Kernel: SYS_SYNC now schedules sync to happen soon

You can pass non-zero argument to the syscall to block until the
sync has finished.

kernel/include/kernel/FS/DevFS/FileSystem.h

@@ -2,6 +2,7 @@
 
 #include <kernel/Device/Device.h>
 #include <kernel/FS/RamFS/FileSystem.h>
+#include <kernel/Semaphore.h>
 
 namespace Kernel
 {
@@ -19,6 +20,8 @@ namespace Kernel
 
 		dev_t get_next_dev();
 
+		void initiate_sync(bool should_block);
+
 	private:
 		DevFileSystem(size_t size)
 			: RamFileSystem(size)
@@ -26,6 +29,10 @@ namespace Kernel
 
 	private:
 		SpinLock m_device_lock;
+
+		Semaphore m_sync_done;
+		Semaphore m_sync_semaphore;
+		volatile bool m_should_sync { false };
 	};
 
 }

kernel/include/kernel/Process.h

@@ -109,7 +109,7 @@ namespace Kernel
 		BAN::ErrorOr<long> sys_fstatat(int fd, const char* path, struct stat* buf, int flag);
 		BAN::ErrorOr<long> sys_stat(const char* path, struct stat* buf, int flag);
 
-		BAN::ErrorOr<long> sys_sync();
+		BAN::ErrorOr<long> sys_sync(bool should_block);
 
 		BAN::ErrorOr<void> mount(BAN::StringView source, BAN::StringView target);
 

kernel/kernel/FS/DevFS/FileSystem.cpp

@@ -5,6 +5,7 @@
 #include <kernel/FS/RamFS/Inode.h>
 #include <kernel/LockGuard.h>
 #include <kernel/Process.h>
+#include <kernel/Storage/StorageDevice.h>
 #include <kernel/Timer/Timer.h>
 
 namespace Kernel
@@ -53,6 +54,67 @@ namespace Kernel
 				}
 			}, nullptr
 		);
+
+		auto* sync_process = Process::create_kernel();
+
+		sync_process->add_thread(MUST(Thread::create_kernel(
+			[](void*)
+			{
+				// NOTE: we lock the device lock here and unlock
+				//       it only while semaphore is blocking
+				s_instance->m_device_lock.lock();
+
+				while (true)
+				{
+					while (!s_instance->m_should_sync)
+					{
+						s_instance->m_device_lock.unlock();
+						s_instance->m_sync_semaphore.block();
+						s_instance->m_device_lock.lock();
+					}
+
+					s_instance->for_each_inode(
+						[](BAN::RefPtr<RamInode> inode)
+						{
+							if (inode->is_device())
+								if (((Device*)inode.ptr())->is_storage_device())
+									if (auto ret = ((StorageDevice*)inode.ptr())->sync_disk_cache(); ret.is_error())
+										dwarnln("disk sync: {}", ret.error());
+							return BAN::Iteration::Continue;
+						}
+					);
+					s_instance->m_should_sync = false;
+					s_instance->m_sync_done.unblock();
+				}
+			}, nullptr, sync_process
+		)));
+
+		sync_process->add_thread(MUST(Kernel::Thread::create_kernel(
+			[](void*)
+			{
+				while (true)
+				{
+					SystemTimer::get().sleep(10000);
+
+					LockGuard _(s_instance->m_device_lock);
+					s_instance->m_should_sync = true;
+					s_instance->m_sync_semaphore.unblock();
+				}
+			}, nullptr, sync_process
+		)));
+
+		sync_process->register_to_scheduler();
+	}
+
+	void DevFileSystem::initiate_sync(bool should_block)
+	{
+		{
+			LockGuard _(m_device_lock);
+			m_should_sync = true;
+			m_sync_semaphore.unblock();
+		}
+		if (should_block)
+			m_sync_done.block();
 	}
 
 	void DevFileSystem::add_device(BAN::StringView path, BAN::RefPtr<RamInode> device)

kernel/kernel/Process.cpp

@@ -767,22 +767,10 @@ namespace Kernel
 		return 0;
 	}
 
-	BAN::ErrorOr<long> Process::sys_sync()
+	BAN::ErrorOr<long> Process::sys_sync(bool should_block)
 	{
-		BAN::ErrorOr<long> ret = 0;
-		DevFileSystem::get().for_each_device(
-			[&](Device* device)
-			{
-				if (device->is_storage_device())
-				{
-					auto success = ((StorageDevice*)device)->sync_disk_cache();
-					if (success.is_error())
-						ret = success.release_error();
-				}
-				return BAN::Iteration::Continue;
-			}
-		);
-		return ret;
+		DevFileSystem::get().initiate_sync(should_block);
+		return 0;
 	}
 
 	BAN::ErrorOr<long> Process::sys_read_dir_entries(int fd, DirectoryEntryList* list, size_t list_size)

kernel/kernel/Syscall.cpp

@@ -185,7 +185,7 @@ namespace Kernel
 			ret = Process::current().sys_stat((const char*)arg1, (struct stat*)arg2, (int)arg3);
 			break;
 		case SYS_SYNC:
-			ret = Process::current().sys_sync();
+			ret = Process::current().sys_sync((bool)arg1);
 			break;
 		case SYS_MMAP:
 			ret = Process::current().sys_mmap((const sys_mmap_t*)arg1);