Rollup merge of rust-lang#41353 - redox-os:master, r=alexcrichton

Improve Process::spawn with piped stdio on Redox

- Adds `dup2`, and uses it for stdio piping
- Removes `O_CLOEXEC` from piped stdio, as `dup` on Redox does not disable O_CLOEXEC

Author: frewsxcv

src/libstd/sys/redox/process.rs

@@ -270,19 +270,22 @@ impl Command {
         }
 
         if let Some(fd) = stdio.stderr.fd() {
-            let _ = syscall::close(2);
-            t!(cvt(syscall::dup(fd, &[])));
-            let _ = syscall::close(fd);
+            t!(cvt(syscall::dup2(fd, 2, &[])));
+            let mut flags = t!(cvt(syscall::fcntl(2, syscall::F_GETFL, 0)));
+            flags &= ! syscall::O_CLOEXEC;
+            t!(cvt(syscall::fcntl(2, syscall::F_SETFL, flags)));
         }
         if let Some(fd) = stdio.stdout.fd() {
-            let _ = syscall::close(1);
-            t!(cvt(syscall::dup(fd, &[])));
-            let _ = syscall::close(fd);
+            t!(cvt(syscall::dup2(fd, 1, &[])));
+            let mut flags = t!(cvt(syscall::fcntl(1, syscall::F_GETFL, 0)));
+            flags &= ! syscall::O_CLOEXEC;
+            t!(cvt(syscall::fcntl(1, syscall::F_SETFL, flags)));
         }
         if let Some(fd) = stdio.stdin.fd() {
-            let _ = syscall::close(0);
-            t!(cvt(syscall::dup(fd, &[])));
-            let _ = syscall::close(fd);
+            t!(cvt(syscall::dup2(fd, 0, &[])));
+            let mut flags = t!(cvt(syscall::fcntl(0, syscall::F_GETFL, 0)));
+            flags &= ! syscall::O_CLOEXEC;
+            t!(cvt(syscall::fcntl(0, syscall::F_SETFL, flags)));
         }
 
         if let Some(g) = self.gid {

src/libstd/sys/redox/syscall/call.rs

@@ -71,6 +71,11 @@ pub fn dup(fd: usize, buf: &[u8]) -> Result<usize> {
     unsafe { syscall3(SYS_DUP, fd, buf.as_ptr() as usize, buf.len()) }
 }
 
+/// Copy and transform a file descriptor
+pub fn dup2(fd: usize, newfd: usize, buf: &[u8]) -> Result<usize> {
+    unsafe { syscall4(SYS_DUP2, fd, newfd, buf.as_ptr() as usize, buf.len()) }
+}
+
 /// Replace the current process with a new executable
 pub fn execve(path: &str, args: &[[usize; 2]]) -> Result<usize> {
     unsafe { syscall4(SYS_EXECVE, path.as_ptr() as usize, path.len(),

src/libstd/sys/redox/syscall/number.rs

@@ -28,6 +28,7 @@ pub const SYS_UNLINK: usize =   SYS_CLASS_PATH | 10;
 
 pub const SYS_CLOSE: usize =    SYS_CLASS_FILE | 6;
 pub const SYS_DUP: usize =      SYS_CLASS_FILE | SYS_RET_FILE | 41;
+pub const SYS_DUP2: usize =     SYS_CLASS_FILE | SYS_RET_FILE | 63;
 pub const SYS_READ: usize =     SYS_CLASS_FILE | SYS_ARG_MSLICE | 3;
 pub const SYS_WRITE: usize =    SYS_CLASS_FILE | SYS_ARG_SLICE | 4;
 pub const SYS_LSEEK: usize =    SYS_CLASS_FILE | 19;