Kernel: waitpid: support -1 as PID (wait for any child)

kernel/src/sys/sched.cpp

@@ -1,5 +1,6 @@
 #include "errno.h"
 #include "memory/VMM.h"
+#include "sys/UserMemory.h"
 #include "thread/Scheduler.h"
 
 void sys_exit(Context* context, int status)
@@ -21,23 +22,3 @@ void sys_sleep(Context* context, uint64_t ms)
     task->state = task->Sleeping;
     Scheduler::task_yield(context);
 }
-
-void sys_waitpid(Context* context, long pid, int* wstatus,
-                 int) // FIXME: Use the value in options and block if WNOHANG has not been specified.
-{
-    Task* child = Scheduler::find_by_pid(pid); // FIXME: Wait for any child process if PID is -1.
-    if (!child)
-    {
-        context->rax = -ESRCH;
-        return;
-    }
-    if (child->state != child->Dying) // FIXME: This should block if WNOHANG has not been specified.
-    {
-        context->rax = 0;
-        return;
-    }
-    uint64_t phys = VMM::get_physical((uint64_t)wstatus);
-    if (phys != (uint64_t)-1) { *(int*)phys = (int)(child->exit_status & 0xff); }
-    child->state = child->Exited;
-    context->rax = (long)child->id;
-}

kernel/src/thread/Scheduler.cpp

@@ -13,6 +13,7 @@
 #include "panic/Panic.h"
 #include "std/stdlib.h"
 #include "std/string.h"
+#include "sys/UserMemory.h"
 #include "sys/elf/ELFLoader.h"
 #include "thread/PIT.h"
 #include "thread/Task.h"
@@ -423,3 +424,50 @@ Task* Scheduler::current_task()
 {
     return sched_current_task;
 }
+
+void sys_waitpid(Context* context, long pid, int* wstatus,
+                 int) // FIXME: Use the value in options and block if WNOHANG has not been specified.
+{
+    Task* child = nullptr;
+    if (pid == -1)
+    {
+        sched_for_each_task([&](Task* task) {
+            if (task->state == task->Dying && task->ppid == sched_current_task->id)
+            {
+                child = task;
+                return false;
+            }
+            return true;
+        });
+        if (!child)
+        {
+            context->rax = 0; // No child has exited, let's return 0.
+            return;
+        }
+    }
+    else
+    {
+        child = Scheduler::find_by_pid(pid);
+        if (!child)
+        {
+            context->rax = -ESRCH;
+            return;
+        }
+    }
+    if (child->state != child->Dying) // FIXME: This should block if WNOHANG has not been specified.
+    {
+        context->rax = 0;
+        return;
+    }
+    if (wstatus)
+    {
+        int* kwstatus = obtain_user_ref(wstatus);
+        if (kwstatus)
+        {
+            *kwstatus = (int)(child->exit_status & 0xff);
+            release_user_ref(kwstatus);
+        }
+    }
+    child->state = child->Exited;
+    context->rax = (long)child->id;
+}