POSIX_TYPED_MEM_GET_INFO(P)POSIX Programmer's ManuaPOSIX_TYPED_MEM_GET_INFO(P)NAMEposix_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; there‐
fore, 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 unspec‐
ified.
The posix_typed_mem_get_info() function may return additional implemen‐
tation-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 sup‐
ported 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 awk‐
ward and imprecise. The posix_typed_mem_get_info() function allows an
application to immediately determine available memory. This is particu‐
larly 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 ALSOfstat() , 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 original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 POSIX_TYPED_MEM_GET_INFO(P)
