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What is the use of ioctl function in Linux?
IOCTL is referred to as Input and Output Control, which is used to talking to device drivers. This system call, available in most driver categories. 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.
Why do we need ioctl?
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 example?
For example, in character drivers, it is the ioctl or unlocked_ioctl (since kernel 2.6. 35) function pointer field in the struct file_operations, which is to be initialized. Again like other system calls, it can be equivalently invoked from the user space using the ioctl() system call, prototyped in
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 inappropriate ioctl for device?
“inappropriate ioctl for device” is the error string for the ENOTTY error. More generally, it is triggered when doing an ioctl on a device that does not support that ioctl, hence the error string. To find out what ioctl is being made that fails, and on what file descriptor, run the script under strace/truss.
Is ioctl system call?
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.
What is magic number in ioctl?
“IOWR”: If the command does both read as well as write from the user. The Magic Number is a unique number or character that will differentiate our set of ioctl calls from the other ioctl calls. some times the major number for the device is used here. Command Number is the number that is assigned to the ioctl .
What does ioctl return?
Return Value On success, 0 is returned. An ioctl() may use the return value as an output parameter and return a non-negative value on success. On error, -1 is returned and the global variable errno is set appropriately.
What is an ioctl call?
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.
Is ioctl a system call?
When to use ioctl in Input / Output Control?
Introducing ioctl () Input/Output Control (ioctl, in short) is a common operation, or system call, available in most driver categories. It is a one-bill-fits-all kind of system call. If there is no other system call that meets a particular requirement, then ioctl () is the one to use.
What are some real time applications of ioctl?
Some real-time applications of ioctl are Ejecting the media from a “cd” drive, change the Baud Rate of Serial port, Adjust the Volume, Reading or Writing device registers, etc. We already have the write and read function in our device driver. But it is not enough for all cases.
When did the ioctl system call first appear?
The ioctl system call first appeared in Version 7 Unix, as a renamed stty. An ioctl call takes as parameters : either an integer value, possibly unsigned (going to the driver) or a pointer to data (either going to the driver, coming back from the driver, or both).
How is an ioctl request code device specific?
It takes a parameter specifying a request code; the effect of a call depends completely on the request code. Request codes are often device-specific. For instance, a CD-ROM device driver which can instruct a physical device to eject a disc would provide an ioctl request code to do so.