feature-gate most Nix functions

Using features reduces build time and size for consumer crates.  By
default all features are enabled.

.cirrus.yml

@@ -20,6 +20,8 @@ build: &BUILD
     - $TOOL +$TOOLCHAIN $BUILD $ZFLAGS --target $TARGET --all-targets
     - $TOOL +$TOOLCHAIN doc $ZFLAGS --no-deps --target $TARGET
     - $TOOL +$TOOLCHAIN clippy $ZFLAGS --target $TARGET -- $CLIPPYFLAGS
+    - if [ -z "$NOHACK" ]; then $TOOL install cargo-hack; fi
+    - if [ -z "$NOHACK" ]; then $TOOL hack $ZFLAGS check --target $TARGET --each-feature; fi
 
 # Tests that do require executing the binaries
 test: &TEST
@@ -50,14 +52,16 @@ task:
     - cargo build --target i686-unknown-freebsd
     - cargo doc --no-deps --target i686-unknown-freebsd
     - cargo test --target i686-unknown-freebsd
+  i386_feature_script:
+    - . $HOME/.cargo/env
+    - cargo hack check --each-feature --target i686-unknown-freebsd
   before_cache_script: rm -rf $CARGO_HOME/registry/index
 
 # Test OSX in a full VM
 task:
-  matrix:
-    - name: OSX x86_64
-      env:
-        TARGET: x86_64-apple-darwin
+  name: OSX x86_64
+  env:
+    TARGET: x86_64-apple-darwin
   osx_instance:
     image: catalina-xcode
   setup_script:
@@ -192,13 +196,17 @@ task:
     # https://github.com/rust-embedded/cross/issues/535
     - name: iOS aarch64
       env:
+        # cargo hack tries to invoke the iphonesimulator SDK for iOS
+        NOHACK: 1
         TARGET: aarch64-apple-ios
         # Rustup only supports cross-building from arbitrary hosts for iOS at
         # 1.49.0 and above.  Below that it's possible to cross-build from an OSX
         # host, but OSX VMs are more expensive than Linux VMs.
         TOOLCHAIN: 1.49.0
     - name: iOS x86_64
       env:
+        # cargo hack tries to invoke the iphonesimulator SDK for iOS
+        NOHACK: 1
         TARGET: x86_64-apple-ios
         TOOLCHAIN: 1.49.0
     # Cross testing on powerpc fails with "undefined reference to renameat2".
@@ -222,6 +230,8 @@ task:
         TARGET: x86_64-unknown-netbsd
     - name: Redox x86_64
       env:
+        # cargo-hack needs a newer compiler
+        NOHACK: 1
         TARGET: x86_64-unknown-redox
         # Redox requires a nightly compiler.
         # If stuff breaks, change nightly to the date in the toolchain_*
@@ -269,6 +279,6 @@ task:
     image: rustlang/rust:nightly
   setup_script:
     - cargo update -Zminimal-versions
-  script:
+  check_script:
     - cargo check
   before_cache_script: rm -rf $CARGO_HOME/registry/index

CHANGELOG.md

@@ -6,6 +6,9 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 ## [0.23.0] - 2021-09-28
 ### Added
 
+- Added fine-grained features flags.  Most Nix functionality can now be
+  conditionally enabled.  By default, all features are enabled.
+  (#[TODO](https://github.com/nix-rust/nix/pull/TODO))
 - Added the `LocalPeerCred` sockopt.
   (#[1482](https://github.com/nix-rust/nix/pull/1482))
 - Added `TimeSpec::from_duration` and `TimeSpec::from_timespec`

Cargo.toml

@@ -10,6 +10,7 @@ categories  = ["os::unix-apis"]
 include = ["src/**/*", "LICENSE", "README.md", "CHANGELOG.md"]
 
 [package.metadata.docs.rs]
+rustdoc-args = ["--cfg", "docsrs"]
 targets = [
   "x86_64-unknown-linux-gnu",
   "aarch64-linux-android",
@@ -32,6 +33,52 @@ cfg-if = "1.0"
 [target.'cfg(not(target_os = "redox"))'.dependencies]
 memoffset = "0.6.3"
 
