some strange constructs (bugs?) in if_tun.c

Martin Birgmeier la5lbtyi at
Thu Jun 2 16:51:08 UTC 2011

I am looking at net/if_tun.c, function tunwrite() (this is 7.4, but 8.2 
is nearly the same):

There is a local variable "error" which is initialized to zero and then 
seemingly never changed, until it is used as a return value if 
m_uiotombuf() fails:

         int             error = 0;
         if ((m = m_uiotombuf(uio, M_DONTWAIT, 0, 0, M_PKTHDR)) == NULL) {
                 return (error);
a little further down, we see
                 if (m->m_len < sizeof(family) &&
                     (m = m_pullup(m, sizeof(family))) == NULL)
                         return (ENOBUFS);

As far as I can see, the first return amounts to "drop the packet, but 
don't tell anything about it", whereas the second amounts to "drop the 
packet and say it's due to ENOBUFS".

However, the first case is much more like ENOBUFS, so shouldn't we 
simply say "return (ENOBUFS)" there and remove the "error" variable 

There seem to be other functions in if_tun.c with a similar strange 
usage of an "error" variable.



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