apps: Add ps

apps/CMakeLists.txt

@@ -26,3 +26,4 @@ luna_app(login.cpp login)
 luna_app(ipc-test.cpp ipc-test)
 luna_app(mount.cpp mount)
 luna_app(umount.cpp umount)
+luna_app(ps.cpp ps)

apps/ps.cpp

@@ -0,0 +1,44 @@
+#include <errno.h>
+#include <os/ArgumentParser.h>
+#include <os/File.h>
+#include <pwd.h>
+#include <sys/pstat.h>
+#include <time.h>
+
+Result<int> luna_main(int argc, char** argv)
+{
+    os::ArgumentParser parser;
+    parser.add_description("Show a list of processes on the system.");
+    parser.add_system_program_info("ps"_sv);
+    parser.parse(argc, argv);
+
+    os::println("UID         PID   PPID       TIME CMD");
+
+    pid_t last = pstat(-1, nullptr);
+    for (pid_t pid = 1; pid <= last; pid++)
+    {
+        static process ps;
+        if (pstat(pid, &ps) < 0)
+        {
+            if (errno == ESRCH) continue;
+            return err(errno);
+        }
+
+        struct tm tm;
+        gmtime_r(&ps.ps_time.tv_sec, &tm);
+
+        char timebuf[256];
+        strftime(timebuf, sizeof(timebuf), "%H:%M:%S", &tm);
+
+        const char* user = "???";
+
+        passwd* pw = getpwuid(ps.ps_uid);
+        if (pw) user = pw->pw_name;
+
+        os::println("%-8s %6d %6d %10s %s", user, ps.ps_pid, ps.ps_ppid, timebuf, ps.ps_name);
+    }
+
+    endpwent();
+
+    return 0;
+}