+[features]
+default = [
+  "acct", "aio", "dir", "env", "event", "features", "fs",
+  "hostname",
+  "inotify", "ioctl", "kmod", "mman", "mount", "mqueue",
+  "net", "personality", "process", "poll", "pthread", "ptrace", "quota",
+  "reboot",
+  "resource", "sched", "signal",
+  "socket",
+  "term", "time", "ucontext", "uio",
+  "users", "zerocopy",
+]
+
+acct = []
+aio = []
+dir = ["fs"]
+env = []
+event = []
+features = []
+fs = []
+hostname = []
+inotify = []
+ioctl = []
+kmod = []
+mman = []
+mount = ["uio"]
+mqueue = ["fs"]
+net = ["socket"]
+personality = []
+poll = []
+pthread = []
+ptrace = ["process"]
+quota = []
+process = []
+reboot = []
+resource = []
+sched = ["process"]
+signal = ["process"]
+socket = []
+term = []
+time = []
+ucontext = ["signal"]
+uio = []
+users = ["features"]
+zerocopy = ["fs", "uio"]
+
 [target.'cfg(target_os = "dragonfly")'.build-dependencies]
 cc = "1"
 

src/fcntl.rs

@@ -5,13 +5,15 @@ use std::ffi::OsString;
 use std::os::raw;
 use std::os::unix::ffi::OsStringExt;
 use std::os::unix::io::RawFd;
-use crate::sys::stat::Mode;
-use crate::{NixPath, Result};
 
 #[cfg(any(target_os = "android", target_os = "linux"))]
 use std::ptr; // For splice and copy_file_range
-#[cfg(any(target_os = "android", target_os = "linux"))]
-use crate::sys::uio::IoVec; // For vmsplice
+#[cfg(feature = "fs")]
+use crate::{
+    NixPath,
+    Result,
+    sys::stat::Mode
+};
 
 #[cfg(any(
     target_os = "linux",
@@ -22,10 +24,13 @@ use crate::sys::uio::IoVec; // For vmsplice
     target_env = "uclibc",
     target_os = "freebsd"
 ))]
-pub use self::posix_fadvise::*;
+#[cfg(feature = "fs")]
+pub use self::posix_fadvise::{PosixFadviseAdvice, posix_fadvise};
 
 #[cfg(not(target_os = "redox"))]
+#[cfg(any(feature = "fs", feature = "process"))]
 libc_bitflags! {
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "fs", feature = "process"))))]
     pub struct AtFlags: c_int {
         AT_REMOVEDIR;
         AT_SYMLINK_FOLLOW;
@@ -39,8 +44,10 @@ libc_bitflags! {
     }
 }
 
+#[cfg(any(feature = "fs", feature = "term"))]
 libc_bitflags!(
     /// Configuration options for opened files.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "fs", feature = "term"))))]
     pub struct OFlag: c_int {
         /// Mask for the access mode of the file.
         O_ACCMODE;
@@ -165,6 +172,9 @@ libc_bitflags!(
     }
 );
 
+feature!{
+#![feature = "fs"]
+
 // The conversion is not identical on all operating systems.
 #[allow(clippy::useless_conversion)]
 pub fn open<P: ?Sized + NixPath>(path: &P, oflag: OFlag, mode: Mode) -> Result<RawFd> {
@@ -209,19 +219,24 @@ pub fn renameat<P1: ?Sized + NixPath, P2: ?Sized + NixPath>(
     })??;
     Errno::result(res).map(drop)
 }
+}
 
 #[cfg(all(
     target_os = "linux",
     target_env = "gnu",
 ))]
+#[cfg(feature = "fs")]
 libc_bitflags! {
+    #[cfg_attr(docsrs, doc(cfg(feature = "fs")))]
     pub struct RenameFlags: u32 {
         RENAME_EXCHANGE;
         RENAME_NOREPLACE;
         RENAME_WHITEOUT;
     }
 }
 
+feature!{
+#![feature = "fs"]
 #[cfg(all(
     target_os = "linux",
     target_env = "gnu",
@@ -348,6 +363,7 @@ pub(crate) fn at_rawfd(fd: Option<RawFd>) -> raw::c_int {
         Some(fd) => fd,
     }
 }
+}
 
 #[cfg(any(target_os = "android", target_os = "linux"))]
 libc_bitflags!(
@@ -364,14 +380,19 @@ libc_bitflags!(
     }
 );
 
+#[cfg(feature = "fs")]
 libc_bitflags!(
     /// Additional configuration flags for `fcntl`'s `F_SETFD`.
+    #[cfg_attr(docsrs, doc(cfg(feature = "fs")))]
     pub struct FdFlag: c_int {
         /// The file descriptor will automatically be closed during a successful `execve(2)`.
         FD_CLOEXEC;
     }
 );
 
