm_len == 0. Thank you.
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