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[lwip-devel] [bug #49914] lwip_sendmsg uses PBUF_REF pbufs


From: Simon Goldschmidt
Subject: [lwip-devel] [bug #49914] lwip_sendmsg uses PBUF_REF pbufs
Date: Fri, 23 Dec 2016 07:01:11 +0000 (UTC)
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.87 Safari/537.36

Follow-up Comment #2, bug #49914 (project lwip):

I can understand your position Joel. And I think we should support zero copy
in this case.

However, the part where "the netif output function is responsible for copying
the pbuf/data" is unclear. Even PBUF_RAM get changed eventually, at least from
TCP.

I guess a clear definition that DMA-enabled drivers must memcpy PBUF_REF pbufs
before sending would be best. However, there are additional problems here as
you have a PBUF_RAM header and PBUF_REF data. Is it allowed for the driver to
change the next pointer of the header pbuf when this pbuf is still referenced
by someone else?

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