fdatasync

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Langue: en

Version: 2007-07-26 (mandriva - 22/10/07)

Section: 2 (Appels système)

NAME

fdatasync - synchronize a file's in-core data with that on disk

SYNOPSIS

#include <unistd.h>

int fdatasync(int fd);

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

fdatasync(): _POSIX_C_SOURCE >= 199309L || _XOPEN_SOURCE >= 500

DESCRIPTION

fdatasync() flushes all data buffers of a file to disk (before the system call returns). It resembles fsync(2) but is not required to update metadata such as the file last access time.

Applications that access databases or log files often write a tiny data fragment (e.g., one line in a log file) and then call fsync(2) immediately in order to ensure that the written data is physically stored on the harddisk. Unfortunately, fsync(2) will always initiate two write operations: one for the newly written data and another one in order to update the modification time stored in the inode. If the modification time is not a part of the transaction concept fdatasync() can be used to avoid unnecessary inode disk write operations.

RETURN VALUE

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

ERRORS

EBADF
fd is not a valid file descriptor open for writing.
EIO
An error occurred during synchronization.
EROFS, EINVAL
fd is bound to a special file which does not support synchronization.

CONFORMING TO

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

In Linux 2.2 and earlier, fdatasync() is equivalent to fsync(2), and so has no performance advantage.

SEE ALSO

fsync(2), sync_file_range(2)
B.O. Gallmeister, POSIX.4, O'Reilly, pp. 220-223 and 343.