munmap_flags()

Unmap previously mapped addresses, exercising more control than possible with munmap()

Synopsis:

#include <sys/mman.h>

int munmap_flags( void * addr,
                  size_t len,
                  unsigned flags );

Arguments:

addr

The beginning of the range of addresses that you want to unmap.

len

The length of the range of addresses, in bytes.

flags

Use the following values:

0

Behave the same as munmap().

UNMAP_INT_REQUIRED

POSIX initialization of the page to all zeros is required the next time the underlying physical memory is allocated.

UNMAP_INT_OPTIONAL

Initialization of the underlying physical memory to zeros on its next allocation is optional.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The munmap_flags() function removes any mappings for pages in the address range starting at addr and continuing for len bytes, rounded up to the next multiple of the page size. Subsequent references to these pages cause a SIGSEGV signal to be set on the process.

If there are no mappings in the specified address range, then munmap_flags() has no effect.

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This function was added in the QNX Neutrino Core OS 6.3.2.

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There are some interactions of the flags argument with the MAP_NOINIT flag of the mmap() function as well as procnto, as detailed below:

• The mmap() function has a new flag, MAP_NOINIT. When specified, the POSIX requirement that the memory be zeroed is relaxed. The physical memory being used for this allocation must have been previously freed with UNMAP_INIT_OPTIONAL for this flag to have any effect.
• The procnto command line now has an -mmemmgr_configuration option. The memmgr_configuration string has a sequence of configuration options to enable (or if preceeded with a ~ character, disable) memory-manager aspects. The configuation options are:

  i

  munmap_flags() (with flags parameter as zero) acts as if UNMAP_INIT_REQUIRED were specified (the default).

  ~i

  munmap_flags() (with flags parameter as zero) acts as if UNMAP_INIT_OPTIONAL were specified.

Returns:

0

Success.

-1

Failure; errno is set.

Errors:

EINVAL

The addresses in the specified range are outside the range allowed for the address space of a process.

ENOSYS

The function munmap_flags() isn't supported by this implementation.

Classification:

QNX Neutrino

See also:

mmap(), mprotect(), munmap(), shm_open(), shm_unlink()

procnto in the Utilities Reference

“Initializing allocated memory” in the Interprocess Communication (IPC) chapter of the System Architecture guide