Kernel: Implement blocking reads

This is a huge step forward!! bc actually runs now, without echo or backspace, but it runs!!

apps/src/sh.c

@@ -187,12 +187,7 @@ int main()
             perror("fread");
             return 1;
         }
-        if (feof(stdin))
-        {
-            clearerr(stdin);
-            msleep(20);
-            continue;
-        }
+        if (feof(stdin)) { return 0; }
         buffer[nread] = 0;
         command_concat(&shell_command, buffer);
     }

kernel/include/fs/VFS.h

@@ -18,6 +18,7 @@ namespace VFS
     typedef ssize_t (*node_write)(Node*, size_t, size_t, const char*);
     typedef Node* (*node_finddir)(Node*, const char*);
     typedef int (*node_mkdir)(Node*, const char*);
+    typedef int (*node_block)(Node*);
 
     struct Node
     {
@@ -30,6 +31,7 @@ namespace VFS
         node_finddir find_func;
         node_mkdir mkdir_func;
         node_write write_func;
+        node_block block_func;
         int tty = 0;
         Node* link;
     };
@@ -39,6 +41,8 @@ namespace VFS
     int mkdir(const char* path, const char* name);
     int mkdir(const char* pathname);
 
+    int would_block(Node* node);
+
     void mount_root(Node* root);
 
     Node* resolve_path(const char* filename, Node* root = nullptr);

kernel/include/fs/devices/Keyboard.h

@@ -7,5 +7,7 @@ namespace KeyboardDevice
 
     ssize_t read(VFS::Node* node, size_t offset, size_t size, char* buffer);
 
+    int would_block(VFS::Node* node);
+
     void append(char c);
 }

kernel/include/thread/Task.h

@@ -15,6 +15,7 @@ struct Task
         Running,
         Sleeping,
         Dying,
+        Blocking,
         Exited
     };
 
@@ -67,4 +68,15 @@ struct Task
     bool has_died();
 
     char name[128];
+
+    struct
+    {
+        size_t size;
+        int fd;
+        char* buf;
+    } blocking_read_info;
+
+    void resume_read();
+
+    bool is_still_blocking();
 };

kernel/src/fs/VFS.cpp

@@ -9,6 +9,13 @@
 
 static VFS::Node* vfs_root;
 
+int VFS::would_block(Node* node)
+{
+    if (!node) { return 0; }
+    if (!node->block_func) { return 0; }
+    return node->block_func(node);
+}
+
 ssize_t VFS::read(Node* node, size_t offset, size_t length, char* buffer)
 {
     if (!node)

kernel/src/fs/devices/Keyboard.cpp

@@ -11,10 +11,16 @@
 char* kbd_buffer = nullptr;
 uint64_t kbd_bufsize = 0;
 
+int KeyboardDevice::would_block(VFS::Node*)
+{
+    return kbd_bufsize == 0;
+}
+
 VFS::Node* KeyboardDevice::create_new(const char* devname)
 {
     VFS::Node* dev = new VFS::Node;
     dev->read_func = KeyboardDevice::read;
+    dev->block_func = KeyboardDevice::would_block;
     dev->inode = 0;
     dev->length = 0;
     dev->type = VFS_DEVICE;

kernel/src/sys/stdio.cpp

@@ -209,6 +209,14 @@ void sys_read(Context* context, int fd, size_t size, char* buffer)
         context->rax = -EBADF;
         return;
     }
+    if (VFS::would_block(current_task->files[fd].node()))
+    {
+        current_task->state = current_task->Blocking;
+        current_task->blocking_read_info.fd = fd;
+        current_task->blocking_read_info.buf = (char*)VMM::get_physical((uint64_t)buffer); // FIXME: Handle errors.
+        current_task->blocking_read_info.size = size;
+        return Scheduler::task_yield(context);
+    }
     ssize_t result = current_task->files[fd].read(size, (char*)VMM::get_physical((uint64_t)buffer));
     context->rax = (size_t)result;
     return;

kernel/src/thread/Scheduler.cpp

@@ -392,6 +392,14 @@ void Scheduler::task_yield(Context* context)
     Task* original_task = sched_current_task;
     do {
         sched_current_task = sched_current_task->next_task;
+        if (sched_current_task->state == sched_current_task->Blocking)
+        {
+            if (!sched_current_task->is_still_blocking())
+            {
+                sched_current_task->resume_read();
+                sched_current_task->state = sched_current_task->Running;
+            }
+        }
         if (sched_current_task->state == sched_current_task->Running)
         {
             if (sched_current_task->id != original_task->id || was_idle)

kernel/src/thread/Task.cpp

@@ -1,4 +1,7 @@
+#define MODULE "sched"
+
 #include "thread/Task.h"
+#include "log/Log.h"
 #include "memory/VMM.h"
 #include "std/string.h"
 
@@ -65,4 +68,18 @@ void Task::switch_to_address_space()
 bool Task::has_died()
 {
     return state == Exited;
+}
+
+void Task::resume_read()
+{
+    VMM::switch_back_to_kernel_address_space();
+    VMM::apply_address_space();
+    VMM::switch_to_previous_user_address_space();
+    regs.rax = files[blocking_read_info.fd].read(blocking_read_info.size, blocking_read_info.buf);
+    VMM::apply_address_space();
+}
+
+bool Task::is_still_blocking()
+{
+    return VFS::would_block(files[blocking_read_info.fd].node());
 }