ptrace: add ptrace::seize for Linux

CHANGELOG.md

@@ -5,6 +5,10 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased] - ReleaseDate
 ### Added
+- Added `ptrace::seize()`: similar to `attach()` on Linux
+  but with better-defined semantics.
+  (#[1154](https://github.com/nix-rust/nix/pull/1154))
+
 - Added `Signal::as_str()`: returns signal name as `&'static str`
   (#[1138](https://github.com/nix-rust/nix/pull/1138))
 

src/sys/ptrace/linux.rs

@@ -315,6 +315,21 @@ pub fn attach(pid: Pid) -> Result<()> {
     }
 }
 
+/// Attach to a running process, as with `ptrace(PTRACE_SEIZE, ...)`
+///
+/// Attaches to the process specified in pid, making it a tracee of the calling process.
+#[cfg(all(target_os = "linux", not(any(target_arch = "mips", target_arch = "mips64"))))]
+pub fn seize(pid: Pid, options: Options) -> Result<()> {
+    unsafe {
+        ptrace_other(
+            Request::PTRACE_SEIZE,
+            pid,
+            ptr::null_mut(),
+            options.bits() as *mut c_void,
+        ).map(drop) // ignore the useless return value
+    }
+}
+
 /// Detaches the current running process, as with `ptrace(PTRACE_DETACH, ...)`
 ///
 /// Detaches from the process specified in pid allowing it to run freely