How is ioctl defined?
In computing, ioctl (an abbreviation of input/output control) is a system call for device-specific input/output operations and other operations which cannot be expressed by regular system calls. It takes a parameter specifying a request code; the effect of a call depends completely on the request code.
What does ioctl do in C?
The ioctl function performs the generic I/O operation command on filedes . A third argument is usually present, either a single number or a pointer to a structure. The meaning of this argument, the returned value, and any error codes depends upon the command used. Often -1 is returned for a failure.
Why is ioctl used?
The ioctl function is useful for implementing a device driver to set the configuration on the device. e.g. a printer that has configuration options to check and set the font family, font size etc. ioctl could be used to get the current font as well as set the font to a new one.
What is ioctl return?
RETURN VALUE top Usually, on success zero is returned. A few ioctl() requests use the return value as an output parameter and return a nonnegative value on success. On error, -1 is returned, and errno is set to indicate the error.
How is ioctl different from read and write?
Show activity on this post. ioctl should only be used for those operations that aren’t provided by default in the kernel. Having to call ioctl to read or write data to your device takes away a lot of the ease of use you have when using the simple read or write calls.
How do I use ioctl device driver?
Steps involved in IOCTL
- Create IOCTL command in driver.
- Write IOCTL function in the driver.
- Create IOCTL command in a Userspace application.
- Use the IOCTL system call in a Userspace.
Is ioctl blocking call?
The IOCTL call has many functions; establishing blocking mode is only one of its functions. The value in COMMAND determines which function IOCTL will perform. The REQARG of 0 specifies non-blocking (a REQARG of 1 would request that socket S be set to blocking mode).
Is ioctl thread safe?
ioctl() is not one of them, so it IS thread-safe. However, ioctl() is a cancellation point, so the thread can be terminated once it reaches ioctl().
What is magic number in ioctl?
To help programmers create unique ioctl command codes, these codes have been split up into several bitfields. The first versions of Linux used 16-bit numbers: the top eight were the “magic” number associated with the device, and the bottom eight were a sequential number, unique within the device.
Is ioctl a blocking call?
How is ioctl implemented in Linux?
ioctl() is typically implemented as part of the corresponding driver, and then an appropriate function pointer is initialised with it, exactly as in other system calls like open() , read() , etc. For example, in character drivers, it is the ioctl or unlocked_ioctl (since kernel 2.6.
Are ioctl calls blocking?
Why would ioctl fail?
If an underlying device driver detects an error, then ioctl() shall fail if: [EINVAL] The request or arg argument is not valid for this device.
What is _iowr?
_IOWR. an. ioctl with both write and read parameters. ‘Write’ and ‘read’ are from the user’s point of view, just like the system calls ‘write’ and ‘read’.
What is Register_chrdev?
The call. register_chrdev(major, name, fops); stores the given name (a string) and fops (a struct file_operations *) in the entry of the array chrdevs[] indexed by the integer major , the major device number of the device. (Devices have a number, the device number, a combination of major and minor device number.
Which of the following ioctl function is used to Reprime the watchdog?
Some watchdog drivers have the ability to report the remaining time before the system will reboot. The WDIOC_GETTIMELEFT is the ioctl that returns the number of seconds before reboot.
What is Chardev?
/* * chardev.c: Creates a read-only char device that says how many times * you’ve read from the dev file */ #include #include #include #include /* for put_user */ /* * Prototypes – this would normally go in a .h file */ int init_module(void); void …
What is a watchdog in programming?
A watchdog timer (WDT) is a timer that monitors microcontroller (MCU) programs to see if they are out of control or have stopped operating. It acts as a “watchdog” watching over MCU operation. A microcontroller (MCU) is a compact processor for controlling electronic devices.
What is Siocgifhwaddr?
SIOCGIFHWADDR, SIOCSIFHWADDR. Get or set the hardware address of a device using ifr_hwaddr. The hardware address is specified in a struct sockaddr. sa_family contains the ARPHRD_* device type, sa_data the L2 hardware address starting from byte 0. Setting the hardware address is a privileged operation.