Comment 8 for bug 1540731

Simple reproduction of failure:

#include <gtest/gtest.h>
#include <gmock/gmock.h>
#include <sys/socket.h>
#include <sys/stat.h>

TEST(IsItBroken, recvmsg)
{
    using namespace testing;

    enum { server, client, size };
    int socket_fd[size];
    int const opt = 1;

    ASSERT_THAT(socketpair(AF_LOCAL, SOCK_STREAM, 0, socket_fd), Eq(0));

    auto const msg = "A random message";
    send(socket_fd[client], msg, sizeof msg, MSG_DONTWAIT | MSG_NOSIGNAL);

    ASSERT_THAT(setsockopt(socket_fd[server], SOL_SOCKET, SO_PASSCRED, &opt, sizeof(opt)), Ne(-1));

    union {
        struct cmsghdr cmh;
        char control[CMSG_SPACE(sizeof(ucred))];
    } control_un;

    control_un.cmh.cmsg_len = CMSG_LEN(sizeof(ucred));
    control_un.cmh.cmsg_level = SOL_SOCKET;
    control_un.cmh.cmsg_type = SCM_CREDENTIALS;

    msghdr msgh;
    msgh.msg_name = nullptr;
    msgh.msg_namelen = 0;
    msgh.msg_iov = nullptr;
    msgh.msg_iovlen = 0;
    msgh.msg_control = control_un.control;
    msgh.msg_controllen = sizeof(control_un.control);

    errno = 0;

    EXPECT_THAT(recvmsg(socket_fd[server], &msgh, MSG_PEEK), Ne(-1));

    for (auto socket : socket_fd) close(socket);
}