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.
What is ioctl call in Linux?
The ioctl() system call manipulates the underlying device parameters of special files. 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
What is SMB ioctl?
The SMB2 IOCTL Request packet is sent by a client to issue an implementation-specific file system control or device control (FSCTL/IOCTL) command across the network. The client MUST set this field to 0, and the server MUST ignore it on receipt.
How is ioctl ( ) implemented in the Linux kernel?
The ioctl () function implementation does a switch … case over the commmand to implement the corresponding functionality. The following has been its prototype in the Linux kernel for quite some time: However, from kernel 2.6.35, it changed to:
What are the parameters of the ioctl function?
The trick lies in using its two key parameters: command and argument. The command is a number representing an operation. The argument command is the corresponding parameter for the operation. The ioctl () function implementation does a switch … case over the commmand to implement the corresponding functionality.
Do you need compat _ ioctl handler in Linux 5.5?
Prior to Linux 5.5, compat_ioctl handlers were required to return -ENOIOCTLCMD in order to use the fallback conversion into native commands. As all subsystems are now responsible for handling compat mode themselves, this is no longer needed, but it may be important to consider when backporting bug fixes to older kernels.
What happens when you call ioctl with unknown command number?
When the ioctl callback is called with an unknown command number, the handler returns either -ENOTTY or -ENOIOCTLCMD, which also results in -ENOTTY being returned from the system call. Some subsystems return -ENOSYS or -EINVAL here for historic reasons, but this is wrong.