Hi i want to pass a data from my char device driver to serial port ttyS0..
I have created a simple char driver module which reads and write and it's my first tym doing it.. i am using debian guest os...
e.g.
echo "hello" > /dev/mydev
now when /dev/mydev receives the data it will then alter the string into something like "hello too" which is passed to my serial port /dev/ttyS0..
how can i alter the string?.. is it possible to use if statement inside mydev?
e.g
if(string=="hello"){
alterstringTO: hello to;
pass "hello to" /dev/ttyS0;
like echoing in terminal..
echo "hello to" > /dev/ttyS0
}
Is that possible?... or is there any other way doing it?
Here some of the code..
ssize_t dev_read(struct file *filp, char *buf, size_t clen, loff_t *f_pos){
short cnt =0;
while(clen && (msg[Pos]!=0))
{
put_user(msg[Pos],buf++);
cnt++;
clen--;
Pos++;
}
return cnt;
}
ssize_t dev_write(struct file *filp, const char *buf, size_t clen, loff_t *f_pos){
short dec = clen-1;
short cnt=0;
memset(msg,0,50);
Pos=0;
while(clen>0)
{
msg[cnt++] = buf[dec--];
clen--;
}
return cnt;
}
Thanks in advance..
Just a comment on writing to the serial port:
Remember the Linux foundations, everything is a file in Linux. To write to the device driver from a program you need to open the file for writing and then you can fprintf whatever data you want. You can do that from user space as well (the recommended way)
Refer to the following man pages:
man fopen
man fread/fwrite
man fprintf
man fclose
I'm not exactly sure what you are trying to achieve here, as the question and the intent seems unclear to me. I'll provide some guidance, but recommend that you edit your question and make it more readable.
Your snippet to compare strings is not correct. You can learn more about how to compare strings in C in here.
Altering a string in C is a basic operation that you learn when you start working with strings. This should help you getting started.
As final remark, please note that programming for the kernel requires extra care. A small mistake may lead to a crash and loss of data. If you really must, then the book Linux Device Drivers 3rd Edition is freely available and can help you further.
Related
I have tried running opensnoop.py but using
fnname_open='do_sys_open'
(which I have seen in other scripts) instead of
fnname_open = b.get_syscall_prefix().decode() + 'open'
# = '__x86_sys_open' on Ubuntu 18.04
but the script then stops printing file names. What is causing the difference?
When using attach_kprobe(event=fn) is fn a system call or an event?
Do you get list of possible syscall from /proc/kallsyms as described here?
A BPF program attached to __x86_sys_open won't have the same result if you attach it to do_sys_open instead because those two functions don't have the same prototype:
long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode);
long sys_open(const char __user *filename, int flags, umode_t mode);
So the filename argument, for example, won't be stored in the same register depending on which function you trace. You will need to edit the BPF program as well to fix this.
I'm currently integrating libFuzzer in a project which parses files on the hard drive. I have some prior experience with AFL, where a command line like this one was used:
afl-fuzz -m500 -i input/ -o output/ -t100 -- program_to_fuzz ##
...where ## was a path to the generated input.
Looking at libFuzzer however, I see that the fuzz targets look like this:
extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
DoSomethingInterestingWithMyAPI(Data, Size);
return 0; // Non-zero return values are reserved for future use.
}
I understand that the input isn't provided in the form of a file, but as a buffer in-memory instead. The problem is that the program I'm trying to fuzz works with files and obtains its data through fread() calls. At no point in time is the whole input supposed to be loaded in memory (where, in the general case, it might not even fit); so there's not much I can do with a const uint8_t*.
Writing the buffer back to the hard drive to get back a file seems extremely inefficient. Is there a way around this?
You can do as in this example from google security team.
The buf_to_file defined here takes your buffer and returns a char* pathname you can then pass to you target:
(from https://github.com/google/security-research-pocs/blob/master/autofuzz/fuzz_utils.h#L27 )
// Write the data provided in buf to a new temporary file. This function is
// meant to be called by LLVMFuzzerTestOneInput() for fuzz targets that only
// take file names (and not data) as input.
//
// Return the path of the newly created file or NULL on error. The caller should
// eventually free the returned buffer (see delete_file).
extern "C" char *buf_to_file(const uint8_t *buf, size_t size);
Be sure to free the ressource with the delete_file function.
You could use LD_PRELOAD and override fread.
I have been trying to write a working program that takes in data from a UDP socket and displays it in an edit control box as you receive the data (My exposure to c++ is also only about a week :P have only done embedded C code before). I have a working program that can send and output data on a button click but I want something that can do it in real time. The aim is scale this up into a larger GUI program that can send control data to hardware and get responses from them.
I have run into various problems including:
The program just not executing my OnReceivefunction (derived from
CAsyncSocket)
Getting the OnReceive function to run on a separate thread so that it can still run after a button has been clicked sending a control packet to the client then waiting for a response in a while loop
Not being able to output the data in the edit box (tried using both CEdit and CString)
ReplaceSel error saying that the type char is incompatible with LPCTSTR
My code is based on this codeproject.com tutorial, being almost exactly what I want but I get the error in 4.
