Allow static and dynamic linking

Currently both `userfaultfd` and `userfaultfd-sys` always load libclang
dynamically. This commit keeps this as the default behavior but adds the
"static" and "runtime" features. The "static" feature will statically
link libclang, while "runtime" will load libclang at runtime.

Users using `default-features=false` will need to specify
`features = ["runtime"]` to maintain current behavior, but they should
be in the minority, given that neither crate currently has default
features.

Author: ureeves

Cargo.toml

@@ -14,12 +14,16 @@ cfg-if = "^1.0.0"
 libc = "0.2.65"
 nix = { version = "0.27", features = ["ioctl"] }
 thiserror = "1.0.4"
-userfaultfd-sys = { path = "userfaultfd-sys", version = "^0.5.0" }
+userfaultfd-sys = { path = "userfaultfd-sys", version = "^0.5.0", default-features = false }
 
 [dev-dependencies]
 nix = { version = "0.27", features = ["poll", "mman", "feature"] }
 
 [features]
-default = []
+default = ["runtime"]
+
 linux4_14 = ["userfaultfd-sys/linux4_14", "nix/process"]
 linux5_7 = ["userfaultfd-sys/linux5_7"]
+
+runtime = ["userfaultfd-sys/runtime"]
+static = ["userfaultfd-sys/static"]

userfaultfd-sys/Cargo.toml

@@ -13,10 +13,14 @@ build = "build.rs"
 cfg-if = "^1.0.0"
 
 [build-dependencies]
-bindgen = { version = "^0.68.1", default-features = false, features = ["runtime"]  }
+bindgen = { version = "^0.68.1", default-features = false }
 cc = "1.0"
 
 [features]
-default = []
+default = ["runtime"]
+
 linux4_14 = []
 linux5_7 = []
+
+runtime = ["bindgen/runtime"]
+static = ["bindgen/static"]