c - Linux kernel module copy_to_user not working -

i attepting write linux kernel module raspberry pi. good, except when try use either copy_to_user, or put_user, returns value of "34336" if print llu, , if print character, nothing.

the interesting thing working, made changes, stopped working, reverted working version, , no longer works.

code module:

    ssize_t st_read(struct file *filp, char *buf, size_t count, loff_t *f_pos)     {             char memory_buffer = 'b';             /* transferring data user space */             copy_to_user(buf,memory_buffer,1);              /* changing reading position best suits */             if (*f_pos == 0) {                     *f_pos+=1;                     return 1;             } else {                     return 0;             }     } 

code reading value:

    fd = open("/dev/systimer", o_rdonly);      // check errors     if(fd < 0) {             perror("open(o_rdonly)");             return errno;     } else             close(fd);      read(fd, &buf, 1);     printf("buffer: %llu\n", buf);     printf("buffer2: %c\n", buf); 

output is:

    buffer: 34336     buffer2: 

thanks.

you have closed before read. should check return value of read()

// check errors if(fd < 0) {         perror("open(o_rdonly)");         return errno;  } else         close(fd);   // <-- closing fd here  read(fd, &buf, 1);   // <-- fd closed