// Copyright 2021 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

mod allocator;
mod constants;
pub mod directory;
pub mod filesystem;
pub mod fsck;
mod graveyard;
mod journal;
mod merge;
mod record;
#[cfg(test)]
mod testing;
pub mod transaction;

pub use directory::Directory;
pub use filesystem::FxFilesystem;
pub use record::ObjectDescriptor;

use {
    crate::{
        device::{
            buffer::{Buffer, BufferRef, MutableBufferRef},
            Device,
        },
        errors::FxfsError,
        lsm_tree::{types::LayerIterator, LSMTree},
        object_handle::{ObjectHandle, ObjectHandleExt, INVALID_OBJECT_ID},
        object_store::{
            filesystem::{Filesystem, Mutations, ObjectFlush},
            record::{
                ExtentKey, ExtentValue, ObjectItem, ObjectKey, ObjectKind, ObjectValue,
                DEFAULT_DATA_ATTRIBUTE_ID,
            },
            transaction::{
                AssociatedObject, LockKey, Mutation, ObjectStoreMutation, Operation,
                StoreInfoMutation, Transaction,
            },
        },
    },
    allocator::Allocator,
    anyhow::{anyhow, bail, Context, Error},
    async_trait::async_trait,
    bincode::{deserialize_from, serialize_into},
    futures::{future::BoxFuture, FutureExt},
    once_cell::sync::OnceCell,
    serde::{Deserialize, Serialize},
    std::{
        cmp::min,
        ops::{Bound, Range},
        sync::{
            atomic::{self, AtomicBool, AtomicU64},
            Arc, Mutex, Weak,
        },
    },
};

// StoreInfo stores information about the object store.  This is stored within the parent object
// store, and is used, for example, to get the persistent layer objects.
#[derive(Clone, Debug, Default, Serialize, Deserialize)]
pub struct StoreInfo {
    // The last used object ID.  Note that this field is not accurate in memory; ObjectStore's
    // last_object_id field is the one to use in that case.
    last_object_id: u64,

    // Object ids for layers.  TODO(csuter): need a layer of indirection here so we can
    // support snapshots.
    layers: Vec<u64>,

    // The object ID for the root directory.
    root_directory_object_id: u64,

    // The object ID for the graveyard.
    // TODO(csuter): Move this out of here.  This can probably be a child of the root directory.
    graveyard_directory_object_id: u64,
}

// TODO(csuter): We should test or put checks in place to ensure this limit isn't exceeded.  It
// will likely involve placing limits on the maximum number of layers.
const MAX_STORE_INFO_SERIALIZED_SIZE: usize = 131072;

#[derive(Default)]
pub struct HandleOptions {
    /// If true, don't COW, write to blocks that are already allocated.
    pub overwrite: bool,
}

/// An object store supports a file like interface for objects.  Objects are keyed by a 64 bit
/// identifier.  And object store has to be backed by a parent object store (which stores metadata
/// for the object store).  The top-level object store (a.k.a. the root parent object store) is
/// in-memory only.
pub struct ObjectStore {
    parent_store: Option<Arc<ObjectStore>>,
    store_object_id: u64,
    device: Arc<dyn Device>,
    block_size: u32,
    filesystem: Weak<dyn Filesystem>,
    last_object_id: AtomicU64,
    store_info: Mutex<Option<StoreInfo>>,
    tree: LSMTree<ObjectKey, ObjectValue>,

    // When replaying the journal, the store cannot read StoreInfo until the whole journal
    // has been replayed, so during that time, store_info_handle will be None and records
    // just get sent to the tree. Once the journal has been replayed, we can open the store
    // and load all the other layer information.
    store_info_handle: OnceCell<StoreObjectHandle<ObjectStore>>,
}

impl ObjectStore {
    fn new(
        parent_store: Option<Arc<ObjectStore>>,
        store_object_id: u64,
        filesystem: Arc<dyn Filesystem>,
        store_info: Option<StoreInfo>,
        tree: LSMTree<ObjectKey, ObjectValue>,
    ) -> Arc<ObjectStore> {
        let device = filesystem.device();
        let block_size = device.block_size();
        let store = Arc::new(ObjectStore {
            parent_store,
            store_object_id,
            device,
            block_size,
            filesystem: Arc::downgrade(&filesystem),
            last_object_id: AtomicU64::new(0),
            store_info: Mutex::new(store_info),
            tree,
            store_info_handle: OnceCell::new(),
        });
        filesystem.register_store(&store);
        store
    }

