Databases
StackOverflow2013
Postsdbo
POCode for writing and reading on a device file from a kernel module?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POCode for writing and reading on a device file from a kernel module?
    primarykey
    data
    text
    <p>I have tried the following code many times .</p> <pre><code>#include&lt;linux/module.h&gt; #include&lt;linux/kernel.h&gt; #include&lt;linux/fs.h&gt; #include&lt;linux/cdev.h&gt; #include&lt;asm/uaccess.h&gt; #include&lt;linux/semaphore.h&gt; MODULE_LICENSE("DUAL BSD/GPL"); static int dev_open(struct inode *,struct file *); static int dev_release(struct inode *,struct file *); ssize_t dev_read(struct file *,char *, size_t ,loff_t *); ssize_t dev_write(struct file *,const char *,size_t ,loff_t *); static int major; int dev_major = 0; int dev_minor = 0; struct cdev *cdev; struct device { char array[100]; struct semaphore sem; }chr_arr; struct file_operations dev_ops = { .owner = THIS_MODULE, .read = dev_read, .write = dev_write, .open = dev_open, .release = dev_release }; ssize_t dev_read(struct file *filp,char *buf,size_t count,loff_t *offset) { int i; i=copy_to_user(buf,chr_arr.array,count); printk(KERN_ALERT"buff:%s",buf); return i; } ssize_t dev_write(struct file *filp,const char *buf,size_t count,loff_t *offset) { //printk(KERN_ALERT"\nsorry,byebye"); int j; //msg_ptr = kmalloc(count,GFP_KERNEL); //for(j=0;j&lt;count;j++) if(count&gt;100) return -1; j = copy_from_user(chr_arr.array,buf,count); //printk(KERN_ALERT"msg_ptr:%s",msg_ptr); return j; } static int dev_open(struct inode *inode,struct file *filp) { filp-&gt;private_data = inode-&gt;i_cdev; if(down_interruptible(&amp;chr_arr.sem)) { printk(KERN_INFO " could not hold semaphore"); return -1; } //printk(KERN_ALERT"ah ha the device is open !now we can go further"); return 0; } static int dev_release(struct inode *inode,struct file *filp) { up(&amp;chr_arr.sem); //module_put(THIS_MODULE); return 0; } static int init_device(void) { int result; dev_t dev_no,dev; result = alloc_chrdev_region(&amp;dev_no,0,1,"chr_dev"); if(result &lt; 0) { printk("sorry no major number left"); return result; } major = MAJOR(dev_no); dev = MKDEV(major,0); cdev = cdev_alloc(); cdev-&gt;ops = &amp;dev_ops; sema_init(&amp;chr_arr.sem,1); printk("the major number allocated is %d\n",major); result = cdev_add(cdev,dev,1); if(result &lt; 0 ) { printk(KERN_INFO "Unable to allocate cdev"); return result; } return 0; } static void clean_device(void) { cdev_del(cdev); unregister_chrdev_region(major,1); } module_init(init_device); module_exit(clean_device); </code></pre> <p>but its giving me the following warning.</p> <pre><code>CC [M] /home/karan/practice/scrw/scrw1.o In file included from /usr/src/linux-2.6.34.10-0.6/arch/x86/include/asm/uaccess.h:571:0, from /home/karan/practice/scrw/scrw1.c:4: In function ‘copy_from_user’,inlined from ‘write’ at /home/karan/practice/scrw/scrw1.c:43:6: /usr/src/linux-2.6.34.10-0.6/arch/x86/include/asm/uaccess_32.h:212:26: warning: call to ‘copy_from_user_overflow’ declared with attribute warning: copy_from_user() buffer size is not provably correct Building modules, stage 2. MODPOST 1 modules CC /home/karan/practice/scrw/scrw1.mod.o LD [M] /home/karan/practice/scrw/scrw1.ko </code></pre> <p>and then when I try to write echo hi > /dev/my_dev the screen freezes after 30 secs or so.</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. This table or related slice is empty.
    1. USkaran421
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POCode for writing and reading on a device file from a kernel module?
      1. This table or related slice is empty.
      1. VTUpMod
    1. COshouldn't you test for count < 100?
      singulars
      1. POCode for writing and reading on a device file from a kernel module?
      1. USypnos
    2. CO@ypnos thats ok but its not working whenever i put echo command it hangs after few secs....
      singulars
      1. POCode for writing and reading on a device file from a kernel module?
      1. USkaran421
    3. COThe problem probably lies somewhere else. Can you show more of your code? You can also try to recompile your kernel with debugging options enabled, that way you might get a stack trace when the freeze occurs.
      singulars
      1. POCode for writing and reading on a device file from a kernel module?
      1. USldx
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload