ERRNO(9) BSD Kernel Developer's Manual ERRNO(9)NAME
errno -- kernel internal error numbers
SYNOPSIS
#include <sys/errno.h>
DESCRIPTION
This section provides an overview of the error numbers used internally by the kernel and indicate neither success nor failure. These error
numbers are not returned to userland code.
DIAGNOSTICS
Kernel functions that indicate success or failure by means of either 0 or an errno(2) value sometimes have a need to indicate that
``special'' handling is required at an upper layer or, in the case of ioctl(2) processing, that ``nothing was wrong but the request was not
handled''. To handle these cases, some negative errno(2) values are defined which are handled by the kernel before returning a different
errno(2) value to userland or simply zero.
The following is a list of the defined names and their meanings as given in <errno.h>. It is important to note that the value -1 is not
used, since it is commonly used to indicate generic failure and leaves it up to the caller to determine the action to take.
-2 EJUSTRETURN Modify regs, just return. No more work is required and the function should just return.
-3 ERESTART Restart syscall. The system call should be restarted. This typically means that the machine dependent system call trap code
will reposition the process's instruction pointer or program counter to re-execute the current system call with no other work
required.
-4 EPASSTHROUGH Operation not handled by this layer. The operation was not handled and should be passed through to another layer. This
often occurs when processing ioctl(2) requests since lower layer processing may not handle something that subsequent code at a higher
level will.
-5 EDUPFD Duplicate file descriptor. This error is returned from the device open routine indicating that the l_dupfd field contains the file
descriptor information to be returned to the caller, instead of the file descriptor that has been opened already. This error is used
by cloning device multiplexors. Cloning device multiplexors open a new file descriptor and associate that file descriptor with the
appropriate cloned device. They set l_dupfd to that new file descriptor and return EDUPFD. vn_open(9) takes the file descriptor
pointed to by l_dupfd and copies it to the file descriptor that the open call will return.
-6 EMOVEFD Move file descriptor. This error is similar to EDUPFD except that the file descriptor in l_dupfd is closed after it has been
copied.
SEE ALSO errno(2), ioctl(9)HISTORY
An errno manual page appeared in Version 6 AT&T UNIX. This errno manual page appeared in NetBSD 3.0.
BSD December 3, 2004 BSD
Check Out this Related Man Page
IOCTL(2) BSD System Calls Manual IOCTL(2)NAME
ioctl -- control device
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/ioctl.h>
int
ioctl(int d, unsigned long request, ...);
DESCRIPTION
The ioctl() function manipulates the underlying device parameters of special files. In particular, many operating characteristics of charac-
ter special files (e.g. terminals) may be controlled with ioctl() requests. The argument d must be an open file descriptor.
An ioctl() request has encoded in it whether the argument is an ``in'', ``out'', or ``inout'' parameter, and the size of the first variadic
argument in bytes. Note that there can be only one variadic argument but cannot be represented as a void * argument in the prototype because
this would require a cast to pass integral types without warnings. Macros and defines used in specifying an ioctl() request are located in
the header <sys/ioctl.h>.
GENERIC IOCTLS
Some ioctls are applicable to any file descriptor. These include:
FIOCLEX
Set close-on-exec flag. The file will be closed when exec(3) is invoked (This is equivalent to fcntl() F_SETFD FD_CLOEXEC and the
fcntl() form should be preferred).
FIONCLEX
Clear close-on-exec flag. The file will remain open across exec(3) (This is equivalent to fcntl() F_SETFD 0 and the fcntl() form
should be preferred).
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 tty
devices, these bytes are typically queued for delivery to the tty hardware. For TCP sockets, these bytes have not yet been acknowl-
edged by the other side of the connection. For files, this operation always returns zero as files do not have send queues.
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.
FIONBIO int
Set non-blocking I/O mode if the argument is non-zero. In non-blocking mode, read(2) or write(2) calls return -1 and set errno to
EAGAIN immediately when no data is available (This is equivalent to fcntl() F_SETFL O_NONBLOCK and the fcntl() form should be pre-
ferred).
FIOASYNC int
Set asynchronous I/O mode if the argument is non-zero (This is equivalent to fcntl() F_SETFL O_ASYNC and the fcntl() form should be
preferred). In asynchronous mode, the process or process group specified by FIOSETOWN will start receiving SIGIO signals when data
is available. The SIGIO signal will be delivered when data is available on the file descriptor.
FIOSETOWN, FIOGETOWN int
Set/get the process or the process group (if negative) that should receive SIGIO signals when data is available (This is equivalent
to fcntl() F_SETOWN pid_t and the fcntl form should be preferred).
RETURN VALUES
If an error has occurred, a value of -1 is returned and errno is set to indicate the error.
ERRORS
ioctl() will fail if:
[EBADF] d is not a valid descriptor.
[EFAULT] argp points outside the process's allocated address space.
[EINVAL] request or argp is not valid.
[ENOTTY] d is not associated with a character special device; or the specified request does not apply to the kind of object that
the descriptor d references.
SEE ALSO mt(1), execve(2), fcntl(2), intro(4), tty(4)HISTORY
An ioctl() function call appeared in Version 7 AT&T UNIX.
BSD December 19, 2010 BSD