libos: Add Process::wait()

apps/init.cpp

@@ -14,7 +14,6 @@
 #include <sys/stat.h>
 #include <sys/syscall.h>
 #include <sys/sysmacros.h>
-#include <sys/wait.h>
 #include <unistd.h>
 
 FILE* g_init_log;
@@ -97,8 +96,7 @@ static Result<void> try_start_service(Service& service)
         fprintf(g_init_log, "[init] waiting for child process %d to finish\n", pid);
 
         int status;
-        pid_t id = waitpid(pid, &status, 0);
-        if (id < 0) { return err(errno); }
+        TRY(os::Process::wait(pid, &status));
 
         fprintf(g_init_log, "[init] child process %d exited with code %d\n", pid, WEXITSTATUS(status));
     }
@@ -312,7 +310,10 @@ int main()
     while (1)
     {
         int status;
-        pid_t child = wait(&status);
+        auto rc = os::Process::wait(os::Process::ANY_CHILD, &status);
+        if (rc.has_error()) continue;
+
+        pid_t child = rc.release_value();
 
         for (auto& service : g_services)
         {

apps/sh.cpp

@@ -11,7 +11,6 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/utsname.h>
-#include <sys/wait.h>
 #include <unistd.h>
 
 using os::File;
@@ -118,11 +117,7 @@ Result<int> luna_main(int argc, char** argv)
 
         if (child == 0) { TRY(execute_command(cmd.view())); }
 
-        if (waitpid(child, NULL, 0) < 0)
-        {
-            perror("waitpid");
-            return 1;
-        }
+        TRY(os::Process::wait(child, nullptr));
     }
 
     return 0;

apps/time.cpp

@@ -3,7 +3,6 @@
 #include <os/Process.h>
 #include <stdio.h>
 #include <sys/resource.h>
-#include <sys/wait.h>
 
 Result<int> luna_main(int argc, char** argv)
 {
@@ -23,11 +22,7 @@ Result<int> luna_main(int argc, char** argv)
         unreachable();
     }
 
-    if (waitpid(pid, nullptr, 0) < 0)
-    {
-        perror("waitpid");
-        return 1;
-    }
+    TRY(os::Process::wait(pid, nullptr));
 
     struct rusage usage;
     if (getrusage(RUSAGE_CHILDREN, &usage) < 0)

libos/include/os/Process.h

@@ -11,6 +11,7 @@
 #include <luna/Result.h>
 #include <luna/String.h>
 #include <sys/types.h>
+#include <sys/wait.h>
 
 namespace os
 {
@@ -57,5 +58,19 @@ namespace os
          * @return Result<void> Always an error, as this function does not return on success.
          */
         static Result<void> exec(StringView path, Slice<String> args, Slice<String> env, bool search_in_path = true);
+
+        // To use as the child argument to wait() to wait for any child.
+        static constexpr pid_t ANY_CHILD = -1;
+
+        /**
+         * @brief Wait for a child process to finish running.
+         *
+         * @param child The process ID of the child process, or ANY_CHILD to wait for any child.
+         * @param status The child's exit status will be stored here. If you don't want it, use nullptr.
+         * @param options Options to pass to waitpid(2).
+         * @return Result<pid_t> The process ID of the child process that was waited for (may not be the same as the
+         * child argument if ANY_CHILD was passed).
+         */
+        static Result<pid_t> wait(pid_t child, int* status, int options = 0);
     };
 }

libos/src/Process.cpp

@@ -62,4 +62,10 @@ namespace os
 
         return err(errno);
     }
+
+    Result<pid_t> Process::wait(pid_t child, int* status, int options)
+    {
+        long rc = syscall(SYS_waitpid, child, status, options);
+        return Result<pid_t>::from_syscall(rc);
+    }
 }