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POSIX_TYPED_MEM_GET_INFO
Section: POSIX Programmer's Manual (3P)
Updated: 2003
Index
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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 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 .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- EXAMPLES
-
- APPLICATION USAGE
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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