Linux World: May 2018

unable to launch vmplayer 14

After installing vmplayer 14 in ubuntu 18.04 player might fail to launch with vmmon modules failing to compile with errors

and

To get around these errors we will need to modify the code of vmmon as given in https://github.com/mkubecek/vmware-host-modules/commit/562121d7bc06 and https://github.com/mkubecek/vmware-host-modules/commit/770c7ffe611520ac96490d235399554c64e87d9f To do the above mentioend changes, you can follow the following steps. Go to the folder

Untar the folder vmmon.tar

This will create a folder vmmon-only which will contain the code for the module vmmon.Now we can follow the changes mentioned in the above two links in the respective files.

After doing the changes recreate the vmmon.tar using the following command

Now we should be able to launch vmplayer and the modules should get compiled successfully.

Basic Char driver for kernel version 4.15.0

In the post, Example Char driver, the code for a basic charchater driver is given along with the steps to insert it into the kernel and create a char device.

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h> // required for various structures related to files liked fops. 
#include <linux/uaccess.h> // required for copy_from and copy_to user functions 
#include <linux/semaphore.h>
#include <linux/cdev.h> 
static int Major;
dev_t dev_no,dev;
struct device1 {
 char array[100];
 struct semaphore sem;
}char_arr;

int open(struct inode *inode, struct file *filp)
{
 
 printk(KERN_INFO "Inside open \n");
 if(down_interruptible(&char_arr.sem)) {
  printk(KERN_INFO " could not hold semaphore");
  return -1;
 }
 return 0;
}

int release(struct inode *inode, struct file *filp) {
 printk (KERN_INFO "Inside close \n");
 printk(KERN_INFO "Releasing semaphore");
 up(&char_arr.sem);
 return 0;
}

ssize_t read(struct file *filp, char *buff, size_t count, loff_t *offp) {
 unsigned long ret;
 printk("Inside read \n");
 ret = copy_to_user(buff, char_arr.array, count);
 return ret;
}

ssize_t write(struct file *filp, const char *buff, size_t count, loff_t *offp) { 
 unsigned long ret;
 printk(KERN_INFO "Inside write \n");
 ret = copy_from_user(char_arr.array, buff, count);
 return count;
}

struct file_operations fops = {
 read:  read,
 write:  write,
 open:   open,
 release: release
};

struct cdev *kernel_cdev;

int char_arr_init (void) {
 int ret;

kernel_cdev = cdev_alloc(); 
  kernel_cdev->ops = &fops;
 kernel_cdev->owner = THIS_MODULE;
 printk (" Inside init module\n");
  ret = alloc_chrdev_region( &dev_no , 0, 1,"chr_arr_dev");
    if (ret < 0) {
  printk("Major number allocation is failed\n");
  return ret; 
 }
 
    Major = MAJOR(dev_no);
    dev = MKDEV(Major,0);
 sema_init(&char_arr.sem,1); 
 printk (" The major number for your device1 is %d\n", Major);
 ret = cdev_add( kernel_cdev,dev,1);
 if(ret < 0 )
 {
 printk(KERN_INFO "Unable to allocate cdev");
 return ret;
 }

return 0;
}

void char_arr_cleanup(void) {
 printk(KERN_INFO " Inside cleanup_module\n");
 cdev_del(kernel_cdev);
 unregister_chrdev_region(Major, 1);
}
MODULE_LICENSE("GPL"); 
module_init(char_arr_init);
module_exit(char_arr_cleanup);

The following is the updated code for the same driver tested for the kernel version 4.15.0.To test the working of the driver please use the code given in post User access for example driver

tar Cannot stat: No such file or directory

tar is a command used to create an archive for the folder to combine the contents of a folder into one archive. If we want to create an archive for the folder named xyz, as xyz.tar , running the command as shown below will throw an error

The problem is because of the wrong sequence of options being passed to the tar command. To get around the error the sequence of options to be passed is as below.

The above command will run with out errors and it should be able to create xyz.tar.

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unable to launch vmplayer 14

Basic Char driver for kernel version 4.15.0

tar Cannot stat: No such file or directory