EDIT: the error in 4. disappears when I change it to a TCHAR but then it outputs random chinese characters. The codeproject.com tutorial outputs the correct characters regardless of char or TCHAR declaration. When debugged my code has type wchar_t instead type char like the other code.
Chinese output
In the working program echoBuffer[0] the character sent and displayed was a 1
UINT ReceiveData(LPVOID pParam)
{
CTesterDlg *dlg = (CTesterDlg*)pParam;
AfxSocketInit(NULL);
CSocket echoServer;
// Create socket for sending/receiving datagrams
if (echoServer.Create(12345, SOCK_DGRAM, NULL) == 0)
{
AfxMessageBox(_T("Create() failed"));
}
for (;;)
{ // Run forever
// Client address
SOCKADDR_IN echoClntAddr;
// Set the size of the in-out parameter
int clntAddrLen = sizeof(echoClntAddr);
// Buffer for echo string
char echoBuffer[ECHOMAX];
// Block until receive message from a client
int recvMsgSize = echoServer.ReceiveFrom(echoBuffer, ECHOMAX, (SOCKADDR*)&echoClntAddr, &clntAddrLen, 0);
if (recvMsgSize < 0)
{
AfxMessageBox(_T("RecvFrom() failed"));
}
echoBuffer[recvMsgSize] = '\0';
dlg->m_edit.ReplaceSel(echoBuffer);
dlg->m_edit.ReplaceSel(_T("\r\n"));
}
}
After reading the link that #IInspectable provided about working with strings and checking the settings differences between the two programs it became clear that the issue lay with an incorrect conversion to UNICODE. My program does not require it so I disabled it.
This has cleared up the issue in 4. and provided solutions for 2 and 3.
I also think I know why another instance of my program would not run OnReceivein 1. because that file was not being defined by one that was already being run by the program, but that is now irrelevant.
I am using Star iOS SDK to print receipts (like a restaurant bill) but am facing problems implementing column settings and cell spacing for proper alignment. I have checked out the documentation but have not found something useful.
The line code manual has some signals/commands which I am unable to understand. Can anyone help me out with that?
The commands referenced in the Line Mode manual need to be converted into bytes and then sent to the printer. The StarIO iOS SDK package you downloaded has a manual called "README_StarIO_POSPrinter_iOS_SDK.pdf". (http://www.starmicronics.com/absolutefm/absolutefm/afmviewfaq.aspx?faqid=175) Did you check out pages 9-15? The StarIO framework is explained here.
Specific to your question about sending commands, page 13 shows you how to write to the port using a byte array, but make sure you add StarIO.framework and open the communication port first.
From the manual:
//Set a byte array to send to the printer
//command = { A, B, C, D, Feed 3mm, Full Cut}
unsigned char command = {0x41, 0x42, 0x43, 0x44, 0x1B, 0x7A, 0x00, 0x1B, 0x64, 0x02};
Uint bytesWritten = 0;
#Try
{
While(bytesWritten < (sizeof command))
{
bytesWritten += [port writePort: command : bytesWritten : sizeof command - bytesWritten];
}
}
#Catch(PortException)
{
//There was an error writing to the port
}
Also described is how to close ports (make sure you close every opened port) and getting printer status.
Let me know if this helps.
I talked to SDK developers of start micronics, as I was facing the same problem using TSP100 model. Here is the reply from one of their tech guy.
"Unlike most of our other models the TSP100 series is a bit unique in that it is raster only meaning that it does not have the text formatting commands that our other printers do (ie, the printer just prints whatever receipt image you send it). Any formatting would be done in your application however you would like to do it before creating the image to send to the printer"
So this is clear that you have to maintain the column width, formatting, alignment etc everything by yourself.
I am writing an UDP client/server programs in C on linux. The thing is that I must add connection check feature. in linux man pages i found example of udp client with this feature( http://www.kernel.org/doc/man-pages/online/pages/man3/getaddrinfo.3.html ). It uses write/read functions to check server response. I tried to apply it to my program, and it looks like this:
char *test = "test";
nlen = strlen(test) + 1;
if (write(sock, test, nlen) != nlen) { // socket with the connection
fprintf(stderr, "partial/failed write\n");
exit(EXIT_FAILURE);
}
nread = read(sock, buf, nlen);
if (nread == -1) {
perror("Connection");
exit(EXIT_FAILURE);
}
the problem is than than i execute program with this bit when server is on, it does nothing except reading input infinite time which it doesn't use too. I tried kill(getpid(), SIGHUP) interrupt, which i found other similar topic here, and shutdown(sock, 1), but nothing seems to work. Could you please tell me a way out how to stop the input read or any other possible option to check if udp server is active?
You should use asynchronous reading.
For this you must use the select() function from "sys/socket.h".
The function monitors the socket descriptor for changes without blocking.
You can find the reference for it here or here or by typing "man select" in your console.
There is an example here for Windows, but its usage is very similar to UNIX.