How to interface with device drivers in an apk

[Shahin Ansari]

Greetings-

In order to learn more about the device drivers on the Android platform, I built an tutorial code and was able to interface with it from a user program. 

Here is the code I used for device driver:

/* Example Minimal Character Device Driver */

#include <linux/module.h>

static int __init hello_init(void)

{

printk("Hello Example Init\n");

return 0;

}

static void __exit hello_exit(void)

{

printk("Hello Example Exit\n");

}

module_init(hello_init);

module_exit(hello_exit);

MODULE_DESCRIPTION("Hello World Example");

MODULE_LICENSE("GPL");

Here is the code for the user space executable:

#include <stdio.h>

#include <stdlib.h>

#include <sys/types.h>

#include <sys/stat.h>

#include <fcntl.h>

#include <unistd.h>

int main(int argc, char **argv)

{

/* Our file descriptor */

int fd;

int rc = 0;

char *rd_buf[16];

printf("%s: entered\n", argv[0]);

/* Open the device */

fd = open("/dev/hello1", O_RDWR);

if ( fd == -1 ) {

perror("open failed");

rc = fd;

exit(-1);

}

printf("%s: open: successful\n", argv[0]);

/* Issue a read */

rc = read(fd, rd_buf, 0);

if ( rc == -1 ) {

perror("read failed");

close(fd);

exit(-1);

}

printf("%s: read: returning %d bytes!\n", argv[0], rc);

close(fd);

return 0;

}

***********************************************

Now I want to move this into an apk, and run it as an app. The only way I know of doing this is via JNI. So I created a HelloJNI project using another online tutorial. I need help with verifying I am on the right track, and what are some of the next steps to get my user program code into my JNI project and run it as an apk. I have already posted to a JNI forum, but I have not heard anything back. I think doing kernel development is a very unique skill, and that may be why other forums can not help me. I have seen similar discussions on this list and have reviewed them to ensure I provide all the information I should.

Thanks in Advance,

Sean

[Durgadoss Ramanathan]

I believe you are on the right track. Did your HelloJNI work ?

Also, JNI may be a preferred way; but not a must. You should be able to use JAVA APIs (BufferedReader & friends) from your app to interact with these files. Watch out for permission issues etc..

Thanks,

Durga

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Durgadoss

[Ramesh rama]

Are you able to Interact with JNI from Apk ?

[Shahin Ansari]

Yes. JNI works. That is, I created a HelloJNI, and the app runs. I then proceeded to add more methods for different data types, and I am able to see the corresponding handles (I think that is what they are called; the translated version of the method I created in the "MainActivity") in my JNI folder header file.