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Re: [PATCH] PKT_SCHED: dsmark must take care of shared/cloned skbs

To: Thomas Graf <tgraf@xxxxxxx>
Subject: Re: [PATCH] PKT_SCHED: dsmark must take care of shared/cloned skbs
From: Patrick McHardy <kaber@xxxxxxxxx>
Date: Mon, 20 Dec 2004 09:06:06 +0100
Cc: jamal <hadi@xxxxxxxxxx>, "David S. Miller" <davem@xxxxxxxxxxxxx>, netdev@xxxxxxxxxxx
In-reply-to: <20041219203641.GL17998@postel.suug.ch>
References: <20041218170017.GH17998@postel.suug.ch> <1103487827.1048.188.camel@jzny.localdomain> <20041219203641.GL17998@postel.suug.ch>
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Thomas Graf wrote:
* jamal <1103487827.1048.188.camel@xxxxxxxxxxxxxxxx> 2004-12-19 15:23

If the qdisc at that level muddies the packet thats fair game - thats
what goes out on the wire. So we should leave the code as is.


Agreed for egress but I think it is needed for stuff like IMQ. It's
debatable whether we should take care of IMQ and alike though.


You shouldn't care about IMQ, but we still need to copy the packet before modifying it if the data is shared. Otherwise we have a race on SMP with AF_PACKET sockets, depending on when the packet is read it can be either modified or not.

Converting dsmark to an action sounds like the best long-term solution.

Regards
Patrick

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