Addressing feedback about inlining documentation and use of nix

Author: ChrisDryden

Cargo.lock

@@ -24,9 +24,8 @@ path = "src/users.rs"
 
 [dependencies]
 clap = { workspace = true }
-uucore = { workspace = true, features = ["utmpx"] }
+uucore = { workspace = true, features = ["utmpx", "process"] }
 fluent = { workspace = true }
-nix = { workspace = true, features = ["signal"] }
 
 [target.'cfg(target_os = "openbsd")'.dependencies]
 utmp-classic = { workspace = true }

src/uu/users/Cargo.toml

@@ -10,12 +10,10 @@ use std::path::Path;
 
 use clap::builder::ValueParser;
 use clap::{Arg, Command};
-#[cfg(not(target_os = "openbsd"))]
-use nix::sys::signal::kill;
-#[cfg(not(target_os = "openbsd"))]
-use nix::unistd::Pid;
 use uucore::error::UResult;
 use uucore::format_usage;
+#[cfg(not(target_os = "openbsd"))]
+use uucore::process::pid_is_alive;
 use uucore::translate;
 
 #[cfg(target_os = "openbsd")]
@@ -37,20 +35,6 @@ fn get_long_usage() -> String {
     translate!("users-long-usage", "default_path" => default_path)
 }
 
-#[inline]
-#[cfg(not(target_os = "openbsd"))]
-fn pid_is_alive(pid: i32) -> bool {
-    if pid <= 0 {
-        return true;
-    }
-
-    match kill(Pid::from_raw(pid), None) {
-        Ok(()) => true,
-        Err(nix::errno::Errno::ESRCH) => false,
-        Err(_) => true,
-    }
-}
-
 #[uucore::main]
 pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     let matches = uucore::clap_localization::handle_clap_result(uu_app(), args)?;

src/uu/users/src/users.rs

@@ -25,9 +25,8 @@ path = "src/who.rs"
 
 [dependencies]
 clap = { workspace = true }
-uucore = { workspace = true, features = ["utmpx"] }
+uucore = { workspace = true, features = ["utmpx", "process"] }
 fluent = { workspace = true }
-nix = { workspace = true, features = ["signal"] }
 
 [[bin]]
 name = "who"

src/uu/who/Cargo.toml

@@ -11,11 +11,10 @@ use crate::uu_app;
 use uucore::display::Quotable;
 use uucore::error::{FromIo, UResult};
 use uucore::libc::{S_IWGRP, STDIN_FILENO, ttyname};
+#[cfg(not(target_os = "openbsd"))]
+use uucore::process::pid_is_alive;
 use uucore::translate;
 
-use nix::sys::signal::kill;
-use nix::unistd::Pid;
-
 use uucore::utmpx::{self, UtmpxRecord, time};
 
 use std::borrow::Cow;
@@ -180,20 +179,6 @@ fn time_string(ut: &UtmpxRecord) -> String {
     ut.login_time().format(&time_format).unwrap()
 }
 
-#[inline]
-#[cfg(not(target_os = "openbsd"))]
-fn pid_is_alive(pid: i32) -> bool {
-    if pid <= 0 {
-        return true;
-    }
-
-    match kill(Pid::from_raw(pid), None) {
-        Ok(()) => true,
-        Err(nix::errno::Errno::ESRCH) => false,
-        Err(_) => true,
-    }
-}
-
 #[inline]
 fn current_tty() -> String {
     unsafe {

src/uu/who/src/platform/unix.rs

@@ -51,6 +51,31 @@ pub fn getpid() -> pid_t {
     unsafe { libc::getpid() }
 }
 
+/// Check if a process with the given PID is alive.
+///
+/// Uses `kill(pid, 0)` which sends signal 0 (null signal) to check process existence
+/// without actually sending a signal. This is a standard POSIX technique for checking
+/// if a process exists.
+///
+/// Returns `true` if:
+/// - The process exists (kill returns 0)
+/// - We lack permission to signal the process (errno != ESRCH)
+///   This means the process exists but we can't signal it
+///
+/// Returns `false` only if:
+/// - errno is ESRCH (No such process), confirming the process doesn't exist
+///
+/// PIDs <= 0 are considered alive for compatibility with utmp records that may
+/// contain special or invalid PID values.
+#[cfg(not(target_os = "openbsd"))]
+pub fn pid_is_alive(pid: i32) -> bool {
+    if pid <= 0 {
+        return true;
+    }
+
+    unsafe { libc::kill(pid, 0) == 0 || *libc::__errno_location() != libc::ESRCH }
+}
+
 /// `getsid()` returns the session ID of the process with process ID pid.
 ///
 /// If pid is 0, getsid() returns the session ID of the calling process.