Fixed an overzealous form validation

core/src/main/java/hudson/model/Slave.java

@@ -405,7 +405,9 @@ public abstract class Slave extends Node implements Serializable {
             if(value.startsWith("\\\\") || value.startsWith("/net/"))
                 return FormValidation.warning(Messages.Slave_Network_Mounted_File_System_Warning());
 
-            if (!value.startsWith("\\") && !value.startsWith("/")) {
+            if (!value.contains("\\") && !value.startsWith("/")) {
+                // Unix-looking path that doesn't start with '/'
+                // TODO: detect Windows-looking relative path
                 return FormValidation.error(Messages.Slave_the_remote_root_must_be_an_absolute_path());
             }
 

test/src/test/groovy/hudson/model/SlaveTest.groovy

@@ -24,10 +24,14 @@
 package hudson.model
 
 import hudson.slaves.DumbSlave
+import hudson.util.FormValidation
 import org.jvnet.hudson.test.GroovyHudsonTestCase
 import org.apache.commons.io.IOUtils
 import hudson.slaves.JNLPLauncher
 
+import static hudson.util.FormValidation.Kind.ERROR
+import static hudson.util.FormValidation.Kind.WARNING
+
 /**
  *
  *
@@ -78,4 +82,13 @@ public class SlaveTest extends GroovyHudsonTestCase {
         con.outputStream.close();
         IOUtils.copy(con.inputStream,System.out)
     }
+
+    public void testRemoteFsCheck() {
+        def d = jenkins.getDescriptorByType(DumbSlave.DescriptorImpl.class)
+        assert d.doCheckRemoteFS("c:\\")==FormValidation.ok();
+        assert d.doCheckRemoteFS("/tmp")==FormValidation.ok();
+        assert d.doCheckRemoteFS("relative/path").kind==ERROR;
+        assert d.doCheckRemoteFS("/net/foo/bar/zot").kind==WARNING;
+        assert d.doCheckRemoteFS("\\\\machine\\folder\\foo").kind==WARNING;
+    }
 }