Implement basic support for POSIX-style select().

Now we can block on both the PTY *and* the GUI event stream in Terminal.

Kernel/Process.cpp

@@ -1909,3 +1909,78 @@ DisplayInfo Process::get_display_info()
     info.framebuffer = m_display_framebuffer_region->linearAddress.asPtr();
     return info;
 }
+
+int Process::sys$select(const Syscall::SC_select_params* params)
+{
+    if (!validate_read_typed(params))
+        return -EFAULT;
+    if (params->writefds && !validate_read_typed(params->writefds))
+        return -EFAULT;
+    if (params->readfds && !validate_read_typed(params->readfds))
+        return -EFAULT;
+    if (params->exceptfds && !validate_read_typed(params->exceptfds))
+        return -EFAULT;
+    if (params->timeout && !validate_read_typed(params->timeout))
+        return -EFAULT;
+    int nfds = params->nfds;
+    fd_set* writefds = params->writefds;
+    fd_set* readfds = params->readfds;
+    fd_set* exceptfds = params->exceptfds;
+    auto* timeout = params->timeout;
+
+    // FIXME: Implement exceptfds support.
+    ASSERT(!exceptfds);
+
+    // FIXME: Implement timeout support.
+    ASSERT(!timeout);
+
+    if (nfds < 0)
+        return -EINVAL;
+
+    // FIXME: Return -EBADF if one of the fd sets contains an invalid fd.
+    // FIXME: Return -EINTR if a signal is caught.
+    // FIXME: Return -EINVAL if timeout is invalid.
+
+    auto transfer_fds = [nfds] (fd_set* set, auto& vector) {
+        if (!set)
+            return;
+        vector.clear_with_capacity();
+        auto bitmap = Bitmap::wrap((byte*)set, FD_SETSIZE);
+        for (int i = 0; i < nfds; ++i) {
+            if (bitmap.get(i))
+                vector.append(i);
+        }
+    };
+
+    transfer_fds(writefds, m_select_write_fds);
+    transfer_fds(readfds, m_select_read_fds);
+
+    block(BlockedSelect);
+    Scheduler::yield();
+
+    int markedfds = 0;
+
+    if (readfds) {
+        memset(readfds, 0, sizeof(fd_set));
+        auto bitmap = Bitmap::wrap((byte*)readfds, FD_SETSIZE);
+        for (int fd : m_select_read_fds) {
+            if (m_fds[fd].descriptor->has_data_available_for_reading(*this)) {
+                bitmap.set(fd, true);
+                ++markedfds;
+            }
+        }
+    }
+
+    if (writefds) {
+        memset(writefds, 0, sizeof(fd_set));
+        auto bitmap = Bitmap::wrap((byte*)writefds, FD_SETSIZE);
+        for (int fd : m_select_write_fds) {
+            if (m_fds[fd].descriptor->can_write(*this)) {
+                bitmap.set(fd, true);
+                ++markedfds;
+            }
+        }
+    }
+
+    return markedfds;
+}

Kernel/Process.h

@@ -69,6 +69,7 @@ public:
         BlockedRead,
         BlockedWrite,
         BlockedSignal,
+        BlockedSelect,
     };
 
     enum RingLevel {
@@ -81,7 +82,7 @@ public:
 
     bool is_blocked() const
     {
-        return m_state == BlockedSleep || m_state == BlockedWait || m_state == BlockedRead || m_state == BlockedSignal;
+        return m_state == BlockedSleep || m_state == BlockedWait || m_state == BlockedRead || m_state == BlockedSignal || m_state == BlockedSelect;
     }
 
     PageDirectory& page_directory() { return *m_page_directory; }
@@ -156,6 +157,7 @@ public:
     void* sys$mmap(const Syscall::SC_mmap_params*);
     int sys$munmap(void*, size_t size);
     int sys$set_mmap_name(void*, size_t, const char*);
+    int sys$select(const Syscall::SC_select_params*);
     ssize_t sys$get_dir_entries(int fd, void*, size_t);
     int sys$getcwd(char*, size_t);
     int sys$chdir(const char*);
@@ -304,6 +306,8 @@ private:
     dword m_timesScheduled { 0 };
     pid_t m_waitee_pid { -1 };
     int m_blocked_fd { -1 };
+    Vector<int> m_select_read_fds;
+    Vector<int> m_select_write_fds;
     size_t m_max_open_file_descriptors { 16 };
     SignalActionData m_signal_action_data[32];
     dword m_pending_signals { 0 };
@@ -394,6 +398,7 @@ static inline const char* toString(Process::State state)
     case Process::BlockedRead: return "Read";
     case Process::BlockedWrite: return "Write";
     case Process::BlockedSignal: return "Signal";
+    case Process::BlockedSelect: return "Select";
     case Process::BeingInspected: return "Inspect";
     }
     ASSERT_NOT_REACHED();

