Add file:datasync/1 for syncing file contents only

file:datasync/1 invokes the POSIX system call "int fdatasync(int fd)".
This system call is similar to "fsync" but, unlike fsync, it does not
update the metadata associated with the file (like the access time for
example). It's used by many DBMSs (MySQL and SQLite of example) to
increase disk IO performance, as it avoids disk seeks and disk write
operations compared to fsync.

More details on it at:

http://linux.die.net/man/2/fdatasync

An example, from the MySQL source:

http://bazaar.launchpad.net/~mysql/mysql-server/mysql-5.1-telco-6.1/annotate/head%3A/mysys/my_sync.c#L61

This new function just calls fsync on systems not implementing fdatasync.

1 files changed, 1 insertions, 0 deletions

diff --git a/erts/emulator/drivers/common/erl_efile.h b/erts/emulator/drivers/common/erl_efile.h
index 9aa941e550..6821a0e2ee 100644
--- a/erts/emulator/drivers/common/erl_efile.h
+++ b/erts/emulator/drivers/common/erl_efile.h
@@ -126,6 +126,7 @@ int efile_readdir(Efile_error* errInfo, char* name,
 int efile_openfile(Efile_error* errInfo, char* name, int flags,
 		   int* pfd, Sint64* pSize);
 void efile_closefile(int fd);
+int efile_fdatasync(Efile_error* errInfo, int fd);
 int efile_fsync(Efile_error* errInfo, int fd);
 int efile_fileinfo(Efile_error* errInfo, Efile_info* pInfo,
 		   char *name, int info_for_link);