memcntl(2) 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) 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
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memcntl(2) memcntl(2)
locations. This operation should be used by applications
that require a memory object to be in a known state.
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.
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memcntl(2) memcntl(2)
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, MCUNLOCKAS was
specified.
SEE ALSO
mmap(2), mprotect(2), plock(2), sysconf(2), mlock(3C), mlockall(3C),
msync(3C).
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