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+.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
+.TH "POSIX_MEM_OFFSET" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
+.\" posix_mem_offset
+.SH NAME
+posix_mem_offset \- find offset and length of a mapped typed memory
+block (\fBADVANCED REALTIME\fP)
+.SH SYNOPSIS
+.LP
+\fB#include <sys/mman.h>
+.br
+.sp
+int posix_mem_offset(const void *restrict\fP \fIaddr\fP\fB, size_t\fP
+\fIlen\fP\fB,
+.br
+\ \ \ \ \ \ off_t *restrict\fP \fIoff\fP\fB, size_t *restrict\fP
+\fIcontig_len\fP\fB,
+.br
+\ \ \ \ \ \ int *restrict\fP \fIfildes\fP\fB); \fP
+\fB
+.br
+\fP
+.SH DESCRIPTION
+.LP
+The \fIposix_mem_offset\fP() function shall return in the variable
+pointed to by \fIoff\fP a value that identifies the offset
+(or location), within a memory object, of the memory block currently
+mapped at \fIaddr\fP. The function shall return in the
+variable pointed to by \fIfildes\fP, the descriptor used (via \fImmap\fP())
+to establish the
+mapping which contains \fIaddr\fP. If that descriptor was closed since
+the mapping was established, the returned value of
+\fIfildes\fP shall be -1. The \fIlen\fP argument specifies the length
+of the block of the memory object the user wishes the
+offset for; upon return, the value pointed to by \fIcontig_len\fP
+shall equal either \fIlen\fP, or the length of the largest
+contiguous block of the memory object that is currently mapped to
+the calling process starting at \fIaddr\fP, whichever is
+smaller.
+.LP
+If the memory object mapped at \fIaddr\fP is a typed memory object,
+then if the \fIoff\fP and \fIcontig_len\fP values
+obtained by calling \fIposix_mem_offset\fP() are used in a call to
+\fImmap\fP() with a file
+descriptor that refers to the same memory pool as \fIfildes\fP (either
+through the same port or through a different port), and
+that was opened with neither the POSIX_TYPED_MEM_ALLOCATE nor the
+POSIX_TYPED_MEM_ALLOCATE_CONTIG flag, the typed memory area that
+is mapped shall be exactly the same area that was mapped at \fIaddr\fP
+in the address space of the process that called
+\fIposix_mem_offset\fP().
+.LP
+If the memory object specified by \fIfildes\fP is not a typed memory
+object, then the behavior of this function is
+implementation-defined.
+.SH RETURN VALUE
+.LP
+Upon successful completion, the \fIposix_mem_offset\fP() function
+shall return zero; otherwise, the corresponding error status
+value shall be returned.
+.SH ERRORS
+.LP
+The \fIposix_mem_offset\fP() function shall fail if:
+.TP 7
+.B EACCES
+The process has not mapped a memory object supported by this function
+at the given address \fIaddr\fP.
+.sp
+.LP
+This function shall not return an error code of [EINTR].
+.LP
+\fIThe following sections are informative.\fP
+.SH EXAMPLES
+.LP
+None.
+.SH APPLICATION USAGE
+.LP
+None.
+.SH RATIONALE
+.LP
+None.
+.SH FUTURE DIRECTIONS
+.LP
+None.
+.SH SEE ALSO
+.LP
+\fImmap\fP() , \fIposix_typed_mem_open\fP() , the Base
+Definitions volume of IEEE\ Std\ 1003.1-2001, \fI<sys/mman.h>\fP
+.SH COPYRIGHT
+Portions of this text are reprinted and reproduced in electronic form
+from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
+-- Portable Operating System Interface (POSIX), The Open Group Base
+Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
+Electrical and Electronics Engineers, Inc and The Open Group. In the
+event of any discrepancy between this version and the original IEEE and
+The Open Group Standard, the original IEEE and The Open Group Standard
+is the referee document. The original Standard can be obtained online at
+http://www.opengroup.org/unix/online.html .