Kernel: Use KResultOr<size_t> throughout the TTY subsystem

Previously the VirtualConsole::on_tty_write() method would return an
incorrect value when an error had occurred. This prompted me to
update the TTY subsystem to use KResultOr<size_t> everywhere.

Kernel/TTY/MasterPTY.cpp

@@ -78,10 +78,10 @@ void MasterPTY::notify_slave_closed(Badge<SlavePTY>)
         m_slave = nullptr;
 }
 
-ssize_t MasterPTY::on_slave_write(const UserOrKernelBuffer& data, ssize_t size)
+KResultOr<size_t> MasterPTY::on_slave_write(const UserOrKernelBuffer& data, size_t size)
 {
     if (m_closed)
-        return -EIO;
+        return EIO;
     return m_buffer.write(data, size);
 }
 

Kernel/TTY/MasterPTY.h

@@ -21,7 +21,7 @@ public:
 
     unsigned index() const { return m_index; }
     String pts_name() const;
-    ssize_t on_slave_write(const UserOrKernelBuffer&, ssize_t);
+    KResultOr<size_t> on_slave_write(const UserOrKernelBuffer&, size_t);
     bool can_write_from_slave() const;
     void notify_slave_closed(Badge<SlavePTY>);
     bool is_closed() const { return m_closed; }

Kernel/TTY/SlavePTY.cpp

@@ -40,11 +40,11 @@ void SlavePTY::echo(u8 ch)
 {
     if (should_echo_input()) {
         auto buffer = UserOrKernelBuffer::for_kernel_buffer(&ch);
-        m_master->on_slave_write(buffer, 1);
+        [[maybe_unused]] auto result = m_master->on_slave_write(buffer, 1);
     }
 }
 
-void SlavePTY::on_master_write(const UserOrKernelBuffer& buffer, ssize_t size)
+void SlavePTY::on_master_write(const UserOrKernelBuffer& buffer, size_t size)
 {
     auto result = buffer.read_buffered<128>(size, [&](u8 const* data, size_t data_size) {
         for (size_t i = 0; i < data_size; ++i)
@@ -55,7 +55,7 @@ void SlavePTY::on_master_write(const UserOrKernelBuffer& buffer, ssize_t size)
         evaluate_block_conditions();
 }
 
-ssize_t SlavePTY::on_tty_write(const UserOrKernelBuffer& data, ssize_t size)
+KResultOr<size_t> SlavePTY::on_tty_write(const UserOrKernelBuffer& data, size_t size)
 {
     m_time_of_last_write = kgettimeofday().to_truncated_seconds();
     return m_master->on_slave_write(data, size);

Kernel/TTY/SlavePTY.h

@@ -17,7 +17,7 @@ class SlavePTY final : public TTY {
 public:
     virtual ~SlavePTY() override;
 
-    void on_master_write(const UserOrKernelBuffer&, ssize_t);
+    void on_master_write(const UserOrKernelBuffer&, size_t);
     unsigned index() const { return m_index; }
 
     time_t time_of_last_write() const { return m_time_of_last_write; }
@@ -27,7 +27,7 @@ public:
 private:
     // ^TTY
     virtual String const& tty_name() const override;
-    virtual ssize_t on_tty_write(const UserOrKernelBuffer&, ssize_t) override;
+    virtual KResultOr<size_t> on_tty_write(const UserOrKernelBuffer&, size_t) override;
     virtual void echo(u8) override;
 
     // ^CharacterDevice

Kernel/TTY/TTY.cpp

@@ -88,7 +88,7 @@ KResultOr<size_t> TTY::write(FileDescription&, u64, const UserOrKernelBuffer& bu
     }
 
