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https://github.com/SerenityOS/serenity
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f6db24dba4
That functionality seems to be too much complicated. We shouldn't overengineer how the copy_mount syscall works, so instead of allowing replacement of the root filesystem, let's make the unshare file descriptor to be configured via a special ioctl call before we initialize a new VFSRootContext object. The special ioctl can either set a new root filesystem for the upcoming VFSRootContext object, or remove it (by passing fd of -1). If there's no specified root filesystem, a new RAMFS instance will be created automatically when invoking the unshare_create syscall. This also simplifies the code in the boot process, hence making it much more readable. It should be noted, that we assumed during pivot_root that the first mountpoint in a context is the root mountpoint, which is probably a fair assumption, but we don't assume this anywhere else in the VFSRootContext code. If this functionality ever comes back, we should ensure that we make some effort to not assume this again.
108 lines
4.0 KiB
C++
108 lines
4.0 KiB
C++
/*
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* Copyright (c) 2026, Liav A. <liavalb@hotmail.co.il>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <AK/StdLibExtras.h>
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#include <AK/StringView.h>
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#include <Kernel/API/Ioctl.h>
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#include <Kernel/API/POSIX/errno.h>
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#include <Kernel/API/Syscall.h>
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#include <Kernel/FileSystem/OpenFileDescription.h>
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#include <Kernel/FileSystem/UnsharedResourceFile.h>
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#include <Kernel/FileSystem/VirtualFileSystem.h>
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#include <Kernel/Library/StdLib.h>
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#include <Kernel/Tasks/Process.h>
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#include <Kernel/FileSystem/VFSRootContext.h>
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#include <Kernel/Tasks/HostnameContext.h>
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#include <Kernel/Tasks/ScopedProcessList.h>
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namespace Kernel {
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ErrorOr<NonnullRefPtr<UnsharedResourceFile>> UnsharedResourceFile::create(UnshareType type)
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{
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return TRY(adopt_nonnull_ref_or_enomem(new (nothrow) UnsharedResourceFile(type)));
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}
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UnsharedResourceFile::UnsharedResourceFile(UnshareType type)
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: m_type(type)
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{
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}
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ErrorOr<unsigned> UnsharedResourceFile::initialize_resource()
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{
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switch (m_type) {
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case UnshareType::ScopedProcessList: {
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auto scoped_process_list = TRY(ScopedProcessList::create());
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return scoped_process_list->id().value();
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}
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case UnshareType::VFSRootContext: {
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return m_root_filesystem.with_exclusive([&](auto& root_filesystem) -> ErrorOr<unsigned> {
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if (root_filesystem) {
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auto vfs_root_context = TRY(VFSRootContext::create_with_filesystem(VFSRootContext::AddToGlobalContextList::Yes, *root_filesystem));
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return vfs_root_context->id().value();
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}
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auto vfs_root_context = TRY(VFSRootContext::create_with_empty_ramfs(VFSRootContext::AddToGlobalContextList::Yes));
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return vfs_root_context->id().value();
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});
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}
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case UnshareType::HostnameContext: {
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// NOTE: Technically, we create a new context, based on the
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// contents of "previous" attached one.
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// However, the process can change the hostname context during
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// this call as we don't really hold a lock on it, but that's
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// really a non-issue because it's not destructive or really harmful
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// and if a process is so **eager** to blindly change hostname contexts
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// with multiple fds, we should not be the ones to stop it from doing that.
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auto current_context = Process::current().hostname_context();
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FixedStringBuffer<UTSNAME_ENTRY_LEN - 1> hostname;
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current_context->buffer().with([&hostname](auto& buffer) {
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hostname.store_characters(buffer.representable_view());
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});
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auto hostname_context = TRY(HostnameContext::create_with_name(hostname.representable_view()));
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return hostname_context->id().value();
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}
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}
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return ENOTSUP;
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}
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UnsharedResourceFile::~UnsharedResourceFile() = default;
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ErrorOr<void> UnsharedResourceFile::ioctl(OpenFileDescription&, unsigned request, Userspace<void*> arg)
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{
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switch (request) {
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case UNSHARE_IOCTL_ATTACH_ROOT_FILESYSTEM_AT_FD: {
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auto current_vfs_root_context = Process::current().vfs_root_context();
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auto credentials = Process::current().credentials();
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auto fd = static_cast<int>(arg.ptr());
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auto description = TRY(Process::current().open_file_description_ignoring_negative(fd));
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return m_root_filesystem.with_exclusive([&credentials, ¤t_vfs_root_context, &description](auto& root_filesystem) -> ErrorOr<void> {
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if (!description) {
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root_filesystem = nullptr;
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return {};
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}
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if (!description->is_directory())
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return ENOTDIR;
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if (!description->metadata().may_execute(credentials))
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return EACCES;
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VERIFY(description->custody());
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root_filesystem = TRY(current_vfs_root_context->mount_point_to_guest_filesystem(*description->custody()));
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return {};
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});
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}
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default:
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return EINVAL;
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}
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}
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ErrorOr<NonnullOwnPtr<KString>> UnsharedResourceFile::pseudo_path(OpenFileDescription const&) const
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{
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return KString::try_create(":unshared-resource-file:"sv);
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}
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}
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