fsync_range(2) [netbsd man page]

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 modi-
     fied 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 written 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 synchro-
     nization 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 function available in AIX.

BSD
								   May 17, 2010 							       BSD

FSYNC(2)						     Linux Programmer's Manual							  FSYNC(2)

NAME

       fsync, fdatasync - synchronize a file's in-core state with storage device

SYNOPSIS

       #include <unistd.h>

       int fsync(int fd);

       int fdatasync(int fd);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       fsync(): _BSD_SOURCE || _XOPEN_SOURCE
		|| /* since glibc 2.8: */ _POSIX_C_SOURCE >= 200112L
       fdatasync(): _POSIX_C_SOURCE >= 199309L || _XOPEN_SOURCE >= 500

DESCRIPTION

       fsync()	transfers  ("flushes")	all  modified  in-core	data  of  (i.e., modified buffer cache pages for) the file referred to by the file
       descriptor fd to the disk device (or other permanent storage device) so that all changed information can be retrieved even after the system
       crashed or was rebooted.  This includes writing through or flushing a disk cache if present.  The call blocks until the device reports that
       the transfer has completed.  It also flushes metadata information associated with the file (see stat(2)).

       Calling fsync() does not necessarily ensure that the entry in the directory containing the  file  has  also  reached  disk.   For  that	an
       explicit fsync() on a file descriptor for the directory is also needed.

       fdatasync()  is similar to fsync(), but does not flush modified metadata unless that metadata is needed in order to allow a subsequent data
       retrieval to be correctly handled.  For example, changes to st_atime or st_mtime (respectively, time of last access and time of last  modi-
       fication;  see  stat(2)) do not require flushing because they are not necessary for a subsequent data read to be handled correctly.  On the
       other hand, a change to the file size (st_size, as made by say ftruncate(2)), would require a metadata flush.

       The aim of fdatasync() is to reduce disk activity for applications that do not require all metadata to be synchronized with the disk.

RETURN VALUE

       On success, these system calls return zero.  On error, -1 is returned, and errno is set appropriately.

ERRORS

       EBADF  fd is not a valid open file descriptor.

       EIO    An error occurred during synchronization.

       EROFS, EINVAL
	      fd is bound to a special file which does not support synchronization.

CONFORMING TO

       4.3BSD, POSIX.1-2001.

AVAILABILITY

       On POSIX systems on which fdatasync() is available, _POSIX_SYNCHRONIZED_IO is defined in <unistd.h> to a value greater than 0.	(See  also
       sysconf(3).)

NOTES

       On some UNIX systems (but not Linux), fd must be a writable file descriptor.

       In Linux 2.2 and earlier, fdatasync() is equivalent to fsync(), and so has no performance advantage.

       The  fsync()  implementations  in  older  kernels  and lesser used filesystems does not know how to flush disk caches.  In these cases disk
       caches need to be disabled using hdparm(8) or sdparm(8) to guarantee safe operation.

SEE ALSO

       bdflush(2), open(2), sync(2), sync_file_range(2), hdparm(8), mount(8), sync(8), update(8)

COLOPHON

       This page is part of release 3.53 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2012-02-27								  FSYNC(2)