    pub fn new_empty(
        parent_store: Option<Arc<ObjectStore>>,
        store_object_id: u64,
        filesystem: Arc<dyn Filesystem>,
    ) -> Arc<Self> {
        Self::new(
            parent_store,
            store_object_id,
            filesystem,
            Some(StoreInfo::default()),
            LSMTree::new(merge::merge),
        )
    }

    pub fn device(&self) -> Arc<dyn Device> {
        self.device.clone()
    }

    pub fn filesystem(&self) -> Arc<dyn Filesystem> {
        self.filesystem.upgrade().unwrap()
    }

    pub fn store_object_id(&self) -> u64 {
        self.store_object_id
    }

    pub fn tree(&self) -> &LSMTree<ObjectKey, ObjectValue> {
        &self.tree
    }

    pub fn root_directory_object_id(&self) -> u64 {
        self.store_info.lock().unwrap().as_ref().unwrap().root_directory_object_id
    }

    pub fn set_root_directory_object_id<'a>(&'a self, transaction: &mut Transaction<'a>, oid: u64) {
        let mut store_info = self.txn_get_store_info(transaction);
        store_info.root_directory_object_id = oid;
        transaction.add_with_object(self.store_object_id, Mutation::store_info(store_info), self);
    }

    pub fn graveyard_directory_object_id(&self) -> u64 {
        self.store_info.lock().unwrap().as_ref().unwrap().graveyard_directory_object_id
    }

    pub fn set_graveyard_directory_object_id<'a>(
        &'a self,
        transaction: &mut Transaction<'a>,
        oid: u64,
    ) {
        let mut store_info = self.txn_get_store_info(transaction);
        store_info.graveyard_directory_object_id = oid;
        transaction.add_with_object(self.store_object_id, Mutation::store_info(store_info), self);
    }

    pub async fn create_child_store<'a>(
        self: &'a Arc<ObjectStore>,
        transaction: &mut Transaction<'a>,
    ) -> Result<Arc<ObjectStore>, Error> {
        let object_id = self.get_next_object_id();
        self.create_child_store_with_id(transaction, object_id).await
    }

    async fn create_child_store_with_id<'a>(
        self: &'a Arc<Self>,
        transaction: &mut Transaction<'a>,
        object_id: u64,
    ) -> Result<Arc<ObjectStore>, Error> {
        self.ensure_open().await?;
        // TODO(csuter): if the transaction rolls back, we need to delete the store.
        let handle = ObjectStore::create_object_with_id(
            self,
            transaction,
            object_id,
            HandleOptions::default(),
        )
        .await?;
        let store = Self::new_empty(
            Some(self.clone()),
            handle.object_id(),
            self.filesystem.upgrade().unwrap(),
        );
        let _ = store.store_info_handle.set(handle);
        Ok(store)
    }

    // When replaying the journal, we need to replay mutation records into the LSM tree, but we
    // cannot properly open the store until all the records have been replayed since some of the
    // records we replay might affect how we open, e.g. they might pertain to new layer files
    // backing this store.  The store will get properly opened whenever an action is taken that
    // needs the store to be opened (via ensure_open).
    pub(super) fn lazy_open_store(
        self: &Arc<ObjectStore>,
        store_object_id: u64,
    ) -> Arc<ObjectStore> {
        Self::new(
            Some(self.clone()),
            store_object_id,
            self.filesystem.upgrade().unwrap(),
            None,
            LSMTree::new(merge::merge),
        )
    }

    pub async fn open_store(
        self: &Arc<ObjectStore>,
        store_object_id: u64,
    ) -> Result<Arc<ObjectStore>, Error> {
        let store = self.lazy_open_store(store_object_id);
        store.ensure_open().await?;
        Ok(store)
    }

