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IOCTL(2) System Calls Manual IOCTL(2) NAME ioctl -- control device LIBRARY Standard C Library (libc, -lc) SYNOPSIS #include <sys/ioctl.h> int ioctl(int fd, unsigned long request, ...); DESCRIPTION The ioctl() system call manipulates the underlying device parameters of special files. In particular, many operating characteristics of char- acter special files (e.g. terminals) may be controlled with ioctl() re- quests. The argument fd must be an open file descriptor. The third argument to ioctl() is traditionally named char *argp. Most uses of ioctl(), however, require the third argument to be a caddr_t or an int. An ioctl() request has encoded in it whether the argument is an "in" argument or "out" argument, 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.h>. GENERIC IOCTLS Some generic ioctls are not implemented for all types of file descrip- tors. These include: FIONREAD int Get the number of bytes that are immediately available for reading. FIONWRITE int Get the number of bytes in the descriptor's send queue. These bytes are data which has been written to the descriptor but which are being held by the kernel for further processing. The nature of the required processing depends on the underlying de- vice. For TCP sockets, these bytes have not yet been acknowl- edged by the other side of the connection. FIONSPACE int Get the free space in the descriptor's send queue. This value is the size of the send queue minus the number of bytes being held in the queue. Note: while this value represents the num- ber of bytes that may be added to the queue, other resource limitations may cause a write not larger than the send queue's space to be blocked. One such limitation would be a lack of network buffers for a write to a network connection. RETURN VALUES If an error has occurred, a value of -1 is returned and errno is set to indicate the error. ERRORS The ioctl() system call will fail if: [EBADF] The fd argument is not a valid descriptor. [ENOTTY] The fd argument is not associated with a character special device. [ENOTTY] The specified request does not apply to the kind of object that the descriptor fd references. [EINVAL] The request or argp argument is not valid. [EFAULT] The argp argument points outside the process's allo- cated address space. SEE ALSO execve(2), fcntl(2), intro(4), tty(4) HISTORY The ioctl() function appeared in Version 7 AT&T UNIX. FreeBSD 13.2 September 11, 2013 IOCTL(2)
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | GENERIC IOCTLS | RETURN VALUES | ERRORS | SEE ALSO | HISTORY
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