Kernel: Move setting file flags and r/w mode to VFS::open()

Previously, VFS::open() would only use the passed flags for permission checking
purposes, and Process::sys$open() would set them on the created FileDescription
explicitly. Now, they should be set by VFS::open() on any files being opened,
including files that the kernel opens internally.

This also lets us get rid of the explicit check for whether or not the returned
FileDescription was a preopen fd, and in fact, fixes a bug where a read-only
preopen fd without any other flags would be considered freshly opened (due to
O_RDONLY being indistinguishable from 0) and granted a new set of flags.

Kernel/FileSystem/File.cpp

@@ -39,6 +39,7 @@ KResultOr<NonnullRefPtr<FileDescription>> File::open(int options)
 {
     auto description = FileDescription::create(*this);
     description->set_rw_mode(options);
+    description->set_file_flags(options);
     return description;
 }
 

Kernel/FileSystem/VirtualFileSystem.cpp

@@ -277,7 +277,10 @@ KResultOr<NonnullRefPtr<FileDescription>> VFS::open(StringView path, int options
         inode.truncate(0);
         inode.set_mtime(kgettimeofday().tv_sec);
     }
-    return FileDescription::create(custody);
+    auto description = FileDescription::create(custody);
+    description->set_rw_mode(options);
+    description->set_file_flags(options);
+    return description;
 }
 
 KResult VFS::mknod(StringView path, mode_t mode, dev_t dev, Custody& base)
@@ -309,8 +312,6 @@ KResult VFS::mknod(StringView path, mode_t mode, dev_t dev, Custody& base)
 
 KResultOr<NonnullRefPtr<FileDescription>> VFS::create(StringView path, int options, mode_t mode, Custody& parent_custody, Optional<UidAndGid> owner)
 {
-    (void)options;
-
     if (!is_socket(mode) && !is_fifo(mode) && !is_block_device(mode) && !is_character_device(mode)) {
         // Turn it into a regular file. (This feels rather hackish.)
         mode |= 0100000;
@@ -332,7 +333,10 @@ KResultOr<NonnullRefPtr<FileDescription>> VFS::create(StringView path, int optio
         return KResult(error);
 
     auto new_custody = Custody::create(&parent_custody, p.basename(), *new_file, parent_custody.mount_flags());
-    return FileDescription::create(*new_custody);
+    auto description = FileDescription::create(*new_custody);
+    description->set_rw_mode(options);
+    description->set_file_flags(options);
+    return description;
 }
 
 KResult VFS::mkdir(StringView path, mode_t mode, Custody& base)

Kernel/Process.cpp

@@ -1971,14 +1971,6 @@ int Process::sys$open(const Syscall::SC_open_params* user_params)
     if (result.is_error())
         return result.error();
     auto description = result.value();
-    if (description->file_flags()) {
-        // We already have file flags set on this description, so
-        // it must be a preopen description (probably, /proc/pid/fd).
-        // So don't reset its flags and r/w mode.
-    } else {
-        description->set_rw_mode(options);
-        description->set_file_flags(options);
-    }
     u32 fd_flags = (options & O_CLOEXEC) ? FD_CLOEXEC : 0;
     m_fds[fd].set(move(description), fd_flags);
     return fd;

Kernel/TTY/PTYMultiplexer.cpp

@@ -66,6 +66,7 @@ KResultOr<NonnullRefPtr<FileDescription>> PTYMultiplexer::open(int options)
 #endif
     auto description = FileDescription::create(move(master));
     description->set_rw_mode(options);
+    description->set_file_flags(options);
     return description;
 }