util: Introduce qemu_get_host_name()

This function offers operating system agnostic way to fetch host
name. It is implemented for both POSIX-like and Windows systems.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

include/qemu/osdep.h

@@ -655,4 +655,14 @@ static inline void qemu_reset_optind(void)
 #endif
 }
 
+/**
+ * qemu_get_host_name:
+ * @errp: Error object
+ *
+ * Operating system agnostic way of querying host name.
+ *
+ * Returns allocated hostname (caller should free), NULL on failure.
+ */
+char *qemu_get_host_name(Error **errp);
+
 #endif

util/oslib-posix.c

@@ -794,3 +794,38 @@ void sigaction_invoke(struct sigaction *action,
     }
     action->sa_sigaction(info->ssi_signo, &si, NULL);
 }
+
+#ifndef HOST_NAME_MAX
+# ifdef _POSIX_HOST_NAME_MAX
+#  define HOST_NAME_MAX _POSIX_HOST_NAME_MAX
+# else
+#  define HOST_NAME_MAX 255
+# endif
+#endif
+
+char *qemu_get_host_name(Error **errp)
+{
+    long len = -1;
+    g_autofree char *hostname = NULL;
+
+#ifdef _SC_HOST_NAME_MAX
+    len = sysconf(_SC_HOST_NAME_MAX);
+#endif /* _SC_HOST_NAME_MAX */
+
+    if (len < 0) {
+        len = HOST_NAME_MAX;
+    }
+
+    /* Unfortunately, gethostname() below does not guarantee a
+     * NULL terminated string. Therefore, allocate one byte more
+     * to be sure. */
+    hostname = g_new0(char, len + 1);
+
+    if (gethostname(hostname, len) < 0) {
+        error_setg_errno(errp, errno,
+                         "cannot get hostname");
+        return NULL;
+    }
+
+    return g_steal_pointer(&hostname);
+}

util/oslib-win32.c

@@ -808,3 +808,16 @@ bool qemu_write_pidfile(const char *filename, Error **errp)
     }
     return true;
 }
+
+char *qemu_get_host_name(Error **errp)
+{
+    wchar_t tmp[MAX_COMPUTERNAME_LENGTH + 1];
+    DWORD size = G_N_ELEMENTS(tmp);
+
+    if (GetComputerNameW(tmp, &size) == 0) {
+        error_setg_win32(errp, GetLastError(), "failed close handle");
+        return NULL;
+    }
+
+    return g_utf16_to_utf8(tmp, size, NULL, NULL, NULL);
+}