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Adjust pbuf reuse documentation a bit: pbufs should never be reused after transmit

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goldsimon 2017-05-18 09:19:08 +02:00
parent 5dd037ea49
commit 8db0001e32
1 changed files with 6 additions and 7 deletions
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13
doc/rawapi.txt
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@ -443,7 +443,7 @@ Call these functions in the order of appearance:
the stack; add this to your main loop or equivalent. the stack; add this to your main loop or equivalent.
--- Optimalization hints --- Optimization hints
The first thing you want to optimize is the lwip_standard_checksum() The first thing you want to optimize is the lwip_standard_checksum()
routine from src/core/inet.c. You can override this standard routine from src/core/inet.c. You can override this standard
@ -486,14 +486,13 @@ remain unchanged until sent. Because the send- (or write-)functions return
when the packets have been enqueued for sending, data must be kept stable when the packets have been enqueued for sending, data must be kept stable
after that, too. after that, too.
This implies that PBUF_RAM/PBUF_POOL pbufs passed to raw-API send functions This implies that *ALL* pbufs passed to send functions must *not* be reused by
must *not* be reused by the application unless their ref-count is 1. the application unless the send function returns an error indicating the pbuf
is not sent/queued for sending.
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! Also, data passed to tcp_write without the copy-flag must not be changed until
sent and ACKed (check the amount of bytes marked as 'sent')!
Therefore, be careful which type of PBUF you use and if you copy TCP data Therefore, be careful which type of PBUF you use and if you copy TCP data
or not! or not!