Remove Linux workarounds for missing CLOEXEC support

Now that #74163 updated the minimum Linux kernel to 2.6.32, we can
assume the availability of APIs that open file descriptors that are
already set to close on exec, including the flags `O_CLOEXEC`,
`SOCK_CLOEXEC`, and `F_DUPFD_CLOEXEC`.

4 files changed, 58 insertions, 187 deletions

diff --git a/src/libstd/sys/unix/fd.rs b/src/libstd/sys/unix/fd.rs
index c481ca8961f..451ebd97c3f 100644
--- a/src/libstd/sys/unix/fd.rs
+++ b/src/libstd/sys/unix/fd.rs
@@ -3,7 +3,6 @@
 use crate::cmp;
 use crate::io::{self, Initializer, IoSlice, IoSliceMut, Read};
 use crate::mem;
-use crate::sync::atomic::{AtomicBool, Ordering};
 use crate::sys::cvt;
 use crate::sys_common::AsInner;
 
@@ -223,50 +222,9 @@ impl FileDesc {
     pub fn duplicate(&self) -> io::Result<FileDesc> {
         // We want to atomically duplicate this file descriptor and set the
         // CLOEXEC flag, and currently that's done via F_DUPFD_CLOEXEC. This
-        // flag, however, isn't supported on older Linux kernels (earlier than
-        // 2.6.24).
-        //
-        // To detect this and ensure that CLOEXEC is still set, we
-        // follow a strategy similar to musl [1] where if passing
-        // F_DUPFD_CLOEXEC causes `fcntl` to return EINVAL it means it's not
-        // supported (the third parameter, 0, is always valid), so we stop
-        // trying that.
-        //
-        // Also note that Android doesn't have F_DUPFD_CLOEXEC, but get it to
-        // resolve so we at least compile this.
-        //
-        // [1]: http://comments.gmane.org/gmane.linux.lib.musl.general/2963
-        #[cfg(any(target_os = "android", target_os = "haiku"))]
-        use libc::F_DUPFD as F_DUPFD_CLOEXEC;
-        #[cfg(not(any(target_os = "android", target_os = "haiku")))]
-        use libc::F_DUPFD_CLOEXEC;
-
-        let make_filedesc = |fd| {
-            let fd = FileDesc::new(fd);
-            fd.set_cloexec()?;
-            Ok(fd)
-        };
-        static TRY_CLOEXEC: AtomicBool = AtomicBool::new(!cfg!(target_os = "android"));
-        let fd = self.raw();
-        if TRY_CLOEXEC.load(Ordering::Relaxed) {
-            match cvt(unsafe { libc::fcntl(fd, F_DUPFD_CLOEXEC, 0) }) {
-                // We *still* call the `set_cloexec` method as apparently some
-                // linux kernel at some point stopped setting CLOEXEC even
-                // though it reported doing so on F_DUPFD_CLOEXEC.
-                Ok(fd) => {
-                    return Ok(if cfg!(target_os = "linux") {
-                        make_filedesc(fd)?
-                    } else {
-                        FileDesc::new(fd)
-                    });
-                }
-                Err(ref e) if e.raw_os_error() == Some(libc::EINVAL) => {
-                    TRY_CLOEXEC.store(false, Ordering::Relaxed);
-                }
-                Err(e) => return Err(e),
-            }
-        }
-        cvt(unsafe { libc::fcntl(fd, libc::F_DUPFD, 0) }).and_then(make_filedesc)
+        // is a POSIX flag that was added to Linux in 2.6.24.
+        let fd = cvt(unsafe { libc::fcntl(self.raw(), libc::F_DUPFD_CLOEXEC, 0) })?;
+        Ok(FileDesc::new(fd))
     }
 }
 
