Kernel: mount system call (#396)

It is now possible to mount ext2 `DiskDevice` devices under Serenity on
any folder in the root filesystem. Currently any user can do this with
any permissions. There's a fair amount of assumptions made here too,
that might not be too good, but can be worked on in the future. This is
a good start to allow more dynamic operation under the OS itself.

It is also currently impossible to unmount and such, and devices will
fail to mount in Linux as the FS 'needs to be cleaned'. I'll work on
getting `umount` done ASAP to rectify this (as well as working on less
assumption-making in the mount syscall. We don't want to just be able
to mount DiskDevices!). This could probably be fixed with some `-t`
flag or something similar.

Kernel/Devices/Device.h

@@ -25,6 +25,7 @@ public:
     uid_t gid() const { return m_gid; }
 
     virtual bool is_device() const override { return true; }
+    virtual bool is_disk_device() const { return false; }
 
 protected:
     Device(unsigned major, unsigned minor);

Kernel/Devices/DiskDevice.cpp

@@ -1,6 +1,7 @@
 #include <Kernel/Devices/DiskDevice.h>
 
-DiskDevice::DiskDevice()
+DiskDevice::DiskDevice(int major, int minor)
+    : BlockDevice(major, minor)
 {
 }
 

Kernel/Devices/DiskDevice.h

@@ -2,11 +2,12 @@
 
 #include <AK/RefCounted.h>
 #include <AK/Types.h>
+#include <Kernel/Devices/BlockDevice.h>
 
 // FIXME: Support 64-bit DiskOffset
 typedef u32 DiskOffset;
 
-class DiskDevice : public RefCounted<DiskDevice> {
+class DiskDevice : public BlockDevice {
 public:
     virtual ~DiskDevice();
 
@@ -20,6 +21,8 @@ public:
     virtual bool read_blocks(unsigned index, u16 count, u8*) = 0;
     virtual bool write_blocks(unsigned index, u16 count, const u8*) = 0;
 
+    virtual bool is_disk_device() const override { return true; };
+
 protected:
-    DiskDevice();
+    DiskDevice(int major, int minor);
 };

Kernel/Devices/DiskPartition.cpp

@@ -8,7 +8,8 @@ NonnullRefPtr<DiskPartition> DiskPartition::create(NonnullRefPtr<DiskDevice> dev
 }
 
 DiskPartition::DiskPartition(NonnullRefPtr<DiskDevice> device, unsigned block_offset)
-    : m_device(move(device))
+    : DiskDevice(100, 0)
+    , m_device(move(device))
     , m_block_offset(block_offset)
 {
 }

Kernel/Devices/DiskPartition.h

@@ -14,6 +14,12 @@ public:
     virtual bool read_blocks(unsigned index, u16 count, u8*) override;
     virtual bool write_blocks(unsigned index, u16 count, const u8*) override;
 
+    // ^BlockDevice
+    virtual ssize_t read(FileDescription&, u8*, ssize_t) override { return 0; }
+    virtual bool can_read(FileDescription&) const override { return true; }
+    virtual ssize_t write(FileDescription&, const u8*, ssize_t) override { return 0; }
+    virtual bool can_write(FileDescription&) const override { return true; }
+
 private:
     virtual const char* class_name() const override;
 

Kernel/Devices/FloppyDiskDevice.cpp

@@ -84,6 +84,7 @@ const char* FloppyDiskDevice::class_name() const
 
 FloppyDiskDevice::FloppyDiskDevice(FloppyDiskDevice::DriveType type)
     : IRQHandler(IRQ_FLOPPY_DRIVE)
+    , DiskDevice(89, (type == FloppyDiskDevice::DriveType::Master) ? 0 : 1)
     , m_io_base_addr((type == FloppyDiskDevice::DriveType::Master) ? 0x3F0 : 0x370)
 {
     initialize();

Kernel/Devices/FloppyDiskDevice.h

@@ -132,7 +132,7 @@ private:
     };
 
 public:
-    static NonnullRefPtr<FloppyDiskDevice> create(DriveType type);
+    static NonnullRefPtr<FloppyDiskDevice> create(DriveType);
     virtual ~FloppyDiskDevice() override;
 
     // ^DiskDevice
@@ -142,6 +142,12 @@ public:
     virtual bool read_blocks(unsigned index, u16 count, u8*) override;
     virtual bool write_blocks(unsigned index, u16 count, const u8*) override;
 
+    // ^BlockDevice
+    virtual ssize_t read(FileDescription&, u8*, ssize_t) override { return 0; }
+    virtual bool can_read(FileDescription&) const override { return true; }
+    virtual ssize_t write(FileDescription&, const u8*, ssize_t) override { return 0; }
+    virtual bool can_write(FileDescription&) const override { return true; }
+
 protected:
     explicit FloppyDiskDevice(DriveType);
 

Kernel/Devices/PATAChannel.cpp

@@ -236,11 +236,12 @@ void PATAChannel::detect_disks()
             heads,
             spt);
 
+        int major = (m_channel_number == 0) ? 3 : 4;
         if (i == 0) {
-            m_master = PATADiskDevice::create(*this, PATADiskDevice::DriveType::Master);
+            m_master = PATADiskDevice::create(*this, PATADiskDevice::DriveType::Master, major, 0);
             m_master->set_drive_geometry(cyls, heads, spt);
         } else {
-            m_slave = PATADiskDevice::create(*this, PATADiskDevice::DriveType::Slave);
+            m_slave = PATADiskDevice::create(*this, PATADiskDevice::DriveType::Slave, major, 1);
             m_slave->set_drive_geometry(cyls, heads, spt);
         }
     }

Kernel/Devices/PATADiskDevice.cpp

@@ -78,13 +78,14 @@
 #define ATA_REG_ALTSTATUS 0x0C
 #define ATA_REG_DEVADDRESS 0x0D
 
-NonnullRefPtr<PATADiskDevice> PATADiskDevice::create(PATAChannel& channel, DriveType type)
+NonnullRefPtr<PATADiskDevice> PATADiskDevice::create(PATAChannel& channel, DriveType type, int major, int minor)
 {
-    return adopt(*new PATADiskDevice(channel, type));
+    return adopt(*new PATADiskDevice(channel, type, major, minor));
 }
 
-PATADiskDevice::PATADiskDevice(PATAChannel& channel, DriveType type)
-    : m_drive_type(type)
+PATADiskDevice::PATADiskDevice(PATAChannel& channel, DriveType type, int major, int minor)
+    : DiskDevice(major, minor)
+    , m_drive_type(type)
     , m_channel(channel)
 {
 }

Kernel/Devices/PATADiskDevice.h

@@ -26,7 +26,7 @@ public:
     };
 
 public:
-    static NonnullRefPtr<PATADiskDevice> create(PATAChannel&, DriveType);
+    static NonnullRefPtr<PATADiskDevice> create(PATAChannel&, DriveType, int major, int minor);
     virtual ~PATADiskDevice() override;
 
     // ^DiskDevice
@@ -38,8 +38,14 @@ public:
 
     void set_drive_geometry(u16, u16, u16);
 
+    // ^BlockDevice
+    virtual ssize_t read(FileDescription&, u8*, ssize_t) override { return 0; }
+    virtual bool can_read(FileDescription&) const override { return true; }
+    virtual ssize_t write(FileDescription&, const u8*, ssize_t) override { return 0; }
+    virtual bool can_write(FileDescription&) const override { return true; }
+
 protected:
-    explicit PATADiskDevice(PATAChannel&, DriveType);
+    explicit PATADiskDevice(PATAChannel&, DriveType, int, int);
 
 private:
     // ^DiskDevice