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NetBSD 6.1.5 - man page for errno (netbsd section 9)

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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 han-
     dled 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 subse-
	     quent 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
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