Re: [libvirt PATCH] scripts: Fix meson-install-symlink.py overwriting existing links

On Tue, Aug 04, 2020 at 06:27:08PM +0200, Erik Skultety wrote: > By default, symlink re-creation fails if the link already exists, more > specifically in case of meson-install-symlink.py: > > Traceback (most recent call last): > File "/<path_to_libvirt_repo>/scripts/meson-install-symlink.py", > line 15, in <module> > os.symlink(target, link) > FileExistsError: File exists: '../default.xml' -> 'default.xml' > > Unfortunately, Python can't mimic "ln -sf", so we have to fix this > differently - create a temporary name which is then going to be used > for the temporary link followed by a rename with the original link's > name. > Note that this solution is racy as mktemp() doesn't guarantee > atomicity in link creation, so theoretically another process could come > and create a file with the same name as the temporary link name, but > a proper solution would be longer and not as elegant. You've just described exactly what python does for "ln -sf foo bar". try stracing it and you'll see it do: symlinkat("foo", AT_FDCWD, "CubmxbFT") = 0 renameat(AT_FDCWD, "CubmxbFT", AT_FDCWD, "bar") = 0