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What does ioctl do 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.
Is ioctl deprecated?
As I understand it, ioctls aren’t totally deprecated, but sysfs is preferred (?) I need to read/write sets of values simultaneously i.e. through one sysfs entry. I’ve read that this isn’t ideal, but is acceptable if necessary (?)
How do I select my magic number ioctl?
To choose ioctl numbers for your driver according to the new convention, you should first check include/asm/ioctl. h and Documentation/ioctl-number. txt . The header defines the bitfields you will be using: type (magic number), ordinal number, direction of transfer, and size of argument.
What is the use of ioctl inode file CMD ARG API?
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.
What is fd in ioctl?
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. int ioctl(int fd, int request.) fd is file descriptor, the one returned by open ; request is request code.
Where can I find the ioctl macro for ioctl?
Macros and defines used in specifying an ioctl () request are located in the file . See NOTES. Usually, on success zero is returned. A few ioctl () requests use the return value as an output parameter and return a nonnegative value on success. On error, -1 is returned, and errno is set to indicate the error.
What is the ioctl return value?
A few ioctl () requests use the return value as an output parameter and return a nonnegative value on success. On error, -1 is returned, and errno is set to indicate the error. EBADF fd is not a valid file descriptor. EFAULT argp references an inaccessible memory area.
How do I use the ioctl explain_errno_ioctl function?
The explain_errno_ioctl function is used to obtain an explanation of an error returned by the ioctl (2) system call. The least the message will contain is the value of strerror(errnum), but usually it will do much better, and indicate the underlying cause in more detail.
What is Erno return in ioctl?
RETURN VALUE top Usually, on success zero is returned. A few ioctl () requests use the return value as an output parameter and return a nonnegative value on success. On error, -1 is returned, and errno is set to indicate the error.