osdep: implement qemu_socketpair() for win32

Manually implement a socketpair() function, using UNIX sockets and
simple peer credential checking.

QEMU doesn't make much use of socketpair, beside vhost-user which is not
available for win32 at this point. However, I intend to use it for
writing some new portable tests.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20230306122751.2355515-5-marcandre.lureau@redhat.com>

include/qemu/sockets.h

@@ -15,7 +15,6 @@ int inet_aton(const char *cp, struct in_addr *ia);
 bool fd_is_socket(int fd);
 int qemu_socket(int domain, int type, int protocol);
 
-#ifndef WIN32
 /**
  * qemu_socketpair:
  * @domain: specifies a communication domain, such as PF_UNIX
@@ -30,7 +29,6 @@ int qemu_socket(int domain, int type, int protocol);
  * Return 0 on success.
  */
 int qemu_socketpair(int domain, int type, int protocol, int sv[2]);
-#endif
 
 int qemu_accept(int s, struct sockaddr *addr, socklen_t *addrlen);
 /*

util/oslib-win32.c

@@ -310,6 +310,116 @@ bool qemu_socket_unselect(int sockfd, Error **errp)
     return qemu_socket_select(sockfd, NULL, 0, errp);
 }
 
+int qemu_socketpair(int domain, int type, int protocol, int sv[2])
+{
+    struct sockaddr_un addr = {
+        0,
+    };
+    socklen_t socklen;
+    int listener = -1;
+    int client = -1;
+    int server = -1;
+    g_autofree char *path = NULL;
+    int tmpfd;
+    u_long arg;
+    int ret = -1;
+
+    g_return_val_if_fail(sv != NULL, -1);
+
+    addr.sun_family = AF_UNIX;
+    socklen = sizeof(addr);
+
+    tmpfd = g_file_open_tmp(NULL, &path, NULL);
+    if (tmpfd == -1 || !path) {
+        errno = EACCES;
+        goto out;
+    }
+
+    close(tmpfd);
+
+    if (strlen(path) >= sizeof(addr.sun_path)) {
+        errno = EINVAL;
+        goto out;
+    }
+
+    strncpy(addr.sun_path, path, sizeof(addr.sun_path) - 1);
+
+    listener = socket(domain, type, protocol);
+    if (listener == -1) {
+        goto out;
+    }
+
+    if (DeleteFile(path) == 0 && GetLastError() != ERROR_FILE_NOT_FOUND) {
+        errno = EACCES;
+        goto out;
+    }
+    g_clear_pointer(&path, g_free);
+
+    if (bind(listener, (struct sockaddr *)&addr, socklen) == -1) {
+        goto out;
+    }
+
+    if (listen(listener, 1) == -1) {
+        goto out;
+    }
+
+    client = socket(domain, type, protocol);
+    if (client == -1) {
+        goto out;
+    }
+
+    arg = 1;
+    if (ioctlsocket(client, FIONBIO, &arg) != NO_ERROR) {
+        goto out;
+    }
+
+    if (connect(client, (struct sockaddr *)&addr, socklen) == -1 &&
+        WSAGetLastError() != WSAEWOULDBLOCK) {
+        goto out;
+    }
+
+    server = accept(listener, NULL, NULL);
+    if (server == -1) {
+        goto out;
+    }
+
+    arg = 0;
+    if (ioctlsocket(client, FIONBIO, &arg) != NO_ERROR) {
+        goto out;
+    }
+
+    arg = 0;
+    if (ioctlsocket(client, SIO_AF_UNIX_GETPEERPID, &arg) != NO_ERROR) {
+        goto out;
+    }
+
+    if (arg != GetCurrentProcessId()) {
+        errno = EPERM;
+        goto out;
+    }
+
+    sv[0] = server;
+    server = -1;
+    sv[1] = client;
+    client = -1;
+    ret = 0;
+
+out:
+    if (listener != -1) {
+        close(listener);
+    }
+    if (client != -1) {
+        close(client);
+    }
+    if (server != -1) {
+        close(server);
+    }
+    if (path) {
+        DeleteFile(path);
+    }
+    return ret;
+}
+
 #undef connect
 int qemu_connect_wrap(int sockfd, const struct sockaddr *addr,
                       socklen_t addrlen)