I am trying to read data from a bluetooth barcode scanner (KDC300) using C. Here is the code I have so far, and the program successfully establishes a bluetooth connection to the scanner, but when a barcode is scanned, no input is displayed on the screen (Eventually more will be done with the data, but we have to get it working first, right).
Here is the program:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <termios.h>
#include <sys/ioctl.h>
int main (int argc, const char * argv[]) {
// define vars
int STOP = 0;
//char buf[255];
if(argv[1])
{
int fd = open("/dev/tty.KDC1", O_RDONLY);
if(fd == -1)
{
printf("%s", strcat("Unable to open /dev/tty.", argv[1]));
}
int res;
while(STOP == 0)
{
while((res = read(fd,buf,255)) == 0);
{
if(res > 0)
{
buf[res]=0;
printf("%s:%d\n", buf, res);
if(buf[sizeof(buf)]=='\n') break;
}
}
}
}
return 0;
}
If anyone has any ideas, I am at a loss on this so far. If it is any help, I can run screen /dev/tty.KDC1 and any barcodes scanned on the scanner appear in the terminal, I just can't do anything with the data.
Jud
This line:
while((res = read(fd,buf,255)) == 0);
Does not do what you think it does. That's a while loop with an empty body.
#tommieb75,
the strcat statement was from the first "go" at the program, I took a variable from argv[1] and appended it to the /dev/tty.* so you could select which device you wanted to monitor.
I am not sure why I had commented out buf, probably stems from looking at the code too much / trying different approaches and forgetting where I was (not much of a C programmer, which is how I can get lost in 30 LOC).
#caf, Good catch on the extra semi-colon after the while loop, unfortunately, even after correcting it, the program doesn't behave correctly.
I am researching the problem further. I can verify (with osx packetlogger) that the computer is getting the data, but the but the buffer never has any data placed in it.
-Jud
---------------Edit--------------
I solved the problem after a little trial and error. Adding the following code to setup the serial connection solved everything:
struct termios theTermios;
memset(&theTermios, 0, sizeof(struct termios));
cfmakeraw(&theTermios);
cfsetspeed(&theTermios, 115200);
theTermios.c_cflag = CREAD | CLOCAL; // turn on READ
theTermios.c_cflag |= CS8;
theTermios.c_cc[VMIN] = 0;
theTermios.c_cc[VTIME] = 10; // 1 sec timeout
ioctl(fileDescriptor, TIOCSETA, &theTermios);
Thanks to the other answers for getting me to this point.
Here is the best info I've found.
The C program on there using termios worked just by adding
#include<string.h>
And changing the baudrate to match my needs.
In your code
printf("%s", strcat("Unable to open /dev/tty.", argv[1]));
Why did you do that? It would be easier to do it this way:
printf("%s: Unable to open /dev/tty.KDC1", argv[0]);
Why the parameter referencing to the command line?
res = read(fd,buf,255)
Why did you have buf declaration commented out above?
Related
My problem is to deal with sparse file reads and understand where the extents of the file are to perform some logic around it.
Since, there is no direct API call to figure these stuff out, I decided to use ioctl api to do this. I got the idea from how cp command deals with problems of copying over sparse files by going through their code and ended up seeing this.
https://github.com/coreutils/coreutils/blob/df88fce71651afb2c3456967a142db0ae4bf9906/src/extent-scan.c#L112
So, I tried to do the same thing in my sample program running in user space and it errors out with "Invalid argument". I am not sure what I am missing or if this is even possible from userspace. I am running on ubuntu 14.04 on an ext4 file system. Could this be a problem with device driver supporting these request modes underneath?
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/fcntl.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <linux/fs.h>
#include "fiemap.h" //This is from https://github.com/coreutils/coreutils/blob/df88fce71651afb2c3456967a142db0ae4bf9906/src/fiemap.h
int main(int argc, char* argv[]) {
int input_fd;
if(argc != 2){
printf ("Usage: ioctl file1");
return 1;
}
/* Create input file descriptor */
input_fd = open (argv [1], O_RDWR);
if (input_fd < 0) {
perror ("open");
return 2;
}
union { struct fiemap f; char c[4096]; } fiemap_buf;
struct fiemap *fiemap = &fiemap_buf.f;
int s = ioctl(input_fd, FS_IOC_FIEMAP, fiemap);
if (s == 0) {
printf("ioctl success\n");
} else {
printf("ioctl failure\n");
char * errmsg = strerror(errno);
printf("error: %d %s\n", errno, errmsg);
}
/* Close file descriptors */
close (input_fd);
return s;
}
As you're not properly setting the fiemap_buf.f parameters before invoking ioctl(), it is likely that the EINVAL is coming from the fiemap invalid contents than from the FS_IOC_FIEMAP request identifier support itself.
