memcntl(2)
memcntl --
memory management control
Synopsis
#include <sys/types.h>
#include <sys/mman.h>
int memcntl( void *addr, size_t len, int cmd, void *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).
(The notation [start, end)
denotes the interval from start to end,
including start but excluding end.)
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:
PROT_READ-
Page can be read.
PROT_WRITE-
Page can be written.
PROT_EXEC-
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:
PROC_TEXT-
process text
PROC_DATA-
process data
where PROC_TEXT specifies all privately mapped segments
with read and execute permission, and PROC_DATA
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:
MC_LOCK-
Lock in memory all pages in the range with attributes attr.
The calling process must have the P_PLOCK privilege.
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 truncation,
an unlock operation is implicitly performed.
If a writable MAP_PRIVATE 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.
MC_LOCKAS-
Lock in memory all pages mapped by the address space with attributes attr.
The calling process must have the P_PLOCK privilege.
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:
MCL_CURRENT-
Lock current mappings
MCL_FUTURE-
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 MCL_FUTURE is specified,
then all mappings subsequently added to the address
space will be locked,
provided sufficient memory is available.
MC_SYNC-
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 MAP_SHARED mapping is the file
the page is mapped to;
the backing storage for a modified MAP_PRIVATE mapping is its swap area.
arg
is a bit pattern built from the flags used to control the behavior of the
operation:
MS_ASYNC-
perform asynchronous writes
MS_SYNC-
perform synchronous writes
MS_INVALIDATE-
invalidate mappings
MS_ASYNC returns immediately once all write operations are scheduled;
with MS_SYNC
the system call will not return until all write operations are completed.
MS_INVALIDATE 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.
MC_UNLOCK-
Unlock all pages in the range with attributes attr.
The calling process must have the P_PLOCK privilege.
At present arg is unused, but must be 0
to ensure compatibility with potential future enhancements.
MC_UNLOCKAS-
Remove address space memory locks,
and locks on all pages in the address space with attributes attr.
The calling process must have the P_PLOCK privilege.
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 MC_SYNC,
are restricted to processes with appropriate privileges
(P_PLOCK).
The memcntl
function subsumes the operations of plock and mctl.
Return values
On success, memcntl returns 0.
On failure, memcntl returns -1 and sets errno to identify the error.
Errors
In the following conditions, memcntl fails and sets errno to:
EAGAIN-
Some or all of the memory identified by the operation could not be
locked when MC_LOCK or MC_LOCKAS is specified.
EBUSY-
Some or all the addresses in the range [addr, addr + len) are
locked and MC_SYNC with MS_INVALIDATE option is specified.
EFAULT-
The page to be locked has been aborted (for example, by a file truncate
operation), or pages following the end of an object are not allocated.
EINVAL-
addr is not a multiple of the page size as returned by
sysconf.
EINVAL-
addr and/or len
do not have the value 0 when MC_LOCKAS or MC_UNLOCKAS is specified.
EINVAL-
arg is not valid for the function specified.
EINVAL-
Invalid selection criteria are specified in attr.
EIO-
An I/O error occurred when attempting to read the page from a device
or a network.
ENOMEM-
The argument
len
has a value less than or equal to 0.
ENOMEM-
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-
The process does not have appropriate privilege (P_PLOCK)
and one of MC_LOCK, MC_LOCKAS, MC_UNLOCK,
MC_UNLOCKAS was specified.
References
mlock(3C),
mlockall(3C),
mmap(2),
mprotect(2),
msync(3C),
plock(2),
sysconf(3C)
Notices
Considerations for threads programming
Sibling threads share (by definition) the same address space;
modifications to the address space by one can be perceived by the others.
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 25 April 2004