The posix_typed_mem_get_info() function shall return, in the
posix_tmi_length field of the posix_typed_mem_info structure
pointed to by info, the maximum length which may be successfully
allocated by the typed memory object designated by fildes. This maximum
length shall take into account the flag POSIX_TYPED_MEM_ALLOCATE or
POSIX_TYPED_MEM_ALLOCATE_CONTIG specified when the typed memory object
represented by fildes was opened. The maximum length is dynamic;
therefore, the value returned is valid only while the current mapping of the
corresponding typed memory pool remains unchanged.
If fildes represents a typed memory object opened with neither the
POSIX_TYPED_MEM_ALLOCATE flag nor the POSIX_TYPED_MEM_ALLOCATE_CONTIG flag
specified, the returned value of info->posix_tmi_length is
The posix_typed_mem_get_info() function may return additional
implementation-defined information in other fields of the
posix_typed_mem_info structure pointed to by info.
If the memory object specified by fildes is not a typed memory object,
then the behavior of this function is undefined.
An application that needs to allocate a block of typed memory with length
dependent upon the amount of memory currently available must either query the
typed memory object to obtain the amount available, or repeatedly invoke
mmap() attempting to guess an appropriate length. While the latter
method is existing practice with malloc(), it is awkward and imprecise.
The posix_typed_mem_get_info() function allows an application to
immediately determine available memory. This is particularly important for
typed memory objects that may in some cases be scarce resources. Note that
when a typed memory pool is a shared resource, some form of mutual-exclusion
or synchronization may be required while typed memory is being queried and
allocated to prevent race conditions.
The existing fstat() function is not suitable for this purpose. We
realize that implementations may wish to provide other attributes of typed
memory objects (for example, alignment requirements, page size, and so on).
The fstat() function returns a structure which is not extensible and,
furthermore, contains substantial information that is inappropriate for typed
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