    pub async fn open_object<S: AsRef<ObjectStore>>(
        owner: &Arc<S>,
        object_id: u64,
        options: HandleOptions,
    ) -> Result<StoreObjectHandle<S>, Error> {
        let store = owner.as_ref().as_ref();
        store.ensure_open().await?;
        let item = store
            .tree
            .find(&ObjectKey::attribute(object_id, DEFAULT_DATA_ATTRIBUTE_ID))
            .await?
            .ok_or(FxfsError::NotFound)?;
        if let ObjectValue::Attribute { size } = item.value {
            Ok(StoreObjectHandle {
                owner: owner.clone(),
                object_id,
                attribute_id: DEFAULT_DATA_ATTRIBUTE_ID,
                block_size: store.block_size.into(),
                size: Mutex::new(size),
                options,
                trace: AtomicBool::new(false),
            })
        } else {
            bail!(FxfsError::Inconsistent);
        }
    }

    async fn create_object_with_id<S: AsRef<ObjectStore>>(
        owner: &Arc<S>,
        transaction: &mut Transaction<'_>,
        object_id: u64,
        options: HandleOptions,
    ) -> Result<StoreObjectHandle<S>, Error> {
        let store = owner.as_ref().as_ref();
        store.ensure_open().await?;
        // If the object ID was specified i.e. this hasn't come via create_object, then we
        // should update last_object_id in case the caller wants to create more objects in
        // the same transaction.
        store.update_last_object_id(object_id);
        transaction.add(
            store.store_object_id(),
            Mutation::insert_object(ObjectKey::object(object_id), ObjectValue::file(1, 0)),
        );
        transaction.add(
            store.store_object_id(),
            Mutation::insert_object(
                ObjectKey::attribute(object_id, DEFAULT_DATA_ATTRIBUTE_ID),
                ObjectValue::attribute(0),
            ),
        );
        Ok(StoreObjectHandle {
            owner: owner.clone(),
            block_size: store.block_size.into(),
            object_id,
            attribute_id: DEFAULT_DATA_ATTRIBUTE_ID,
            size: Mutex::new(0),
            options,
            trace: AtomicBool::new(false),
        })
    }

    pub async fn create_object<S: AsRef<ObjectStore>>(
        owner: &Arc<S>,
        mut transaction: &mut Transaction<'_>,
        options: HandleOptions,
    ) -> Result<StoreObjectHandle<S>, Error> {
        let object_id = owner.as_ref().as_ref().get_next_object_id();
        ObjectStore::create_object_with_id(owner, &mut transaction, object_id, options).await
    }

    /// Adjusts the reference count for a given object.  If the reference count reaches zero, the
    /// object is destroyed and any extents are deallocated.
    pub async fn adjust_refs(
        &self,
        transaction: &mut Transaction<'_>,
        oid: u64,
        delta: i64,
    ) -> Result<(), Error> {
        let item = self.tree.find(&ObjectKey::object(oid)).await?.ok_or(FxfsError::NotFound)?;
        let (refs, allocated_size) =
            if let ObjectValue::Object { kind: ObjectKind::File { refs, allocated_size } } =
                item.value
            {
                (
                    if delta < 0 {
                        refs.checked_sub((-delta) as u64)
                    } else {
                        refs.checked_add(delta as u64)
                    }
                    .ok_or(anyhow!("refs underflow/overflow"))?,
                    allocated_size,
                )
            } else {
                bail!(FxfsError::NotFile);
            };
        if refs == 0 {
            let layer_set = self.tree.layer_set();
            let mut merger = layer_set.merger();
            let allocator = self.allocator();
            let mut iter = merger.seek(Bound::Included(&ObjectKey::attribute(oid, 0))).await?;
            // Loop over all the extents and deallocate them.
            // TODO(csuter): deal with overflowing a transaction.
            while let Some(item) = iter.get() {
                if item.key.object_id != oid {
                    break;
                }
                if let Some((
                    _,
                    _,
                    ExtentKey { range },
                    ExtentValue { device_offset: Some(device_offset) },
                )) = item.into()
                {
                    let range = *device_offset..*device_offset + (range.end - range.start);
                    allocator.deallocate(transaction, range).await;
                }
                iter.advance().await?;
            }
            transaction.add(
                self.store_object_id,
                Mutation::merge_object(ObjectKey::tombstone(oid), ObjectValue::None),
            );
        } else {
            transaction.add(
                self.store_object_id,
                Mutation::replace_or_insert_object(
                    item.key,
                    ObjectValue::file(refs, allocated_size),
                ),
            );
        }
        Ok(())
    }

