Deprecate FutexOperation instead of futex (#1118)

With `rustix::thread::futex` being both a deprecated function and
a public module, I'm seeing warnings like this when I use it in
some simple testcases:

```console
warning: use of deprecated function `rustix::thread::futex`: There are now individual functions available to perform futex operations with improved type safety. See the futex module.
 --> test.rs:2:21
  |
2 | use rustix::thread::futex;
  |                     ^^^^^
  |
  = note: `#[warn(deprecated)]` on by default
```

To fix this, move the deprecation from the `futex` function to the
`FutexOperation` enum. This has the same effect, but doesn't
produce the warning then the `futex` module is used.

Also while using the API, I found `futex::FutexFlags` to be a little
redundant, so I think it makes sense to rename it to `futex::Flags`,
and similarly rename `futex::FUTEX_WAITERS` to `futex::WAITERS` and
so on.

This also splits `FutexOperation` into two enums internally, so that
the public `FutexOperation` which is `#[non_exhausitive]` can continue
to have its original contents, and the private enum can add new opcodes.

src/backend/libc/thread/futex.rs

@@ -1,25 +1,23 @@
 use crate::backend::c;
 
 bitflags::bitflags! {
-    /// `FUTEX_*` flags for use with [`futex`].
+    /// `FUTEX_*` flags for use with the functions in [`futex`].
     ///
     /// [`futex`]: mod@crate::thread::futex
     #[repr(transparent)]
     #[derive(Copy, Clone, Eq, PartialEq, Hash, Debug)]
-    pub struct FutexFlags: u32 {
+    pub struct Flags: u32 {
         /// `FUTEX_PRIVATE_FLAG`
         const PRIVATE = bitcast!(c::FUTEX_PRIVATE_FLAG);
         /// `FUTEX_CLOCK_REALTIME`
         const CLOCK_REALTIME = bitcast!(c::FUTEX_CLOCK_REALTIME);
     }
 }
 
-/// `FUTEX_*` operations for use with [`futex`].
-///
-/// [`futex`]: mod@crate::thread::futex
+/// `FUTEX_*` operations for use with the futex syscall wrappers.
 #[derive(Debug, Copy, Clone, Eq, PartialEq)]
 #[repr(u32)]
-pub enum FutexOperation {
+pub(crate) enum Operation {
     /// `FUTEX_WAIT`
     Wait = bitcast!(c::FUTEX_WAIT),
     /// `FUTEX_WAKE`
@@ -50,8 +48,43 @@ pub enum FutexOperation {
     LockPi2 = bitcast!(c::FUTEX_LOCK_PI2),
 }
 
+/// `FUTEX_*` operations for use with the [`futex`] function.
+///
+/// [`futex`]: fn@crate::thread::futex
+#[deprecated(
+    since = "0.38.35",
+    note = "
+    The `futex` function and `FutexOperation` enum are deprecated. There are
+    individual functions available to perform futex operations with improved
+    type safety. See the `rustix::thread::futex` module."
+)]
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+#[repr(u32)]
+pub enum FutexOperation {
+    /// `FUTEX_WAIT`
+    Wait = bitcast!(c::FUTEX_WAIT),
+    /// `FUTEX_WAKE`
+    Wake = bitcast!(c::FUTEX_WAKE),
+    /// `FUTEX_FD`
+    Fd = bitcast!(c::FUTEX_FD),
+    /// `FUTEX_REQUEUE`
+    Requeue = bitcast!(c::FUTEX_REQUEUE),
+    /// `FUTEX_CMP_REQUEUE`
+    CmpRequeue = bitcast!(c::FUTEX_CMP_REQUEUE),
+    /// `FUTEX_WAKE_OP`
+    WakeOp = bitcast!(c::FUTEX_WAKE_OP),
+    /// `FUTEX_LOCK_PI`
+    LockPi = bitcast!(c::FUTEX_LOCK_PI),
+    /// `FUTEX_UNLOCK_PI`
+    UnlockPi = bitcast!(c::FUTEX_UNLOCK_PI),
+    /// `FUTEX_TRYLOCK_PI`
+    TrylockPi = bitcast!(c::FUTEX_TRYLOCK_PI),
+    /// `FUTEX_WAIT_BITSET`
+    WaitBitset = bitcast!(c::FUTEX_WAIT_BITSET),
+}
+
 /// `FUTEX_WAITERS`
-pub const FUTEX_WAITERS: u32 = linux_raw_sys::general::FUTEX_WAITERS;
+pub const WAITERS: u32 = linux_raw_sys::general::FUTEX_WAITERS;
 
