From c76419c0cf983f1ecd3d36aa236cc4e3f9cff733 Mon Sep 17 00:00:00 2001
From: Marc Fournier <marc.fournier@camptocamp.com>
Date: Wed, 5 Oct 2016 08:09:09 +0200
Subject: [PATCH] contrib/docker: add LD_PRELOAD wrapper to fopen/open/opendir
 syscalls

---
 contrib/docker/rootfs_prefix/Makefile        |  2 +
 contrib/docker/rootfs_prefix/rootfs_prefix.c | 63 ++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+)
 create mode 100644 contrib/docker/rootfs_prefix/Makefile
 create mode 100644 contrib/docker/rootfs_prefix/rootfs_prefix.c

diff --git a/contrib/docker/rootfs_prefix/Makefile b/contrib/docker/rootfs_prefix/Makefile
new file mode 100644
index 00000000..f26bebd0
--- /dev/null
+++ b/contrib/docker/rootfs_prefix/Makefile
@@ -0,0 +1,2 @@
+rootfs_prefix.so: rootfs_prefix.c
+	$(CC) -Wall -Werror -fPIC -shared -o rootfs_prefix.so rootfs_prefix.c -ldl
diff --git a/contrib/docker/rootfs_prefix/rootfs_prefix.c b/contrib/docker/rootfs_prefix/rootfs_prefix.c
new file mode 100644
index 00000000..d41f0625
--- /dev/null
+++ b/contrib/docker/rootfs_prefix/rootfs_prefix.c
@@ -0,0 +1,63 @@
+#define _GNU_SOURCE
+
+#include <stdio.h>
+#include <error.h>
+#include <dlfcn.h>
+#include <string.h>
+#include <errno.h>
+#include <dirent.h>
+
+#define PREFIX "/rootfs"
+#define BUFSIZE 256
+
+const char *add_prefix(const char *orig, char *prefixed) {
+	int status;
+	int errno;
+
+	if ((strncmp(orig, "/proc", 5) == 0) ||
+		(strncmp(orig, "/sys", 4) == 0)) {
+
+		status = snprintf(prefixed, BUFSIZE, "%s%s", PREFIX, orig);
+		if ((unsigned int)status >= BUFSIZE) {
+			error(status, ENAMETOOLONG, "'%s' got truncated when adding '%s' prefix: '%s'",
+				orig, PREFIX, prefixed);
+			return orig;
+		} else if (status < 1) {
+			error(status, errno, "adding '%s' prefix to file path failed: '%s' -> '%s'",
+				PREFIX, orig, prefixed);
+			return orig;
+		} else {
+			return (const char*) prefixed;
+		}
+
+	} else {
+		return orig;
+	}
+}
+
+FILE *fopen(const char *path, const char *mode) {
+	char filename[BUFSIZE] = "\0";
+
+	FILE *(*original_fopen)(const char*, const char*);
+	original_fopen = dlsym(RTLD_NEXT, "fopen");
+
+	return (*original_fopen)(add_prefix(path, filename), mode);
+}
+
+DIR *opendir(const char *name) {
+	char filename[BUFSIZE] = "\0";
+
+	DIR *(*original_opendir)(const char*);
+	original_opendir = dlsym(RTLD_NEXT, "opendir");
+
+	return (*original_opendir)(add_prefix(name, filename));
+}
+
+int *open(const char *pathname, int flags) {
+	char filename[BUFSIZE] = "\0";
+
+	int *(*original_open)(const char*, int);
+	original_open = dlsym(RTLD_NEXT, "open");
+
+	return (*original_open)(add_prefix(pathname, filename), flags);
+}
-- 
2.11.0