git, for example, can do this on a large repository when checking for updated files (because it needs to check the modification timestamp of every file in the r

git, for example, can do this on a large repository when checking for updated files (because it needs to check the modification timestamp of every file in the repo), and for a lot of common operations it's actually the bottleneck (and one reason why it is often faster on linux: the VFS layer in linux puts a lot of effort into making such operations as fast as possible, somewhat appropriately Linus was the one who did a lot of that work originally). In C it works pretty much as expected, and most of the overhead is in the kernel.