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Re: [lwip-users] Collision in PBUF_RAM

From: Marcus Bäckman
Subject: Re: [lwip-users] Collision in PBUF_RAM
Date: Thu, 22 Apr 2010 19:29:13 +0200

Marcus Bäckman wrote:

> I have encounted a collision problem in PBUF_RAM. udp.c uses pbuf_alloc(PBUF_IP,

> UDP_HLEN, PBUF_RAM) and this buffer will be queued for transmission in the

> ethernet driver. The reference count of this buffer is increased in the ethernet layer,

> and the buffer is freed at a later point when it has been transmitted.

> I have noticed that (sometimes) the pbuf allocated in udp.c points to the same payload

> which is used by a pbuf (also previously allocated in udp.c) waiting to be transmitted.

> The pbuf's differs but they point to the same payload.

> The pbuf waiting to be transmitted has not been freed at the point udp.c allocates

> a new pbuf (the reference count is 2).


Just wanted to give you an update of my findings. It turned out to be explained by "bug #29361: ip_frag has problems with zero-copy DMA MACs". I am using a zero-copy approach.




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