Kernel/LibC: Implement flock

kernel/include/kernel/OpenFileDescriptorSet.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <BAN/Array.h>
+#include <BAN/HashSet.h>
 #include <kernel/FS/Inode.h>
 #include <kernel/FS/VirtualFileSystem.h>
 
@@ -43,6 +44,8 @@ namespace Kernel
 		void close_all();
 		void close_cloexec();
 
+		BAN::ErrorOr<void> flock(int fd, int op);
+
 		BAN::ErrorOr<size_t> read(int fd, BAN::ByteSpan);
 		BAN::ErrorOr<size_t> write(int fd, BAN::ConstByteSpan);
 
@@ -69,6 +72,15 @@ namespace Kernel
 			off_t offset { 0 };
 			int status_flags;
 
+			struct flock_t
+			{
+				bool locked;
+				bool shared;
+				ThreadBlocker thread_blocker;
+				BAN::HashSet<pid_t> lockers;
+			};
+			flock_t flock;
+
 			friend class BAN::RefPtr<OpenFileDescription>;
 		};
 

kernel/include/kernel/Process.h

@@ -112,6 +112,8 @@ namespace Kernel
 
 		BAN::ErrorOr<long> sys_symlinkat(const char* path1, int fd, const char* path2);
 
+		BAN::ErrorOr<long> sys_flock(int fd, int op);
+
 		BAN::ErrorOr<long> sys_pread(int fd, void* buffer, size_t count, off_t offset);
 		BAN::ErrorOr<long> sys_pwrite(int fd, const void* buffer, size_t count, off_t offset);
 

kernel/kernel/OpenFileDescriptorSet.cpp

@@ -5,6 +5,7 @@
 #include <kernel/OpenFileDescriptorSet.h>
 
 #include <fcntl.h>
+#include <sys/file.h>
 #include <sys/socket.h>
 
 namespace Kernel
@@ -310,6 +311,17 @@ namespace Kernel
 		TRY(validate_fd(fd));
 
 		auto& open_file = m_open_files[fd];
+
+		if (auto& flock = open_file.description->flock; Thread::current().has_process() && flock.lockers.contains(Process::current().pid()))
+		{
+			flock.lockers.remove(Process::current().pid());
+			if (flock.lockers.empty())
+			{
+				flock.locked = false;
+				flock.thread_blocker.unblock();
+			}
+		}
+
 		open_file.inode()->on_close(open_file.status_flags());
 		open_file.description.clear();
 		open_file.descriptor_flags = 0;
@@ -336,6 +348,63 @@ namespace Kernel
 		}
 	}
 
+	BAN::ErrorOr<void> OpenFileDescriptorSet::flock(int fd, int op)
+	{
+		const auto pid = Process::current().pid();
+
+		LockGuard _(m_mutex);
+
+		for (;;)
+		{
+			TRY(validate_fd(fd));
+
+			auto& flock = m_open_files[fd].description->flock;
+			switch (op & ~LOCK_NB)
+			{
+				case LOCK_UN:
+					flock.lockers.remove(pid);
+					if (flock.lockers.empty())
+					{
+						flock.locked = false;
+						flock.thread_blocker.unblock();
+					}
+					return {};
+				case LOCK_SH:
+					if (!flock.locked)
+					{
+						TRY(flock.lockers.insert(pid));
+						flock.locked = true;
+						flock.shared = true;
+						return {};
+					}
+					if (flock.shared)
+					{
+						TRY(flock.lockers.insert(pid));
+						return {};
+					}
+					break;
+				case LOCK_EX:
+					if (!flock.locked)
+					{
+						TRY(flock.lockers.insert(pid));
+						flock.locked = true;
+						flock.shared = false;
+						return {};
+					}
+					if (flock.lockers.contains(pid))
+						return {};
+					break;
+				default:
+					return BAN::Error::from_errno(EINVAL);
+			}
+
+			if (op & LOCK_NB)
+				return BAN::Error::from_errno(EWOULDBLOCK);
+
+			TRY(Thread::current().block_or_eintr_indefinite(flock.thread_blocker, &m_mutex));
+		}
+	}
+
 	BAN::ErrorOr<size_t> OpenFileDescriptorSet::read(int fd, BAN::ByteSpan buffer)
 	{
 		BAN::RefPtr<Inode> inode;

kernel/kernel/Process.cpp

@@ -1208,6 +1208,16 @@ namespace Kernel
 		return 0;
 	}
 
+	BAN::ErrorOr<long> Process::sys_flock(int fd, int op)
+	{
+		auto maybe_error = m_open_file_descriptors.flock(fd, op);
+		if (maybe_error.is_error() && maybe_error.error().get_error_code() == ENOMEM)
+			return BAN::Error::from_errno(ENOLCK);
+		if (maybe_error.is_error())
+			return maybe_error.error();
+		return 0;
+	}
+
 	BAN::ErrorOr<long> Process::sys_pread(int fd, void* buffer, size_t count, off_t offset)
 	{
 		auto inode = TRY(m_open_file_descriptors.inode_of(fd));

userspace/libraries/LibC/CMakeLists.txt

@@ -33,6 +33,7 @@ set(LIBC_SOURCES
 	strings.cpp
 	sys/banan-os.cpp
 	sys/epoll.cpp
+	sys/file.cpp
 	sys/ioctl.cpp
 	sys/mman.cpp
 	sys/resource.cpp

userspace/libraries/LibC/include/sys/file.h

@@ -0,0 +1,17 @@
+#ifndef _SYS_FILE_H
+#define _SYS_FILE_H 1
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+#define LOCK_UN 0
+#define LOCK_EX 1
+#define LOCK_SH 2
+#define LOCK_NB 4
+
+int flock(int fd, int op);
+
+__END_DECLS
+
+#endif

userspace/libraries/LibC/include/sys/syscall.h

@@ -107,6 +107,7 @@ __BEGIN_DECLS
 	O(SYS_EPOLL_CREATE1,	epoll_create1)	\
 	O(SYS_EPOLL_CTL,		epoll_ctl)		\
 	O(SYS_EPOLL_PWAIT2,		epoll_pwait2)	\
+	O(SYS_FLOCK,			flock)			\
 
 enum Syscall
 {

userspace/libraries/LibC/sys/file.cpp

@@ -0,0 +1,8 @@
+#include <sys/file.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+int flock(int fd, int op)
+{
+	return syscall(SYS_FLOCK, fd, op);
+}