Kernel+LibC: Implement fsync

Author: https://github.com/SeekingBlues
Commit: https://github.com/SerenityOS/serenity/commit/a81b21c1a7f
Pull-request: https://github.com/SerenityOS/serenity/pull/9983

Kernel/API/Syscall.h

@@ -79,6 +79,7 @@ enum class NeedsBigProcessLock {
     S(fork, NeedsBigProcessLock::Yes)                       \
     S(fstat, NeedsBigProcessLock::Yes)                      \
     S(fstatvfs, NeedsBigProcessLock::Yes)                   \
+    S(fsync, NeedsBigProcessLock::Yes)                      \
     S(ftruncate, NeedsBigProcessLock::Yes)                  \
     S(futex, NeedsBigProcessLock::Yes)                      \
     S(get_dir_entries, NeedsBigProcessLock::Yes)            \

Kernel/CMakeLists.txt

@@ -204,6 +204,7 @@ set(KERNEL_SOURCES
     Syscalls/exit.cpp
     Syscalls/fcntl.cpp
     Syscalls/fork.cpp
+    Syscalls/fsync.cpp
     Syscalls/ftruncate.cpp
     Syscalls/futex.cpp
     Syscalls/get_dir_entries.cpp

Kernel/FileSystem/File.h

@@ -96,6 +96,7 @@ public:
     virtual String absolute_path(const OpenFileDescription&) const = 0;
 
     virtual KResult truncate(u64) { return EINVAL; }
+    virtual KResult sync() { return EINVAL; }
     virtual KResult chown(OpenFileDescription&, UserID, GroupID) { return EBADF; }
     virtual KResult chmod(OpenFileDescription&, mode_t) { return EBADF; }
 

Kernel/FileSystem/FileSystem.cpp

@@ -51,7 +51,7 @@ FileSystem::DirectoryEntryView::DirectoryEntryView(const StringView& n, InodeIde
 
 void FileSystem::sync()
 {
-    Inode::sync();
+    Inode::sync_all();
 
     NonnullRefPtrVector<FileSystem, 32> file_systems;
     {

Kernel/FileSystem/Inode.cpp

@@ -29,7 +29,7 @@ SpinlockProtected<Inode::AllInstancesList>& Inode::all_instances()
     return s_all_instances;
 }
 
-void Inode::sync()
+void Inode::sync_all()
 {
     NonnullRefPtrVector<Inode, 32> inodes;
     Inode::all_instances().with([&](auto& all_inodes) {
@@ -45,6 +45,13 @@ void Inode::sync()
     }
 }
 
+void Inode::sync()
+{
+    if (is_metadata_dirty())
+        flush_metadata();
+    fs().flush_writes();
+}
+
 KResultOr<NonnullOwnPtr<KBuffer>> Inode::read_entire(OpenFileDescription* description) const
 {
     auto builder = TRY(KBufferBuilder::try_create());

Kernel/FileSystem/Inode.h

@@ -87,7 +87,8 @@ public:
     void set_shared_vmobject(Memory::SharedInodeVMObject&);
     RefPtr<Memory::SharedInodeVMObject> shared_vmobject() const;
 
-    static void sync();
+    static void sync_all();
+    void sync();
 
     bool has_watchers() const { return !m_watchers.is_empty(); }
 

Kernel/FileSystem/InodeFile.cpp

@@ -107,6 +107,12 @@ KResult InodeFile::truncate(u64 size)
     return KSuccess;
 }
 
+KResult InodeFile::sync()
+{
+    m_inode->sync();
+    return KSuccess;
+}
+
 KResult InodeFile::chown(OpenFileDescription& description, UserID uid, GroupID gid)
 {
     VERIFY(description.inode() == m_inode);

Kernel/FileSystem/InodeFile.h

@@ -39,6 +39,7 @@ public:
     virtual String absolute_path(const OpenFileDescription&) const override;
 
     virtual KResult truncate(u64) override;
+    virtual KResult sync() override;
     virtual KResult chown(OpenFileDescription&, UserID, GroupID) override;
     virtual KResult chmod(OpenFileDescription&, mode_t) override;
 

Kernel/FileSystem/OpenFileDescription.cpp

@@ -383,6 +383,12 @@ KResult OpenFileDescription::truncate(u64 length)
     return m_file->truncate(length);
 }
 
+KResult OpenFileDescription::sync()
+{
+    MutexLocker locker(m_lock);
+    return m_file->sync();
+}
+
 bool OpenFileDescription::is_fifo() const
 {
     return m_file->is_fifo();

Kernel/FileSystem/OpenFileDescription.h

@@ -122,6 +122,7 @@ public:
     void set_original_custody(Badge<VirtualFileSystem>, Custody& custody);
 
     KResult truncate(u64);
+    KResult sync();
 
     off_t offset() const { return m_current_offset; }
 

Kernel/Process.h

@@ -363,6 +363,7 @@ public:
     KResultOr<FlatPtr> sys$fchmod(int fd, mode_t);
     KResultOr<FlatPtr> sys$chown(Userspace<const Syscall::SC_chown_params*>);
     KResultOr<FlatPtr> sys$fchown(int fd, UserID, GroupID);
+    KResultOr<FlatPtr> sys$fsync(int fd);
     KResultOr<FlatPtr> sys$socket(int domain, int type, int protocol);
     KResultOr<FlatPtr> sys$bind(int sockfd, Userspace<const sockaddr*> addr, socklen_t);
     KResultOr<FlatPtr> sys$listen(int sockfd, int backlog);

Kernel/Syscalls/fsync.cpp

@@ -0,0 +1,19 @@
+/*
+ * Copyright (c) 2021, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/Process.h>
+
+namespace Kernel {
+
+KResultOr<FlatPtr> Process::sys$fsync(int fd)
+{
+    VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this);
+    REQUIRE_PROMISE(stdio);
+    auto description = TRY(fds().open_file_description(fd));
+    return description->sync();
+}
+
+}

Userland/Libraries/LibC/unistd.cpp

@@ -709,10 +709,10 @@ void sysbeep()
     syscall(SC_beep);
 }
 
-int fsync([[maybe_unused]] int fd)
+int fsync(int fd)
 {
-    dbgln("FIXME: Implement fsync()");
-    return 0;
+    int rc = syscall(SC_fsync, fd);
+    __RETURN_WITH_ERRNO(rc, rc, -1);
 }
 
 int halt()