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Commit c64cefc0 authored by Yifan Hong's avatar Yifan Hong
Browse files

libsnapshot: add GetCurrentSlot 

Factor out obscure logic that reads boot indicator path.
GetCurrentSlot() returns three states:
- None (read failure)
- Old (before reboot)
- New (after reboot)
Use these "logical" slot values for simpler code.

Test: libsnapshot_test
Change-Id: I1fa2ce4916c5a1652d25682ec1f11e101c858822
parent babc2931

fs_mgr/libsnapshot/include/libsnapshot/snapshot.h

+4 −0
Original line number Diff line number Diff line
@@ -496,6 +496,10 @@ class SnapshotManager final { 
    // as a sanity check.

    bool EnsureNoOverflowSnapshot(LockedFile* lock);



    enum class Slot { Unknown, Source, Target };

    friend std::ostream& operator<<(std::ostream& os, SnapshotManager::Slot slot);

    Slot GetCurrentSlot();



    std::string gsid_dir_;

    std::string metadata_dir_;

    std::unique_ptr<IDeviceInfo> device_;

fs_mgr/libsnapshot/snapshot.cpp

+41 −40
Original line number Diff line number Diff line
@@ -171,19 +171,27 @@ bool SnapshotManager::TryCancelUpdate(bool* needs_merge) { 


    if (state == UpdateState::Unverified) {

        // We completed an update, but it can still be canceled if we haven't booted into it.

        auto slot = GetCurrentSlot();

        if (slot != Slot::Target) {

            LOG(INFO) << "Canceling previously completed updates (if any)";

            return RemoveAllUpdateState(file.get());

        }

    }

    *needs_merge = true;

    return true;

}



SnapshotManager::Slot SnapshotManager::GetCurrentSlot() {

    auto boot_file = GetSnapshotBootIndicatorPath();

    std::string contents;

    if (!android::base::ReadFileToString(boot_file, &contents)) {

            PLOG(WARNING) << "Cannot read " << boot_file << ", proceed to canceling the update:";

            return RemoveAllUpdateState(file.get());

        PLOG(WARNING) << "Cannot read " << boot_file;

        return Slot::Unknown;

    }

    if (device_->GetSlotSuffix() == contents) {

            LOG(INFO) << "Canceling a previously completed update";

            return RemoveAllUpdateState(file.get());

        }

        return Slot::Source;

    }

    *needs_merge = true;

    return true;

    return Slot::Target;

}



bool SnapshotManager::RemoveAllUpdateState(LockedFile* lock) {
@@ -505,15 +513,9 @@ bool SnapshotManager::InitiateMerge() { 
        return false;

    }



    std::string old_slot;

    auto boot_file = GetSnapshotBootIndicatorPath();

    if (!android::base::ReadFileToString(boot_file, &old_slot)) {

        LOG(ERROR) << "Could not determine the previous slot; aborting merge";

        return false;

    }

    auto new_slot = device_->GetSlotSuffix();

    if (new_slot == old_slot) {

        LOG(ERROR) << "Device cannot merge while booting off old slot " << old_slot;

    auto slot = GetCurrentSlot();

    if (slot != Slot::Target) {

        LOG(ERROR) << "Device cannot merge while not booting from new slot";

        return false;

    }
@@ -1097,13 +1099,11 @@ bool SnapshotManager::CollapseSnapshotDevice(const std::string& name, 
}



bool SnapshotManager::HandleCancelledUpdate(LockedFile* lock) {

    std::string old_slot;

    auto boot_file = GetSnapshotBootIndicatorPath();

    if (!android::base::ReadFileToString(boot_file, &old_slot)) {

        PLOG(ERROR) << "Unable to read the snapshot indicator file: " << boot_file;

    auto slot = GetCurrentSlot();

    if (slot == Slot::Unknown) {

        return false;

    }

    if (device_->GetSlotSuffix() != old_slot) {

    if (slot == Slot::Target) {

        // We're booted into the target slot, which means we just rebooted

        // after applying the update.

        if (!HandleCancelledUpdateOnNewSlot(lock)) {
@@ -1271,14 +1271,9 @@ bool SnapshotManager::NeedSnapshotsInFirstStageMount() { 
    // ultimately we'll fail to boot. Why not make it a fatal error and have

    // the reason be clearer? Because the indicator file still exists, and

    // if this was FATAL, reverting to the old slot would be broken.

    std::string old_slot;

    auto boot_file = GetSnapshotBootIndicatorPath();

    if (!android::base::ReadFileToString(boot_file, &old_slot)) {

        PLOG(ERROR) << "Unable to read the snapshot indicator file: " << boot_file;

        return false;

    }

    if (device_->GetSlotSuffix() == old_slot) {

        LOG(INFO) << "Detected slot rollback, will not mount snapshots.";

    auto slot = GetCurrentSlot();

    if (slot != Slot::Target) {

        LOG(INFO) << "Not booting from new slot. Will not mount snapshots.";

        return false;

    }
@@ -2156,6 +2151,17 @@ bool SnapshotManager::UnmapAllPartitions() { 
    return ok;

}



std::ostream& operator<<(std::ostream& os, SnapshotManager::Slot slot) {

    switch (slot) {

        case SnapshotManager::Slot::Unknown:

            return os << "unknown";

        case SnapshotManager::Slot::Source:

            return os << "source";

        case SnapshotManager::Slot::Target:

            return os << "target";

    }

}



bool SnapshotManager::Dump(std::ostream& os) {

    // Don't actually lock. Dump() is for debugging purposes only, so it is okay

    // if it is racy.
@@ -2166,11 +2172,8 @@ bool SnapshotManager::Dump(std::ostream& os) { 


    ss << "Update state: " << ReadUpdateState(file.get()) << std::endl;



    auto boot_file = GetSnapshotBootIndicatorPath();

    std::string boot_indicator;

    if (android::base::ReadFileToString(boot_file, &boot_indicator)) {

        ss << "Boot indicator: old slot = " << boot_indicator << std::endl;

    }

    ss << "Current slot: " << device_->GetSlotSuffix() << std::endl;

    ss << "Boot indicator: booting from " << GetCurrentSlot() << " slot" << std::endl;



    bool ok = true;

    std::vector<std::string> snapshots;
@@ -2283,11 +2286,9 @@ bool SnapshotManager::HandleImminentDataWipe(const std::function<void()>& callba 
            //

            // Since the rollback is inevitable, we don't treat a HAL failure

            // as an error here.

            std::string old_slot;

            auto boot_file = GetSnapshotBootIndicatorPath();

            if (android::base::ReadFileToString(boot_file, &old_slot) &&

                device_->GetSlotSuffix() != old_slot) {

                LOG(ERROR) << "Reverting to slot " << old_slot << " since update will be deleted.";

            auto slot = GetCurrentSlot();

            if (slot == Slot::Target) {

                LOG(ERROR) << "Reverting to old slot since update will be deleted.";

                device_->SetSlotAsUnbootable(slot_number);

            }

            break;