oracular (2) msync.2freebsd.gz

Provided by: freebsd-manpages_12.2-2_all bug

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.