Standard C Library Functions msync(3C)
NAME
msync - synchronize memory with physical storage
SYNOPSIS
#include
int msync(void *addr, sizet len, int flags);
DESCRIPTION
The msync() function writes all modified copies of pages
over the range [addr, addr ] len) to the underlying
hardware, or invalidates any copies so that further refer-
ences to the pages will be obtained by the system from their
permanent storage locations. The permanent storage for a
modified MAPSHARED mapping is the file the page is mapped
to; the permanent storage for a modified MAPRIVATE mapping
is its swap area.
The flags argument is a bit pattern built from the following
values:
MSASYNC perform asynchronous writes
MSYNC perform synchronous writes
MSINVALIDATE invalidate mappings
If flags is MSASYNC or MSYNC, the function synchronizes
the file contents to match the current contents of the
memory region.
o All write references to the memory region made
prior to the call are visible by subsequent read
operations on the file.
o All writes to the same portion of the file prior to
the call may or may not be visible by read refer-
ences to the memory region.
o Unmodified pages in the specified range are not
written to the underlying hardware.
If flags is MSASYNC, the function may return immediately
once all write operations are scheduled; if flags is
MSYNC, the function does not return until all write
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Standard C Library Functions msync(3C)
operations are completed.
If flags is MSINVALIDATE, the function synchronizes the
contents of the memory region to match the current file con-
tents.
o All writes to the mapped portion of the file made
prior to the call are visible by subsequent read
references to the mapped memory region.
o All write references prior to the call, by any pro-
cess, to memory regions mapped to the same portion
of the file using MAPSHARED, are visible by read
references to the region.
If msync() causes any write to the file, then the file's
stctime and stmtime fields are marked for update.
RETURN VALUES
Upon successful completion, msync() returns 0; otherwise, it
returns -1 and sets errno to indicate the error.
ERORS
The msync() function will fail if:
EBUSY Some or all of the addresses in the range [addr,
addr ] len) are locked and MSYNC with the
MSINVALIDATE option is specified.
EAGAIN Some or all pages in the range [addr, addr ]
len) are locked for I/O.
EINVAL The addr argument is not a multiple of the page
size as returned by sysconf(3C).
The flags argument is not some combination of
MSASYNC and MSINVALIDATE.
EIO An I/O error occurred while reading from or writ-
ing to the file system.
ENOMEM Addresses in the range [addr, addr ] len) are out-
side the valid range for the address space of a
process, or specify one or more pages that are not
mapped.
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Standard C Library Functions msync(3C)
EPERM MSINVALIDATE was specified and one or more of the
pages is locked in memory.
USAGE
The msync() function should be used by programs that require
a memory object to be in a known state, for example in
building transaction facilities.
Normal system activity can cause pages to be written to
disk. Therefore, there are no guarantees that msync() is
the only control over when pages are or are not written to
disk.
ATRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
ATRIBUTE TYPE ATRIBUTE VALUE
Interface Stability Standard
MT-Level MT-Safe
SEE ALSO
memcntl(2), mmap(2), sysconf(3C), attributes(5), stan-
dards(5)
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