ERRNO(9) BSD Kernel Developer's Manual ERRNO(9)NAMEerrno — 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” han‐
dling is required at an upper layer or, in the case of ioctl(2) process‐
ing, 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 ALSOerrno(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
