LinuxQuestions.org - calling sys_read inside sys_write returns number of bytes read as zero

Hi All,

I am intercepting sys_write system call and within my_sys_write i will call the original syswrite.
Before calling the original sys_write, i have to get the contents of the file which will be replaced
by the current write.
So i open a new file descriptor inside my_sys_write and read the current buffer before calling the
original sys_write.
I have a problem in reading the current buffer using sys_read which returns zero .
I am giving the relevant code below

Code:

ssize_t  my_sys_write(unsigned int fd, const char * buf, size_t count)

{

          // Get the name of absolute name from file descritpor

          // calling the sys_open to get a new handle for reading 

        int openForRead = OriginalSysOpen(absoluteFileName,O_RDONLY,0777);

          // calling sys_read and storing the contents in the tmpBuf, bytesRead always return zero

        int bytesRead = OriginalSysRead(openForRead,tmpBuf, count );

        printk("  OPENFILEHANDLE %d BYTESREAD %d \n", openForRead,bytesRead);

        OriginalSysClose(openForRead);

        int returnValue = OriginalSysWrite(fd,buf,count);

        return returnValue;

}

After few hours of frustation, i am posting here to get some help.