contrib/docker: add LD_PRELOAD wrapper to fopen/open/opendir syscalls

diff --git a/contrib/docker/rootfs_prefix/Makefile b/contrib/docker/rootfs_prefix/Makefile
new file mode 100644 (file)
index 0000000..f26bebd
--- /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 (file)
index 0000000..d41f062
--- /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);
+}