    /// Returns all objects that exist in the parent store that pertain to this object store.
    pub fn parent_objects(&self) -> Vec<u64> {
        assert!(self.store_info_handle.get().is_some());
        let mut objects = Vec::new();
        // We should not include the ID of the store itself, since that should be referred to in the
        // volume directory.
        objects.extend_from_slice(&self.store_info.lock().unwrap().as_ref().unwrap().layers);
        objects
    }

    /// Returns root objects for this store.
    pub fn root_objects(&self) -> Vec<u64> {
        let mut objects = Vec::new();
        let store_info = self.store_info.lock().unwrap();
        if store_info.as_ref().unwrap().root_directory_object_id != INVALID_OBJECT_ID {
            objects.push(store_info.as_ref().unwrap().root_directory_object_id);
        }
        if store_info.as_ref().unwrap().graveyard_directory_object_id != INVALID_OBJECT_ID {
            objects.push(store_info.as_ref().unwrap().graveyard_directory_object_id);
        }
        objects
    }

    pub fn store_info(&self) -> StoreInfo {
        self.store_info.lock().unwrap().as_ref().unwrap().clone()
    }

    async fn ensure_open(&self) -> Result<(), Error> {
        if self.parent_store.is_none() || self.store_info_handle.get().is_some() {
            return Ok(());
        }

        self.open_impl().await
    }

    // This returns a BoxFuture because of the cycle: open_object -> ensure_open -> open_impl ->
    // open_object.
    fn open_impl<'a>(&'a self) -> BoxFuture<'a, Result<(), Error>> {
        async move {
            // TODO(csuter): we need to introduce an async lock here.
            let parent_store = self.parent_store.as_ref().unwrap();
            let handle = ObjectStore::open_object(
                &parent_store,
                self.store_object_id,
                HandleOptions::default(),
            )
            .await?;
            let need_store_info = self.store_info.lock().unwrap().is_none();
            let layer_object_ids = if need_store_info && handle.get_size() > 0 {
                let serialized_info = handle.contents(MAX_STORE_INFO_SERIALIZED_SIZE).await?;
                let store_info: StoreInfo = deserialize_from(&serialized_info[..])?;
                let layer_object_ids = store_info.layers.clone();
                self.update_last_object_id(store_info.last_object_id);
                *self.store_info.lock().unwrap() = Some(store_info);
                layer_object_ids
            } else {
                self.store_info.lock().unwrap().as_ref().unwrap().layers.clone()
            };
            let mut handles = Vec::new();
            for object_id in layer_object_ids {
                handles.push(
                    ObjectStore::open_object(&parent_store, object_id, HandleOptions::default())
                        .await?,
                );
            }
            self.tree.append_layers(handles.into()).await?;
            let _ = self.store_info_handle.set(handle);
            Ok(())
        }
        .boxed()
    }

    fn get_next_object_id(&self) -> u64 {
        self.last_object_id.fetch_add(1, atomic::Ordering::Relaxed) + 1
    }

    fn allocator(&self) -> Arc<dyn Allocator> {
        self.filesystem().allocator()
    }

    fn txn_get_store_info(&self, transaction: &Transaction<'_>) -> StoreInfo {
        match transaction.get_store_info(self.store_object_id) {
            None => self.store_info(),
            Some(store_info) => store_info.clone(),
        }
    }

    fn update_last_object_id(&self, object_id: u64) {
        let _ = self.last_object_id.fetch_update(
            atomic::Ordering::Relaxed,
            atomic::Ordering::Relaxed,
            |oid| if object_id > oid { Some(object_id) } else { None },
        );
    }
}

