Kernel: Wait 10 seconds to find root device

If root device is initialized asynchronously it may not be ready when
main initialization thread is finished. This patch adds searching for
root device every 500 ms for 10 seconds.

bootloader/bios/command_line.S

@@ -83,5 +83,5 @@ command_line_enter_msg:
 command_line:
 # 100 character command line
 command_line_buffer:
-	.ascii "root=/dev/sda2"
-	.skip 100 - 28
+	.ascii "root=UUID=9C87D2AF-566A-4517-971A-57BA86EEA88D"
+	.skip 100 - (. - command_line_buffer)

kernel/kernel/FS/VirtualFileSystem.cpp

@@ -6,6 +6,7 @@
 #include <kernel/FS/VirtualFileSystem.h>
 #include <kernel/Lock/LockGuard.h>
 #include <kernel/Storage/Partition.h>
+#include <kernel/Timer/Timer.h>
 
 #include <fcntl.h>
 
@@ -14,21 +15,13 @@ namespace Kernel
 
 	static BAN::RefPtr<VirtualFileSystem> s_instance;
 
-	void VirtualFileSystem::initialize(BAN::StringView root_path)
+	static BAN::ErrorOr<BAN::RefPtr<BlockDevice>> find_partition_by_uuid(BAN::StringView uuid)
 	{
-		ASSERT(!s_instance);
-		s_instance = MUST(BAN::RefPtr<VirtualFileSystem>::create());
+		ASSERT(uuid.size() == 36);
 
-		BAN::RefPtr<BlockDevice> root_device;
-		if (root_path.size() >= 5 && root_path.substring(0, 5) == "UUID="_sv)
-		{
-			auto uuid = root_path.substring(5);
-			if (uuid.size() != 36)
-				panic("Invalid UUID specified for root '{}'", uuid);
-
-			BAN::RefPtr<Partition> root_partition;
+		BAN::RefPtr<BlockDevice> result;
 		DevFileSystem::get().for_each_inode(
-				[&root_partition, uuid](BAN::RefPtr<Inode> inode) -> BAN::Iteration
+			[&result, uuid](BAN::RefPtr<Inode> inode) -> BAN::Iteration
 			{
 				if (!inode->is_device())
 					return BAN::Iteration::Continue;
@@ -37,33 +30,91 @@ namespace Kernel
 				auto* partition = static_cast<Partition*>(inode.ptr());
 				if (partition->uuid() != uuid)
 					return BAN::Iteration::Continue;
-					root_partition = partition;
+				result = partition;
 				return BAN::Iteration::Break;
 			}
 		);
-			if (!root_partition)
-				panic("Could not find partition with UUID '{}'", uuid);
-			root_device = root_partition;
+
+		if (!result)
+			return BAN::Error::from_errno(ENOENT);
+		return result;
+	}
+
+	static BAN::ErrorOr<BAN::RefPtr<BlockDevice>> find_block_device_by_name(BAN::StringView name)
+	{
+		auto device_inode = TRY(DevFileSystem::get().root_inode()->find_inode(name));
+		if (!device_inode->mode().ifblk())
+			return BAN::Error::from_errno(ENOTBLK);
+		return BAN::RefPtr<BlockDevice>(static_cast<BlockDevice*>(device_inode.ptr()));
+	}
+
+	static BAN::RefPtr<BlockDevice> find_root_device(BAN::StringView root_path)
+	{
+		enum class RootType
+		{
+			PartitionUUID,
+			BlockDeviceName,
+		};
+
+		BAN::StringView entry;
+		RootType type;
+
+		if (root_path.size() >= 5 && root_path.substring(0, 5) == "UUID="_sv)
+		{
+			entry = root_path.substring(5);
+			if (entry.size() != 36)
+				panic("Invalid UUID '{}'", entry);
+			type = RootType::PartitionUUID;
 		}
 		else if (root_path.size() >= 5 && root_path.substring(0, 5) == "/dev/"_sv)
 		{
-			auto device_name = root_path.substring(5);
-
-			auto device_result = DevFileSystem::get().root_inode()->find_inode(device_name);
-			if (device_result.is_error())
-				panic("Could not open root device '{}': {}", root_path, device_result.error());
-
-			auto device_inode = device_result.release_value();
-			if (!device_inode->mode().ifblk())
-				panic("Root inode '{}' is not an block device", root_path);
-
-			root_device = static_cast<BlockDevice*>(device_inode.ptr());
+			entry = root_path.substring(5);
+			if (entry.empty() || entry.contains('/'))
+				panic("Invalid root path '{}'", root_path);
+			type = RootType::BlockDeviceName;
 		}
 		else
 		{
-			panic("Unknown root path format '{}' specified", root_path);
+			panic("Unsupported root path format '{}'", root_path);
 		}
 
+		constexpr size_t timeout_ms = 10'000;
+		constexpr size_t sleep_ms = 500;
+
+		for (size_t i = 0; i < timeout_ms / sleep_ms; i++)
+		{
+			BAN::ErrorOr<BAN::RefPtr<BlockDevice>> ret = BAN::Error::from_errno(EINVAL);
+
+			switch (type)
+			{
+				case RootType::PartitionUUID:
+					ret = find_partition_by_uuid(entry);
+					break;
+				case RootType::BlockDeviceName:
+					ret = find_block_device_by_name(entry);
+					break;
+			}
+
+			if (!ret.is_error())
+				return ret.release_value();
+
+			if (ret.error().get_error_code() != ENOENT)
+				panic("could not open root device '{}': {}", root_path, ret.error());
+
+			SystemTimer::get().sleep_ms(sleep_ms);
+		}
+
+		panic("could not find root device '{}' after {} ms", root_path, timeout_ms);
+	}
+
+	void VirtualFileSystem::initialize(BAN::StringView root_path)
+	{
+		ASSERT(!s_instance);
+		s_instance = MUST(BAN::RefPtr<VirtualFileSystem>::create());
+
+		auto root_device = find_root_device(root_path);
+		ASSERT(root_device);
+
 		auto filesystem_result = FileSystem::from_block_device(root_device);
 		if (filesystem_result.is_error())
 			panic("Could not create filesystem from '{}': {}", root_path, filesystem_result.error());