memcntl(2) UNIX System V memcntl(2)
NAME
memcntl - memory management control
SYNOPSIS
#include <sys/types.h>
#include <sys/mman.h>
int memcntl(caddrt addr, sizet len, int cmd, caddrt 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 sysconf(3C). 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 can be read.
PROTWRITE Page can be written.
PROTEXEC Page can be executed.
The selection criteria are constructed by an OR of the attribute bits and
must match exactly.
In addition, the following criteria may be specified:
PROCTEXT process text
PROCDATA process data
where PROCTEXT specifies all privately mapped segments with read and
execute permission, and PROCDATA specifies all privately mapped segments
with write permission.
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) UNIX System V 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.
MCSYNC Write to their backing storage locations all modified pages in
the range with attributes attr. Optionally, invalidate cache
copies. The backing storage for a modified MAPSHARED mapping
is the file the page is mapped to; the backing storage for a
modified MAPPRIVATE mapping is its swap area. arg is a bit
pattern built from the flags used to control the behavior of
the operation:
MSASYNC perform asynchronous writes
MSSYNC perform synchronous writes
MSINVALIDATE invalidate mappings
MSASYNC returns immediately once all write operations are
scheduled; with MSSYNC the system call will not return until
all write operations are completed.
MSINVALIDATE invalidates all cached copies of data in memory,
so that further references to the pages will be obtained by the
system from their backing storage locations. This operation
should be used by applications that require a memory object to
be in a known state.
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memcntl(2) UNIX System V memcntl(2)
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 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, with the
exception of MCSYNC, are restricted to processes with superuser
effective user ID . The memcntl function subsumes the operations of plock
and mctl.
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.
EBUSY if some or all the addresses in the range [addr, addr + len)
are locked and MCSYNC with MSINVALIDATE option is
specified.
EINVAL if addr is not a multiple of the page size as returned by
sysconf.
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.
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memcntl(2) UNIX System V memcntl(2)
EPERM if the process's effective user ID is not superuser and one
of MCLOCK, MCLOCKAS, MCUNLOCK, MCUNLOCKAS was specified.
SEE ALSO
mmap(2), mprotect(2), plock(2), sysconf(2), mlock(3C), mlockall(3C),
msync(3C).
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