#[async_trait]
impl Mutations for ObjectStore {
    async fn apply_mutation(&self, mutation: Mutation, replay: bool) {
        // It's not safe to fully open a store until replay is fully complete (because
        // subsequent mutations could render current records invalid). The exception to
        // this is the root parent object store which contains the extents for the journal
        // file: whilst we are replaying we need to be able to track new extents for the
        // journal file so that we can read from it whilst we are replaying.
        assert!(!replay || self.store_info_handle.get().is_none() || self.parent_store.is_none());

        match mutation {
            Mutation::ObjectStore(ObjectStoreMutation { item, op }) => {
                self.update_last_object_id(item.key.object_id);
                match op {
                    Operation::Insert => self.tree.insert(item).await,
                    Operation::ReplaceOrInsert => self.tree.replace_or_insert(item).await,
                    Operation::Merge => {
                        let lower_bound = item.key.key_for_merge_into();
                        self.tree.merge_into(item, &lower_bound).await;
                    }
                }
            }
            Mutation::ObjectStoreInfo(StoreInfoMutation(store_info)) => {
                *self.store_info.lock().unwrap() = Some(store_info);
            }
            Mutation::TreeSeal => self.tree.seal().await,
            Mutation::TreeCompact => {
                if replay {
                    self.tree.reset_immutable_layers();
                }
            }
            _ => panic!("unexpected mutation: {:?}", mutation), // TODO(csuter): can't panic
        }
    }

    fn drop_mutation(&self, _mutation: Mutation) {}

    /// Push all in-memory structures to the device. This is not necessary for sync since the
    /// journal will take care of it.  This is supposed to be called when there is either memory or
    /// space pressure (flushing the store will persist in-memory data and allow the journal file to
    /// be trimmed).
    async fn flush(&self) -> Result<(), Error> {
        if self.parent_store.is_none() {
            return Ok(());
        }
        self.ensure_open().await?;
        // TODO(csuter): This whole process needs to be within a transaction, or otherwise safe in
        // the event of power loss.
        let filesystem = self.filesystem();
        let object_manager = filesystem.object_manager();
        if !object_manager.needs_flush(self.store_object_id) {
            return Ok(());
        }

        let parent_store = self.parent_store.as_ref().unwrap();
        let graveyard = object_manager.graveyard().ok_or(anyhow!("Missing graveyard!"))?;

        let object_sync = ObjectFlush::new(object_manager, self.store_object_id);
        let mut transaction = filesystem.clone().new_transaction(&[]).await?;
        let object_handle =
            ObjectStore::create_object(parent_store, &mut transaction, HandleOptions::default())
                .await?;
        let object_id = object_handle.object_id();
        graveyard.add(&mut transaction, parent_store.store_object_id(), object_id);
        transaction.add_with_object(self.store_object_id(), Mutation::TreeSeal, &object_sync);
        transaction.commit().await;

        self.tree.compact(&object_handle).await?;

        let mut serialized_info = Vec::new();
        let mut new_store_info = self.store_info();

        let mut transaction = filesystem.clone().new_transaction(&[]).await?;

        // Move all the existing layers to the graveyard.
        for object_id in new_store_info.layers {
            graveyard.add(&mut transaction, parent_store.store_object_id(), object_id);
        }

        new_store_info.last_object_id = self.last_object_id.load(atomic::Ordering::Relaxed);
        new_store_info.layers = vec![object_id];
        serialize_into(&mut serialized_info, &new_store_info)?;
        let mut buf = self.device.allocate_buffer(serialized_info.len());
        buf.as_mut_slice().copy_from_slice(&serialized_info[..]);

        self.store_info_handle
            .get()
            .unwrap()
            .txn_write(&mut transaction, 0u64, buf.as_ref())
            .await?;
        transaction.add(self.store_object_id(), Mutation::TreeCompact);
        graveyard.remove(&mut transaction, parent_store.store_object_id(), object_id);
        // TODO(csuter): This isn't thread-safe.
        *self.store_info.lock().unwrap() = Some(new_store_info);
        transaction.commit().await;

        self.tree.set_layers(Box::new([object_handle])).await.expect("set_layers failed");

        object_sync.commit();
        Ok(())
    }
}

impl AsRef<ObjectStore> for ObjectStore {
    fn as_ref(&self) -> &ObjectStore {
        self
    }
}

impl AssociatedObject for ObjectStore {
    fn will_apply_mutation(&self, mutation: &Mutation) {
        match mutation {
            Mutation::ObjectStoreInfo(StoreInfoMutation(store_info)) => {
                *self.store_info.lock().unwrap() = Some(store_info.clone());
            }
            _ => {}
        }
    }
}