diff --git a/src/libstd/sys/unix/fs.rs b/src/libstd/sys/unix/fs.rs
index 29cdbf05354..acb18e6d064 100644
--- a/src/libstd/sys/unix/fs.rs
+++ b/src/libstd/sys/unix/fs.rs
@@ -708,56 +708,7 @@ impl File {
         // However, since this is a variadic function, C integer promotion rules mean that on
         // the ABI level, this still gets passed as `c_int` (aka `u32` on Unix platforms).
         let fd = cvt_r(|| unsafe { open64(path.as_ptr(), flags, opts.mode as c_int) })?;
-        let fd = FileDesc::new(fd);
-
-        // Currently the standard library supports Linux 2.6.18 which did not
-        // have the O_CLOEXEC flag (passed above). If we're running on an older
-        // Linux kernel then the flag is just ignored by the OS. After we open
-        // the first file, we check whether it has CLOEXEC set. If it doesn't,
-        // we will explicitly ask for a CLOEXEC fd for every further file we
-        // open, if it does, we will skip that step.
-        //
-        // The CLOEXEC flag, however, is supported on versions of macOS/BSD/etc
-        // that we support, so we only do this on Linux currently.
-        #[cfg(target_os = "linux")]
-        fn ensure_cloexec(fd: &FileDesc) -> io::Result<()> {
-            use crate::sync::atomic::{AtomicUsize, Ordering};
-
-            const OPEN_CLOEXEC_UNKNOWN: usize = 0;
-            const OPEN_CLOEXEC_SUPPORTED: usize = 1;
-            const OPEN_CLOEXEC_NOTSUPPORTED: usize = 2;
-            static OPEN_CLOEXEC: AtomicUsize = AtomicUsize::new(OPEN_CLOEXEC_UNKNOWN);
-
-            let need_to_set;
-            match OPEN_CLOEXEC.load(Ordering::Relaxed) {
-                OPEN_CLOEXEC_UNKNOWN => {
-                    need_to_set = !fd.get_cloexec()?;
-                    OPEN_CLOEXEC.store(
-                        if need_to_set {
-                            OPEN_CLOEXEC_NOTSUPPORTED
-                        } else {
-                            OPEN_CLOEXEC_SUPPORTED
-                        },
-                        Ordering::Relaxed,
-                    );
-                }
-                OPEN_CLOEXEC_SUPPORTED => need_to_set = false,
-                OPEN_CLOEXEC_NOTSUPPORTED => need_to_set = true,
-                _ => unreachable!(),
-            }
-            if need_to_set {
-                fd.set_cloexec()?;
-            }
-            Ok(())
-        }
-
-        #[cfg(not(target_os = "linux"))]
-        fn ensure_cloexec(_: &FileDesc) -> io::Result<()> {
-            Ok(())
-        }
-
-        ensure_cloexec(&fd)?;
-        Ok(File(fd))
+        Ok(File(FileDesc::new(fd)))
     }
 
     pub fn file_attr(&self) -> io::Result<FileAttr> {
diff --git a/src/libstd/sys/unix/net.rs b/src/libstd/sys/unix/net.rs
index 3717c660b57..011325fddc5 100644
--- a/src/libstd/sys/unix/net.rs
+++ b/src/libstd/sys/unix/net.rs
@@ -54,31 +54,26 @@ impl Socket {
 
     pub fn new_raw(fam: c_int, ty: c_int) -> io::Result<Socket> {
         unsafe {
-            // On linux we first attempt to pass the SOCK_CLOEXEC flag to
-            // atomically create the socket and set it as CLOEXEC. Support for
-            // this option, however, was added in 2.6.27, and we still support
-            // 2.6.18 as a kernel, so if the returned error is EINVAL we
-            // fallthrough to the fallback.
-            #[cfg(target_os = "linux")]
-            {
-                match cvt(libc::socket(fam, ty | libc::SOCK_CLOEXEC, 0)) {
-                    Ok(fd) => return Ok(Socket(FileDesc::new(fd))),
-                    Err(ref e) if e.raw_os_error() == Some(libc::EINVAL) => {}
-                    Err(e) => return Err(e),
-                }
-            }
-
-            let fd = cvt(libc::socket(fam, ty, 0))?;
-            let fd = FileDesc::new(fd);
-            fd.set_cloexec()?;
-            let socket = Socket(fd);
+            cfg_if::cfg_if! {
+                if #[cfg(target_os = "linux")] {
+                    // On Linux we pass the SOCK_CLOEXEC flag to atomically create
+                    // the socket and set it as CLOEXEC, added in 2.6.27.
+                    let fd = cvt(libc::socket(fam, ty | libc::SOCK_CLOEXEC, 0))?;
+                    Ok(Socket(FileDesc::new(fd)))
+                } else {
+                    let fd = cvt(libc::socket(fam, ty, 0))?;
+                    let fd = FileDesc::new(fd);
+                    fd.set_cloexec()?;
+                    let socket = Socket(fd);
 
