kernel+sh: Implement interruptible syscalls

apps/sh.cpp

@@ -31,6 +31,11 @@ static Result<void> execute_command(StringView command)
     return os::Process::exec(args[0].view(), args.slice());
 }
 
+// Do nothing, but we need a handler so read() returns EINTR.
+static void sigint_handler(int)
+{
+}
+
 struct utsname g_sysinfo;
 
 const char* hostname = "";
@@ -41,7 +46,6 @@ Result<int> luna_main(int argc, char** argv)
 {
     StringView path;
     StringView command;
-    bool interactive { false };
 
     SharedPtr<File> input_file;
 
@@ -54,17 +58,15 @@ Result<int> luna_main(int argc, char** argv)
 
     if (!command.is_empty()) TRY(execute_command(command));
 
-    if (path == "-")
-    {
-        input_file = File::standard_input();
-        interactive = true;
-    }
+    if (path == "-") { input_file = File::standard_input(); }
     else
     {
         input_file = TRY(File::open(path, File::ReadOnly));
         input_file->set_close_on_exec();
     }
 
+    bool interactive = isatty(input_file->fd());
+
     if (interactive)
     {
         // Set up everything to form a prompt.
@@ -77,6 +79,8 @@ Result<int> luna_main(int argc, char** argv)
         if (pw) { username = pw->pw_name; }
         else { username = getenv("USER"); }
         endpwent();
+
+        signal(SIGINT, sigint_handler);
     }
 
     while (1)
@@ -87,7 +91,14 @@ Result<int> luna_main(int argc, char** argv)
             os::print("%s@%s:%s%c ", username, hostname, cwd.chars(), prompt_end);
         }
 
-        auto cmd = TRY(input_file->read_line());
+        auto maybe_cmd = input_file->read_line();
+        if (maybe_cmd.has_error())
+        {
+            if (maybe_cmd.error() == EINTR) continue;
+            return maybe_cmd.release_error();
+        }
+
+        auto cmd = maybe_cmd.release_value();
         if (cmd.is_empty())
         {
             if (interactive) puts("exit");

kernel/src/sys/file.cpp

@@ -10,7 +10,7 @@
 #include <luna/SafeArithmetic.h>
 #include <sys/types.h>
 
-Result<u64> sys_read(Registers*, SyscallArgs args)
+Result<u64> sys_read(Registers* regs, SyscallArgs args)
 {
     int fd = (int)args[0];
     u8* buf = (u8*)args[1];
@@ -31,6 +31,13 @@ Result<u64> sys_read(Registers*, SyscallArgs args)
         if (descriptor.should_block()) kernel_sleep(10);
         else
             return err(EAGAIN);
+
+        if (current->interrupted)
+        {
+            kdbgln("signal: read interrupted by signal");
+            if (current->will_invoke_signal_handler()) return err(EINTR);
+            current->process_pending_signals(regs);
+        }
     }
 
     usize nread = TRY(descriptor.inode->read(buf, descriptor.offset, size));

kernel/src/sys/usleep.cpp

@@ -11,5 +11,7 @@ Result<u64> sys_usleep(Registers*, SyscallArgs args)
 
     kernel_sleep(us / 1000);
 
-    return 0;
+    auto* current = Scheduler::current();
+
+    return current->sleep_ticks_left;
 }

kernel/src/sys/waitpid.cpp

@@ -1,9 +1,10 @@
+#include "Log.h"
 #include "memory/MemoryManager.h"
 #include "sys/Syscall.h"
 #include "thread/Scheduler.h"
 #include <bits/waitpid.h>
 
-Result<u64> sys_waitpid(Registers*, SyscallArgs args)
+Result<u64> sys_waitpid(Registers* regs, SyscallArgs args)
 {
     pid_t pid = (pid_t)args[0];
     int* status_ptr = (int*)args[1];
@@ -21,7 +22,16 @@ Result<u64> sys_waitpid(Registers*, SyscallArgs args)
 
         if (options & WNOHANG) return err(EAGAIN);
 
+    wait_for_child:
         if (thread->state != ThreadState::Exited) kernel_wait(pid);
+        if (current->interrupted)
+        {
+            kdbgln("signal: waitpid interrupted by signal");
+            if (current->will_invoke_signal_handler()) return err(EINTR);
+            current->process_pending_signals(regs);
+            goto wait_for_child;
+        }
+
         check(thread->state == ThreadState::Exited);
     }
     else if (pid == -1)
@@ -33,7 +43,16 @@ Result<u64> sys_waitpid(Registers*, SyscallArgs args)
         {
             if (options & WNOHANG) return err(EAGAIN);
 
+        wait_for_any_child:
             kernel_wait(pid);
+            if (current->interrupted)
+            {
+                kdbgln("signal: waitpid interrupted by signal");
+                if (current->will_invoke_signal_handler()) return err(EINTR);
+                current->process_pending_signals(regs);
+                goto wait_for_any_child;
+            }
+
             check(current->child_being_waited_for.value_or(-1) != -1);
 
             thread = TRY(Result<Thread*>::from_option(Scheduler::find_by_pid(*current->child_being_waited_for), ESRCH));

kernel/src/thread/Scheduler.cpp

@@ -135,6 +135,7 @@ namespace Scheduler
         thread->state = ThreadState::None;
         thread->is_kernel = false;
         thread->id = 1;
+        thread->pgid = 1;
         thread->name = name;
         thread->auth = Credentials { .uid = 0, .euid = 0, .suid = 0, .gid = 0, .egid = 0, .sgid = 0 };
 

kernel/src/thread/Thread.cpp

@@ -133,6 +133,7 @@ static constexpr DefaultSignalAction default_actions[] = {
 
 void Thread::process_pending_signals(Registers* current_regs)
 {
+    interrupted = false;
     for (int i = 0; i < NSIG; i++)
     {
         int signo = i + 1;
@@ -175,10 +176,33 @@ void Thread::process_pending_signals(Registers* current_regs)
     }
 }
 
+bool Thread::will_invoke_signal_handler()
+{
+    for (int i = 0; i < NSIG; i++)
+    {
+        if (pending_signals & (1 << i))
+        {
+            int signo = i + 1;
+            if (signo != SIGKILL && signo != SIGSTOP && signal_mask & (1 << i)) continue;
+            auto handler = signal_handlers[i];
+            if (handler.sa_handler == SIG_IGN || handler.sa_handler == SIG_DFL) return false;
+            if (signo == SIGKILL || signo == SIGSTOP) return false;
+            return true;
+        }
+    }
+    return false;
+}
+
 void Thread::send_signal(int signo)
 {
     check(signo > 0 && signo <= NSIG);
     pending_signals |= 1 << (signo - 1);
+
+    if (state == ThreadState::Waiting || state == ThreadState::Sleeping)
+    {
+        interrupted = true;
+        wake_up();
+    }
 }
 
 bool FileDescriptor::should_append()

kernel/src/thread/Thread.h

@@ -84,6 +84,7 @@ struct Thread : public LinkedListNode<Thread>
     struct sigaction signal_handlers[NSIG];
     sigset_t signal_mask { 0 };
     sigset_t pending_signals { 0 };
+    bool interrupted { false };
 
     FPData fp_data;
 
@@ -139,6 +140,8 @@ struct Thread : public LinkedListNode<Thread>
 
     void process_pending_signals(Registers* current_regs);
 
+    bool will_invoke_signal_handler();
+
     bool deliver_signal(int signo, Registers* current_regs);
     void sigreturn(Registers* current_regs);