uip has no reassembly, so every fragment it receives is discarded and
logged. A neighbour that broadcasts fragmented traffic therefore produces a
continuous stream of "ip: fragment dropped." rather than an occasional one,
at roughly thirteen lines a second on a quiet segment, which buries every
other console message.
The message carries real information: a sudden burst of it says something
about the network. What carries none is repeating it per fragment. Report
the count once per five second window instead, which keeps the signal and
ends the flood.
The count is printed through the no_syslog primitives, as the original
message was, so the flood cannot move from the console into the log ring.
itoa() writes through write_char(), which also feeds the ring, so it gets
a no_syslog twin beside it rather than a private copy of its digits.
Building with SDCC 4.6.0 emits tons of warnings e.g.:
cmd_parser.c:31: warning 356: object in read-only code space should be const
cmd_parser.c:36: warning 357: pointer to object in read-only code space should be pointer to const
These of course become fatal when building with --Werror.
Comparing resultant binaries, it seems that a single string is shifted
(deduplication?) but the numbers emitted at the end of the build are
otherwise identical.
The TODO next to the disabled TCP checksum code asks which bit of the RX tag
carries the result. It is bit 2 of byte 1: the hardware sets it when the L4
checksum is bad.
That answers the question for UDP as well, which was not being checked either
because UIP_CONF_UDP_CHECKSUMS is 0. Both paths now read the flag instead of
running a checksum over the payload on the 8051.
A zero UDP checksum, which is optional in IPv4, is not flagged by the hardware,
so DHCP keeps working and no extra condition is needed.
rx_headers lives in rtlplayground.c, which the host tests do not link, so
test_httpd_tx carries the storage itself the way it already carries uip_buf.
A zeroed descriptor reads as a good checksum, so the existing scenarios are
unaffected.
A new scenario sets the flag on a request and expects it counted as a checksum
error and left unanswered, then sends the same request with the flag clear and
expects it served. Built against uip.c without this change, those first two
checks fail and the two control checks still pass, so the scenario tells the
two versions apart rather than merely exercising the code.
Costs 156 bytes of code on SWTGW218AS and no extra XDATA.
Drives the unmodified httpd.c and uip.c through a handshake and a GET
from a client that moves its receive window, and compares the bytes that
reach the wire with the file they are meant to carry. The served file
holds a position-dependent pattern, so a repeat or a gap is reported at
its offset rather than as content that differs somewhere.
The first scenario holds the window still and must pass: it is the check
that the bench itself is sound, before the two moving-window scenarios
are believed.
bloqaudio
Matt Merhar
d00f