[dpdk-dev] problem with rte_pktmbuf_prepend (possible bug?)

Mario Gianni m.gianni at engineer.com
Wed Feb 19 15:04:33 CET 2014

This is my init function:

pktmbuf_pool[socketid] = rte_mempool_create(
 sizeof(struct rte_pktmbuf_pool_private),
 rte_pktmbuf_pool_init, NULL,
 rte_pktmbuf_init, NULL,
I copied it from a sample code.

Anyway it seems to me that mbuf_free does not reset the *data pointer, actually I have partially resolved by prepending manually the data without moving the * data pointer at all albeit it's not a very clean solution.

Could this be a bug in the DPDK mbuf_free() function?
----- Original Message -----
From: Benson, Bryan
Sent: 02/18/14 06:16 PM
To: Periklis Akritidis, Mario Gianni
Subject: RE: [dpdk-dev] problem with rte_pktmbuf_prepend (possible bug?)

Whoa, be careful, we used a custom init function and had a nasty bug because we assumed it was called on mbuf_free as well. The rte_pktmbuf_init function pointer passed into mempool create is only used at pool initialization time, not when an mbuf is freed - A reference to the obj_initi function is not stored anywhere for future use during mbuf_free. Some of the fields are reset when the NIC has completed the send of the mbufs, but it does not use a custom function ptr. Thanks, Bryan Benson ________________________________________ From: dev [dev-bounces at dpdk.org] on behalf of Periklis Akritidis [akritid at niometrics.com] Sent: Tuesday, February 18, 2014 6:19 AM To: Mario Gianni Cc: dev at dpdk.org Subject: Re: [dpdk-dev] problem with rte_pktmbuf_prepend (possible bug?) Hi Mario, Are you passing rte_pktmbuf_init as the obj_init argument to rte_mempool_create? It is called when the mbuf if freed and it will reset the fields. I vaguely remember I had the same issue at some point and resolved it somehow. This comes to mind. Cheers, Periklis On 18 Feb, 2014, at 6:27 pm, Mario Gianni <m.gianni at engineer.com> wrote: > Hi all, I'm experimenting some code with DPDK v1.5.0 and I have the following problem: > > I have a thread that receives packets from NIC, once I received a packet I want to prepend some data to it and I try to do so through the function rte_pktmbuf_prepend() > then the packet is enqueued in a ring buffer where it will be used by a client thread before being dropped through the function rte_pktmbuf_free() called by the client thread. > > Now, if I try to send packets to this program I have the following behaviour: > In a first time it seems to work correctly, then after a certain number of received packets (approximately the same number as the number of mbufs present in the mempool) if I call the rte_pktmbuf_headroom it returns that the headroom is shrinking more than the expected, until after a certain number of packets the headroom goes to zero. > > It seems like that when I call the rte_pktmbuf_free() function it doesn't reset the data position inside the mbuf, so when I call for a second time the mbuf the headroom continues to shrink until it finishes. > > > Do you have any idea of this strange behaviour?Could it be a bug in the prepend/free function? > > > Thank you, > > Mario

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