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Add an option that atomically tests for the existence of a file and
creates it if the file does not exist, by passing the O_EXCL flag
to open() on Unix and CREATE_NEW flag on Windows. Support for O_EXCL
varies across platforms and filesystems.
{ok, Fd} = file:open("/tmp/foo", [write,exclusive]),
{error, eexist} = file:open("/tmp/foo", [write,exclusive]).
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Useful for informing the Operating System about the access pattern
for a file's data, so that it can adapt the caching strategy to
maximize disk IO performance.
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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.
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* bg/file-del_dir:
Adjust test of file:del_dir("..") to accept {error,einval}
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On FreeBSD, file:del_dir("..") will return {error,einval} rather
than the expected {error,eexist}, and so will file:del_dir("../.."),
and so on.
It could be argued that we should change the implementation of
file:del_dir/1 to remap the error code (as some other error codes
are remapped to reduce the differences between different platforms),
but the consistency gained does not seem to be worth the effort.
Therefore, until we'll find a real-world use case where it is
essential to have consistent error codes for file:del_dir("..") on
all platforms, change the test case to accept both errors.
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