Functions either should generate error messages for everything they do
themselves, or for nothing and let the caller do it. But they certainly
shouldn't generate errors for some messages but not for others. Since
the function in this case is one that generates messages on its own, it
really should do that for everything, not just for some things, hence.
The check, if the directory/file already exists is only executed, if
there is a symlink target specified. In case of "/root", there is none,
so it is unconditionally tried to create the directory.
In case of a readonly filesystem, errno != EEXIST, but errno == EROFS,
so base_filesystem_create() and switch_root does not succeed.
This patch checks for existance not only in the symlink case.