// TODO(csuter): We should probably be a little more frugal about what we store here since there
// could be a lot of these structures. We could remove block_size and change the size to be atomic.
pub struct StoreObjectHandle<S> {
    owner: Arc<S>,
    object_id: u64,
    block_size: u64,
    attribute_id: u64,
    size: Mutex<u64>,
    options: HandleOptions,
    trace: AtomicBool,
}

impl<S: AsRef<ObjectStore> + Send + Sync + 'static> StoreObjectHandle<S> {
    pub fn owner(&self) -> &Arc<S> {
        &self.owner
    }

    pub fn store(&self) -> &ObjectStore {
        self.owner.as_ref().as_ref()
    }

    /// Extend the file with the given extent.  The only use case for this right now is for files
    /// that must exist at certain offsets on the device, such as super-blocks.
    pub async fn extend<'a>(
        &'a self,
        transaction: &mut Transaction<'a>,
        device_range: Range<u64>,
    ) -> Result<(), Error> {
        let old_end = round_up(self.txn_get_size(transaction), self.block_size);
        let new_size = old_end + device_range.end - device_range.start;
        self.store().allocator().reserve(transaction, device_range.clone()).await;
        transaction.add_with_object(
            self.store().store_object_id,
            Mutation::replace_or_insert_object(
                ObjectKey::attribute(self.object_id, self.attribute_id),
                ObjectValue::attribute(new_size),
            ),
            self,
        );
        transaction.add(
            self.store().store_object_id,
            Mutation::merge_object(
                ObjectKey::extent(self.object_id, self.attribute_id, old_end..new_size),
                ObjectValue::extent(device_range.start),
            ),
        );
        self.update_allocated_size(transaction, device_range.end - device_range.start, 0).await
    }

    async fn write_cow<'a>(
        &'a self,
        transaction: &mut Transaction<'a>,
        mut offset: u64,
        buf: BufferRef<'_>,
    ) -> Result<(), Error> {
        let mut aligned = round_down(offset, self.block_size)
            ..round_up(offset + buf.len() as u64, self.block_size);
        let mut buf_offset = 0;
        if offset + buf.len() as u64 > self.txn_get_size(transaction) {
            transaction.add_with_object(
                self.store().store_object_id,
                Mutation::replace_or_insert_object(
                    ObjectKey::attribute(self.object_id, self.attribute_id),
                    ObjectValue::attribute(offset + buf.len() as u64),
                ),
                self,
            );
        }
        let deallocated = self.deallocate_old_extents(transaction, aligned.clone()).await?;
        let mut allocated = 0;
        let allocator = self.store().allocator();
        let trace = self.trace.load(atomic::Ordering::Relaxed);
        while buf_offset < buf.len() {
            let device_range = allocator
                .allocate(transaction, aligned.end - aligned.start)
                .await
                .context("allocation failed")?;
            if trace {
                log::info!(
                    "{}.{} A {:?}",
                    self.store().store_object_id,
                    self.object_id,
                    device_range
                );
            }
            allocated += device_range.end - device_range.start;
            let extent_len = device_range.end - device_range.start;
            let end = aligned.start + extent_len;
            let len = min(buf.len() - buf_offset, (end - offset) as usize);
            assert!(len > 0);
            self.write_at(
                offset,
                buf.subslice(buf_offset..buf_offset + len),
                device_range.start + offset % self.block_size,
            )
            .await?;
            transaction.add(
                self.store().store_object_id,
                Mutation::merge_object(
                    ObjectKey::extent(self.object_id, self.attribute_id, aligned.start..end),
                    ObjectValue::extent(device_range.start),
                ),
            );
            aligned.start += extent_len;
            buf_offset += len;
            offset += len as u64;
        }
        self.update_allocated_size(transaction, allocated, deallocated).await
    }

