report from Philip A. Prindeville <philipp@zembu.com>:
I was working on a device driver for a certain ethernet chipset that
occassionally wraps in its buffer, and causes a resulting mbuf chain
with only a few dozen bytes in the first mbuf of the chain.
I wouldn't have thought this would be a problem, until I ran some
stress tests that flooded the ethernet receiver with packets and
started to get panics here:
250
251 if (m->m_pkthdr.len < sizeof(struct ip))
252 goto tooshort;
253
254 #ifdef DIAGNOSTIC
255 if (m->m_len < sizeof(struct ip))
256 panic("ipintr mbuf too short");
257 #endif
258
259 if (m->m_len < sizeof (struct ip) &&
260 (m = m_pullup(m, sizeof (struct ip))) == 0) {
261 ipstat.ips_toosmall++;
262 return;
263 }
264 ip = mtod(m, struct ip *);
and the panic was at line 256. But if I #undef'd DIAGNOSTICS,
then the m_pullup() at line 260 does the right thing and the packet
ends up being processed just fine.
So I started wondering, (a) why was the test checking for
something that apparently wasn't a fatal condition but rather
one that is subsequently recovered from a couple of lines later
and (b) why panic as a diagnostic "aid" from a recoverable
condition rather than just (say) log a message to the console?
All of this seems overly severe for no reason that is readily
apparent to me.
and not likely to become so. Comments on each configuration
are below.
+ Force CPU386 - This BSP was developed as part of the initial
port of RTEMS to the i386. This board has been unavailable
for a long time now.
+ GO32 - This BSP and some CPU code supported djgpp v1.x. This
version is now quite old. No one has stepped forward to
update the code to v2.x which may be technically impossible
anyway. More importantly, go32 has been superceded by the pc386 BSP.
and not likely to become so. Comments on each configuration
are below.
+ Force CPU386 - This BSP was developed as part of the initial
port of RTEMS to the i386. This board has been unavailable
for a long time now.
+ GO32 - This BSP and some CPU code supported djgpp v1.x. This
version is now quite old. No one has stepped forward to
update the code to v2.x which may be technically impossible
anyway. More importantly, go32 has been superceded by the pc386 BSP.
now prototypes the malloc family in stdlib.h. This causes conflicts
with the way the network stack overrides the definitions of malloc.
As best I (being Joel) can tell, commenting stdlib.h out keeps the
files compiling and referencing the desired malloc/free but results
in more warnings.
