POSIX_TYPED_MEM_GET_INFO(3)POSIX Programmer's ManualPOSIX_TYPED_MEM_GET_INFO(3)



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

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.1-2017, <sys_mman.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       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 .



IEEE/The Open Group                  2017          POSIX_TYPED_MEM_GET_INFO(3)
