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Fixed bug #29271 (Application can't re-use pbufs) by updating the doc to not allow reusing pbufs after passing them to a send function

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goldsimon 2010-05-04 19:36:49 +00:00
parent 71f5fdef42
commit 4d1ff2418e
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doc/rawapi.txt
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@ -481,3 +481,24 @@ to match your application and network.
For a production release it is recommended to set LWIP_STATS to 0.
Note that speed performance isn't influenced much by simply setting
high values to the memory options.
For more optimization hints take a look at the lwIP wiki.
--- Zero-copy MACs
To achieve zero-copy on transmit, the data passed to the raw API must
remain unchanged until sent. Because the send- (or write-)functions return
when the packets have been enqueued for sending, data must be kept stable
after that, too.
This implies that PBUF_RAM/PBUF_POOL pbufs passed to raw-API send functions
must *not* be reused by the application unless their ref-count is 1.
For no-copy pbufs (PBUF_ROM/PBUF_REF), data must be kept unchanged, too,
but the stack/driver will/must copy PBUF_REF'ed data when enqueueing, while
PBUF_ROM-pbufs are just enqueued (as ROM-data is expected to never change).
Also, data passed to tcp_write without the copy-flag must not be changed!
Therefore, be careful which type of PBUF you use and if you copy TCP data
or not!