Size of Buffer in recvfrom in Solaris vs Linux

[SeytmourButts]

I have a C program that reads custom icmp packets off a socket. The program has been used for years on Solaris, but I am now having to port it to Linux.

Got it all compliled on Linux and when I ran it and sent in a test icmp packet, the size of the packet appears to be quite larger on Linux than it was on Solaris.

On both Linux and Solaris, when I print out "rc", I get about the same size of bytes read, which is 276.

char recv_buffer[8184];

if ((rc = recvfrom(sd, recv_buffer, 8184, iFlag, &sFrom, &iFromLen)) == -1)
{
do something
}
else 
{
ip_recv_ptr = (struct ip *) recv_buffer;
printf("Length of data received %d\n", ip_recv_ptr->ip_len);
}

I cast recv_buffer to a pointer of type struct ip and then print out the size of the data received.

On Solaris, ip_recv_ptr->ip_len prints out 248

On Linux, ip_recv_ptr->ip_len prints out 5113

Now this is a really big difference. I am reading the same packet of size 270`ish off the socket on both Solaris and Linux, but the amount of data in recv_buffer is 248 on Solaris and 5113 on Linux.

So, I am really lost as to what is happening. The source code is that same and the test packet is the same. Any ideas? on what's going on here?

Thanks

[firedraco]

Perhaps Linux does not append a '\0' to the data, so it just keeps going until it finds a '\0'.

You could try intializing your buffer to all nulls.

[helios]

Hmm...
248 = 0xF8
5113 = 0x13F9
Possibly an endianness issue coupled with integers of different sizes?

[SeytmourButts]

I just added this, but the results were the same.

memset(recv_buffer,'\0', 8184);

[SeytmourButts]

Can you explain about the "integers of different sizes" a bit more or what I should be looking at?

[helios]

Check that sizeof(ip_recv_ptr->ip_len) is the same on both implementations (Linux and Solaris).
I could do a quick check if you post the definition of struct ip and the raw data you're sending.

[SeytmourButts]

I did a sizeof of both SOlaris and Linux....

printf("Sizeof: %d\n", sizeof(ip_recv_ptr->ip_len))

And got the same results on both...

Sizeof: 2

[SeytmourButts]

Here is the definition of struct ip on Linux....

struct ip
  {
#if __BYTE_ORDER == __LITTLE_ENDIAN
    unsigned int ip_hl:4;               /* header length */
    unsigned int ip_v:4;                /* version */
#endif
#if __BYTE_ORDER == __BIG_ENDIAN
    unsigned int ip_v:4;                /* version */
    unsigned int ip_hl:4;               /* header length */
#endif
    u_int8_t ip_tos;                    /* type of service */
    u_short ip_len;                     /* total length */
    u_short ip_id;                      /* identification */
    u_short ip_off;                     /* fragment offset field */
#define IP_RF 0x8000                    /* reserved fragment flag */
#define IP_DF 0x4000                    /* dont fragment flag */
#define IP_MF 0x2000                    /* more fragments flag */
#define IP_OFFMASK 0x1fff               /* mask for fragmenting bits */
    u_int8_t ip_ttl;                    /* time to live */
    u_int8_t ip_p;                      /* protocol */
    u_short ip_sum;                     /* checksum */
    struct in_addr ip_src, ip_dst;      /* source and dest address */
  }; 

Here is the definition of struct ip on Solaris....

struct ip {
#ifdef _BIT_FIELDS_LTOH
        uchar_t ip_hl:4,                /* header length */
                ip_v:4;                 /* version */
#else
        uchar_t ip_v:4,                 /* version */
                ip_hl:4;                /* header length */
#endif
        uchar_t ip_tos;                 /* type of service */
        short   ip_len;                 /* total length */
        ushort_t ip_id;                 /* identification */
        short   ip_off;                 /* fragment offset field */
#define IP_DF 0x4000                    /* dont fragment flag */
#define IP_MF 0x2000                    /* more fragments flag */
        uchar_t ip_ttl;                 /* time to live */
        uchar_t ip_p;                   /* protocol */
        ushort_t ip_sum;                /* checksum */
        struct  in_addr ip_src, ip_dst; /* source and dest address */
}; 

[helios]

Sorry. I got nothing, then.

[SeytmourButts]

No problem. I will keep looking. Maybe focus on the calls to socket(), socketopt(), and recvfrom(). Maybe there is something different on Linux with these calls.

[Biju Scaria]

I think the recvfrom() implementation is different in Linux. The following link might be helpful:

http://developers.sun.com/solaris/articles/solaris_linux_app.html

[SeytmourButts]

I checked out the link, but I don't see much of any difference in recvfrom() on Linux.