[lxc-devel] [lxd/master] lxc-to-lxd: Fix handling on snap

[stgraber on Github]

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From e93904bdb54f595d3df438663a9f70b7d652f2d8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?St=C3=A9phane=20Graber?= <stgraber at ubuntu.com>
Date: Fri, 27 Nov 2020 00:43:20 -0500
Subject: [PATCH] lxc-to-lxd: Fix handling on snap
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Running lxc-to-lxd from a snap environment is tricky.

We can't just use the previous approach of resolving the main container
dir through HostPath as any included file will cause a config read
failure. We also can't just have the snap run the entire binary on the
host as the linker would fail on liblxc.

Instead, this approach lets the loader take care of the dynamic
libraries and we then attach to the host mount namespace and process the
rest from there.

Signed-off-by: Stéphane Graber <stgraber at ubuntu.com>
---
 lxc-to-lxd/main.go         | 42 ++++++++++++++++++++++++++++++++++++++
 lxc-to-lxd/main_migrate.go |  2 +-
 2 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/lxc-to-lxd/main.go b/lxc-to-lxd/main.go
index a350214eda..66259f25eb 100644
--- a/lxc-to-lxd/main.go
+++ b/lxc-to-lxd/main.go
@@ -1,5 +1,47 @@
 package main
 
+/*
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <sched.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+__attribute__((constructor)) void init(void) {
+	int ret;
+	int mntns_fd;
+
+	if (getenv("SNAP") == NULL)
+		return;
+
+	mntns_fd = open("/proc/1/ns/mnt", O_RDONLY | O_CLOEXEC);
+	if (ret < 0) {
+		fprintf(stderr, "Failed open mntns: %s\n", strerror(errno));
+		_exit(EXIT_FAILURE);
+	}
+
+	ret = setns(mntns_fd, CLONE_NEWNS);
+	close(mntns_fd);
+	if (ret < 0) {
+		fprintf(stderr, "Failed setns to outside mount namespace: %s\n", strerror(errno));
+		_exit(EXIT_FAILURE);
+	}
+
+	ret = chdir("/");
+	if (ret < 0) {
+		fprintf(stderr, "Failed chdir /: %s\n", strerror(errno));
+		_exit(EXIT_FAILURE);
+	}
+
+	// We're done, jump back to Go
+}
+*/
+import "C"
 import (
 	"os"
 
diff --git a/lxc-to-lxd/main_migrate.go b/lxc-to-lxd/main_migrate.go
index 7937b847f0..5012afbe85 100644
--- a/lxc-to-lxd/main_migrate.go
+++ b/lxc-to-lxd/main_migrate.go
@@ -71,7 +71,7 @@ func (c *cmdMigrate) RunE(cmd *cobra.Command, args []string) error {
 	}
 
 	// Retrieve LXC containers
-	for _, container := range liblxc.Containers(shared.HostPathFollow(c.flagLXCPath)) {
+	for _, container := range liblxc.Containers(c.flagLXCPath) {
 		if !c.flagAll && !shared.StringInSlice(container.Name(), c.flagContainers) {
 			continue
 		}