 /// `FUTEX_OWNER_DIED`
-pub const FUTEX_OWNER_DIED: u32 = linux_raw_sys::general::FUTEX_OWNER_DIED;
+pub const OWNER_DIED: u32 = linux_raw_sys::general::FUTEX_OWNER_DIED;

src/backend/libc/thread/syscalls.rs

@@ -11,11 +11,10 @@ use core::mem::MaybeUninit;
 use core::sync::atomic::AtomicU32;
 #[cfg(linux_kernel)]
 use {
-    super::futex::FutexOperation,
     crate::backend::conv::{borrowed_fd, ret_c_int, ret_usize},
     crate::fd::BorrowedFd,
     crate::pid::Pid,
-    crate::thread::FutexFlags,
+    crate::thread::futex,
     crate::utils::as_mut_ptr,
 };
 #[cfg(not(any(
@@ -420,14 +419,14 @@ pub(crate) fn setresgid_thread(
 #[cfg(linux_kernel)]
 pub(crate) unsafe fn futex_val2(
     uaddr: *const AtomicU32,
-    op: FutexOperation,
-    flags: FutexFlags,
+    op: super::futex::Operation,
+    flags: futex::Flags,
     val: u32,
     val2: u32,
     uaddr2: *const AtomicU32,
     val3: u32,
 ) -> io::Result<usize> {
-    // the least significant four bytes of the timeout pointer are used as `val2`.
+    // The least-significant four bytes of the timeout pointer are used as `val2`.
     // ["the kernel casts the timeout value first to unsigned long, then to uint32_t"](https://man7.org/linux/man-pages/man2/futex.2.html),
     // so we perform that exact conversion in reverse to create the pointer.
     let timeout = val2 as usize as *const Timespec;
@@ -493,8 +492,8 @@ pub(crate) unsafe fn futex_val2(
 #[cfg(linux_kernel)]
 pub(crate) unsafe fn futex_timeout(
     uaddr: *const AtomicU32,
-    op: FutexOperation,
-    flags: FutexFlags,
+    op: super::futex::Operation,
+    flags: futex::Flags,
     val: u32,
     timeout: *const Timespec,
     uaddr2: *const AtomicU32,
@@ -574,8 +573,8 @@ pub(crate) unsafe fn futex_timeout(
 ))]
 unsafe fn futex_old_timespec(
     uaddr: *const AtomicU32,
-    op: FutexOperation,
-    flags: FutexFlags,
+    op: super::futex::Operation,
+    flags: futex::Flags,
     val: u32,
     timeout: *const Timespec,
     uaddr2: *const AtomicU32,

src/backend/linux_raw/conv.rs

@@ -792,15 +792,15 @@ impl<'a, Num: ArgNumber> From<(crate::net::SocketType, crate::net::SocketFlags)>
 #[cfg(feature = "thread")]
 impl<'a, Num: ArgNumber>
     From<(
-        crate::backend::thread::futex::FutexOperation,
-        crate::thread::FutexFlags,
+        crate::backend::thread::futex::Operation,
+        crate::thread::futex::Flags,
     )> for ArgReg<'a, Num>
 {
     #[inline]
     fn from(
         pair: (
-            crate::backend::thread::futex::FutexOperation,
-            crate::thread::FutexFlags,
+            crate::backend::thread::futex::Operation,
+            crate::thread::futex::Flags,
         ),
     ) -> Self {
         c_uint(pair.0 as u32 | pair.1.bits())

src/backend/linux_raw/thread/futex.rs

@@ -1,10 +1,10 @@
 bitflags::bitflags! {
-    /// `FUTEX_*` flags for use with [`futex`].
+    /// `FUTEX_*` flags for use with the functions in [`futex`].
     ///
     /// [`futex`]: mod@crate::thread::futex
     #[repr(transparent)]
     #[derive(Copy, Clone, Eq, PartialEq, Hash, Debug)]
-    pub struct FutexFlags: u32 {
+    pub struct Flags: u32 {
         /// `FUTEX_PRIVATE_FLAG`
         const PRIVATE = linux_raw_sys::general::FUTEX_PRIVATE_FLAG;
         /// `FUTEX_CLOCK_REALTIME`
@@ -16,12 +16,10 @@ bitflags::bitflags! {
     }
 }
 
-/// `FUTEX_*` operations for use with [`futex`].
-///
-/// [`futex`]: mod@crate::thread::futex
+/// `FUTEX_*` operations for use with the futex syscall wrappers.
 #[derive(Debug, Copy, Clone, Eq, PartialEq)]
 #[repr(u32)]
-pub enum FutexOperation {
+pub(crate) enum Operation {
     /// `FUTEX_WAIT`
     Wait = linux_raw_sys::general::FUTEX_WAIT,
     /// `FUTEX_WAKE`
@@ -52,8 +50,43 @@ pub enum FutexOperation {
     LockPi2 = linux_raw_sys::general::FUTEX_LOCK_PI2,
 }
 
