libfspkg.c

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/vfs.h>
#include <unistd.h>
#include <stdlib.h>
#include <dirent.h>
#include <dlfcn.h>
#include <stdio.h>
#include <fcntl.h>
#include <errno.h>

struct file_op {
   /*
    * file ops 
    */
   int         (*open) (const char *pathname, int flags, ...);
   int         (*close) (int fd);
               ssize_t(*readlink) (const char *path, char *buf, size_t bufsiz);
               ssize_t(*read) (int fd, void *buf, size_t count);

   /*
    * file ops: spillover 
    */

   /*
    * access ops 
    */
   int         (*access) (const char *pathname, int mode);
   int         (*statfs) (const char *path, struct statfs * buf);

   /*
    * access ops: spillover 
    */

   /*
    * directory ops 
    */
   DIR        *(*opendir) (const char *name);
   struct dirent *(*readdir) (DIR * dirp);
   int         (*closedir) (DIR * dirp);

   /*
    * directory ops: spillover 
    */
};

struct file_op real_ops;
struct file_op pkg_ops;

#define FAIL	{ \
        fprintf(stderr, "%s:%d:%s failed loading real symbol", __FILE__, __LINE__, __FUNCTION__); \
        abort(); \
}
static void _init_lib(void) {
   if (!(real_ops.open = dlsym(RTLD_DEFAULT, "open")))
      FAIL;
   if (!(real_ops.close = dlsym(RTLD_DEFAULT, "close")))
      FAIL;
   if (!(real_ops.readlink = dlsym(RTLD_DEFAULT, "readlink")))
      FAIL;
   if (!(real_ops.read = dlsym(RTLD_DEFAULT, "read")))
      FAIL;
   if (!(real_ops.access = dlsym(RTLD_DEFAULT, "access")))
      FAIL;
   if (!(real_ops.statfs = dlsym(RTLD_DEFAULT, "statfs")))
      FAIL;
   if (!(real_ops.opendir = dlsym(RTLD_DEFAULT, "opendir")))
      FAIL;
   if (!(real_ops.readdir = dlsym(RTLD_DEFAULT, "readdir")))
      FAIL;
   if (!(real_ops.closedir = dlsym(RTLD_DEFAULT, "closedir")))
      FAIL;
}

static void _init(void) {
   fprintf(stderr, "_init called\n");
   _init_lib();
}

int open(const char *pathname, int flags, ...) {
   return real_ops.open(pathname, flags);
}

int close(int fd) {
   return real_ops.close(fd);
}

ssize_t readlink(const char *path, char *buf, size_t bufsiz) {
   return real_ops.readlink(path, buf, bufsiz);
}

ssize_t read(int fd, void *buf, size_t count) {
   return real_ops.read(fd, buf, count);
}

int access(const char *path, int mode) {
   return real_ops.access(path, mode);
}

int statfs(const char *path, struct statfs *buf) {
   return real_ops.statfs(path, buf);
}

DIR        *opendir(const char *name) {
   return real_ops.opendir(name);
}

struct dirent *readdir(DIR * dirp) {
   return real_ops.readdir(dirp);
}

int closedir(DIR * dirp) {
   return real_ops.closedir(dirp);
}