[ovs-dev] question about mirror code

[Huanle Han]

2016-01-25 1:00 GMT+08:00 Ben Pfaff <blp at ovn.org>:

> On Sun, Jan 24, 2016 at 11:59:57PM +0800, Huanle Han wrote:
> > I think a more line "mirrors &= ~ctx->mirrors;" is needed at the end of
> the
> > "while" loop.
> > Otherwise, duplicated mirror action may be applied in recursive
> > mirror_packet called by output_normal.
>
> Did you arrive at that conclusion from testing or code inspection?  I
> believe that dup_mirrors always includes the mirror we're handling, so
> that "mirrors &= ~dup_mirrors;" in the while loop should include that
> case; also note the "mirrors &= ~ctx->mirrors;" at the beginning of the
> function.
>
> The test case 2 confirm this conclusion. Suppose we have 2 mirrors A and B
(they are not duplicated). "mirror_packet" may be called recursively:
 mirror_packet()
    output_normal(ctx, xbundle, out_vlan)
        ......
            mirror_packet()
 when it's iterating mirror A on top "mirror_packet", mirror B is applied
in the recursive "mirror_packet". So we should reject the mirror B in top
mirror_packet on next iteration.
 "mirrors &= ~ctx->mirrors;" at the beginning of the function or "mirrors
&= ~dup_mirrors;" in while loop could not include this case.

> Here are the test cases:
> >
> > Test case for the bug I mentioned in previous mail:
> > 1. setup port:  vnet0 tag = 201, vnet1 tag=200
> > 2. setup flow: add-flow in_port=vnet0,actions:vnet1
> > 3. setup mirror( mirror1 or mirror2 ). and packet from vnet0 to vnet1
> >    a) mirror1:  select_all=false, select_src_port=[         ],
> > select_dst_port=[vnet1], select_vlan=[200], output=vnet2
> >        ==> result: this mirror works.
> >    b) mirror2:  select_all=false, select_src_port=[vnet0],
> > select_dst_port=[vnet1], select_vlan=[200], output=vnet2
> >        ==> result: this mirror doesn't work.
> >
> > Test case for the bug I mentioned in this mail:
> > 1.  set port: vnet0, vnet1, vnet2
> > 2.  setup 2 mirrors:
> >     mirror1:  select_all=true,output_vlan=500
> >     mirror2:  select_all=true,output_vlan=501
> > 3. packet from vnet0, result: duplicated mirror actions are generated.
>
> Do you mean that you ran these test cases with the patch I supplied, and
> saw this bug?
>

Yes, I ran them with your patch.
I think the patch have fixed the problem in test case 1.
But It leads to a new bug(test case 2). That's why I saied "mirrors &=
~ctx->mirrors;" is needed.