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ioctl(2) [freebsd man page]

IOCTL(2)						      BSD System Calls Manual							  IOCTL(2)

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 character special files (e.g. terminals) may be controlled with ioctl() requests. 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 descriptors. 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 device. For TCP sockets, these bytes have not yet been acknowledged 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 number 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 allocated address space. SEE ALSO
execve(2), fcntl(2), intro(4), tty(4) HISTORY
The ioctl() function appeared in Version 7 AT&T UNIX. BSD
September 11, 2013 BSD

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ioctl(2)							   System Calls 							  ioctl(2)

ioctl - control device SYNOPSIS
#include <unistd.h> #include <stropts.h> int ioctl(int fildes, int request, /* arg */ ...); DESCRIPTION
The ioctl() function performs a variety of control functions on devices and STREAMS. For non-STREAMS files, the functions performed by this call are device-specific control functions. The request argument and an optional third argument with varying type are passed to the file designated by fildes and are interpreted by the device driver. For STREAMS files, specific functions are performed by the ioctl() function as described in streamio(7I). The fildes argument is an open file descriptor that refers to a device. The request argument selects the control function to be performed and depends on the device being addressed. The arg argument represents a third argument that has additional information that is needed by this specific device to perform the requested function. The data type of arg depends upon the particular control request, but it is either an int or a pointer to a device-specific data structure. In addition to device-specific and STREAMS functions, generic functions are provided by more than one device driver (for example, the gen- eral terminal interface.) See termio(7I)). RETURN VALUES
Upon successful completion, the value returned depends upon the device control function, but must be a non-negative integer. Otherwise, -1 is returned and errno is set to indicate the error. ERRORS
The ioctl() function will fail for any type of file if: EBADF The fildes argument is not a valid open file descriptor. EINTR A signal was caught during the execution of the ioctl() function. EINVAL The STREAM or multiplexer referenced by fildes is linked (directly or indirectly) downstream from a multiplexer. The ioctl() function will also fail if the device driver detects an error. In this case, the error is passed through ioctl() without change to the caller. A particular driver might not have all of the following error cases. Under the following conditions, requests to device drivers may fail and set errno to indicate the error EFAULT The request argument requires a data transfer to or from a buffer pointed to by arg, but arg points to an illegal address. EINVAL The request or arg argument is not valid for this device. EIO Some physical I/O error has occurred. ENOLINK The fildes argument is on a remote machine and the link to that machine is no longer active. ENOTTY The fildes argument is not associated with a STREAMS device that accepts control functions. ENXIO The request and arg arguments are valid for this device driver, but the service requested can not be performed on this particu- lar subdevice. ENODEV The fildes argument refers to a valid STREAMS device, but the corresponding device driver does not support the ioctl() function. STREAMS errors are described in streamio(7I). ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ SEE ALSO
attributes(5), standards(5), streamio(7I), termio(7I) SunOS 5.11 15 Feb 1996 ioctl(2)
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