top: implement user count for linux

Author: Bluemangoo

Cargo.lock

@@ -22,6 +22,9 @@ chrono = { workspace = true }
 systemstat = { workspace = true }
 bytesize = { workspace = true }
 
+[target.'cfg(target_os="linux")'.dependencies]
+libsystemd-sys = "0.9.3"
+
 [lib]
 path = "src/top.rs"
 

src/uu/top/Cargo.toml

@@ -51,6 +51,7 @@ pub(crate) fn header(arg: &ArgMatches) -> String {
     )
 }
 
+#[cfg(not(target_os = "linux"))]
 fn todo() -> String {
     "TODO".into()
 }
@@ -85,11 +86,77 @@ fn uptime() -> String {
     res
 }
 
+fn format_user(user: u64) -> String {
+    match user {
+        0 => "0 user".to_string(),
+        1 => "1 user".to_string(),
+        _ => format!("{} users", user),
+    }
+}
+
 //TODO: Implement active user count
+#[cfg(not(target_os = "linux"))]
 fn user() -> String {
     todo()
 }
 
+#[cfg(target_os = "linux")]
+// see: https://gitlab.com/procps-ng/procps/-/blob/4740a0efa79cade867cfc7b32955fe0f75bf5173/library/uptime.c#L63-L115
+fn user() -> String {
+    use libc::{endutxent, free, getutxent, setutxent};
+    use libsystemd_sys::daemon::sd_booted;
+    use libsystemd_sys::login::{sd_get_sessions, sd_session_get_class};
+    use std::ffi::{c_char, c_void, CStr};
+    use std::ptr;
+
+    unsafe {
+        // systemd
+        if sd_booted() > 0 {
+            let mut sessions_list: *mut *mut c_char = ptr::null_mut();
+            let mut num_user = 0;
+            let sessions = sd_get_sessions(&mut sessions_list); // rust-systemd does not implement this
+
+            if sessions > 0 {
+                for i in 0..sessions {
+                    let mut class: *mut c_char = ptr::null_mut();
+
+                    if sd_session_get_class(
+                        *sessions_list.add(i as usize) as *const c_char,
+                        &mut class,
+                    ) < 0
+                    {
+                        continue;
+                    }
+                    if CStr::from_ptr(class).to_str().unwrap().starts_with("user") {
+                        num_user += 1;
+                    }
+                    free(class as *mut c_void);
+                }
+            }
+
+            for i in 0..sessions {
+                free(*sessions_list.add(i as usize) as *mut c_void);
+            }
+            free(sessions_list as *mut c_void);
+
+            return format_user(num_user);
+        }
+
+        // utmp
+        let mut num_user = 0;
+        setutxent();
+        let mut ut = getutxent();
+        while !ut.is_null() {
+            if ((*ut).ut_type == 7) && ((*ut).ut_user[0] != ('\0' as i8)) {
+                num_user += 1;
+            }
+            ut = getutxent();
+        }
+        endutxent();
+        format_user(num_user)
+    }
+}
+
 #[cfg(not(target_os = "windows"))]
 fn load_average() -> String {
     let binding = systemstat().read().unwrap();
@@ -214,9 +281,7 @@ fn memory(arg: &ArgMatches) -> String {
             "e" => (1_152_921_504_606_846_976, "EiB"),
             _ => (bytesize::MIB, "MiB"),
         },
-        None => {
-            (bytesize::MIB, "MiB")
-        }
+        None => (bytesize::MIB, "MiB"),
     };
 
     format!(