SunOS man pages : memcntl (2)
System Calls memcntl(2)
NAME
memcntl - memory management control
SYNOPSIS
#include <sys/types.h>
#include <sys/mman.h>
int memcntl(caddr_t addr, size_t len, int cmd, caddr_t arg,
int attr, int mask);
DESCRIPTION
The memcntl() function allows the calling process to apply
a variety of control operations over the address space iden-
tified by the mappings established for the address range
[addr, addr + len).
The addr argument 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 cri-
teria:
SHARED
Page is mapped shared.
PRIVATE
Page is mapped private.
The following attributes specify page protection selection
criteria. The selection criteria are constructed by a bit-
wise OR operation on the attribute bits and must match
exactly.
PROT_READ
Page can be read.
PROT_WRITE
Page can be written.
PROT_EXEC
Page can be executed.
The following criteria may also be specified:
PROC_TEXT
Process text.
PROC_DATA
Process data.
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System Calls memcntl(2)
The PROC_TEXT attribute specifies all privately mapped seg-
ments with read and execute permission, and the PROC_DATA
attribute 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. A given page may be locked multiple times
through different mappings; however, within a given
mapping, page locks do not nest. Multiple lock opera-
tions 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 visi-
ble through a different mapping in the locking pro-
cess) is locked in memory as long as the locking pro-
cess 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 writ-
able 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 com-
patibility with potential future enhancements.
MC_LOCKAS
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 enhance-
ments.
The arg argument 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
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System Calls memcntl(2)
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. The arg argu-
ment 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 function 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 applica-
tions that require a memory object to be in a known
state.
MC_UNLOCK
Unlock all pages in the range with attributes attr. At
present arg is unused, but must be 0 to ensure compa-
tibility with potential future enhancements.
MC_UNLOCKAS
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 0; it is reserved for future use.
Locks established with the lock operations are not inherited
by a child process after fork(2). The memcntl() function
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System Calls memcntl(2)
fails if it attempts to lock more memory than a system-
specific limit.
Due to the potential impact on system resources, all opera-
tions, with the exception of MC_SYNC, are restricted to
processes with super-user effective user ID.
USAGE
The memcntl() function subsumes the operations of plock(3C)
and mctl(3UCB).
RETURN VALUES
Upon successful completion, memcntl() returns 0; otherwise,
it returns -1 and sets errno to indicate an error.
ERRORS
The memcntl() function will fail if:
EAGAIN
Some or all of the memory identified by the operation
could not be locked when MC_LOCK or MC_LOCKAS was
specified.
EBUSY Some or all of the addresses in the range [addr, addr
+ len) are locked and MC_SYNC with the MS_INVALIDATE
option was specified.
EINVAL
The addr argument specifies invalid selection criteria
or is not a multiple of the page size as returned by
sysconf(3C); the addr and/or len argument does not
have the value 0 when MC_LOCKAS or MC_UNLOCKAS is
specified; or the arg argument is not valid for the
function specified.
ENOMEM
Some or all of the addresses in the range [addr, addr
+ len) are invalid for the address space of a process
or specify one or more pages which are not mapped.
EPERM The process's effective user ID is not super-user and
MC_LOCK, MC_LOCKAS, MC_UNLOCK, or MC_UNLOCKAS was
specified.
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
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System Calls memcntl(2)
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| MT-Level | MT-Safe |
|_____________________________|_____________________________|
SEE ALSO
fork(2) mmap(2), mprotect(2), mctl(3UCB), mlock(3C),
mlockall(3C), msync(3C), plock(3C), sysconf(3C), attributes(5)
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