FSYNC(2) | System Calls Manual | FSYNC(2) |
int
fsync(int fd);
int
fsync_range(int fd, int how, off_t start, off_t length);
fsync_range() is similar, but provides control over the region of the file to be synchronized, and the method of synchronization.
These functions should be used by programs that require a file to be in a known state, for example, in building a simple transaction facility.
Note that writing the data to a permanent storage device does not necessarily write the data to permanent storage media within that device; for example, after writing data to a disk device, the data might reside in a cache within the device, but not yet on more permanent storage within the device. Neither fsync() nor the default behavior of fsync_range() (without the FDISKSYNC flag) will flush disk caches, because they assume that storage devices are able to ensure that completed writes are transferred to media some time between the write and a power failure or system crash.
fsync_range() causes all modified data starting at start for length length of fd to be written to a permanent storage device. If the length parameter is zero, fsync_range() will synchronize all of the file data.
fsync_range() takes a how parameter which contains one or more of the following flags:
The FDATASYNC and FFILESYNC flags are mutually exclusive. Either of those flags may be combined with the FDISKSYNC flag.
Note that fsync_range() requires that the file fd must be open for writing, whereas fsync() does not.
Additionally, fsync_range() fails if:
The fsync_range() function call first appeared in NetBSD 2.0 and is modeled after the function available in AIX.
September 22, 2013 | NetBSD 7.2 |