fsync, fdatasync - synchronize a file's complete in-core state with
that on disk
int fsync(int fd);
int fdatasync(int fd);
fsync copies all in-core parts of a file to disk, and waits until the
device reports that all parts are on stable storage. It also updates
metadata stat information. It does not necessarily ensure that the
entry in the directory containing the file has also reached disk. For
that an explicit fsync on the file descriptor of the directory is also
fdatasync does the same as fsync but only flushes user data, not the
meta data like the mtime or atime.
On success, zero is returned. On error, -1 is returned, and errno is
EBADF fd is not a valid file descriptor open for writing.
fd is bound to a special file which does not support synchronization.
EIO An error occurred during synchronization.
In case the hard disk has write cache enabled, the data may not really
be on permanent storage when fsync/fdatasync return.
When an ext2 file system is mounted with the sync option, directory
entries are also implicitely synced by fsync.
On kernels before 2.4, fsync on big files can be inefficient. An
alternative might be to use the O_SYNC flag to open(2).
POSIX.1b (formerly POSIX.4)
bdflush(2), open(2), sync(2), mount(8), update(8), sync(8)
Linux 1.3.85 2001-04-18 FSYNC(2)
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