HP-UX Reference (11i v3 07/02) - 2 System Calls (vol 5)

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mlock(2) mlock(2)

NAME

mlock() - lock a segment of the process virtual address space in memory

SYNOPSIS

#include <sys/mman.h>

int mlock( const void * addr, size_t len) ;

DESCRIPTION

The mlock() system call allows the calling process to lock a segment of the process virtual address space

into memory. Any addressable segment of the process’ address space may be locked. Locked segments are

immune to all routine swapping.

addr must be a valid address in the process virtual address space. addr + len must also be a valid address

in the process virtual address space.

Locks are applied at page boundaries that encompass the range from addr to addr + len. If any address

within the range is not valid, an error is returned and no locks are applied.

munlock() or munlockall() can be used to unlock memory segments (or all memory segments)

locked with mlock().

Regardless of how many times a process locks a page, a single munlock() or munlockall() will

unlock it. An

munlock() of a page within a range speciﬁed in an mlock() call results in only the range

speciﬁed in the

munlock() being unlocked.

When memory is shared by multiple processes and mlocks are applied to the same physical page by multi-

ple processes, a page remains locked until the last lock is removed from that page.

Locks applied with mlock() are not inherited by a child process.

The user must have the MLOCK privilege.

Although plock() and the mlock() family of functions may be used together in an application, each

may affect the other in unexpected ways. This practice is not recommended.

Security Restrictions

Some or all of the actions associated with this system call require the MLOCK privilege. Processes owned

by the superuser have this privilege. Processes owned by other users may have this privilege, depending on

system conﬁguration. See privileges (5) for more information about privileged access on systems that sup-

port ﬁne-grained privileges.

RETURN VALUE

mlock() returns the following values:

0 Successful completion.

-1 Failure. The requested operation is not performed. errno

is set to indicate the error.

ERRORS

mlock() fails, errno is set to one of the following values:

[ENOMEM] One or more addresses in the speciﬁed range is not valid within the process address

space.

[EAGAIN] There is not enough lockable memory in the system to satisfy the locking request.

[EINVAL] The len parameter was zero.

[EPERM] The user does not have the MLOCK privilege.

EXAMPLES

The following call to mlock() locks the ﬁrst 10 pages of the calling process in memory:

mlock(sbrk(0), 40960);