msync(3C)						   Standard C Library Functions 						 msync(3C)

NAME

       msync - synchronize memory with physical storage

SYNOPSIS

       #include <sys/mman.h>

       int msync(void *addr, size_t 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 references to the pages will be obtained by the system from their permanent storage locations. The permanent storage
       for  a  modified MAP_SHARED mapping is the file the page is mapped to; the permanent storage for a modified MAP_PRIVATE mapping is its swap
       area.

       The flags argument is a bit pattern built from the following values:

       MS_ASYNC        perform asynchronous writes

       MS_SYNC	       perform synchronous writes

       MS_INVALIDATE   invalidate mappings

       If flags is MS_ASYNC or MS_SYNC, 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 references to the memory region.

	 o  Unmodified pages in the specified range are not written to the underlying hardware.

       If flags is MS_ASYNC, the function may return immediately once all write operations are scheduled; if flags is MS_SYNC, the  function  does
       not return until all write operations are completed.

       If flags is MS_INVALIDATE, the function synchronizes the contents of the memory region to match the current file contents.

	 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 process, to memory regions mapped to the same portion of the file using MAP_SHARED, are
	    visible by read references to the region.

       If msync() causes any write to the file, then the file's st_ctime and st_mtime fields are marked for update.

RETURN VALUES

       Upon successful completion, msync() returns 0; otherwise, it returns -1 and sets errno to indicate the error.

ERRORS

       The msync() function will fail if:

       EBUSY	       Some or all of the addresses in the range [addr, addr + len) are locked and MS_SYNC with the MS_INVALIDATE option is speci-
		       fied.

       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 MS_ASYNC and MS_INVALIDATE.

       EIO	       An I/O error occurred while reading from or writing to the file system.

       ENOMEM	       Addresses in the range [addr, addr + len) are outside the valid range for the address space of a process, or specify one or
		       more pages that are not mapped.

       EPERM	       MS_INVALIDATE 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.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       memcntl(2), mmap(2), sysconf(3C), attributes(5), standards(5)

SunOS 5.10							    24 Jul 2002 							 msync(3C)