kernel+libc: Add O_NONBLOCK

kernel/src/fs/VFS.h

@@ -32,6 +32,8 @@ namespace VFS
 
         virtual Result<void> truncate(usize size) = 0;
 
+        virtual bool blocking() const = 0;
+
         // Metadata accessors
         virtual usize size() = 0;
 
@@ -73,6 +75,11 @@ namespace VFS
             return err(ENOTDIR);
         }
 
+        bool blocking() const override
+        {
+            return false;
+        }
+
         InodeType type() const override
         {
             return InodeType::RegularFile;

kernel/src/fs/devices/ConsoleDevice.cpp

@@ -17,3 +17,8 @@ Result<usize> ConsoleDevice::write(const u8* buf, usize, usize length)
     TextConsole::write((const char*)buf, length);
     return length;
 }
+
+bool ConsoleDevice::blocking() const
+{
+    return false;
+}

kernel/src/fs/devices/ConsoleDevice.h

@@ -11,5 +11,7 @@ class ConsoleDevice : public Device
 
     Result<usize> write(const u8*, usize, usize) override;
 
+    bool blocking() const override;
+
     virtual ~ConsoleDevice() = default;
 };

kernel/src/fs/devices/Device.h

@@ -8,5 +8,7 @@ class Device
 
     virtual Result<usize> write(const u8* buf, usize offset, usize length) = 0;
 
+    virtual bool blocking() const = 0;
+
     virtual ~Device() = default;
 };

kernel/src/fs/devices/NullDevice.h

@@ -17,5 +17,10 @@ class NullDevice : public Device
         return 0;
     }
 
+    bool blocking() const override
+    {
+        return false;
+    }
+
     virtual ~NullDevice() = default;
 };

kernel/src/fs/tmpfs/FileSystem.h

@@ -134,6 +134,11 @@ namespace TmpFS
             return err(EINVAL);
         }
 
+        bool blocking() const override
+        {
+            return m_device->blocking();
+        }
+
         usize size() override
         {
             return 0;
@@ -196,6 +201,11 @@ namespace TmpFS
             return err(EISDIR);
         }
 
+        bool blocking() const override
+        {
+            return false;
+        }
+
         usize size() override
         {
             return 0;

kernel/src/sys/file.cpp

@@ -21,6 +21,13 @@ Result<u64> sys_read(Registers*, SyscallArgs args)
 
     if (!descriptor.is_readable()) return err(EBADF);
 
+    while (descriptor.inode->blocking())
+    {
+        if (descriptor.should_block()) kernel_sleep(10);
+        else
+            return err(EAGAIN);
+    }
+
     usize nread = TRY(descriptor.inode->read(buf, descriptor.offset, size));
 
     descriptor.offset += nread;

kernel/src/sys/open.cpp

@@ -7,7 +7,7 @@
 #include <bits/open-flags.h>
 
 // These flags are needed after open(), the rest only affect open().
-constexpr int FLAGS_TO_KEEP = O_RDWR | O_APPEND;
+constexpr int FLAGS_TO_KEEP = O_RDWR | O_APPEND | O_NONBLOCK;
 
 Result<u64> sys_open(Registers*, SyscallArgs args)
 {

kernel/src/thread/Thread.cpp

@@ -50,6 +50,11 @@ bool FileDescriptor::should_append()
     return flags & O_APPEND;
 }
 
+bool FileDescriptor::should_block()
+{
+    return flags & O_NONBLOCK;
+}
+
 bool FileDescriptor::is_readable()
 {
     return flags & O_RDONLY;

kernel/src/thread/Thread.h

@@ -29,6 +29,7 @@ struct FileDescriptor
     int flags { 0 };
 
     bool should_append();
+    bool should_block();
     bool is_writable();
     bool is_readable();
 };

libc/include/bits/open-flags.h

@@ -10,5 +10,6 @@
 #define O_CREAT 8
 #define O_EXCL 16
 #define O_TRUNC 32
+#define O_NONBLOCK 64
 
 #endif