oracle: error overriding PWRITE64 with LD_PRELOAD

[klayme]

Hi all.
I'm trying to override PWRITE64 syscall (and maybe others) when using oracle database.
I created a shared library and it runs my code, but when I call the original pwrite, it errors out.
I guess there's something wrong in my code, but I'm new at c languaje, can someone tell me what am I doing wrong? This is the code;

#define _GNU_SOURCE
#include <stdio.h>
#include <dlfcn.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>


ssize_t pwrite64(int fd, const void *buf, size_t count, off_t offset) {
ssize_t (*real_open)(int fd, const void *buf, size_t count, off_t offset);
static int filedesc;
ssize_t retorno;

filedesc=open("/home/oracle/prman/traza_pwrite64",O_RDWR);
pwrite(filedesc, "first trace \n", 19,0);
close(filedesc);

if (!real_open) {
real_open = dlsym(RTLD_NEXT, "pwrite64");
}

filedesc=open("/home/oracle/prman/traza_pwrite64",O_RDWR);
pwrite(filedesc, "scnd trace \n", 19,0);
close(filedesc);

retorno=real_open(fd, buf, count, offset);

filedesc=open("/home/oracle/prman/traza_pwrite64",O_RDWR);
pwrite(filedesc, "third trace \n", 19,0);
close(filedesc);

return retorno;
}

When Oracle uses pwrite64 it errors, and third trace is never written into the trace file, can somebody help me?

[klayme]

Hi all. Thanks for your time.
I think the only problem was that I had to initialize real_open pointer to NULL before point it to the original PWRITE64 function:

real_open=NULL;

this seems to make it work

Thanks again