[Click] Is it possible for a packet to exist twice inside of a router?

[Eddie Kohler]

Hi,

server at mail.utexas.edu wrote:
> Is it possible, for example, for the same exact packet to exist in multiple
> queues? I ask, because if you were storing your packets in a central location
> and then fetching them back when you got to transmit, you'd need to delete
> packets from that central location when they were no longer needed.
> 
> If there can only be one copy, then a discard from a queue would always delete
> packets from that shared memory. If there can be multiple, you'd have to keep a
> counter of how many copies exist.
> 
> Which is the case?
> 
> Thanks!

It's a smidgeon more complicated than this.

Click Packets consist of a common header, with information like annotations 
and packet length, and the packet data itself.

A Packet *header* exists at most once in the configuration.  To make a packet 
copy, you call "p->clone()", which returns a new Packet.  But packet *data* 
can be referred to by multiple Packet headers.  It is reference counted; when 
the last Packet header is deleted, the packet data goes away too.  As Bart 
points out, you can call Packet::uniqueify() to get a unique copy of the 
packet data.

Eddie