+/// `FUTEX_*` operations for use with the [`futex`] function.
+///
+/// [`futex`]: fn@crate::thread::futex
+#[deprecated(
+    since = "0.38.35",
+    note = "
+    The `futex` function and `FutexOperation` enum are deprecated. There are
+    individual functions available to perform futex operations with improved
+    type safety. See the `rustix::thread::futex` module."
+)]
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+#[repr(u32)]
+pub enum FutexOperation {
+    /// `FUTEX_WAIT`
+    Wait = linux_raw_sys::general::FUTEX_WAIT,
+    /// `FUTEX_WAKE`
+    Wake = linux_raw_sys::general::FUTEX_WAKE,
+    /// `FUTEX_FD`
+    Fd = linux_raw_sys::general::FUTEX_FD,
+    /// `FUTEX_REQUEUE`
+    Requeue = linux_raw_sys::general::FUTEX_REQUEUE,
+    /// `FUTEX_CMP_REQUEUE`
+    CmpRequeue = linux_raw_sys::general::FUTEX_CMP_REQUEUE,
+    /// `FUTEX_WAKE_OP`
+    WakeOp = linux_raw_sys::general::FUTEX_WAKE_OP,
+    /// `FUTEX_LOCK_PI`
+    LockPi = linux_raw_sys::general::FUTEX_LOCK_PI,
+    /// `FUTEX_UNLOCK_PI`
+    UnlockPi = linux_raw_sys::general::FUTEX_UNLOCK_PI,
+    /// `FUTEX_TRYLOCK_PI`
+    TrylockPi = linux_raw_sys::general::FUTEX_TRYLOCK_PI,
+    /// `FUTEX_WAIT_BITSET`
+    WaitBitset = linux_raw_sys::general::FUTEX_WAIT_BITSET,
+}
+
 /// `FUTEX_WAITERS`
-pub const FUTEX_WAITERS: u32 = linux_raw_sys::general::FUTEX_WAITERS;
+pub const WAITERS: u32 = linux_raw_sys::general::FUTEX_WAITERS;
 
 /// `FUTEX_OWNER_DIED`
-pub const FUTEX_OWNER_DIED: u32 = linux_raw_sys::general::FUTEX_OWNER_DIED;
+pub const OWNER_DIED: u32 = linux_raw_sys::general::FUTEX_OWNER_DIED;

src/backend/linux_raw/thread/syscalls.rs

@@ -5,7 +5,6 @@
 //! See the `rustix::backend` module documentation for details.
 #![allow(unsafe_code, clippy::undocumented_unsafe_blocks)]
 
-use super::futex::FutexOperation;
 use crate::backend::c;
 use crate::backend::conv::{
     by_mut, by_ref, c_int, c_uint, ret, ret_c_int, ret_c_int_infallible, ret_usize, slice,
@@ -14,7 +13,7 @@ use crate::backend::conv::{
 use crate::fd::BorrowedFd;
 use crate::io;
 use crate::pid::Pid;
-use crate::thread::{ClockId, FutexFlags, NanosleepRelativeResult, Timespec};
+use crate::thread::{futex, ClockId, NanosleepRelativeResult, Timespec};
 use core::mem::MaybeUninit;
 use core::sync::atomic::AtomicU32;
 #[cfg(target_pointer_width = "32")]
@@ -208,14 +207,14 @@ pub(crate) fn gettid() -> Pid {
 #[inline]
 pub(crate) unsafe fn futex_val2(
     uaddr: *const AtomicU32,
-    op: FutexOperation,
-    flags: FutexFlags,
+    op: super::futex::Operation,
+    flags: futex::Flags,
     val: u32,
     val2: u32,
     uaddr2: *const AtomicU32,
     val3: u32,
 ) -> io::Result<usize> {
-    // the least significant four bytes of the timeout pointer are used as `val2`.
+    // The least-significant four bytes of the timeout pointer are used as `val2`.
     // ["the kernel casts the timeout value first to unsigned long, then to uint32_t"](https://man7.org/linux/man-pages/man2/futex.2.html),
     // so we perform that exact conversion in reverse to create the pointer.
     let timeout = val2 as usize as *const Timespec;
@@ -247,8 +246,8 @@ pub(crate) unsafe fn futex_val2(
 #[inline]
 pub(crate) unsafe fn futex_timeout(
     uaddr: *const AtomicU32,
-    op: FutexOperation,
-    flags: FutexFlags,
+    op: super::futex::Operation,
+    flags: futex::Flags,
     val: u32,
     timeout: *const Timespec,
     uaddr2: *const AtomicU32,
@@ -290,8 +289,8 @@ pub(crate) unsafe fn futex_timeout(
 #[cfg(target_pointer_width = "32")]
 unsafe fn futex_old_timespec(
     uaddr: *const AtomicU32,
-    op: FutexOperation,
-    flags: FutexFlags,
+    op: super::futex::Operation,
+    flags: futex::Flags,
     val: u32,
     timeout: *const Timespec,
     uaddr2: *const AtomicU32,
@@ -321,7 +320,6 @@ unsafe fn futex_old_timespec(
         c_uint(val3)
     ))
 }
-
 #[inline]
 pub(crate) fn setns(fd: BorrowedFd<'_>, nstype: c::c_int) -> io::Result<c::c_int> {
     unsafe { ret_c_int(syscall_readonly!(__NR_setns, fd, c_int(nstype))) }