POSIX_MEM_OFFSET(P) POSIX Programmer's Manual POSIX_MEM_OFFSET(P)
posix_mem_offset - find offset and length of a mapped typed memory block (ADVANCED REAL-
int posix_mem_offset(const void *restrict addr, size_t len,
off_t *restrict off, size_t *restrict contig_len,
int *restrict fildes);
The posix_mem_offset() function shall return in the variable pointed to by off a value
that identifies the offset (or location), within a memory object, of the memory block cur-
rently mapped at addr. The function shall return in the variable pointed to by fildes, the
descriptor used (via mmap()) to establish the mapping which contains addr. If that
descriptor was closed since the mapping was established, the returned value of fildes
shall be -1. The len argument specifies the length of the block of the memory object the
user wishes the offset for; upon return, the value pointed to by contig_len shall equal
either len, or the length of the largest contiguous block of the memory object that is
currently mapped to the calling process starting at addr, whichever is smaller.
If the memory object mapped at addr is a typed memory object, then if the off and con-
tig_len values obtained by calling posix_mem_offset() are used in a call to mmap() with a
file descriptor that refers to the same memory pool as fildes (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 addr in the address
space of the process that called posix_mem_offset().
If the memory object specified by fildes is not a typed memory object, then the behavior
of this function is implementation-defined.
Upon successful completion, the posix_mem_offset() function shall return zero; otherwise,
the corresponding error status value shall be returned.
The posix_mem_offset() function shall fail if:
EACCES The process has not mapped a memory object supported by this function at the given
This function shall not return an error code of [EINTR].
The following sections are informative.
mmap() , posix_typed_mem_open() , the Base Definitions volume of IEEE Std 1003.1-2001,
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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 POSIX_MEM_OFFSET(P)