illumos gate

POSIX says: If the size of the option value is greater than option_len , the value stored in the object pointed to by the option_value argument shall be silently truncated.

But illumos does this:

$ cat <<EOF > test.c
#include <sys/types.h>
#include <sys/socket.h>

#include <stdio.h>

int
main(void)
{
        int f = socket(AF_INET, SOCK_DGRAM, 0);
        printf("f: %d\n", f);

        char buf[16];
        int len = sizeof buf;
        int ret = getsockopt(f, SOL_SOCKET, SO_REUSEADDR, buf, &len);
        printf("ret: %d, len: %d\n", ret, len);

        len = 1;
        ret = getsockopt(f, SOL_SOCKET, SO_REUSEADDR, buf, &len);
        printf("ret: %d, len: %d\n", ret, len);

        return 0;
}
EOF
$ /usr/gcc/10/bin/gcc -Wall -lsocket -lnsl test.c
$ ./a.out 
f: 3
ret: 0, len: 4
ret: -1, len: 1
$

The exactly same code on linux works properly:

$ ./a.out 
f: 3
ret: 0, len: 4
ret: 0, len: 1
$