-            // macOS and iOS use `SO_NOSIGPIPE` as a `setsockopt`
-            // flag to disable `SIGPIPE` emission on socket.
-            #[cfg(target_vendor = "apple")]
-            setsockopt(&socket, libc::SOL_SOCKET, libc::SO_NOSIGPIPE, 1)?;
+                    // macOS and iOS use `SO_NOSIGPIPE` as a `setsockopt`
+                    // flag to disable `SIGPIPE` emission on socket.
+                    #[cfg(target_vendor = "apple")]
+                    setsockopt(&socket, libc::SOL_SOCKET, libc::SO_NOSIGPIPE, 1)?;
 
-            Ok(socket)
+                    Ok(socket)
+                }
+            }
         }
     }
 
@@ -86,24 +81,20 @@ impl Socket {
         unsafe {
             let mut fds = [0, 0];
 
-            // Like above, see if we can set cloexec atomically
-            #[cfg(target_os = "linux")]
-            {
-                match cvt(libc::socketpair(fam, ty | libc::SOCK_CLOEXEC, 0, fds.as_mut_ptr())) {
-                    Ok(_) => {
-                        return Ok((Socket(FileDesc::new(fds[0])), Socket(FileDesc::new(fds[1]))));
-                    }
-                    Err(ref e) if e.raw_os_error() == Some(libc::EINVAL) => {}
-                    Err(e) => return Err(e),
+            cfg_if::cfg_if! {
+                if #[cfg(target_os = "linux")] {
+                    // Like above, set cloexec atomically
+                    cvt(libc::socketpair(fam, ty | libc::SOCK_CLOEXEC, 0, fds.as_mut_ptr()))?;
+                    Ok((Socket(FileDesc::new(fds[0])), Socket(FileDesc::new(fds[1]))))
+                } else {
+                    cvt(libc::socketpair(fam, ty, 0, fds.as_mut_ptr()))?;
+                    let a = FileDesc::new(fds[0]);
+                    let b = FileDesc::new(fds[1]);
+                    a.set_cloexec()?;
+                    b.set_cloexec()?;
+                    Ok((Socket(a), Socket(b)))
                 }
             }
-
-            cvt(libc::socketpair(fam, ty, 0, fds.as_mut_ptr()))?;
-            let a = FileDesc::new(fds[0]);
-            let b = FileDesc::new(fds[1]);
-            a.set_cloexec()?;
-            b.set_cloexec()?;
-            Ok((Socket(a), Socket(b)))
         }
     }
 
@@ -177,30 +168,20 @@ impl Socket {
     pub fn accept(&self, storage: *mut sockaddr, len: *mut socklen_t) -> io::Result<Socket> {
         // Unfortunately the only known way right now to accept a socket and
         // atomically set the CLOEXEC flag is to use the `accept4` syscall on
-        // Linux. This was added in 2.6.28, however, and because we support
-        // 2.6.18 we must detect this support dynamically.
-        #[cfg(target_os = "linux")]
-        {
-            syscall! {
-                fn accept4(
-                    fd: c_int,
-                    addr: *mut sockaddr,
-                    addr_len: *mut socklen_t,
-                    flags: c_int
-                ) -> c_int
-            }
-            let res = cvt_r(|| unsafe { accept4(self.0.raw(), storage, len, libc::SOCK_CLOEXEC) });
-            match res {
-                Ok(fd) => return Ok(Socket(FileDesc::new(fd))),
-                Err(ref e) if e.raw_os_error() == Some(libc::ENOSYS) => {}
-                Err(e) => return Err(e),
+        // Linux. This was added in 2.6.28, glibc 2.10 and musl 0.9.5.
+        cfg_if::cfg_if! {
+            if #[cfg(target_os = "linux")] {
+                let fd = cvt_r(|| unsafe {
+                    libc::accept4(self.0.raw(), storage, len, libc::SOCK_CLOEXEC)
+                })?;
+                Ok(Socket(FileDesc::new(fd)))
+            } else {
+                let fd = cvt_r(|| unsafe { libc::accept(self.0.raw(), storage, len) })?;
+                let fd = FileDesc::new(fd);
+                fd.set_cloexec()?;
+                Ok(Socket(fd))
             }
         }
-
-        let fd = cvt_r(|| unsafe { libc::accept(self.0.raw(), storage, len) })?;
-        let fd = FileDesc::new(fd);
-        fd.set_cloexec()?;
-        Ok(Socket(fd))
     }
 
