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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
1 changed files with 21 additions and 0 deletions
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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. For a production release it is recommended to set LWIP_STATS to 0.
Note that speed performance isn't influenced much by simply setting Note that speed performance isn't influenced much by simply setting
high values to the memory options. 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!