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POLinux Char Driver: blocking ioctl call
 

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  1. POLinux Char Driver: blocking ioctl call
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    <p>I am new to driver development, and I am trying to write a simple char driver that has ioctl that allows user process to get the time(timespec) that my char driver took on last read and write. </p> <pre class="lang-c prettyprint-override"><code>long charmem_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) { struct charmem_dev *dev = filp-&gt;private_data; if (down_interruptible(&amp;dev-&gt;sem)) { printk(KERN_WARNING "I got booted!!\n"); return -ERESTARTSYS; } printk(KERN_WARNING "charmem: in ioctl; cmd = %d, arg = %d\n", (int)cmd, (int)arg); switch(cmd) { case IOCTL_GET_LAST_READ_TIME: printk("charmem_ioctl: returning last read time delta, exiting...\n"); up(&amp;dev-&gt;sem); return dev-&gt;last_read_delta.tv_nsec; break; case IOCTL_GET_LAST_WRITE_TIME: printk("charmem_ioctl: returning last write time delta, exiting...\n"); up(&amp;dev-&gt;sem); return dev-&gt;last_write_delta.tv_nsec; break; case IOCTL_RESET_READ: /*return read-pointer to the start of buffer*/ dev-&gt;rp = dev-&gt;buffer; break; case IOCTL_RESET_WRITE: /*return write-pointer to the start of buffer*/ dev-&gt;wp = dev-&gt;buffer; break; case IOCTL_LOAD_BUFFER_TO_CACHE: load_buffer_to_cache(dev-&gt;buffer, dev-&gt;buffer_size); break; default: printk("charmem_ioctl: invalid ioctl command, exiting...\n"); up(&amp;dev-&gt;sem); return -EFAULT; } up(&amp;dev-&gt;sem); return 0; } struct file_operations charmem_fops = { .owner = THIS_MODULE, .llseek = no_llseek, .read = charmem_read, .write = charmem_write, .unlocked_ioctl = charmem_ioctl, .open = charmem_open, .release = charmem_release, }; </code></pre> <p><code>main.c</code> -- user program that tests my char device:</p> <pre class="lang-c prettyprint-override"><code>int fd = 0, ret = 0; fd = open("/dev/charmem0", O_RDWR); if (fd &lt; 0) { printf("/dev/charmem0 unable to access (fd = %d)... EXITING\n", fd); return -1; } ret = write(fd,msg1,10); ret = read(fd,user_buffer,10); read_delta = ioctl(fd, IOCTL_GET_LAST_READ_TIME); printf("read_delta : %d\n ", read_delta); write_delta = ioctl(fd, IOCTL_GET_LAST_WRITE_TIME); printf("write_delta : %d\n ", write_delta); </code></pre> <p><code>main.c</code> is the program that tests my char device; the program blocks after printing out <code>read_delta</code> value, and I am assuming that it blocks on ioctl. What am I doing wrong in my code?</p>
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    1. USCristian Ciupitu
    1. USMidnight Blue
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    1. COWhat makes you think something is wrong? (NB: You should not return EFAULT, but ENOTTY in the default case.)
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      1. POLinux Char Driver: blocking ioctl call
      1. USjørgensen
    2. COWhat do you see in the kernel log when you run your program? When your userspace program is blocked, what does /proc/<PID>/stack show (where "<PID>" is replaced by the PID number of the blocked process using your ioctl)?
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      1. POLinux Char Driver: blocking ioctl call
      1. USRoland
    3. COWhat are you seeing in dmesg? Can you ctrl-C and kill the program when it blocks?
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      1. POLinux Char Driver: blocking ioctl call
      1. USutopiabound
 

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