Kernel+CrashDaemon: Use a ".partial" suffix for incomplete coredumps

The Kernel will now write to a .partial file until it is done writing,
and then rename the file by removing the extension.

This makes the final coredump appear atomically on the file system and
thus remove the need for special handling of partial files in
CrashDaemon.

Author: LucasChollet

Kernel/Tasks/Process.cpp

@@ -831,10 +831,21 @@ ErrorOr<void> Process::dump_core()
         return {};
     }
     auto coredump_path = TRY(name().with([&](auto& process_name) {
-        return KString::formatted("{}/{}_{}_{}", coredump_directory_path->view(), process_name.representable_view(), pid().value(), kgettimeofday().seconds_since_epoch());
+        return KString::formatted("{}/{}_{}_{}.partial", coredump_directory_path->view(), process_name.representable_view(), pid().value(), kgettimeofday().seconds_since_epoch());
     }));
     auto coredump = TRY(Coredump::try_create(*this, coredump_path->view()));
-    return coredump->write();
+    TRY(coredump->write());
+
+    auto output_directory = KLexicalPath::dirname(coredump_path->view());
+    auto vfs_root_context_root_custody = vfs_root_context()->root_custody().with([](auto& custody) -> NonnullRefPtr<Custody> {
+        return custody;
+    });
+    auto dump_directory = TRY(VirtualFileSystem::open_directory(vfs_root_context(), credentials(), output_directory, *vfs_root_context_root_custody));
+
+    auto new_path = TRY(KString::try_create(coredump_path->view().trim(".partial"sv)));
+    TRY(VirtualFileSystem::rename(vfs_root_context(), credentials(), dump_directory, coredump_path->view(), dump_directory, new_path->view()));
+
+    return {};
 }
 
 ErrorOr<void> Process::dump_perfcore()

Userland/Services/CrashDaemon/main.cpp

@@ -4,32 +4,11 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include <AK/LexicalPath.h>
-#include <Kernel/API/InodeWatcherEvent.h>
 #include <LibCore/FileWatcher.h>
 #include <LibCore/MappedFile.h>
 #include <LibCore/Process.h>
 #include <LibCore/System.h>
 #include <LibMain/Main.h>
-#include <spawn.h>
-#include <sys/stat.h>
-#include <time.h>
-#include <unistd.h>
-
-static void wait_until_coredump_is_ready(ByteString const& coredump_path)
-{
-    while (true) {
-        struct stat statbuf;
-        if (stat(coredump_path.characters(), &statbuf) < 0) {
-            perror("stat");
-            VERIFY_NOT_REACHED();
-        }
-        if (statbuf.st_mode & 0400) // Check if readable
-            break;
-
-        usleep(10000); // sleep for 10ms
-    }
-}
 
 static void launch_crash_reporter(ByteString const& coredump_path, bool unlink_on_exit)
 {
@@ -49,13 +28,14 @@ ErrorOr<int> serenity_main(Main::Arguments)
     TRY(watcher.add_watch("/tmp/coredump", Core::FileWatcherEvent::Type::ChildCreated));
 
     while (true) {
-        auto event = watcher.wait_for_event();
-        VERIFY(event.has_value());
-        if (event.value().type != Core::FileWatcherEvent::Type::ChildCreated)
+        auto event = watcher.wait_for_event().value();
+        if (event.type != Core::FileWatcherEvent::Type::ChildCreated)
             continue;
-        auto& coredump_path = event.value().event_path;
+        auto& coredump_path = event.event_path;
+        if (coredump_path.ends_with(".partial"sv))
+            continue;
+
         dbgln("New coredump file: {}", coredump_path);
-        wait_until_coredump_is_ready(coredump_path);
 
         auto file_or_error = Core::MappedFile::map(coredump_path);
         if (file_or_error.is_error()) {