Kernel/Scheduler.cpp

@@ -64,6 +64,22 @@ bool Scheduler::pick_next()
             return true;
         }
 
+        if (process.state() == Process::BlockedSelect) {
+            for (int fd : process.m_select_read_fds) {
+                if (process.m_fds[fd].descriptor->has_data_available_for_reading(process)) {
+                    process.unblock();
+                    return true;
+                }
+            }
+            for (int fd : process.m_select_write_fds) {
+                if (process.m_fds[fd].descriptor->can_write(process)) {
+                    process.unblock();
+                    return true;
+                }
+            }
+            return true;
+        }
+
         if (process.state() == Process::Skip1SchedulerPass) {
             process.set_state(Process::Skip0SchedulerPasses);
             return true;

Kernel/Syscall.cpp

@@ -98,6 +98,8 @@ static dword handle(RegisterDump& regs, dword function, dword arg1, dword arg2,
         return current->sys$waitpid((pid_t)arg1, (int*)arg2, (int)arg3);
     case Syscall::SC_mmap:
         return (dword)current->sys$mmap((const SC_mmap_params*)arg1);
+    case Syscall::SC_select:
+        return current->sys$select((const SC_select_params*)arg1);
     case Syscall::SC_munmap:
         return current->sys$munmap((void*)arg1, (size_t)arg2);
     case Syscall::SC_gethostname:

Kernel/Syscall.h

@@ -71,8 +71,11 @@
     __ENUMERATE_SYSCALL(gui_destroy_window) \
     __ENUMERATE_SYSCALL(gui_get_window_backing_store) \
     __ENUMERATE_SYSCALL(gui_invalidate_window) \
+    __ENUMERATE_SYSCALL(select) \
 
 
+struct fd_set;
+
 namespace Syscall {
 
 enum Function {
@@ -102,6 +105,14 @@ struct SC_mmap_params {
     int32_t offset; // FIXME: 64-bit off_t?
 };
 
+struct SC_select_params {
+    int nfds;
+    fd_set* readfds;
+    fd_set* writefds;
+    fd_set* exceptfds;
+    struct timeval* timeout;
+};
+
 void initialize();
 int sync();
 

LibC/Makefile

@@ -41,6 +41,7 @@ LIBC_OBJS = \
        math.o \
        utime.o \
        gui.o \
+       sys/select.o \
        entry.o
 
 OBJS = $(AK_OBJS) $(WIDGETS_OBJS) $(LIBC_OBJS)

Terminal/main.cpp

@@ -9,6 +9,7 @@
 #include <Widgets/GraphicsBitmap.h>
 #include <Widgets/Painter.h>
 #include <sys/ioctl.h>
+#include <sys/select.h>
 #include <gui.h>
 #include "Terminal.h"
 
@@ -53,9 +54,14 @@ static void make_shell(int ptm_fd)
     }
 }
 
+static int max(int a, int b)
+{
+    return a > b ? a : b;
+}
+
 int main(int, char**)
 {
-    int ptm_fd = open("/dev/ptm0", O_RDWR | O_NONBLOCK);
+    int ptm_fd = open("/dev/ptm0", O_RDWR);
     if (ptm_fd < 0) {
         perror("open");
         return 1;
@@ -63,7 +69,7 @@ int main(int, char**)
 
     make_shell(ptm_fd);
 
-    int event_fd = open("/dev/gui_events", O_RDONLY | O_NONBLOCK);
+    int event_fd = open("/dev/gui_events", O_RDONLY);
     if (event_fd < 0) {
         perror("open");
         return 1;
@@ -74,38 +80,53 @@ int main(int, char**)
     terminal.paint();
 
