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POSIX_TYPED_MEM_GET_INFO(P) 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 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 speci-
fied, 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 mal-
loc(), 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 allo-
cated 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
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 .
POSIX 2003 POSIX_TYPED_MEM_GET_INFO(P)
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