Is rename() without fsync() safe?

Is it safe to call rename(tmppath, path) without calling fsync(tmppath_fd) first?

I want the path to always point to a complete file. I care mainly about Ext4. Is the rename() promised to be safe in all future Linux kernel versions?

A usage example in Python:

def store_atomically(path, data):
    tmppath = path + ".tmp"
    output = open(tmppath, "wb")
    output.write(data)

    output.flush()
    os.fsync(output.fileno())  # The needed fsync().
    output.close()
    os.rename(tmppath, path)

Answer

No.

Look at libeatmydata, and this presentation:

Eat My Data: How Everybody Gets File IO Wrong

http://www.oscon.com/oscon2008/public/schedule/detail/3172

by Stewart Smith from MySql.

In case it is offline/no longer available, I keep a copy of it:

• The video here
• The presentation slides (online version of slides)