Kernel+LibC: Turn errno codes into a strongly typed enum

..and allow implicit creation of KResult and KResultOr from ErrnoCode.
This means that kernel functions that return those types can finally
do "return EINVAL;" and it will just work.

There's a handful of functions that still deal with signed integers
that should be converted to return KResults.

Kernel/Devices/BXVGADevice.cpp

@@ -179,12 +179,12 @@ KResultOr<Region*> BXVGADevice::mmap(Process& process, FileDescription&, Virtual
 {
     REQUIRE_PROMISE(video);
     if (!shared)
-        return KResult(-ENODEV);
+        return ENODEV;
     ASSERT(offset == 0);
     ASSERT(size == framebuffer_size_in_bytes());
     auto vmobject = AnonymousVMObject::create_for_physical_range(m_framebuffer_address, framebuffer_size_in_bytes());
     if (!vmobject)
-        return KResult(-ENOMEM);
+        return ENOMEM;
     return process.allocate_region_with_vmobject(
         preferred_vaddr,
         framebuffer_size_in_bytes(),

Kernel/Devices/FullDevice.cpp

@@ -50,7 +50,7 @@ KResultOr<size_t> FullDevice::read(FileDescription&, size_t, UserOrKernelBuffer&
 {
     ssize_t count = min(static_cast<size_t>(PAGE_SIZE), size);
     if (!buffer.memset(0, count))
-        return KResult(-EFAULT);
+        return EFAULT;
     return count;
 }
 
@@ -58,7 +58,7 @@ KResultOr<size_t> FullDevice::write(FileDescription&, size_t, const UserOrKernel
 {
     if (size == 0)
         return 0;
-    return KResult(-ENOSPC);
+    return ENOSPC;
 }
 
 }

Kernel/Devices/KeyboardDevice.cpp

@@ -386,7 +386,7 @@ KResultOr<size_t> KeyboardDevice::read(FileDescription&, size_t, UserOrKernelBuf
             return (ssize_t)data_bytes;
         });
         if (n < 0)
-            return KResult(n);
+            return KResult((ErrnoCode)-n);
         ASSERT((size_t)n == sizeof(Event));
         nread += sizeof(Event);
 

Kernel/Devices/MBVGADevice.cpp

@@ -55,12 +55,12 @@ KResultOr<Region*> MBVGADevice::mmap(Process& process, FileDescription&, Virtual
 {
     REQUIRE_PROMISE(video);
     if (!shared)
-        return KResult(-ENODEV);
+        return ENODEV;
     ASSERT(offset == 0);
     ASSERT(size == framebuffer_size_in_bytes());
     auto vmobject = AnonymousVMObject::create_for_physical_range(m_framebuffer_address, framebuffer_size_in_bytes());
     if (!vmobject)
-        return KResult(-ENOMEM);
+        return ENOMEM;
     return process.allocate_region_with_vmobject(
         preferred_vaddr,
         framebuffer_size_in_bytes(),

Kernel/Devices/PS2MouseDevice.cpp

@@ -288,7 +288,7 @@ KResultOr<size_t> PS2MouseDevice::read(FileDescription&, size_t, UserOrKernelBuf
 #endif
         size_t bytes_read_from_packet = min(remaining_space_in_buffer, sizeof(MousePacket));
         if (!buffer.write(&packet, nread, bytes_read_from_packet))
-            return KResult(-EFAULT);
+            return EFAULT;
         nread += bytes_read_from_packet;
         remaining_space_in_buffer -= bytes_read_from_packet;
 

Kernel/Devices/RandomDevice.cpp

@@ -50,7 +50,7 @@ KResultOr<size_t> RandomDevice::read(FileDescription&, size_t, UserOrKernelBuffe
         return (ssize_t)data_size;
     });
     if (!success)
-        return KResult(-EFAULT);
+        return EFAULT;
     return size;
 }
 

Kernel/Devices/SB16.cpp

@@ -236,11 +236,11 @@ KResultOr<size_t> SB16::write(FileDescription&, size_t, const UserOrKernelBuffer
     if (!m_dma_region) {
         auto page = MM.allocate_supervisor_physical_page();
         if (!page)
-            return KResult(-ENOMEM);
+            return ENOMEM;
         auto vmobject = AnonymousVMObject::create_with_physical_page(*page);
         m_dma_region = MM.allocate_kernel_region_with_vmobject(*vmobject, PAGE_SIZE, "SB16 DMA buffer", Region::Access::Write);
         if (!m_dma_region)
-            return KResult(-ENOMEM);
+            return ENOMEM;
     }
 
 #ifdef SB16_DEBUG
@@ -249,7 +249,7 @@ KResultOr<size_t> SB16::write(FileDescription&, size_t, const UserOrKernelBuffer
     ASSERT(length <= PAGE_SIZE);
     const int BLOCK_SIZE = 32 * 1024;
     if (length > BLOCK_SIZE) {
-        return KResult(-ENOSPC);
+        return ENOSPC;
     }
 
     u8 mode = (u8)SampleFormat::Signed | (u8)SampleFormat::Stereo;
@@ -257,7 +257,7 @@ KResultOr<size_t> SB16::write(FileDescription&, size_t, const UserOrKernelBuffer
     const int sample_rate = 44100;
     set_sample_rate(sample_rate);
     if (!data.read(m_dma_region->vaddr().as_ptr(), length))
-        return KResult(-EFAULT);
+        return EFAULT;
     dma_start(length);
 
     // 16-bit single-cycle output.

Kernel/Devices/SerialDevice.cpp

@@ -59,7 +59,7 @@ KResultOr<size_t> SerialDevice::read(FileDescription&, size_t, UserOrKernelBuffe
         return (ssize_t)data_size;
     });
     if (nwritten < 0)
-        return KResult(nwritten);
+        return KResult((ErrnoCode)-nwritten);
 
     return size;
 }
@@ -83,7 +83,7 @@ KResultOr<size_t> SerialDevice::write(FileDescription&, size_t, const UserOrKern
         return (ssize_t)data_size;
     });
     if (nread < 0)
-        return KResult(nread);
+        return KResult((ErrnoCode)-nread);
     return (size_t)nread;
 }
 

Kernel/Devices/ZeroDevice.cpp

@@ -48,7 +48,7 @@ KResultOr<size_t> ZeroDevice::read(FileDescription&, size_t, UserOrKernelBuffer&
 {
     ssize_t count = min(static_cast<size_t>(PAGE_SIZE), size);
     if (!buffer.memset(0, count))
-        return KResult(-EFAULT);
+        return EFAULT;
     return count;
 }