NAME

posix_typed_mem_get_info - query typed memory information (ADVANCED REALTIME)

SYNOPSIS

[TYM] #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].

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>

CHANGE HISTORY

First released in Issue 6. Derived from IEEE Std 1003.1j-2000.