     pub fn duplicate(&self) -> io::Result<Socket> {
diff --git a/src/libstd/sys/unix/pipe.rs b/src/libstd/sys/unix/pipe.rs
index f2a2eabef91..02a43923708 100644
--- a/src/libstd/sys/unix/pipe.rs
+++ b/src/libstd/sys/unix/pipe.rs
@@ -1,11 +1,8 @@
 use crate::io::{self, IoSlice, IoSliceMut};
 use crate::mem;
-use crate::sync::atomic::{AtomicBool, Ordering};
 use crate::sys::fd::FileDesc;
 use crate::sys::{cvt, cvt_r};
 
-use libc::c_int;
-
 ////////////////////////////////////////////////////////////////////////////////
 // Anonymous pipes
 ////////////////////////////////////////////////////////////////////////////////
@@ -13,15 +10,11 @@ use libc::c_int;
 pub struct AnonPipe(FileDesc);
 
 pub fn anon_pipe() -> io::Result<(AnonPipe, AnonPipe)> {
-    syscall! { fn pipe2(fds: *mut c_int, flags: c_int) -> c_int }
-    static INVALID: AtomicBool = AtomicBool::new(false);
-
     let mut fds = [0; 2];
 
     // Unfortunately the only known way right now to create atomically set the
     // CLOEXEC flag is to use the `pipe2` syscall on Linux. This was added in
-    // 2.6.27, however, and because we support 2.6.18 we must detect this
-    // support dynamically.
+    // 2.6.27, glibc 2.9 and musl 0.9.3.
     if cfg!(any(
         target_os = "dragonfly",
         target_os = "freebsd",
@@ -29,30 +22,18 @@ pub fn anon_pipe() -> io::Result<(AnonPipe, AnonPipe)> {
         target_os = "netbsd",
         target_os = "openbsd",
         target_os = "redox"
-    )) && !INVALID.load(Ordering::SeqCst)
-    {
-        // Note that despite calling a glibc function here we may still
-        // get ENOSYS. Glibc has `pipe2` since 2.9 and doesn't try to
-        // emulate on older kernels, so if you happen to be running on
-        // an older kernel you may see `pipe2` as a symbol but still not
-        // see the syscall.
-        match cvt(unsafe { pipe2(fds.as_mut_ptr(), libc::O_CLOEXEC) }) {
-            Ok(_) => {
-                return Ok((AnonPipe(FileDesc::new(fds[0])), AnonPipe(FileDesc::new(fds[1]))));
-            }
-            Err(ref e) if e.raw_os_error() == Some(libc::ENOSYS) => {
-                INVALID.store(true, Ordering::SeqCst);
-            }
-            Err(e) => return Err(e),
-        }
+    )) {
+        cvt(unsafe { libc::pipe2(fds.as_mut_ptr(), libc::O_CLOEXEC) })?;
+        Ok((AnonPipe(FileDesc::new(fds[0])), AnonPipe(FileDesc::new(fds[1]))))
+    } else {
+        cvt(unsafe { libc::pipe(fds.as_mut_ptr()) })?;
+
+        let fd0 = FileDesc::new(fds[0]);
+        let fd1 = FileDesc::new(fds[1]);
+        fd0.set_cloexec()?;
+        fd1.set_cloexec()?;
+        Ok((AnonPipe(fd0), AnonPipe(fd1)))
     }
-    cvt(unsafe { libc::pipe(fds.as_mut_ptr()) })?;
-
-    let fd0 = FileDesc::new(fds[0]);
-    let fd1 = FileDesc::new(fds[1]);
-    fd0.set_cloexec()?;
-    fd1.set_cloexec()?;
-    Ok((AnonPipe(fd0), AnonPipe(fd1)))
 }
 
 impl AnonPipe {