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Linux 2.6 - man page for posix_typed_mem_get_info (linux section 3posix)

POSIX_TYPED_MEM_GET_INFO(P)	    POSIX Programmer's Manual	      POSIX_TYPED_MEM_GET_INFO(P)

NAME
       posix_typed_mem_get_info - query typed memory information (ADVANCED REALTIME)

SYNOPSIS
       #include <sys/mman.h>

       int posix_typed_mem_get_info(int fildes,
	      struct posix_typed_mem_info *info);

DESCRIPTION
       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  suc-
       cessfully  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_CON-
       TIG  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_ALLO-
       CATE flag nor the POSIX_TYPED_MEM_ALLOCATE_CONTIG flag specified, the  returned	value  of
       info->posix_tmi_length is unspecified.

       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.

RETURN VALUE
       Upon  successful  completion,  the  posix_typed_mem_get_info() function shall return zero;
       otherwise, the corresponding error status value shall be returned.

ERRORS
       The posix_typed_mem_get_info() function shall fail if:

       EBADF  The fildes argument is not a valid open file descriptor.

       ENODEV The fildes argument is not connected to a memory object supported by this function.

       This function shall not return an error code of [EINTR].

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       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	appropri-
       ate  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 implemen-
       tations	may wish to provide other attributes of typed memory objects (for example, align-
       ment 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 memory objects.

FUTURE DIRECTIONS
       None.

SEE ALSO
       fstat()	,  mmap()  ,  posix_typed_mem_open()   ,   the	 Base	Definitions   volume   of
       IEEE Std 1003.1-2001, <sys/mman.h>

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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003		      POSIX_TYPED_MEM_GET_INFO(P)


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