rustix: enable rustix::thread::futex without linux-raw-sys

It's desirable to enable futex for some cases that will be
run on Android.  The strategy is just to define the constants
needed by the libc ourselves, if libc doesn't provide the
necessary constant.  Long-term, that could make the libc
backend only depend on libc.

Author: gurchetansingh

src/backend/libc/c.rs

@@ -511,6 +511,14 @@ pub(crate) use statx_flags::*;
 #[cfg(target_os = "android")]
 pub(crate) use __fsid_t as fsid_t;
 
+// Android's libc crate is missing some constants.
+#[cfg(target_os = "android")]
+pub(crate) const CLONE_NEWTIME: c_int = 0x00000080;
+#[cfg(target_os = "android")]
+pub(crate) const FUTEX_WAITERS: u32 = 0x80000000;
+#[cfg(target_os = "android")]
+pub(crate) const FUTEX_OWNER_DIED: u32 = 0x40000000;
+
 // FreeBSD added `timerfd_*` in FreeBSD 14. NetBSD added then in NetBSD 10.
 #[cfg(all(feature = "time", any(target_os = "freebsd", target_os = "netbsd")))]
 syscall!(pub(crate) fn timerfd_create(

src/backend/libc/thread/futex.rs

@@ -17,6 +17,14 @@ bitflags::bitflags! {
     }
 }
 
+const FUTEX2_SIZE_U8: u32 = 0;
+const FUTEX2_SIZE_U16: u32 = 1;
+const FUTEX2_SIZE_U32: u32 = 2;
+const FUTEX2_SIZE_U64: u32 = 3;
+const FUTEX2_SIZE_MASK: u32 = 3;
+const FUTEX2_NUMA: u32 = 4;
+const FUTEX2_PRIVATE: u32 = 128;
+
 bitflags::bitflags! {
     /// `FUTEX2_*` flags for use with the functions in [`Waitv`].
     ///
@@ -29,22 +37,19 @@ bitflags::bitflags! {
     #[derive(Copy, Clone, Eq, PartialEq, Hash, Debug)]
     pub struct WaitFlags: u32 {
         /// `FUTEX_U8`
-        const SIZE_U8 = linux_raw_sys::general::FUTEX2_SIZE_U8;
+        const SIZE_U8 = FUTEX2_SIZE_U8;
         /// `FUTEX_U16`
-        const SIZE_U16 = linux_raw_sys::general::FUTEX2_SIZE_U16;
+        const SIZE_U16 = FUTEX2_SIZE_U16;
         /// `FUTEX_U32`
-        const SIZE_U32 = linux_raw_sys::general::FUTEX2_SIZE_U32;
+        const SIZE_U32 = FUTEX2_SIZE_U32;
         /// `FUTEX_U64`
-        const SIZE_U64 = linux_raw_sys::general::FUTEX2_SIZE_U64;
+        const SIZE_U64 = FUTEX2_SIZE_U64;
         /// `FUTEX_SIZE_MASK`
-        const SIZE_MASK = linux_raw_sys::general::FUTEX2_SIZE_MASK;
-
+        const SIZE_MASK = FUTEX2_SIZE_MASK;
         /// `FUTEX2_NUMA`
-        const NUMA = linux_raw_sys::general::FUTEX2_NUMA;
-
+        const NUMA = FUTEX2_NUMA;
         /// `FUTEX2_PRIVATE`
-        const PRIVATE = linux_raw_sys::general::FUTEX2_PRIVATE;
-
+        const PRIVATE = FUTEX2_PRIVATE;
         /// <https://docs.rs/bitflags/*/bitflags/#externally-defined-flags>
         const _ = !0;
     }
@@ -85,7 +90,7 @@ pub(crate) enum Operation {
 }
 
 /// `FUTEX_WAITERS`
-pub const WAITERS: u32 = linux_raw_sys::general::FUTEX_WAITERS;
+pub const WAITERS: u32 = c::FUTEX_WAITERS;
 
 /// `FUTEX_OWNER_DIED`
-pub const OWNER_DIED: u32 = linux_raw_sys::general::FUTEX_OWNER_DIED;
+pub const OWNER_DIED: u32 = c::FUTEX_OWNER_DIED;

src/backend/libc/thread/syscalls.rs

@@ -341,13 +341,13 @@ pub(crate) fn setns(fd: BorrowedFd<'_>, nstype: c::c_int) -> io::Result<c::c_int
     unsafe { ret_c_int(setns(borrowed_fd(fd), nstype)) }
 }
 
-#[cfg(linux_kernel)]
+#[cfg(all(linux_kernel, linux_raw_dep))]
 #[inline]
 pub(crate) unsafe fn unshare(flags: crate::thread::UnshareFlags) -> io::Result<()> {
     ret(c::unshare(flags.bits() as i32))
 }
 
-#[cfg(linux_kernel)]
+#[cfg(all(linux_kernel, linux_raw_dep))]
 #[inline]
 pub(crate) fn capget(
     header: &mut linux_raw_sys::general::__user_cap_header_struct,
@@ -369,7 +369,7 @@ pub(crate) fn capget(
     }
 }
 
-#[cfg(linux_kernel)]
+#[cfg(all(linux_kernel, linux_raw_dep))]
 #[inline]
 pub(crate) fn capset(
     header: &mut linux_raw_sys::general::__user_cap_header_struct,
@@ -666,8 +666,9 @@ pub(crate) fn futex_waitv(
     timeout: Option<&Timespec>,
     clockid: ClockId,
 ) -> io::Result<usize> {
+    use crate::backend::c::clockid_t;
     use futex::Wait as FutexWait;
-    use linux_raw_sys::general::__kernel_clockid_t as clockid_t;
+
     syscall! {
         fn futex_waitv(
             waiters: *const FutexWait,

src/thread/mod.rs

@@ -6,16 +6,16 @@ mod clock;
 pub mod futex;
 #[cfg(linux_kernel)]
 mod id;
-#[cfg(linux_kernel)]
+#[cfg(all(linux_kernel, linux_raw_dep))]
 mod libcap;
 #[cfg(linux_kernel)]
 mod membarrier;
-#[cfg(linux_kernel)]
+#[cfg(all(linux_kernel, linux_raw_dep))]
 mod prctl;
 #[cfg(any(freebsdlike, linux_kernel, target_os = "fuchsia"))]
 mod sched;
 mod sched_yield;
-#[cfg(linux_kernel)]
+#[cfg(all(linux_kernel, linux_raw_dep))]
 mod setns;
 
 #[cfg(not(target_os = "redox"))]
@@ -25,13 +25,14 @@ pub use id::*;
 #[cfg(linux_kernel)]
 // #[expect(deprecated, reason = "CapabilityFlags is deprecated")]
 #[allow(deprecated)]
+#[cfg(all(linux_kernel, linux_raw_dep))]
 pub use libcap::{capabilities, set_capabilities, CapabilityFlags, CapabilitySet, CapabilitySets};
 #[cfg(linux_kernel)]
 pub use membarrier::*;
-#[cfg(linux_kernel)]
+#[cfg(all(linux_kernel, linux_raw_dep))]
 pub use prctl::*;
 #[cfg(any(freebsdlike, linux_kernel, target_os = "fuchsia"))]
 pub use sched::*;
 pub use sched_yield::sched_yield;
-#[cfg(linux_kernel)]
+#[cfg(all(linux_kernel, linux_raw_dep))]
 pub use setns::*;