Don't try to use /dev/null on Fuchsia

src/libstd/sys/unix/process/process_common.rs

@@ -1,19 +1,27 @@
 use crate::os::unix::prelude::*;
 
-use crate::ffi::{OsString, OsStr, CString, CStr};
+use crate::ffi::{OsString, OsStr, CString};
 use crate::fmt;
 use crate::io;
 use crate::ptr;
 use crate::sys::fd::FileDesc;
-use crate::sys::fs::{File, OpenOptions};
+use crate::sys::fs::File;
 use crate::sys::pipe::{self, AnonPipe};
 use crate::sys_common::process::{CommandEnv, DefaultEnvKey};
 use crate::collections::BTreeMap;
 
+#[cfg(not(target_os = "fuchsia"))]
+use {
+    crate::ffi::CStr,
+    crate::sys::fs::OpenOptions,
+};
+
 use libc::{c_int, gid_t, uid_t, c_char, EXIT_SUCCESS, EXIT_FAILURE};
 
 cfg_if::cfg_if! {
-    if #[cfg(target_os = "redox")] {
+    if #[cfg(target_os = "fuchsia")] {
+        // fuchsia doesn't have /dev/null
+    } else if #[cfg(target_os = "redox")] {
         const DEV_NULL: &'static str = "null:\0";
     } else {
         const DEV_NULL: &'static str = "/dev/null\0";
@@ -83,6 +91,11 @@ pub enum ChildStdio {
     Inherit,
     Explicit(c_int),
     Owned(FileDesc),
+
+    // On Fuchsia, null stdio is the default, so we simply don't specify
+    // any actions at the time of spawning.
+    #[cfg(target_os = "fuchsia")]
+    Null,
 }
 
 pub enum Stdio {
@@ -301,6 +314,7 @@ pub fn to_child_stdio(&self, readable: bool)
                 Ok((ChildStdio::Owned(theirs.into_fd()), Some(ours)))
             }
 
+            #[cfg(not(target_os = "fuchsia"))]
             Stdio::Null => {
                 let mut opts = OpenOptions::new();
                 opts.read(readable);
@@ -311,6 +325,11 @@ pub fn to_child_stdio(&self, readable: bool)
                 let fd = File::open_c(&path, &opts)?;
                 Ok((ChildStdio::Owned(fd.into_fd()), None))
             }
+
+            #[cfg(target_os = "fuchsia")]
+            Stdio::Null => {
+                Ok((ChildStdio::Null, None))
+            }
         }
     }
 }
@@ -333,6 +352,9 @@ pub fn fd(&self) -> Option<c_int> {
             ChildStdio::Inherit => None,
             ChildStdio::Explicit(fd) => Some(fd),
             ChildStdio::Owned(ref fd) => Some(fd.raw()),
+
+            #[cfg(target_os = "fuchsia")]
+            ChildStdio::Null => None,
         }
     }
 }

src/libstd/sys/unix/process/process_fuchsia.rs

@@ -52,7 +52,7 @@ unsafe fn do_exec(&mut self, stdio: ChildPipes, maybe_envp: Option<&CStringArray
             None => ptr::null(),
         };
 
-        let transfer_or_clone = |opt_fd, target_fd| if let Some(local_fd) = opt_fd {
+        let make_action = |local_io: &ChildStdio, target_fd| if let Some(local_fd) = local_io.fd() {
             fdio_spawn_action_t {
                 action: FDIO_SPAWN_ACTION_TRANSFER_FD,
                 local_fd,
@@ -60,6 +60,10 @@ unsafe fn do_exec(&mut self, stdio: ChildPipes, maybe_envp: Option<&CStringArray
                 ..Default::default()
             }
         } else {
+            if let ChildStdio::Null = local_io {
+                // acts as no-op
+                return Default::default();
+            }
             fdio_spawn_action_t {
                 action: FDIO_SPAWN_ACTION_CLONE_FD,
                 local_fd: target_fd,
@@ -69,9 +73,9 @@ unsafe fn do_exec(&mut self, stdio: ChildPipes, maybe_envp: Option<&CStringArray
         };
 
         // Clone stdin, stdout, and stderr
-        let action1 = transfer_or_clone(stdio.stdin.fd(), 0);
-        let action2 = transfer_or_clone(stdio.stdout.fd(), 1);
-        let action3 = transfer_or_clone(stdio.stderr.fd(), 2);
+        let action1 = make_action(&stdio.stdin, 0);
+        let action2 = make_action(&stdio.stdout, 1);
+        let action3 = make_action(&stdio.stderr, 2);
         let actions = [action1, action2, action3];
 
         // We don't want FileDesc::drop to be called on any stdio. fdio_spawn_etc
@@ -86,7 +90,8 @@ unsafe fn do_exec(&mut self, stdio: ChildPipes, maybe_envp: Option<&CStringArray
         zx_cvt(fdio_spawn_etc(
             0,
             FDIO_SPAWN_CLONE_JOB | FDIO_SPAWN_CLONE_LDSVC | FDIO_SPAWN_CLONE_NAMESPACE,
-            self.get_argv()[0], self.get_argv().as_ptr(), envp, 3, actions.as_ptr(),
+            self.get_argv()[0], self.get_argv().as_ptr(), envp,
+            actions.len() as size_t, actions.as_ptr(),
             &mut process_handle,
             ptr::null_mut(),
         ))?;

src/libstd/sys/unix/process/zircon.rs

@@ -120,7 +120,7 @@ pub struct fdio_spawn_action_t {
 extern {
     pub fn fdio_spawn_etc(job: zx_handle_t, flags: u32, path: *const c_char,
                           argv: *const *const c_char, envp: *const *const c_char,
-                          action_count: u64, actions: *const fdio_spawn_action_t,
+                          action_count: size_t, actions: *const fdio_spawn_action_t,
                           process: *mut zx_handle_t, err_msg: *mut c_char) -> zx_status_t;
 }