According to `man open`:

> The file is opened in append mode. Before each write(2), the file offset
is positioned at the end of the file, as if with lseek(2). The modi‐
fication of the file offset and the write operation are performed as a
single atomic step.

Cleanup to allow use of most functions when linking the library, including mounting and creating filesystems

POSIX says this should work, and some software seems to rely on that.

This seems to be a warning with the latest Rust, and an error due to #![deny(warnings)]

Matches Posix.