memcntl(2) DG/UX 4.30 memcntl(2)
NAME
memcntl - memory management control
SYNOPSIS
#include <sys/types.h>
#include <sys/mman.h>
int memcntl(addr, len, cmd, arg, attr, mask);
caddr_t addr;
size_t len;
int cmd;
caddr_t arg;
int attr;
int mask;
DESCRIPTION
The function memcntl allows the calling process to apply a
variety of control operations over the address space
identified by the mappings established for the address range
[addr, addr + len).
addr must be a multiple of the pagesize as returned by
getpagesize(2). The scope of the control operations can be
further defined with additional selection criteria (in the
form of attributes) according to the bit pattern contained
in attr.
The following attributes specify page mapping selection
criteria:
SHARED Page is mapped shared.
PRIVATE Page is mapped private.
The following attributes specify page protection selection
criteria:
PROTREAD Page has read permission.
PROTWRITE Page has write permission.
PROTEXEC Page has execute permission.
The selection criteria are constructed by an OR of the
attribute bits.
Selection criteria can be used to describe various abstract
memory objects within the address space on which to operate.
If an operation shall not be constrained by the selection
criteria, attr must have the value 0.
The operation to be performed is identified by the argument
cmd. The symbolic names for the operations are defined in
<sys/mman.h> as follows:
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memcntl(2) DG/UX 4.30 memcntl(2)
MCLOCK Lock in memory all pages in the range with
attributes attr. A given page may be locked
multiple times through different mappings;
however, within a given mapping, page locks do not
nest. Multiple lock operations on the same
address in the same process will all be removed
with a single unlock operation. A page locked in
one process and mapped in another (or visible
through a different mapping in the locking
process) is locked in memory as long as the
locking process does neither an implicit nor
explicit unlock operation. If a locked mapping is
removed, or a page is deleted through file removal
or truncation, an unlock operation is implicitly
performed. If a writable MAPPRIVATE page in the
address range is changed, the lock will be
transferred to the private page.
At present arg is unused, but must be 0 to ensure
compatibility with potential future enhancements.
MCLOCKAS Lock in memory all pages mapped by the address
space with attributes attr. At present addr and
len are unused, but must be NULL and 0
respectively, to ensure compatibility with
potential future enhancements. arg is a bit
pattern built from the flags:
MCLCURRENT Lock current mappings
MCLFUTURE Lock future mappings
The value of arg determines whether the pages to
be locked are those currently mapped by the
address space, those that will be mapped in the
future, or both. If MCLFUTURE is specified, then
all mappings subsequently added to the address
space will be locked, provided sufficient memory
is available.
MCUNLOCK Unlock all pages in the range with attributes
attr. At present arg is unused, but must be 0 to
ensure compatibility with potential future
enhancements.
MCUNLOCKAS
Remove address space memory locks, and locks on
all pages in the address space with attributes
attr. At present addr, len, and arg are unused,
but must be NULL, 0 and 0 respectively, to ensure
compatibility with potential future enhancements.
The mask argument must be zero; it is reserved for future
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memcntl(2) DG/UX 4.30 memcntl(2)
use.
Locks established with the lock operations are not inherited
by a child process after fork. memcntl fails if it attempts
to lock more memory than a system-specific limit.
Due to the potential impact on system resources, all
operations are restricted to processes with superuser
effective user ID. The memcntl function subsumes the
operations of plock(2).
RETURN VALUE
Upon successful completion, the function memcntl returns a
value of 0; otherwise, it returns a value of -1 and sets
errno to indicate an error.
ERRORS
Under the following conditions, the function memcntl fails
and sets errno to:
EAGAIN if some or all of the memory identified by the
operation could not be locked when MCLOCK or
MCLOCKAS is specified.
EINVAL if addr is not a multiple of the page size as
returned by getpagesize(2).
EINVAL if addr and/or len do not have the value 0 when
MCLOCKAS or MCUNLOCKAS is specified.
EINVAL if arg is not valid for the function specified.
EINVAL if invalid selection criteria are specified in
attr.
ENOMEM if some or all the addresses in the range [addr,
addr + len) are invalid for the address space of
the process or pages not mapped are specified.
EPERM if the process's effective user ID is not
superuser and one of MCLOCK, MCLOCKAS,
MCUNLOCK, or MCUNLOCKAS was specified.
SEE ALSO
mmap(2), plock(2), getpagesize(2).
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