+/*
+ * Attempt a "-t nfs -o vers=4" or "-t nfs4" mount.
+ *
+ * Returns TRUE if successful, otherwise FALSE.
+ * "errno" is set to reflect the individual error.
+ */
+static int nfs_try_mount_v4(struct nfsmount_info *mi)
+{
+ struct addrinfo *ai;
+ int ret = 0;
+
+ for (ai = mi->address; ai != NULL; ai = ai->ai_next) {
+ ret = nfs_do_mount_v4(mi, ai->ai_addr, ai->ai_addrlen);
+ if (ret != 0)
+ return ret;
+
+ switch (errno) {
+ case ECONNREFUSED:
+ case EHOSTUNREACH:
+ continue;
+ default:
+ goto out;
+ }
+ }
+out:
+ return ret;
+}
+
+/*
+ * Handle NFS version and transport protocol
+ * autonegotiation.
+ *
+ * When no version or protocol is specified on the
+ * command line, mount.nfs negotiates with the server
+ * to determine appropriate settings for the new
+ * mount point.
+ *
+ * Returns TRUE if successful, otherwise FALSE.
+ * "errno" is set to reflect the individual error.
+ */
+static int nfs_autonegotiate(struct nfsmount_info *mi)
+{
+ int result;
+
+ result = nfs_try_mount_v4(mi);
+ if (result)
+ return result;
+
+ switch (errno) {
+ case EPROTONOSUPPORT:
+ /* A clear indication that the server or our
+ * client does not support NFS version 4. */
+ goto fall_back;
+ case ENOENT:
+ /* Legacy Linux servers don't export an NFS
+ * version 4 pseudoroot. */
+ goto fall_back;
+ case EPERM:
+ /* Linux servers prior to 2.6.25 may return
+ * EPERM when NFS version 4 is not supported. */
+ goto fall_back;
+ default:
+ return result;
+ }
+
+fall_back:
+ return nfs_try_mount_v3v2(mi);
+}
+