Cargo Features

sys-mount = { version = "3.0.1", default-features = false, features = ["loop"] }
default = loop

The loop feature is set by default whenever sys-mount is added without default-features = false somewhere in the dependency tree.

loop default = loopdev

Features from optional dependencies

In crates that don't use the dep: syntax, optional dependencies automatically become Cargo features.

loopdev loop

Enables loopdev-3