dropbox_ext4.c

/*
 * dropbox_ext4.c
 *
 * Compile like this:
 *   gcc -shared -fPIC -ldl -o libdropbox_ext4.so dropbox_ext4.c
 *
 * Run Dropbox like this:
 *   LD_PRELOAD=./libdropbox_ext4.so ~/.dropbox-dist/dropboxd
 */
 
#define _GNU_SOURCE
 
#include <stdlib.h>
#include <sys/vfs.h>
#include <linux/magic.h>
#include <dlfcn.h>
 
int (*orig_statfs)(const char *path, struct statfs64 *buf) = NULL;
 
int statfs64(const char *path, struct statfs64 *buf) {
  if (orig_statfs == NULL) {
    orig_statfs = dlsym(RTLD_NEXT, "statfs64");
  }
  int retval = orig_statfs(path, buf);
  if (retval == 0) {
    buf->f_type = EXT4_SUPER_MAGIC;
  }
  return retval;
}

Dropbox_fix.markdown

Hey guys,

I have a really terrible hack, but it appears to work, so...

Dropbox calls statfs64 to get the filesystem type. Now, if only there was a way to change its return value to "ext4"... oh wait, there is!

Here's code of the new function: dropbox_ext4.c

/*
 * dropbox_ext4.c
 *
 * Compile like this:
 *   gcc -shared -fPIC -ldl -o libdropbox_ext4.so dropbox_ext4.c
 *
 * Run Dropbox like this:
 *   LD_PRELOAD=./libdropbox_ext4.so ~/.dropbox-dist/dropboxd
 */
 
#define _GNU_SOURCE
 
#include <stdlib.h>
#include <sys/vfs.h>
#include <linux/magic.h>
#include <dlfcn.h>
 
int (*orig_statfs)(const char *path, struct statfs64 *buf) = NULL;
 
int statfs64(const char *path, struct statfs64 *buf) {
  if (orig_statfs == NULL) {
    orig_statfs = dlsym(RTLD_NEXT, "statfs64");
  }
  int retval = orig_statfs(path, buf);
  if (retval == 0) {
    buf->f_type = EXT4_SUPER_MAGIC;
  }
  return retval;
}

Here's the compiled shared library, if you trust me enough to use it: libdropbox_ext4.so

If you manually start the Dropbox daemon like this, it will use the fake function:

LD_PRELOAD=libdropbox_ext4.so ~/.dropbox-dist/dropboxd

And, hopefully, it will accept any filesystem you throw at it. Of course, I can't promise that nothing will blow up.

If Dropbox starts up automatically, it won't pick up the hack. I'll let someone else figure out how to make it more permanent.

(via)