posix_typed_mem_open: otevřít zadaný objekt paměti (POKROČILÝ REÁLNÝ ČAS)

Originální popis anglicky: posix_typed_mem_open - open a typed memory object ( ADVANCED REALTIME)

Návod, kniha: POSIX Programmer's Manual

STRUČNĚ

#include <sys/mman.h> int posix_typed_mem_open(const char * name, int oflag, int tflag);

POPIS / INSTRUKCE

The posix_typed_mem_open() function shall establish a connection between the typed memory object specified by the string pointed to by name and a file descriptor. It shall create an open file description that refers to the typed memory object and a file descriptor that refers to that open file description. The file descriptor is used by other functions to refer to that typed memory object. It is unspecified whether the name appears in the file system and is visible to other functions that take pathnames as arguments. The name argument shall conform to the construction rules for a pathname. If name begins with the slash character, then processes calling posix_typed_mem_open() with the same value of name shall refer to the same typed memory object. If name does not begin with the slash character, the effect is implementation-defined. The interpretation of slash characters other than the leading slash character in name is implementation-defined. Each typed memory object supported in a system shall be identified by a name which specifies not only its associated typed memory pool, but also the path or port by which it is accessed. That is, the same typed memory pool accessed via several different ports shall have several different corresponding names. The binding between names and typed memory objects is established in an implementation-defined manner. Unlike shared memory objects, there is no way within IEEE Std 1003.1-2001 for a program to create a typed memory object. The value of tflag shall determine how the typed memory object behaves when subsequently mapped by calls to mmap(). At most, one of the following flags defined in <sys/mman.h> may be specified:

POSIX_TYPED_MEM_ALLOCATE

Allocate on mmap().

POSIX_TYPED_MEM_ALLOCATE_CONTIG

Allocate contiguously on mmap().

POSIX_TYPED_MEM_MAP_ALLOCATABLE

Map on mmap(), without affecting allocatability.

 

If tflag has the flag POSIX_TYPED_MEM_ALLOCATE specified, any subsequent call to mmap() using the returned file descriptor shall result in allocation and mapping of typed memory from the specified typed memory pool. The allocated memory may be a contiguous previously unallocated area of the typed memory pool or several non-contiguous previously unallocated areas (mapped to a contiguous portion of the process address space). If tflag has the flag POSIX_TYPED_MEM_ALLOCATE_CONTIG specified, any subsequent call to mmap() using the returned file descriptor shall result in allocation and mapping of a single contiguous previously unallocated area of the typed memory pool (also mapped to a contiguous portion of the process address space). If tflag has none of the flags POSIX_TYPED_MEM_ALLOCATE or POSIX_TYPED_MEM_ALLOCATE_CONTIG specified, any subsequent call to mmap() using the returned file descriptor shall map an application-chosen area from the specified typed memory pool such that this mapped area becomes unavailable for allocation until unmapped by all processes. If tflag has the flag POSIX_TYPED_MEM_MAP_ALLOCATABLE specified, any subsequent call to mmap() using the returned file descriptor shall map an application-chosen area from the specified typed memory pool without an effect on the availability of that area for allocation; that is, mapping such an object leaves each byte of the mapped area unallocated if it was unallocated prior to the mapping or allocated if it was allocated prior to the mapping. The appropriate privilege to specify the POSIX_TYPED_MEM_MAP_ALLOCATABLE flag is implementation-defined. If successful, posix_typed_mem_open() shall return a file descriptor for the typed memory object that is the lowest numbered file descriptor not currently open for that process. The open file description is new, and therefore the file descriptor shall not share it with any other processes. It is unspecified whether the file offset is set. The FD_CLOEXEC file descriptor flag associated with the new file descriptor shall be cleared. The behavior of msync(), ftruncate(), and all file operations other than mmap(), posix_mem_offset(), posix_typed_mem_get_info(), fstat(), dup(), dup2(), and close(), is unspecified when passed a file descriptor connected to a typed memory object by this function. The file status flags of the open file description shall be set according to the value of oflag. Applications shall specify exactly one of the three access mode values described below and defined in the <fcntl.h> header, as the value of oflag.

O_RDONLY

Open for read access only.

O_WRONLY

Open for write access only.

O_RDWR

Open for read or write access.

 

NÁVRATOVÁ HODNOTA

Upon successful completion, the posix_typed_mem_open() function shall return a non-negative integer representing the lowest numbered unused file descriptor. Otherwise, it shall return -1 and set errno to indicate the error.

CHYBY / ERRORY

The posix_typed_mem_open() function shall fail if:

EACCES

The typed memory object exists and the permissions specified by oflag are denied.

EINTR

The posix_typed_mem_open() operation was interrupted by a signal.

EINVAL

The flags specified in tflag are invalid (more than one of POSIX_TYPED_MEM_ALLOCATE, POSIX_TYPED_MEM_ALLOCATE_CONTIG, or POSIX_TYPED_MEM_MAP_ALLOCATABLE is specified).

EMFILE

Too many file descriptors are currently in use by this process.

ENAMETOOLONG

The length of the name argument exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}.

ENFILE

Too many file descriptors are currently open in the system.

ENOENT

The named typed memory object does not exist.

EPERM

The caller lacks the appropriate privilege to specify the flag POSIX_TYPED_MEM_MAP_ALLOCATABLE in argument tflag.

 

The following sections are informative.

PŘÍKLADY POUŽITÍ

None.

APPLICATION USAGE

None.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SOUVISEJÍCÍ

close() , dup() , exec() , fcntl() , fstat() , ftruncate() , mmap() , msync() , posix_mem_offset() , posix_typed_mem_get_info() , umask() , the Base Definitions volume of IEEE Std 1003.1-2001, <fcntl.h>, <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 .