kernel: Make the MBR code read from a device instead of an inode

kernel/src/arch/x86_64/disk/ATA.cpp

@@ -332,15 +332,16 @@ namespace ATA
                     return false;
                 }
 
-                if (ATADevice::create(m_drives[drive]).has_error())
+                auto rc = ATADevice::create(m_drives[drive]);
+
+                if (rc.has_error())
                 {
                     kwarnln("ata: Failed to register ATA drive %d:%d in DeviceRegistry", m_channel_index, drive);
                     continue;
                 }
 
-                // FIXME: Do not hardcode the path like this.
-                /* auto inode = VFS::resolve_path("/dev/cdrom", Credentials {}).value();
-                MBR::identify(inode); */
+                auto device = rc.release_value();
+                MBR::identify(device);
             }
         }
 
@@ -728,11 +729,12 @@ namespace ATA
 
 static u32 next_minor = 0;
 
-Result<void> ATADevice::create(SharedPtr<ATA::Drive> drive)
+Result<SharedPtr<Device>> ATADevice::create(SharedPtr<ATA::Drive> drive)
 {
     auto device = TRY(adopt_shared_if_nonnull(new (std::nothrow) ATADevice()));
     device->m_drive = drive;
-    return DeviceRegistry::register_special_device(DeviceRegistry::Disk, next_minor++, device, "cdrom", 0400);
+    TRY(DeviceRegistry::register_special_device(DeviceRegistry::Disk, next_minor++, device, "cdrom", 0400));
+    return (SharedPtr<Device>)device;
 }
 
 Result<u64> ATADevice::read(u8* buf, usize offset, usize size) const

kernel/src/fs/MBR.cpp

@@ -3,13 +3,13 @@
 
 namespace MBR
 {
-    Result<bool> identify(SharedPtr<VFS::Inode> inode)
+    Result<bool> identify(SharedPtr<Device> device)
     {
-        // Cannot read a partition table from a pipe/socket/character device! Who is even coming up with this silliness?
-        if (!VFS::is_seekable(inode)) return false;
+        // Cannot read a partition table from a character device! Who is even coming up with this silliness?
+        if (!device->is_block_device()) return false;
 
         DiskHeader hdr;
-        usize nread = TRY(inode->read((u8*)&hdr, 0, sizeof(hdr)));
+        usize nread = TRY(device->read((u8*)&hdr, 0, sizeof(hdr)));
         check(nread == 512);
 
         if (hdr.signature[0] != MBR_SIGNATURE_1 || hdr.signature[1] != MBR_SIGNATURE_2) return false;

kernel/src/fs/MBR.h

@@ -1,6 +1,6 @@
 #pragma once
 
-#include "fs/VFS.h"
+#include "fs/devices/DeviceRegistry.h"
 #include <luna/Types.h>
 
 #define MBR_BOOTABLE 0x80
@@ -31,5 +31,5 @@ namespace MBR
 
     static_assert(sizeof(DiskHeader) == 512ul);
 
-    Result<bool> identify(SharedPtr<VFS::Inode> inode);
+    Result<bool> identify(SharedPtr<Device> device);
 };