Follow-up of the #44565 bug fix, renamed the misnamed
PPP_INPROC_MULTITHREADED to PPP_INPROC_IRQ_SAFE because it is
IRQ safe but not thread safe.
Updated PPP documentation which now clearly state when and how
this feature can be used.
lwip/src/netif/ppp/pppol2tp.c: In function ‘pppol2tp_udp_send’:
lwip/src/netif/ppp/pppol2tp.c:1229:3: warning: ‘err’ may be used uninitialized in this function [-Wmaybe-uninitialized]
return err;
^
Renamed pppos_drop() → pppos_input_drop()
Renamed pppos_free_current_input_packet() → pppos_input_free_current_packet()
Moved pppos_output_last() after pppos_output_append()
Moved pppos_input_free_current_packet() before pppos_input_drop()
We actually allocated a pbuf chain only to iterate later the linked list
calling sio_write() for each pbuf, improved by calling sio_write() when
buffer is full and by recycling the pbuf, therefore only using one pbuf
for PPPoS output path.
Reworked pppos_write() and pppos_netif_output() to share more common
code into pppos_output_append() and pppos_output_last().
If PPP_INPROC_MULTITHREADED is true, then user does not what to use
the TCPIP API. Disabling the TCPIP API helps the user to understand
that PPP_INPROC_MULTITHREADED must not be used if he wish to use
the TCPIP API.
!NO_SYS users may now use as well the TCPIP API for PPPoS input data,
this way they can disable PPP_INPROC_MULTITHREADED and run pppos_input()
inside the lwIP thread, which fixes, at least for them, all the
threading issues related to PPP_INPROC_MULTITHREADED.
If PPP_INPROC_MULTITHREADED is not enabled, we can free unfinished
RX pbuf from the pppos_disconnect() function because pppos_input()
is running in the same context. Thanks to the pppos->open flags we
now only need to free remaining pbuf in the disconnect function
if PPP_INPROC_MULTITHREADED is not enabled.
Don't process input data if PPPoS is closed, it helps using
pppos_input() from a different context to prevent pppos_input() to
modify PPPoS RX machine state on a closed PPPoS session. It also
prevents allocating pbuf (which are going to be tossed out by PPP core)
and parsing serial input on a closed session.
It only mitigates the fact that this function is actually NOT thread
safe in absolutely all cases, it does not fix it but it helps for a low
cost.
For example user application should never call pppos_input() while
pppos_connect() or pppos_listen() is currently running because both of
them are freeing any input pbuf left over from the last session before
resetting the PPPoS state, they really have to to prevent pbuf leaks.
We cannot fix that easily because we don't have spinlock with an
irqsave/irqrestore helper for IRQ contexts. Mutex cannot be used in
interrupt contexts (or again, with an IRQ mutex helper).
We are going to improve the documentation on this point.
