[PATCH AUTOSEL 4.19 03/11] um: port_user: Improve error handling when port-helper is not found

[Sasha Levin <sashal@kernel.org>]

From: Glenn Washburn <development@efficientek.com>

[ Upstream commit 3cb5a7f167c620a8b0e38b0446df2e024d2243dc ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/um/drivers/port_user.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/um/drivers/port_user.c b/arch/um/drivers/port_user.c
index 5f56d11b886f..f66dc4efc64e 100644
--- 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>
@@ -175,6 +176,17 @@ 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;
-- 
2.35.1