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NetBSD 6.1.5 - man page for fsync (netbsd section 2)

FSYNC(2)			     BSD System Calls Manual				 FSYNC(2)

NAME
     fsync, fsync_range -- synchronize a file's in-core state with that on disk

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <unistd.h>

     int
     fsync(int fd);

     int
     fsync_range(int fd, int how, off_t start, off_t length);

DESCRIPTION
     fsync() causes all modified data and attributes of fd to be moved to a permanent storage
     device.  This normally results in all in-core modified copies of buffers for the associated
     file to be written to a disk.

     fsync() should be used by programs that require a file to be in a known state, for example,
     in building a simple transaction facility.

     fsync_range() causes all modified data starting at start for length length of fd to be writ-
     ten to permanent storage.	Note that fsync_range() requires that the file fd must be open
     for writing.

     fsync_range() may flush the file data in one of two manners:

	   FDATASYNC  Synchronize the file data and sufficient meta-data to retrieve the data for
		      the specified range.

	   FFILESYNC  Synchronize all modified file data and meta-data for the specified range.

     By default, fsync_range() does not flush disk caches, assuming that storage media are able
     to ensure completed writes are transfered to media.  The FDISKSYNC flag may be included in
     the how parameter to trigger flushing of all disk caches for the file.

     If the length parameter is zero, fsync_range() will synchronize all of the file data.

RETURN VALUES
     A 0 value is returned on success.	A -1 value indicates an error.

ERRORS
     fsync() or fsync_range() fail if:

     [EBADF]		fd is not a valid descriptor.

     [EINVAL]		fd refers to a socket, not to a file.

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

     Additionally, fsync_range() fails if:

     [EBADF]		fd is not open for writing.

     [EINVAL]		start + length is less than start.

NOTES
     For optimal efficiency, the fsync_range() call requires that the file system containing the
     file referenced by fd support partial synchronization of file data.  For file systems which
     do not support partial synchronization, the entire file will be synchronized and the call
     will be the equivalent of calling fsync().

SEE ALSO
     sync(2), sync(8)

HISTORY
     The fsync() function call appeared in 4.2BSD.

     The fsync_range() function call first appeared in NetBSD 2.0 and is modeled after the func-
     tion available in AIX.

BSD					   May 17, 2010 				      BSD


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