Why glibc's fstat() is slow

I looked a bit further, and it turns out that the original statx implementation did support passing NULL filename to emulate fstat, but this support was explicitly dropped in [1].

It feels really weird that Linus bashed glibc for "being silly" but merged this change... OTOH back in 2017 archs without fstat syscall didn't exist, so it wasn't a problem for C libraries.

[1] https://git.kernel.org/torvalds/c/1e2f82d1e9d12223b4cbd1f...