FSYNC(2) NetBSD System Calls Manual FSYNC(2)
fsync, fsync_range -- synchronize a file's in-core state with that on disk
Standard C Library (libc, -lc)
#include <unistd.h> int fsync(int fd); int fsync_range(int fd, int how, off_t start, off_t length);
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 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 stor- age media are able to ensure completed writes are transfered to media. The FDISKSYNC flag may be included in the how parameter to trigger flush- ing of all disk caches for the file. If the length parameter is zero, fsync_range() will synchronize all of the file data.
A 0 value is returned on success. A -1 value indicates an error.
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.
For optimal efficiency, the fsync_range() call requires that the file system containing the file referenced by fd support partial synchroniza- tion of file data. For file systems which do not support partial syn- chronization, the entire file will be synchronized and the call will be the equivalent of calling fsync().
The fsync() function call appeared in 4.2BSD. The fsync_range() function call first appeared in NetBSD 2.0 and is mod- eled after the function available in AIX. NetBSD 6.0 May 17, 2010 NetBSD 6.0
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