Bug 5877

A socket's sb_cc field includes the length of control data (like the
source address, for PR_ADDR protocols, and any control info like if
SO_TIMESTAMP, IP_RECVIF, etc. are set).

Problems with this include:
- FIONREAD just returns sb_cc, but not all these bytes are readable
- This count is used to determine the high/low water marks on the
  socket.
Advantages are:
- sb_cc is really the length of the attached mbufs, so it's simple
  to compute.

Fix: 

Make sb_cc reflect the number of data bytes in the socket buffer,
instead of the amount of data+control.  This may be as simple as
fixing sballoc() and sbfree() in sys/socketvar.h to only count
MT_HEADER, MT_DATA, MT_OOBDATA mbufs, or may be much more involved.
How-To-Repeat: 
Adel Abushaev <adel@ksu.ru> reported the problem and included this pair of
test programs.

/* client.c */
#include <stdio.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

void main()
{
   int sockfd;
   struct sockaddr_in servaddr_in;
   char buffer[512];

   memset(&servaddr_in, 0, sizeof(struct sockaddr_in));
  
   servaddr_in.sin_family = AF_INET;
   servaddr_in.sin_addr.s_addr = inet_addr("127.0.0.1");
   servaddr_in.sin_port = htons(4000);

   sockfd = socket(AF_INET, SOCK_DGRAM, 0);
   if (sockfd <= 0) 
   {
         perror("socket"); return;
   }

   sendto(sockfd, buffer, 512, 0, (struct sockaddr *)&servaddr_in,
          sizeof(struct sockaddr_in));

   close(sockfd);
}

/* server.c */ 
#include <stdio.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/stat.h>
#include <sys/fcntl.h>
#include <sys/ioctl.h>

#ifdef SOLARIS
#include <sys/filio.h>
#endif

void main()
{
   int sockfd;
   struct sockaddr_in myaddr_in, peeraddr_in;
   unsigned addrlen;
   char buffer[512];
   struct timeval tim;
   int optval;
   fd_set fdsread, fdswrite, fdsexcept;

   memset(&myaddr_in, 0, sizeof(struct sockaddr_in));
   memset(&peeraddr_in, 0, sizeof(struct sockaddr_in));
  
   myaddr_in.sin_family = AF_INET;
   myaddr_in.sin_addr.s_addr = INADDR_ANY;
   myaddr_in.sin_port = htons(4000);

   sockfd = socket(AF_INET, SOCK_DGRAM, 0);
   if (sockfd <= 0) 
   {
         perror("socket"); return;
   }

   if (bind(sockfd, (struct sockaddr *)&myaddr_in, sizeof(struct sockaddr_in))
      < 0) 
   {
        perror("bind"); return;
   }

   FD_ZERO(&fdsread); FD_ZERO(&fdswrite); FD_ZERO(&fdsexcept);
   FD_SET(sockfd, &fdsread);
   tim.tv_sec=60; tim.tv_usec=0;
   select(sockfd+1, &fdsread, &fdswrite, &fdsexcept, &tim);
   if (FD_ISSET(sockfd, &fdsread))
   {
     ioctl(sockfd, FIONREAD, &optval); printf("ioctl: %d\n",optval); 
     optval=recvfrom(sockfd, buffer, 512, 0, (struct sockaddr *)&peeraddr_in,
          &addrlen); printf("recv: %d\n",optval);
     ioctl(sockfd, FIONREAD, &optval); printf("ioctl: %d\n",optval); 
   }

   close(sockfd);
}