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Fix symlink resolution when mounting #3673

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Fix symlink resolution when mounting #3673

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e5e2ec4
[Daemon] fix symlinks not resolving at mount time
Sploder12 Sep 12, 2024
4bb0fc1
[daemon][unit test] Add mount symlink resolution tests
Sploder12 Sep 12, 2024
e352056
Format changes
Sploder12 Sep 12, 2024
607afba
[daemon][unit test] Fix tests expected path on Windows and MacOS
Sploder12 Sep 14, 2024
06347b0
[daemon] Move symlink resolution to VMMount ctor
Sploder12 Sep 16, 2024
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2 changes: 2 additions & 0 deletions include/multipass/vm_mount.h
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Original file line number Diff line number Diff line change
Expand Up @@ -39,6 +39,8 @@ class VMMount
explicit VMMount(const QJsonObject& json);
VMMount(const std::string& sourcePath, id_mappings gidMappings, id_mappings uidMappings, MountType mountType);

void resolve_source_path();

QJsonObject serialize() const;

const std::string& get_source_path() const noexcept;
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8 changes: 5 additions & 3 deletions src/daemon/daemon.cpp
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Expand Up @@ -3270,11 +3270,13 @@ bool mp::Daemon::create_missing_mounts(std::unordered_map<std::string, VMMount>&
return mount_specs.size() != initial_mount_count;
}

mp::MountHandler::UPtr mp::Daemon::make_mount(VirtualMachine* vm, const std::string& target, const VMMount& mount)
mp::MountHandler::UPtr mp::Daemon::make_mount(VirtualMachine* vm, const std::string& target, VMMount mount)
{
mount.resolve_source_path();

return mount.get_mount_type() == VMMount::MountType::Classic
? std::make_unique<SSHFSMountHandler>(vm, config->ssh_key_provider.get(), target, mount)
: vm->make_native_mount_handler(target, mount);
? std::make_unique<SSHFSMountHandler>(vm, config->ssh_key_provider.get(), target, std::move(mount))
: vm->make_native_mount_handler(target, std::move(mount));
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This one doesn't help much unless you change make_native_mount_handler to take by value and move too. Otherwise you're asking for one extra temporary.

}

QFutureWatcher<mp::Daemon::AsyncOperationStatus>*
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2 changes: 1 addition & 1 deletion src/daemon/daemon.h
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Expand Up @@ -173,7 +173,7 @@ public slots:
std::unordered_map<std::string, MountHandler::UPtr>& vm_mounts,
VirtualMachine* vm);

MountHandler::UPtr make_mount(VirtualMachine* vm, const std::string& target, const VMMount& mount);
MountHandler::UPtr make_mount(VirtualMachine* vm, const std::string& target, VMMount mount);

struct AsyncOperationStatus
{
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32 changes: 32 additions & 0 deletions src/utils/vm_mount.cpp
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Expand Up @@ -17,6 +17,8 @@

#include <multipass/vm_mount.h>

#include <multipass/file_ops.h>

#include <QJsonArray>

namespace mp = multipass;
Expand Down Expand Up @@ -111,6 +113,36 @@
{
}

void mp::VMMount::resolve_source_path()
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Good call making this a method on the mount. Thinking about it a little further now, I wonder if we should just call this in the constructor and avoid the intermediate state at all. But I haven't looked deep for implications. WDYT?

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I was thinking about the same thing. This seems to be a private function to me.

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I think doing it in the constructor would be good, I'll look into it and any implications it has.

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It seems that doing it in the constructor makes it so that the source path is persisted as the place the symlink points to. This changes the behavior a bit so that symlinks are only ever resolved once instead of when the daemon restarts. It's still a fix for the issue but acts a bit different, what do you think?

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Hmm. I wouldn't mind just replacing the original path with the target of the symlink, but doing so completely. IOW, making sure that the source path is discarded and has no further effect. I would like to avoid recording something for a while (either persisted or just in memory) and then something else later.

Also, keep in mind that this will need to deal with "legacy" mounts, i.e., mounts that people established before this PR. You may find that they would already be transformed when the daemon restarts, but it is something to check.

{
std::error_code err;
fs::path path{source_path};

auto status = MP_FILEOPS.symlink_status(path, err);

if (status.type() == fs::file_type::symlink)
{
auto symlink_path = MP_FILEOPS.read_symlink(path, err);

if (err)
throw std::runtime_error(
fmt::format("Mount symlink source path \"{}\" could not be read: {}.", source_path, err.message()));

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if (symlink_path.is_relative())
symlink_path = path.parent_path() / symlink_path;

path = fs::weakly_canonical(symlink_path, err);

if (err)
throw std::runtime_error(
fmt::format("Mount symlink source path \"{}\" could not be made weakly canonical: {}.",
source_path,
err.message()));

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source_path = path.string();
}
}

QJsonObject mp::VMMount::serialize() const
{
QJsonObject ret;
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42 changes: 42 additions & 0 deletions tests/test_daemon_mount.cpp
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Expand Up @@ -17,6 +17,7 @@

