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Kernel+Userland: Add immutable mounts

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Immutable mounts are mounts that can't be changed in any aspect, if the
VFSRootContext that hold them is used by a process. This includes two
operations on a mount:
1. Trying to remove the mount from the mount table.
2. Trying to change the flags of the mount.

The condition of a VFSRootContext being held by a process or not is
crucial, as the intention is to allow removal of mounts that marked as
immutable if the VFSRootContext is not being used anymore (for example,
if the container that was created with such context stopped).

Marking mounts as immutable on the first VFS root context essentially
ensures they will never be modified because there will be a process
using that context (which is the "main" VFS root context in the system
runtime).

It should be noted that setting a mount as immutable can be done in
creation time of the mount by passing the MS_IMMUTABLE flag, or by doing
a remount with MS_IMMUTABLE flag.
This commit is contained in:
Liav A.
2024-08-09 01:44:22 +03:00
committed by Sönke Holz
parent d6bdb9a3ed
commit 1dfc9e2df3
12 changed files with 316 additions and 199 deletions
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46
Kernel/Tasks/PowerStateSwitchTask.cpp
View File

@@ -57,50 +57,6 @@ void PowerStateSwitchTask::spawn(PowerStateCommand command)
g_power_state_switch_task = move(power_state_switch_task_thread);
}
static ErrorOr<void> unmount_mounts_on_vfs_root_context(VFSRootContext& vfs_root_context)
{
// NOTE: We are going to tear down the entire VFS root context from its mounts.
// To do this properly, we swap out the original root custody with the empty
// root custody for vfs root context of kernel processes.
vfs_root_context.root_custody().with([](auto& custody) {
custody = VFSRootContext::empty_context_custody_for_kernel_processes();
});
auto unmount_was_successful = true;
while (unmount_was_successful) {
unmount_was_successful = false;
Vector<Mount&, 16> mounts;
TRY(vfs_root_context.mounts().with([&mounts](auto& list) -> ErrorOr<void> {
for (auto& mount : list) {
TRY(mounts.try_append(const_cast<Mount&>(mount)));
}
return {};
}));
if (mounts.is_empty())
break;
auto const remaining_mounts = mounts.size();
while (!mounts.is_empty()) {
auto& mount = mounts.take_last();
TRY(mount.guest_fs().flush_writes());
auto mount_path = TRY(mount.absolute_path());
auto& mount_inode = mount.guest();
auto const result = VirtualFileSystem::unmount(vfs_root_context, mount_inode, mount_path->view());
if (result.is_error()) {
dbgln("Error during unmount of {}: {}", mount_path, result.error());
// FIXME: For unknown reasons the root FS stays busy even after everything else has shut down and was unmounted.
// Until we find the underlying issue, allow an unclean shutdown here.
if (remaining_mounts <= 1)
dbgln("BUG! One mount remaining; the root file system may not be unmountable at all. Shutting down anyways.");
} else {
unmount_was_successful = true;
}
}
}
return {};
}
ErrorOr<void> PowerStateSwitchTask::perform_shutdown(PowerStateSwitchTask::DoReboot do_reboot)
{
// We assume that by this point userland has tried as much as possible to shut down everything in an orderly fashion.
@@ -146,7 +102,7 @@ ErrorOr<void> PowerStateSwitchTask::perform_shutdown(PowerStateSwitchTask::DoReb
});
for (size_t index = 0; index < collected_contexts_count; index++) {
VERIFY(contexts[index]);
TRY(unmount_mounts_on_vfs_root_context(*contexts[index]));
TRY(contexts[index]->do_full_teardown({}));
}
} while (collected_contexts_count > 0);