Hi Samuel, This is a bug. As you rightfully pointed, we shouldn't modify the original packet but instead copy out the relevant bits before modifying them. Copying the entire data buffer is simpler, but sub-optimal. We should only copy out the headers that are being modified. We already have the infrastructure to do this. I will create an issue to track it.
Thanks! Saurabh > -----Original Message----- > From: dev [mailto:dev-boun...@openvswitch.org] On Behalf Of Samuel > Ghinet > Sent: Saturday, August 02, 2014 5:03 AM > To: dev@openvswitch.org > Subject: [ovs-dev] Cloning packets for "action: set field" > > Hello guys, > > I wanted to ask you: do you have buffer management functionality to > duplicate a packet? > > I have seen that the function OvsOutputBeforeSetAction CLONES instead of > duplicating the packet. > > Did you know that, when cloning a packet, both the old and the cloned > packet reference the same data (buffer)? > So that setting bytes, say, in the ipv4 header of the cloned NET_BUFFER > actually modifies the original NET_BUFFER as well? > > Also, we are not allowed to set data in the original packet. We must create a > clone / duplicate for this. > For tunneling (i.e. adding headroom) cloning is ok, because the clone writes > bytes to the "unused" area of the buffer, or allocates a new MDL for the > headroom (which is removed at Complete). > > The procedure for setting data within the buffer using cloning is a bit more > complicated: > You must allocate a new MDL, copy the 'modified' data into its buffer, and > chain it to the cloned NET_BUFFER (replacing the old MDL). And at Complete, > you must free your MDL and put the old MDL back. > A simpler method would be to duplicate the buffer, instead of cloning it. > > Here the architecture of a cloned NET_BUFFER_LIST is presented: > https://urldefense.proofpoint.com/v1/url?u=http://msdn.microsoft.com/en > - > us/library/windows/hardware/ff544929%28v%3Dvs.85%29.aspx&k=oIvRg1% > 2BdGAgOoM1BIlLLqw%3D%3D%0A&r=pEkjsHfytvHEWufeZPpgqSOJMdMjuZ > PbesVsNhCUc0E%3D%0A&m=jhsFuJNgUaiglvJZi08Spr39W%2F4PBNhLh4%2B > MJdlvCis%3D%0A&s=c65b8be59f4145534cbfafbc06598cd82b85bd4b2f95caee > d5edd4f657fabed3 > > Samuel Ghinet > _______________________________________________ > dev mailing list > dev@openvswitch.org > https://urldefense.proofpoint.com/v1/url?u=http://openvswitch.org/mailm > an/listinfo/dev&k=oIvRg1%2BdGAgOoM1BIlLLqw%3D%3D%0A&r=pEkjsHfytv > HEWufeZPpgqSOJMdMjuZPbesVsNhCUc0E%3D%0A&m=jhsFuJNgUaiglvJZi08 > Spr39W%2F4PBNhLh4%2BMJdlvCis%3D%0A&s=a2e562875bfab9326b93c55ff0 > 3bc9dd974c081a4449c5a7a8977b175de72691 _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
