What is ioctl in Linux kernel?

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. The ioctl system call first appeared in Version 7 of Unix under that name.

How does ioctl work in Linux?

ioctl could be used to get the current font as well as set the font to a new one. A user application uses ioctl to send a code to a printer telling it to return the current font or to set the font to a new one. fd is file descriptor, the one returned by open ; request is request code.

Is ioctl a 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).

What is ioctl error?

The operation that is requested has invalid parameters or an invalid combination of parameters. This error code also results if the IOCTL is not supported for the device. [EWRPROTECT] An operation that modifies the media was attempted on a write-protected tape or a device opened with the O_RDONLY flag.

How do I use ioctl?

Steps involved in IOCTL

  1. Create IOCTL command in driver.
  2. Write IOCTL function in the driver.
  3. Create IOCTL command in a Userspace application.
  4. Use the IOCTL system call in a Userspace.

Is ioctl portable?

Direct calling of the ioctl system call is not portable on some architectures #8653.

How is ioctl different from read and write?

1 Answer. 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.

What is ioctl based interface in Linux?

ioctl based interfaces — The Linux Kernel documentation ioctl based interfaces ¶ ioctl () is the most common way for applications to interface with device drivers. It is flexible and easily extended by adding new commands and can be passed through character devices, block devices as well as sockets and other special file descriptors.

How to send multiple arguments using ioctl in Linux device driver?

Our value 23456 has been passed to the kernel and it was updated. This is a simple example of using ioctl in Linux device driver. If you want to send multiple arguments, put those variables into the structure, and pass the address of the structure.

What is the command number in ioctl?

The command number, or request number, is the second argument passed to the ioctl system call. While this can be any 32-bit number that uniquely identifies an action for a particular driver, there are a number of conventions around defining them.

What is an ioctl () request?

An ioctl () request has encoded in it whether the argument is an in parameter or out parameter, and the size of the argument argp in bytes. Macros and defines used in specifying an ioctl () request are located in the file . See NOTES. Usually, on success zero is returned.