     for (;;) {
-        byte buffer[1024];
-        ssize_t ptm_nread = read(ptm_fd, buffer, sizeof(buffer));
-        if (ptm_nread > 0) {
-            for (ssize_t i = 0; i < ptm_nread; ++i)
+        fd_set rfds;
+        FD_ZERO(&rfds);
+        FD_SET(ptm_fd, &rfds);
+        FD_SET(event_fd, &rfds);
+        int nfds = select(max(ptm_fd, event_fd) + 1, &rfds, nullptr, nullptr, nullptr);
+        if (nfds < 0) {
+            dbgprintf("Terminal(%u) select() failed :( errno=%d\n", getpid(), errno);
+        }
+
+        if (FD_ISSET(ptm_fd, &rfds)) {
+            byte buffer[1024];
+            ssize_t nread = read(ptm_fd, buffer, sizeof(buffer));
+            if (nread < 0) {
+                perror("read(ptm)");
+                continue;
+            }
+            assert(nread != 0);
+            for (ssize_t i = 0; i < nread; ++i)
                 terminal.on_char(buffer[i]);
             terminal.paint();
         }
 
-        GUI_Event event;
-        ssize_t nread = read(event_fd, &event, sizeof(event));
-        if (nread < 0) {
-            perror("read");
-            return 1;
-        }
-        if (nread == 0)
-            continue;
-        assert(nread == sizeof(event));
-        dbgprintf("(Terminal:%d) ", getpid());
-        switch (event.type) {
-        case GUI_Event::Type::Paint: dbgprintf("WID=%x Paint [%d,%d %dx%d]\n", event.window_id, event.paint.rect.location.x, event.paint.rect.location.y, event.paint.rect.size.width, event.paint.rect.size.height); break;
-        case GUI_Event::Type::MouseDown: dbgprintf("WID=%x MouseDown %d,%d\n", event.window_id, event.mouse.position.x, event.mouse.position.y); break;
-        case GUI_Event::Type::MouseUp: dbgprintf("WID=%x MouseUp %d,%d\n", event.window_id, event.mouse.position.x, event.mouse.position.y); break;
-        case GUI_Event::Type::MouseMove: dbgprintf("WID=%x MouseMove %d,%d\n", event.window_id, event.mouse.position.x, event.mouse.position.y); break;
-        case GUI_Event::Type::KeyDown: dbgprintf("WID=%x KeyDown 0x%b (%c)\n", event.window_id, event.key.character, event.key.character); break;
-        default:
-            ASSERT_NOT_REACHED();
-        }
+        if (FD_ISSET(event_fd, &rfds)) {
+            GUI_Event event;
+            ssize_t nread = read(event_fd, &event, sizeof(event));
+            if (nread < 0) {
+                perror("read(event)");
+                return 1;
+            }
+            assert(nread != 0);
+            assert(nread == sizeof(event));
+            dbgprintf("(Terminal:%d) ", getpid());
+            switch (event.type) {
+            case GUI_Event::Type::Paint: dbgprintf("WID=%x Paint [%d,%d %dx%d]\n", event.window_id, event.paint.rect.location.x, event.paint.rect.location.y, event.paint.rect.size.width, event.paint.rect.size.height); break;
+            case GUI_Event::Type::MouseDown: dbgprintf("WID=%x MouseDown %d,%d\n", event.window_id, event.mouse.position.x, event.mouse.position.y); break;
+            case GUI_Event::Type::MouseUp: dbgprintf("WID=%x MouseUp %d,%d\n", event.window_id, event.mouse.position.x, event.mouse.position.y); break;
+            case GUI_Event::Type::MouseMove: dbgprintf("WID=%x MouseMove %d,%d\n", event.window_id, event.mouse.position.x, event.mouse.position.y); break;
+            case GUI_Event::Type::KeyDown: dbgprintf("WID=%x KeyDown 0x%b (%c)\n", event.window_id, event.key.character, event.key.character); break;
+            default:
+                ASSERT_NOT_REACHED();
+            }
 
-        if (event.type == GUI_Event::Type::Paint) {
-            terminal.paint();
-        } else if (event.type == GUI_Event::Type::KeyDown) {
-            write(ptm_fd, &event.key.character, 1);
+            if (event.type == GUI_Event::Type::Paint) {
+                terminal.paint();
+            } else if (event.type == GUI_Event::Type::KeyDown) {
+                write(ptm_fd, &event.key.character, 1);
+            }
         }
     }
     return 0;

VirtualFileSystem/UnixTypes.h

@@ -2,6 +2,9 @@
 
 extern "C" {
 
+#define FD_SETSIZE 64
+struct fd_set { unsigned char bits[FD_SETSIZE / 8];  };
+
 namespace Unix {
 
 #define WNOHANG 1