Analysis of information sources in references of the Wikipedia article "Maildir" in English language version.
All this trouble is rather pointless. Only the first step is what really guarantees that the mails won't get overwritten, the rest just sounds nice. Even though they might catch a problem once in a while, they give no guaranteed protection and will just as easily pass duplicate filenames through to overwrite existing mails. Step 2 is pointless because there's a race condition between steps 2 and 3. PID/host combination by itself should already guarantee that it never finds such a file. If it does, something's broken and the stat() check won't help since another process might be doing the same thing at the same time, and you end up writing to the same file in tmp/, causing the mail to get corrupted. In step 4 the link() would also fail if identical file was already in the maildir, right? Wrong. The file may already have been moved to cur/ directory, and since it may contain any number of flags by then you can't check with a simple stat() anymore if it exists or not. So really, all that's important in not getting mails overwritten in your maildir is the step 1: Always create filenames that are guaranteed to be unique. Forget about the 2 second waits and such that the Qmail's man page talks about
That specification requires that the action of the function be atomic.
