lwIP aims to support zero-copy TX, and thus, must internally handle
all cases that pbufs are referenced rather than copied upon low-level
output. However, in the current situation, the arp/ndp packet queuing
routines conservatively copy entire packets, even when unnecessary in
cases where lwIP is used in a zero-copy compliant manner. This patch
moves the decision whether to copy into a centralized macro, allowing
zero-copy compliant applications to override the macro to avoid the
unnecessary copies. The macro defaults to the safe behavior, though.
This commit changes netconn_write_partly to use msg.w.offset to set
bytes_written for both blocking and non-blocking connections
This is correct because msg.w.offset is the canonical output from
the do_write call and in the case that not all bytes were written,
(a bug?) returning the full size to the caller is dangerous
Lastly, this commit adds an assert for the blocking case to sanity
check that all the bytes we requested were written. This will help
catch bugs in do_write
This commit makes a couple of cleanups discussed in patch #8882:
1) msg.w.offset should not be set to 0 in the error case. It is
only valid when err == ERR_OK
2) Remove out-of-date comment which indicated the entire write had
completed (not true for non-blocking write)
This also updates the documentation on offset to include that offset
is only valid when err == ERR_OK
This moves the write_offset variable from struct netconn to struct api_msg
This optimizes the storage by only having the space claimed when it is
needed (during a netconn_write_partly() call) and not throughout the
lifetime of the netconn
This also reduces code space/execution by not having to separately manage
clearing/checking write_offset from the current_msg pointer
Lastly, we also save execution by using msg.w.offset as the output
rather than marshaling the result to msg.w.len. Previously, len was used
as input length of dataptr and output for the write operation.
netconn_write_partly() also has access to msg.w.offset, so we can use
that
The forward declaration was added in commit
e2c2afbbe01762345ef99561a40b05033e166941 for use in struct
lwip_setgetsockopt_data, but became dead after commit
5d2e93e5f0a7e85ecf96d76950c5ee02aceecc89 where the sock pointer was
removed from lwip_setgetsockopt_data
