Re: Replacing wmem_packet_scope() with pinfo->pool?

["Dr. Matthias St. Pierre" <Matthias.St.Pierre () ncp-e com>]

Hi Evan and Pascal,

> > At a first glance, we already have pinfo->pool which maintains the
> > lifetime of the packet_info object. As far as I can reason, this is
> > almost/effectively the same as the existing wmem_packet_scope - it
> > gets cleaned up later in the dissection flow, but there's still only
> > ever one which gets reused for each packet.
>
> That's also my understanding.

FWIW: Incidentally, I asked myself the same question only recently, because I noticed that packet-isakmp dissector used 
 wmem_packet_scope() in most locations, except for the following two locations, where it allocates memory for the 
decrypted packets:

https://gitlab.com/wireshark/wireshark/-/blob/86e2fda11e199b8d0e874147e60a1ba1f0ddb803/epan/dissectors/packet-isakmp.c#L2355
https://gitlab.com/wireshark/wireshark/-/blob/86e2fda11e199b8d0e874147e60a1ba1f0ddb803/epan/dissectors/packet-isakmp.c#L5960

Finally, I found the following explanation in README.wmem, which states that the scope of the pinfo pool is slightly 
larger than the packet scope:

> 2.3 The Pinfo Pool

> Certain allocations (such as AT_STRINGZ address allocations and anything that
> might end up being passed to add_new_data_source) need their memory to stick
> around a little longer than the usual packet scope - basically until the
> next packet is dissected. This is, in fact, the scope of Wireshark's pinfo
> structure, so the pinfo struct has a 'pool' member which is a wmem pool scoped
> to the lifetime of the pinfo struct.

https://gitlab.com/wireshark/wireshark/-/blob/86e2fda11e199b8d0e874147e60a1ba1f0ddb803/doc/README.wmem#L74-81


Matthias

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