     constexpr size_t num_chars = 256;
-    return buffer.read_buffered<num_chars>(size, [&](u8 const* data, size_t buffer_bytes) {
+    return buffer.read_buffered<num_chars>(size, [&](u8 const* data, size_t buffer_bytes) -> KResultOr<size_t> {
         u8 modified_data[num_chars * 2];
         size_t modified_data_size = 0;
         for (size_t i = 0; i < buffer_bytes; ++i) {
@@ -96,18 +96,19 @@ KResultOr<size_t> TTY::write(FileDescription&, u64, const UserOrKernelBuffer& bu
                 modified_data[modified_data_size++] = out_ch;
             });
         }
-        ssize_t bytes_written = on_tty_write(UserOrKernelBuffer::for_kernel_buffer(modified_data), modified_data_size);
-        VERIFY(bytes_written != 0);
-        if (bytes_written < 0 || !(m_termios.c_oflag & OPOST) || !(m_termios.c_oflag & ONLCR))
-            return bytes_written;
-        if ((size_t)bytes_written == modified_data_size)
-            return (ssize_t)buffer_bytes;
+        auto bytes_written_or_error = on_tty_write(UserOrKernelBuffer::for_kernel_buffer(modified_data), modified_data_size);
+        VERIFY(bytes_written_or_error.is_error() || bytes_written_or_error.value() != 0);
+        if (bytes_written_or_error.is_error() || !(m_termios.c_oflag & OPOST) || !(m_termios.c_oflag & ONLCR))
+            return bytes_written_or_error;
+        auto bytes_written = bytes_written_or_error.value();
+        if (bytes_written == modified_data_size)
+            return buffer_bytes;
 
         // Degenerate case where we converted some newlines and encountered a partial write
 
         // Calculate where in the input buffer the last character would have been
         size_t pos_data = 0;
-        for (ssize_t pos_modified_data = 0; pos_modified_data < bytes_written; ++pos_data) {
+        for (size_t pos_modified_data = 0; pos_modified_data < bytes_written; ++pos_data) {
             if (data[pos_data] == '\n')
                 pos_modified_data += 2;
             else
@@ -118,7 +119,7 @@ KResultOr<size_t> TTY::write(FileDescription&, u64, const UserOrKernelBuffer& bu
             if (pos_modified_data > bytes_written)
                 --pos_data;
         }
-        return (ssize_t)pos_data;
+        return pos_data;
     });
 }
 

Kernel/TTY/TTY.h

@@ -53,7 +53,7 @@ public:
     virtual mode_t required_mode() const override { return 0620; }
 
 protected:
-    virtual ssize_t on_tty_write(const UserOrKernelBuffer&, ssize_t) = 0;
+    virtual KResultOr<size_t> on_tty_write(const UserOrKernelBuffer&, size_t) = 0;
     void set_size(unsigned short columns, unsigned short rows);
 
     TTY(unsigned major, unsigned minor);

Kernel/TTY/VirtualConsole.cpp

@@ -265,7 +265,7 @@ void VirtualConsole::on_key_pressed(KeyEvent event)
     });
 }
 
-ssize_t VirtualConsole::on_tty_write(const UserOrKernelBuffer& data, ssize_t size)
+KResultOr<size_t> VirtualConsole::on_tty_write(const UserOrKernelBuffer& data, size_t size)
 {
     ScopedSpinLock global_lock(ConsoleManagement::the().tty_write_lock());
     ScopedSpinLock lock(m_lock);
@@ -276,9 +276,7 @@ ssize_t VirtualConsole::on_tty_write(const UserOrKernelBuffer& data, ssize_t siz
     });
     if (m_active)
         flush_dirty_lines();
-    if (result.is_error())
-        return result.error();
-    return (ssize_t)result.value();
+    return result;
 }
 
 void VirtualConsole::set_active(bool active)

Kernel/TTY/VirtualConsole.h

@@ -91,7 +91,7 @@ private:
     virtual void on_key_pressed(KeyEvent) override;
 
     // ^TTY
-    virtual ssize_t on_tty_write(const UserOrKernelBuffer&, ssize_t) override;
+    virtual KResultOr<size_t> on_tty_write(const UserOrKernelBuffer&, size_t) override;
     virtual String const& tty_name() const override { return m_tty_name; }
     virtual void echo(u8) override;
 

Kernel/UserOrKernelBuffer.h

@@ -133,12 +133,13 @@ public:
             auto to_copy = min(sizeof(buffer), len - nread);
             if (!read(buffer, nread, to_copy))
                 return EFAULT;
-            ssize_t copied = f(buffer, to_copy);
-            if (copied < 0)
-                return copied;
-            VERIFY((size_t)copied <= to_copy);
-            nread += (size_t)copied;
-            if ((size_t)copied < to_copy)
+            KResultOr<size_t> copied_or_error = f(buffer, to_copy);
+            if (copied_or_error.is_error())
+                return copied_or_error.error();
+            auto copied = copied_or_error.value();
+            VERIFY(copied <= to_copy);
+            nread += copied;
+            if (copied < to_copy)
                 break;
         }
         return nread;