um: port_user: Improve error handling when port-helper is not found

Check if port-helper exists and is executable. If not, write an error
message to the kernel log with information to help the user diagnose the
issue and exit with an error. If UML_PORT_HELPER was not set, write a
message suggesting that the user set it. This makes it easier to understand
why telneting to the UML instance is failing and what can be done to fix it.

Signed-off-by: Glenn Washburn <development@efficientek.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

diff --git a/arch/um/drivers/port_user.c b/arch/um/drivers/port_user.c
index 3e32351dadad81eb7d6d7a0b0680262eff09f6b1..3c62ae81df62cd03fb611bac1d9e67470619f766 100644 (file)
--- a/arch/um/drivers/port_user.c
+++ b/arch/um/drivers/port_user.c
@@ -5,6 +5,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <errno.h>
 #include <termios.h>
 #include <unistd.h>
@@ -179,6 +180,17 @@ int port_connection(int fd, int *socket, int *pid_out)
        if (new < 0)
                return -errno;
 
+       err = os_access(argv[2], X_OK);
+       if (err < 0) {
+               printk(UM_KERN_ERR "port_connection : error accessing port-helper "
+                      "executable at %s: %s\n", argv[2], strerror(-err));
+               if (env == NULL)
+                       printk(UM_KERN_ERR "Set UML_PORT_HELPER environment "
+                               "variable to path to uml-utilities port-helper "
+                               "binary\n");
+               goto out_close;
+       }
+
        err = os_pipe(socket, 0, 0);
        if (err < 0)
                goto out_close;