For instance, the ioctl_fiemap() (from kernel) will evaluate the fiemap.fm_extent_count in order to determine if it is greater than FIEMAP_MAX_EXTENTS and return -EINVAL in that case. Since no memory reset nor parameterization is being performed on fiemap, this is very likely the root cause of the problem.
Note that from the coreutils code you referenced, it performs the correct parameterization of fiemap before calling ioctl():
fiemap->fm_start = scan->scan_start;
fiemap->fm_flags = scan->fm_flags;
fiemap->fm_extent_count = count;
fiemap->fm_length = FIEMAP_MAX_OFFSET - scan->scan_start;
Note fiemap is not recommended as you have to be sure to pass FIEMAP_FLAG_SYNC which has side effects. The lseek(), SEEK_DATA and SEEK_HOLE interface is the recommended one, though note that will, depending on file system, represent unwritten extents (allocated zeros) as holes.
I want to shred some temp files produced by my C program before the files are removed.
Currently I am using
system("shred /tmp/datafile");
system("rm /tmp/datafile");
from within my program, but I think instead of calling the system function is not the best way (correct me if I am wrong..) Is there any other way I can do it? How do I shred the file from within my code itself? A library, or anything? Also, about deletion part, is this answer good?
Can I ask why you think this is not the best way to achieve this? It looks like a good solution to me, if it is genuinely necessary to destroy the file contents irretrievably.
The advantage of this way of doing it are:
the program already exists (so it's faster to develop); and
the program is already trusted.
The second is an important point. It's possible to overstate the necessity of elaborately scrubbing files (Peter Gutmann, in a remark quoted on the relevant wikipedia page, has described some uses of his method as ‘voodoo’), but that doesn't matter: in any security context, using a pre-existing tool is almost always more defensible than using something home-made.
About the only criticism I'd make of your current approach, using system(3), is that since it looks up the shred program in the PATH, it would be possible in principle for someone to play games with that and get up to mischief. But that's easily dealt with: use fork(2) and execve(2) to invoke a specific binary using its full path.
That said, if this is just a low-impact bit of tidying up, then it might be still more straightforward to simply mmap the file and quickly write zeros into it.
You can use the following code:
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <stdio.h>
#define BUF_SIZE 4096
#define ABS_FILE_PATH "/tmp/aaa"
int main()
{
//get file size
struct stat stat_buf;
if (stat(ABS_FILE_PATH, &stat_buf) == -1)
return errno;
off_t fsize = stat_buf.st_size;
//get file for writing
int fd = open(ABS_FILE_PATH, O_WRONLY);
if (fd == -1)
return errno;
//fill file with 0s
void *buf = malloc(BUF_SIZE);
memset(buf, 0, BUF_SIZE);
ssize_t ret = 0;
off_t shift = 0;
while((ret = write(fd, buf,
((fsize - shift >BUF_SIZE)?
BUF_SIZE:(fsize - shift)))) > 0)
shift += ret;
close(fd);
free(buf);
if (ret == -1)
return errno;
//remove file
if (remove(ABS_FILE_PATH) == -1)
return errno;
return 0;
}
I have usb char device which I managed to bind to /dev/device0 with usb skeleton 2.2 driver (only with few comments to understand it).
Now I have to write user application, which will send and recieve commands as ascii chars.
I am able to send commands with write without problems, but I don't know how to read properly from device.
As I don't know how long the message will be, I tried something like this
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char** argv)
{
char *c, *ret;
int fd,err;
ret = malloc(1);
char *dev = "/dev/device0";
fd = open(dev, O_RDWR);
printf("fd: %d\n", fd);
if (fd == -1) {
printf("fopen() failed");
exit(1);
}
command = "command1";
write(fd, command, strlen(command));
while (read(fd, ret,1)!=EOF)
{
fprintf(stderr,"%c\n",ret);
}
close(fd);
return 0;
}
but it doesn't work, it seems to deadlock somehow or get into state very similar to that. I was able to find, that the number of reads is random, usually 3-6 and then the program waits (maybe waiting for data from device, but I'm not sure with this), during last read function wait_event_interruptible() in driver's read() function returns -512 and meanwhile the callback function of penultimate read isn't called.
