What is ioctl () in Linux?

What is ioctl () in Linux?

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.

Why ioctl is used in Linux?

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.

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).

What is ioctl error?

The following codes and their descriptions apply to IOCTL operations. [EINVAL] 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.

Where is ioctl in Linux?

<sys/ioctl

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 <sys/ioctl.

What are ioctl commands?

Ioctl which stand for Input Output control is a system call used in linux to implement system calls which are not be available in the kernel by default. The major use of this is in case of handling some specific operations of a device for which the kernel does not have a system call by default.

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.

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 does ioctl return?

Terminal and sockets returned value
If successful, ioctl() returns 0. If unsuccessful, ioctl() returns -1 and sets errno to one of the following values: Error Code. Description.

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.

Is ioctl deprecated?

The IOCTL_INTERNAL_USB_ENABLE_PORT IOCTL has been deprecated.

Is ioctl asynchronous?

But every ioctl() call is different, and none of them were designed for asynchronous execution, so an ioctl() implementation within io_uring would have no choice but to execute every call in a separate thread.
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By Jonathan Corbet.

Is ioctl synchronous?

Ioctls are synchronous system calls and are similar to read and write calls in that regard.