focal (3) posix_typed_mem_get_info.3posix.gz

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PROLOG
       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.


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 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
       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 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 memory objects.


FUTURE DIRECTIONS
       None.


SEE ALSO
       fstat(), mmap(), posix_typed_mem_open()

       The Base Definitions volume of POSIX.1‐2008, <sys_mman.h>


       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition,
       Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open  Group  Base
       Specifications  Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc
       and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .

       Any  typographical  or formatting errors that appear in this page are most likely to have been introduced
       during  the  conversion  of  the  source  files  to  man  page  format.  To  report  such   errors,   see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .