Section: Linux Programmer's Manual (2)
ioctl - control device
int ioctl(int fd, unsigned long request, ...);
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
must be an open file descriptor.
The second argument is a device-dependent request code.
The third argument is an untyped pointer to memory.
(from the days before
was valid C), and will be so named for this discussion.
has encoded in it whether the argument is an
parameter, and the size of the argument
Macros and defines used in specifying an
are located in the file
Usually, on success zero is returned.
requests use the return value as an output parameter
and return a nonnegative value on success.
On error, -1 is returned, and
is set appropriately.
is not a valid file descriptor.
references an inaccessible memory area.
is not valid.
is not associated with a character special device.
The specified request does not apply to the kind of object that the
No single standard.
Arguments, returns, and semantics of
vary according to the device driver in question (the call is used as a
catch-all for operations that don't cleanly fit the UNIX stream I/O
for a list of many of the known
system call appeared in Version 7 AT&T UNIX.
In order to use this call, one needs an open file descriptor.
call has unwanted side effects, that can be avoided under Linux
by giving it the
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