.\"	$NetBSD: errno.9,v 1.5 2010/03/22 18:58:33 joerg Exp $
.\"
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.Dd May 16, 2018
.Dt ERRNO 9
.Os
.Sh NAME
.Nm errno
.Nd kernel internal error numbers
.Sh SYNOPSIS
.In sys/errno.h
.Sh 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.
.Sh DIAGNOSTICS
Kernel functions that indicate success or failure by means of either 0
or an
.Xr errno 2
value sometimes have a need to indicate that
.Dq special
handling is required at an upper layer or, in the case of
.Xr ioctl 2
processing, that
.Dq nothing was wrong but the request was not handled .
To handle these cases, some negative
.Xr errno 2
values are defined which are handled by the kernel before returning a
different
.Xr errno 2
value to userland or simply zero.
.Pp
The following is a list of the defined names and their meanings as
given in
.In errno.h .
.\"It is important to note that the value \-1 is
.\".Em not
.\"used, since it is commonly used to indicate generic failure and leaves
.\"it up to the caller to determine the action to take.
.Bl -hang -width Ds
.It Er \-1 ERESTART Em "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.
.It Er \-2 EJUSTRETURN Em "Do not modify regs, just return" .
No more work is required and the function should just return.
.It Er \-3 ENOIOCTL Em "Ioctl not handled by this layer" .
The
.Xr ioctl 2
was not handled and should be passed through to another layer.
.It Er \-4 EMOUNTEXIT Em "Mountpoint released via vfs_start()" .
Specific to
.Xr mfs 8 .
.El
.Sh SEE ALSO
.Xr errno 2 ,
.Xr ioctl 9
.Sh HISTORY
An
.Nm
manual page appeared in
.At v6 .
This
.Nm
manual page appeared in
.Nx 3.0 .