Kernel/Devices: Introduce the Device Control Device

This device will assist userspace to manage hotplug events.
A userspace application reads a DeviceEvent entry until the return value
is zero which indicates no events that are queued and waiting for
processing.
Trying to read with a buffer smaller than sizeof(DeviceEvent) results in
EOVERFLOW.
For now, there's no ioctl mechanism for this device but in the future an
acknowledgement mechanism can be implemented via ioctl(2) interface.

1 files changed, 29 insertions, 0 deletions

diff --git a/Kernel/Devices/DeviceManagement.cpp b/Kernel/Devices/DeviceManagement.cpp
index 5f68d1cfb4..3315c80e21 100644
--- a/Kernel/Devices/DeviceManagement.cpp
+++ b/Kernel/Devices/DeviceManagement.cpp
@@ -37,6 +37,11 @@ UNMAP_AFTER_INIT void DeviceManagement::attach_null_device(NullDevice const& dev
     m_null_device = device;
 }
 
+UNMAP_AFTER_INIT void DeviceManagement::attach_device_control_device(DeviceControlDevice const& device)
+{
+    m_device_control_device = device;
+}
+
 DeviceManagement& DeviceManagement::the()
 {
     return *s_the;
@@ -52,6 +57,14 @@ Device* DeviceManagement::get_device(MajorNumber major, MinorNumber minor)
     });
 }
 
+Optional<DeviceEvent> DeviceManagement::dequeue_top_device_event(Badge<DeviceControlDevice>)
+{
+    SpinlockLocker locker(m_event_queue_lock);
+    if (m_event_queue.is_empty())
+        return {};
+    return m_event_queue.dequeue();
+}
+
 void DeviceManagement::before_device_removal(Badge<Device>, Device& device)
 {
     u64 device_id = encoded_device(device.major(), device.minor());
@@ -59,6 +72,14 @@ void DeviceManagement::before_device_removal(Badge<Device>, Device& device)
         VERIFY(map.contains(device_id));
         map.remove(encoded_device(device.major(), device.minor()));
     });
+
+    {
+        DeviceEvent event { DeviceEvent::State::Removed, device.is_block_device(), device.major().value(), device.minor().value() };
+        SpinlockLocker locker(m_event_queue_lock);
+        m_event_queue.enqueue(event);
+    }
+    if (m_device_control_device)
+        m_device_control_device->evaluate_block_conditions();
 }
 
 void DeviceManagement::after_inserting_device(Badge<Device>, Device& device)
@@ -75,6 +96,14 @@ void DeviceManagement::after_inserting_device(Badge<Device>, Device& device)
             VERIFY_NOT_REACHED();
         }
     });
+
+    {
+        DeviceEvent event { DeviceEvent::State::Inserted, device.is_block_device(), device.major().value(), device.minor().value() };
+        SpinlockLocker locker(m_event_queue_lock);
+        m_event_queue.enqueue(event);
+    }
+    if (m_device_control_device)
+        m_device_control_device->evaluate_block_conditions();
 }
 
 void DeviceManagement::for_each(Function<void(Device&)> callback)