#include "common.h"
#include "daemon_test_fixture.h"
#include "mock_file_ops.h"
#include "mock_logger.h"
#include "mock_mount_handler.h"
#include "mock_platform.h"
Expand Down Expand Up @@ -267,3 +268,44 @@ TEST_F(TestDaemonMount, performanceMountsNotImplementedHasErrorFails)
EXPECT_EQ(status.error_code(), grpc::StatusCode::FAILED_PRECONDITION);
EXPECT_THAT(status.error_message(), StrEq("The native mounts feature is not implemented on this backend."));
}

TEST_F(TestDaemonMount, symlinkSourceGetsResolved)
{
const auto [temp_dir, filename] = plant_instance_json(fake_json_contents(mac_addr, extra_interfaces));
config_builder.data_directory = temp_dir->path();

const auto [mock_file_ops, _] = mpt::MockFileOps::inject();
EXPECT_CALL(*mock_file_ops, symlink_status).WillOnce(Return(mp::fs::file_status{mp::fs::file_type::symlink}));
EXPECT_CALL(*mock_file_ops, read_symlink)
.WillOnce(Return(mp::fs::path{config_builder.data_directory.toStdString()}));

auto original_implementation_of_mkpath = [](const QDir& dir, const QString& dirName) -> bool {
return MP_FILEOPS.FileOps::mkpath(dir, dirName);
};
EXPECT_CALL(*mock_file_ops, mkpath).WillRepeatedly(original_implementation_of_mkpath);

auto original_implementation_of_open = [](QFileDevice& dev, QIODevice::OpenMode mode) -> bool {
return MP_FILEOPS.FileOps::open(dev, mode);
};
EXPECT_CALL(*mock_file_ops, open(A<QFileDevice&>(), A<QIODevice::OpenMode>()))
.WillRepeatedly(original_implementation_of_open);

auto original_implementation_of_commit = [](QSaveFile& file) -> bool { return MP_FILEOPS.FileOps::commit(file); };
EXPECT_CALL(*mock_file_ops, commit).WillRepeatedly(original_implementation_of_commit);

mp::Daemon daemon{config_builder.build()};

mp::MountRequest request;
request.set_source_path(mount_dir.path().toStdString());
request.set_mount_type(mp::MountRequest::NATIVE);
auto entry = request.add_target_paths();
entry->set_instance_name(mock_instance_name);
entry->set_target_path(fake_target_path);

auto status = call_daemon_slot(daemon,
&mp::Daemon::mount,
request,
StrictMock<mpt::MockServerReaderWriter<mp::MountReply, mp::MountRequest>>{});

EXPECT_TRUE(status.ok());
}
46 changes: 46 additions & 0 deletions tests/test_vm_mount.cpp
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Expand Up @@ -16,6 +16,7 @@
*/

#include "common.h"
#include "mock_file_ops.h"

#include <multipass/vm_mount.h>

Expand Down Expand Up @@ -139,4 +140,49 @@ TEST_F(TestVMMount, duplicateGidsThrowsWithDuplicateTargetID)
HasSubstr("1002:1001"),
HasSubstr("1000:1001"))));
}

TEST_F(TestVMMount, notSymlinkSourcePathUnchanged)
{
const auto [mock_file_ops, _] = mpt::MockFileOps::inject();
EXPECT_CALL(*mock_file_ops, symlink_status).WillOnce(Return(mp::fs::file_status{mp::fs::file_type::regular}));
EXPECT_CALL(*mock_file_ops, read_symlink).Times(0);

mp::VMMount mount{"src", {}, {}, mp::VMMount::MountType::Classic};

mount.resolve_source_path();

EXPECT_EQ(mount.get_source_path(), "src");
}

TEST_F(TestVMMount, absoluteSymlinkSourcePathResolved)
{
auto source_path = mp::fs::weakly_canonical("/tmp/src");
auto symlink_path = mp::fs::weakly_canonical("/home/dest");

const auto [mock_file_ops, _] = mpt::MockFileOps::inject();
EXPECT_CALL(*mock_file_ops, symlink_status).WillOnce(Return(mp::fs::file_status{mp::fs::file_type::symlink}));
EXPECT_CALL(*mock_file_ops, read_symlink).WillOnce(Return(symlink_path));

mp::VMMount mount{source_path.string(), {}, {}, mp::VMMount::MountType::Classic};

mount.resolve_source_path();

EXPECT_EQ(mount.get_source_path(), symlink_path.string());
}

TEST_F(TestVMMount, relativeSymlinkSourcePathResolved)
{
auto source_path = mp::fs::weakly_canonical("/tmp/src");

const auto [mock_file_ops, _] = mpt::MockFileOps::inject();
EXPECT_CALL(*mock_file_ops, symlink_status).WillOnce(Return(mp::fs::file_status{mp::fs::file_type::symlink}));
EXPECT_CALL(*mock_file_ops, read_symlink).WillOnce(Return(mp::fs::path{"./dest"}));

mp::VMMount mount{source_path.string(), {}, {}, mp::VMMount::MountType::Classic};

mount.resolve_source_path();

EXPECT_EQ(mount.get_source_path(), source_path.replace_filename("dest").string());
}

} // namespace
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