How can unlinking be postponed?

[Doug Gwyn <gwyn>]

> ...  Does the directory entry disappear immediately but not
> the i-node and its associated disk space?

Exactly.

> If that's so, shouldn't any
> syscall except read return an error value since the process making that
> call is under the reasonable impression that the file's still there when
> it isn't?

? Any meaningful system call (e.g., lseek, stat) still works.  Only
an attempt to locate the unlinked directory entry will fail.  There
is no reason to put special-case code for this into the kernel.

> Is there no way for a file to be removed upon a process' exit?

You can use onexit() if your system has it (it probably doesn't).
Any file made by tmpfile(3) will vanish upon process termination.