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msync(2) [freebsd man page]

MSYNC(2)						      BSD System Calls Manual							  MSYNC(2)

NAME
msync -- synchronize a mapped region LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <sys/mman.h> int msync(void *addr, size_t len, int flags); DESCRIPTION
The msync() system call writes any modified pages back to the file system and updates the file modification time. If len is 0, all modified pages within the region containing addr will be flushed; if len is non-zero, only those pages containing addr and len-1 succeeding locations will be examined. The flags argument may be specified as follows: MS_ASYNC Return immediately MS_SYNC Perform synchronous writes MS_INVALIDATE Invalidate all cached data RETURN VALUES
The msync() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error. ERRORS
The msync() system call will fail if: [EBUSY] Some or all of the pages in the specified region are locked and MS_INVALIDATE is specified. [EINVAL] The addr argument is not a multiple of the hardware page size. [ENOMEM] The addresses in the range starting at addr and continuing for len bytes are outside the range allowed for the address space of a process or specify one or more pages that are not mapped. [EINVAL] The flags argument was both MS_ASYNC and MS_INVALIDATE. Only one of these flags is allowed. [EIO] An error occurred while writing at least one of the pages in the specified region. SEE ALSO
madvise(2), mincore(2), mlock(2), mprotect(2), munmap(2) HISTORY
The msync() system call first appeared in 4.4BSD. BUGS
The msync() system call is usually not needed since BSD implements a coherent file system buffer cache. However, it may be used to associate dirty VM pages with file system buffers and thus cause them to be flushed to physical media sooner rather than later. BSD
March 18, 2012 BSD

Check Out this Related Man Page

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)
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