Why is this happening and how do I find out whether there are any data the device sent?
char *ret;
Memory is not allocated to your pointer ret and you are writing to that location which is UB.Hence you might see a crash. Allocate memory to your pointer.
Edits:
Else
If you just want to reach character by character have
char ret;
read():
read returns the number of characters it read. When it reaches the end
of the file, it won't be able to read any more (at all) and it'll
return 0, not EOF.
So make the below changes:
while (read(fd, ret,1)!= 0)
{
fprintf(stderr,"%c\n",ret);
}
There are probably several problems with the code below. Found it online after searching for a way to get keyboard input in linux. I've verified the correct event for keyboard input. The reason it seems fishy to me is regardless of what i put in the filepath, it always seems to pass the error check (the open call returns something greater than 0). Something is obviously wrong, so suggestions are welcome.
This won't run correctly unless you run the exe as su.
When i want to read in my keystroke, do i just use something like fgets on the file descriptor in an infinite while loop(would that even work)? I want it to be constantly polling for keyboard inputs. Any tips on decoding the inputs from the keyboard event?
Thanks again! This project of mine may be overly ambitious, as it's been a really long time since i've done any coding.
#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
#include <fcntl.h>
#include <linux/input.h>
#include <unistd.h>
// Edit this line to reflect your filepath
#define FILE_PATH "/dev/input/event4"
int main()
{
printf("Starting KeyEvent Module\n");
size_t file; //will change this to int file; to make it possible to be negative
const char *str = FILE_PATH;
printf("File Path: %s\n", str);
error check here
if((file = open(str, O_RDONLY)) < 0)
{
printf("ERROR:File can not open\n");
exit(0);
}
struct input_event event[64];
size_t reader;
reader = read(file, event, sizeof(struct input_event) * 64);
printf("DO NOT COME HERE...\n");
close(file);
return 0;
}
the problem is here:
size_t file;
size_t is unsigned, so it will always be >=0
it should have been:
int file;
the open call returns something greater than 0
open returns int, but you put in in an unsigned variable (size_t is usually unsigned), so you fail to detect when it is <0
I am working on what I believe should be a simple program I have googled around and all I can find is stuff for C#, C++.
What I would like to accomplish is to start my program written in C and have it listen for certain keystrokes. I have a function written that will move a servo so I would like to integrate the Up and Down arrow keys to execute the function to move the servo one direction or the other. Is this possible in C?
Are you working on linux or windows? Based on that, there are alternatives that can be used.
If you are working on windows, a function should be familiar to you : kbhit()? Though it is now deprecated, the working knowledge of it could be useful :)
Assuming that you are working on linux, have you tried NCurses?
Taken from [Here]: (http://www.linuxmisc.com/9-unix-programmer/d5b30f8d1faf8d82.htm)
The problem is three-fold:
You have to check if data is available without blocking. A simple
'read' or fgets' or whatever will block your process until data is
available -- you don't want that.
You have to bypass any buffering
because otherwise you would have to check both the buffer and the
device.
You need to coerce the terminal driver to give you data as
it's available rather than accumulating the whole thing into a
line.
From the same page:
That said, I present the following awkward, hastily-written,
uncommented code, which may be instructive or may not ( edited in part by me, was missing parenthesis and not indented)
#include <stdio.h>
#include <termios.h>
#include <unistd.h>
#include <sys/time.h>
#include <sys/types.h>
static struct termios orig_term;
void u_cleanup(void)
{
tcsetattr(0, TCSANOW, &orig_term);
}
int u_kbhit(void)
{
struct termios t;
int ret;
fd_set rfd;
struct timeval to;
static int first_hit=0;
if(first_hit==0)
{
if(tcgetattr(0, &t)!=0) exit(0);
orig_term=t;
cfmakeraw(&t);
if(tcsetattr(0, TCSANOW, &t)!=0) exit(0);
atexit(u_cleanup);
first_hit=1;
}
FD_ZERO(&rfd);
FD_SET(0, &rfd);
to.tv_sec=0;
to.tv_usec=0;
if(select(1, &rfd, NULL, NULL, &to)==1) return 1;
return 0;
}
int u_getchar(void)
{
int ret;
fd_set rfc;
unsigned char buf;
if(read(0, &buf, 1)!=1) ret=0;
else ret=buf;
return ret;
}
int main(void)
{
while(1)
{
if(u_kbhit())
{
int key=u_getchar();
printf("hit: %d\r\n", key);
if(key==3)
{
printf("you hit control-c\r\n");
exit(0);
}
}
usleep(100);
}
return 0; // inaccessible code, to prevent compiler warning
}