+feature!{
+#![feature = "fs"]
+
 #[cfg(not(target_os = "redox"))]
 #[derive(Debug, Eq, Hash, PartialEq)]
 #[non_exhaustive]
@@ -455,6 +476,7 @@ pub fn fcntl(fd: RawFd, arg: FcntlArg) -> Result<c_int> {
     Errno::result(res)
 }
 
+// TODO: convert to libc_enum
 #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
 #[non_exhaustive]
 pub enum FlockArg {
@@ -483,10 +505,13 @@ pub fn flock(fd: RawFd, arg: FlockArg) -> Result<()> {
 
     Errno::result(res).map(drop)
 }
+}
 
 #[cfg(any(target_os = "android", target_os = "linux"))]
+#[cfg(feature = "zerocopy")]
 libc_bitflags! {
     /// Additional flags to `splice` and friends.
+    #[cfg_attr(docsrs, doc(cfg(feature = "zerocopy")))]
     pub struct SpliceFFlags: c_uint {
         /// Request that pages be moved instead of copied.
         ///
@@ -505,6 +530,9 @@ libc_bitflags! {
     }
 }
 
+feature!{
+#![feature = "zerocopy"]
+
 /// Copy a range of data from one file to another
 ///
 /// The `copy_file_range` system call performs an in-kernel copy between
@@ -577,7 +605,12 @@ pub fn tee(fd_in: RawFd, fd_out: RawFd, len: usize, flags: SpliceFFlags) -> Resu
 }
 
 #[cfg(any(target_os = "linux", target_os = "android"))]
-pub fn vmsplice(fd: RawFd, iov: &[IoVec<&[u8]>], flags: SpliceFFlags) -> Result<usize> {
+pub fn vmsplice(
+    fd: RawFd,
+    iov: &[crate::sys::uio::IoVec<&[u8]>],
+    flags: SpliceFFlags
+    ) -> Result<usize>
+{
     let ret = unsafe {
         libc::vmsplice(
             fd,
@@ -588,10 +621,13 @@ pub fn vmsplice(fd: RawFd, iov: &[IoVec<&[u8]>], flags: SpliceFFlags) -> Result<
     };
     Errno::result(ret).map(|r| r as usize)
 }
+}
 
 #[cfg(any(target_os = "linux"))]
+#[cfg(feature = "fs")]
 libc_bitflags!(
     /// Mode argument flags for fallocate determining operation performed on a given range.
+    #[cfg_attr(docsrs, doc(cfg(feature = "fs")))]
     pub struct FallocateFlags: c_int {
         /// File size is not changed.
         ///
@@ -620,11 +656,15 @@ libc_bitflags!(
     }
 );
 
+feature!{
+#![feature = "fs"]
+
 /// Manipulates file space.
 ///
 /// Allows the caller to directly manipulate the allocated disk space for the
 /// file referred to by fd.
 #[cfg(any(target_os = "linux"))]
+#[cfg(feature = "fs")]
 pub fn fallocate(
     fd: RawFd,
     mode: FallocateFlags,
@@ -635,6 +675,7 @@ pub fn fallocate(
     Errno::result(res).map(drop)
 }
 
+
 #[cfg(any(
     target_os = "linux",
     target_os = "android",
@@ -649,9 +690,11 @@ mod posix_fadvise {
     use std::os::unix::io::RawFd;
     use crate::Result;
 
+    #[cfg(feature = "fs")]
     libc_enum! {
         #[repr(i32)]
         #[non_exhaustive]
+        #[cfg_attr(docsrs, doc(cfg(feature = "fs")))]
         pub enum PosixFadviseAdvice {
             POSIX_FADV_NORMAL,
             POSIX_FADV_SEQUENTIAL,
@@ -662,6 +705,8 @@ mod posix_fadvise {
         }
     }
 
+    feature!{
+    #![feature = "fs"]
     pub fn posix_fadvise(
         fd: RawFd,
         offset: libc::off_t,
@@ -676,6 +721,7 @@ mod posix_fadvise {
             Err(Errno::from_i32(res))
         }
     }
+    }
 }
 
 #[cfg(any(
@@ -694,3 +740,4 @@ pub fn posix_fallocate(fd: RawFd, offset: libc::off_t, len: libc::off_t) -> Resu
         Ok(errno) => Err(Errno::from_i32(errno)),
     }
 }
+}