From: Tobin C. Harding <me@tobin.cc>
Date: Wed, 15 Aug 2018 23:43:02 +0000 (+1000)
Subject: usernsexec: Make err out vebose for unshare error
X-Git-Tag: lxc-3.1.0~159^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ede912b440c579da4653ac9ded6d292b80e19f06;p=thirdparty%2Flxc.git

usernsexec: Make err out vebose for unshare error

Currently if lxc-usernsexec is run on a kernel without user namespaces
enabled the error message is

	unshare: Invalid argument
	read pipe: Success

This error message 'Invalid argument' does not point at the root cause
of the error.  We can help the user out by giving a more detailed error
message and also not using perror() if errno==0.

Improve error message by
 - Printing unshare flags
 - Printing suggested cause of failure (user namespace not enabled)
 - Print error message with fprintf() if errno==0 (EOF)

Signed-off-by: Tobin C. Harding <me@tobin.cc>
---

diff --git a/src/lxc/cmd/lxc_usernsexec.c b/src/lxc/cmd/lxc_usernsexec.c
index c342a90a0..107668273 100644
--- a/src/lxc/cmd/lxc_usernsexec.c
+++ b/src/lxc/cmd/lxc_usernsexec.c
@@ -375,7 +375,8 @@ int main(int argc, char *argv[])
 
 		ret = unshare(flags);
 		if (ret < 0) {
-			perror("unshare");
+			fprintf(stderr,
+				"Failed to unshare mount and user namespace\n");
 			return 1;
 		}
 		buf[0] = '1';
@@ -399,9 +400,13 @@ int main(int argc, char *argv[])
 
 	close(pipe_fds1[1]);
 	close(pipe_fds2[0]);
-	if (lxc_read_nointr(pipe_fds1[0], buf, 1) < 1) {
+	ret = lxc_read_nointr(pipe_fds1[0], buf, 1);
+	if (ret < 0) {
 		perror("read pipe");
 		exit(EXIT_FAILURE);
+	} else if (ret == 0) {
+		fprintf(stderr, "Failed to read from pipe\n");
+		exit(EXIT_FAILURE);
 	}
 
 	buf[0] = '1';