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Kernel+LibCore+LibC: Split the mount syscall into multiple syscalls

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This is a preparation before we can create a usable mechanism to use
filesystem-specific mount flags.
To keep some compatibility with userland code, LibC and LibCore mount
functions are kept being usable, but now instead of doing an "atomic"
syscall, they do multiple syscalls to perform the complete procedure of
mounting a filesystem.

The FileBackedFileSystem IntrusiveList in the VFS code is now changed to
be protected by a Mutex, because when we mount a new filesystem, we need
to check if a filesystem is already created for a given source_fd so we
do a scan for that OpenFileDescription in that list. If we fail to find
an already-created filesystem we create a new one and register it in the
list if we successfully mounted it. We use a Mutex because we might need
to initiate disk access during the filesystem creation, which will take
other mutexes in other parts of the kernel, therefore making it not
possible to take a spinlock while doing this.
This commit is contained in:
Liav A 2022-12-15 11:42:40 +02:00 • committed by Jelle Raaijmakers
parent 63fc36d00d
commit 23a7ccf607
39 changed files with 651 additions and 214 deletions
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20
Kernel/FileSystem/VirtualFileSystem.h
View file

@ -14,11 +14,14 @@
#include <AK/RefPtr.h>
#include <Kernel/FileSystem/FileBackedFileSystem.h>
#include <Kernel/FileSystem/FileSystem.h>
#include <Kernel/FileSystem/Initializer.h>
#include <Kernel/FileSystem/InodeIdentifier.h>
#include <Kernel/FileSystem/InodeMetadata.h>
#include <Kernel/FileSystem/Mount.h>
#include <Kernel/FileSystem/MountFile.h>
#include <Kernel/FileSystem/UnveilNode.h>
#include <Kernel/Forward.h>
#include <Kernel/Locking/MutexProtected.h>
#include <Kernel/Locking/SpinlockProtected.h>
namespace Kernel {
@ -49,11 +52,13 @@ public:
static void initialize();
static VirtualFileSystem& the();
static ErrorOr<FileSystemInitializer const*> find_filesystem_type_initializer(StringView fs_type);
VirtualFileSystem();
~VirtualFileSystem();
ErrorOr<void> mount_root(FileSystem&);
ErrorOr<void> mount(FileSystem&, Custody& mount_point, int flags);
ErrorOr<void> mount(MountFile&, OpenFileDescription*, Custody& mount_point, int flags);
ErrorOr<void> bind_mount(Custody& source, Custody& mount_point, int flags);
ErrorOr<void> remount(Custody& mount_point, int new_flags);
ErrorOr<void> unmount(Custody& mount_point);
@ -82,8 +87,6 @@ public:
ErrorOr<void> for_each_mount(Function<ErrorOr<void>(Mount const&)>) const;
ErrorOr<NonnullRefPtr<FileBackedFileSystem>> find_already_existing_or_create_file_backed_file_system(OpenFileDescription& description, Function<ErrorOr<NonnullRefPtr<FileSystem>>(OpenFileDescription&)> callback);
InodeIdentifier root_inode_id() const;
void sync_filesystems();
@ -105,6 +108,8 @@ private:
ErrorOr<void> validate_path_against_process_veil(Custody const& path, int options);
ErrorOr<void> validate_path_against_process_veil(StringView path, int options);
ErrorOr<void> add_file_system_to_mount_table(FileSystem& file_system, Custody& mount_point, int flags);
bool is_vfs_root(InodeIdentifier) const;
ErrorOr<void> traverse_directory_inode(Inode&, Function<ErrorOr<void>(FileSystem::DirectoryEntryView const&)>);
@ -120,7 +125,14 @@ private:
SpinlockProtected<RefPtr<Custody>, LockRank::None> m_root_custody {};
SpinlockProtected<IntrusiveList<&Mount::m_vfs_list_node>, LockRank::None> m_mounts {};
SpinlockProtected<IntrusiveList<&FileBackedFileSystem::m_file_backed_file_system_node>, LockRank::None> m_file_backed_file_systems_list {};
// NOTE: The FileBackedFileSystem list is protected by a mutex because we need to scan it
// to search for existing filesystems for already used block devices and therefore when doing
// that we could fail to find a filesystem so we need to create a new filesystem which might
// need to do disk access (i.e. taking Mutexes in other places) and then register that new filesystem
// in this list, to avoid TOCTOU bugs.
MutexProtected<IntrusiveList<&FileBackedFileSystem::m_file_backed_file_system_node>> m_file_backed_file_systems_list {};
SpinlockProtected<IntrusiveList<&FileSystem::m_file_system_node>, LockRank::FileSystem> m_file_systems_list {};
};