What is ioctl interface?
An ioctl interface is a single system call by which userspace may communicate with device drivers. Requests on a device driver are vectored with respect to this ioctl system call, typically by a handle to the device and a request number.
What is the purpose of 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 a Netdevice?
The net device structure, defined in file linux/include/netdevice. h, is the data structure that defines an instance of a network interface. It tracks the state information of all the network interface devices attached to the TCP/IP stack. It contains the string that is the name of the interface.
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).
How does ioctl work in Linux?
The ioctl() system call manipulates the underlying device parameters of special files. In particular, many operating characteristics of character special files (e.g., terminals) may be controlled with ioctl() requests. The argument fd must be an open file descriptor.
What is Net_device structure?
struct net_device — The DEVICE structure. It mixes I/O data with strictly “high-level” data, and it has to know about almost every data structure used in the INET module.
How do I resolve inappropriate ioctl?
1 Answer. You can’t get rid of it and there’s no reason to remove it anyway. This comes from bash checking whether the input is coming from a terminal (it calls isatty ).
Which is the most common ioctl based interface?
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.
When to use ioctl in Input / Output Control?
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.
Where to find ioctl in a character driver?
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 that is to be initialised. Again, like other system calls, it can be equivalently invoked from user-space using the ioctl () system call, prototyped in as:
Are there negative error codes for ioctl commands?
The old command still needs to be implemented in the kernel for compatibility, but this can be a wrapper around the new implementation. ioctl commands can return negative error codes as documented in errno (3); these get turned into errno values in user space. On success, the return code should be zero.