Jörn Engel wrote:

The bad news for posix_fallocate() is that even if libc is smart enough
to write random data, mmap() can still cause problems.

This is not smart, quite to the contrary.  The standard guarantees that
all not-yet-written-to places in the file are zero.  And if a block has
already been written posix_fallocate cannot change it.

-- 
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