• I want to append data to a file in /tmp.
• If the file doesn't exist I want to create it
• I don't care if someone else owns the file. The data is not secret.
• I do not want someone to be able to race-condition this into writing somewhere else, or to another file.

What is the best way to do this?

Here's my thought:

fd = open("/tmp/some-benchmark-data.txt", O_APPEND | O_CREAT | O_NOFOLLOW | O_WRONLY, 0644);
fstat(fd, &st);
if (st.st_nlink != 1) {
    HARD LINK ATTACK!
}

What's the right way? Besides not using a world-writable directory.