    // All the extents for the range must have been preallocated using preallocate_range or from
    // existing writes.
    async fn overwrite(&self, mut offset: u64, buf: BufferRef<'_>) -> Result<(), Error> {
        let tree = &self.store().tree;
        let layer_set = tree.layer_set();
        let mut merger = layer_set.merger();
        let end = offset + buf.len() as u64;
        let mut iter = merger
            .seek(Bound::Included(
                &ObjectKey::extent(self.object_id, self.attribute_id, offset..end).search_key(),
            ))
            .await?;
        let mut pos = 0;
        loop {
            let (device_offset, to_do) = match iter.get().and_then(Into::into) {
                Some((
                    object_id,
                    attribute_id,
                    ExtentKey { range },
                    ExtentValue { device_offset: Some(device_offset) },
                )) if object_id == self.object_id
                    && attribute_id == self.attribute_id
                    && range.start <= offset =>
                {
                    (
                        device_offset + (offset - range.start),
                        min(buf.len() - pos, (range.end - offset) as usize),
                    )
                }
                _ => bail!("offset {} not allocated", offset),
            };
            self.write_at(offset, buf.subslice(pos..pos + to_do), device_offset).await?;
            pos += to_do;
            if pos == buf.len() {
                break;
            }
            offset += to_do as u64;
            iter.advance().await?;
        }
        Ok(())
    }

    async fn write_at(
        &self,
        offset: u64,
        buf: BufferRef<'_>,
        mut device_offset: u64,
    ) -> Result<(), Error> {
        // Deal with alignment.
        let start_align = (offset % self.block_size) as usize;
        let start_offset = offset - start_align as u64;
        let trace = self.trace.load(atomic::Ordering::Relaxed);
        let remainder = if start_align > 0 {
            let (head, remainder) =
                buf.split_at(min(self.block_size as usize - start_align, buf.len()));
            let mut align_buf = self.store().device.allocate_buffer(self.block_size as usize);
            let read = self.read(start_offset, align_buf.as_mut()).await?;
            align_buf.as_mut_slice()[read..].fill(0);
            align_buf.as_mut_slice()[start_align..(start_align + head.len())]
                .copy_from_slice(head.as_slice());
            device_offset -= start_align as u64;
            if trace {
                log::info!(
                    "{}.{} WH {:?}",
                    self.store().store_object_id(),
                    self.object_id,
                    device_offset..device_offset + align_buf.len() as u64
                );
            }
            self.store().device.write(device_offset, align_buf.as_ref()).await?;
            device_offset += self.block_size;
            remainder
        } else {
            buf
        };
        if remainder.len() > 0 {
            let end = offset + buf.len() as u64;
            let end_align = (end % self.block_size) as usize;
            let (whole_blocks, tail) = remainder.split_at(remainder.len() - end_align);
            if whole_blocks.len() > 0 {
                if trace {
                    log::info!(
                        "{}.{} W {:?}",
                        self.store().store_object_id(),
                        self.object_id,
                        device_offset..device_offset + whole_blocks.len() as u64
                    );
                }
                self.store().device.write(device_offset, whole_blocks).await?;
                device_offset += whole_blocks.len() as u64;
            }
            if tail.len() > 0 {
                let mut align_buf = self.store().device.allocate_buffer(self.block_size as usize);
                let read = self.read(end - end_align as u64, align_buf.as_mut()).await?;
                align_buf.as_mut_slice()[read..].fill(0);
                &align_buf.as_mut_slice()[..tail.len()].copy_from_slice(tail.as_slice());
                if trace {
                    log::info!(
                        "{}.{} WT {:?}",
                        self.store().store_object_id(),
                        self.object_id,
                        device_offset..device_offset + align_buf.len() as u64
                    );
                }
                self.store().device.write(device_offset, align_buf.as_ref()).await?;
            }
        }
        Ok(())
    }

    // Returns the amount deallocated.
    async fn deallocate_old_extents(
        &self,
        transaction: &mut Transaction<'_>,
        range: Range<u64>,
    ) -> Result<u64, Error> {
        assert_eq!(range.start % self.block_size as u64, 0);
        assert_eq!(range.end % self.block_size as u64, 0);
        let tree = &self.store().tree;
        let layer_set = tree.layer_set();
        let key = ExtentKey::new(range);
        let lower_bound =
            ObjectKey::with_extent_key(self.object_id, self.attribute_id, key.search_key());
        let mut merger = layer_set.merger();
        let mut iter = merger.seek(Bound::Included(&lower_bound)).await?;
        let allocator = self.store().allocator();
        let mut deallocated = 0;
        let trace = self.trace.load(atomic::Ordering::Relaxed);
        loop {
            let (extent_key, extent_value) = match iter.get().and_then(Into::into) {
                Some((oid, attribute_id, extent_key, extent_value))
                    if oid == self.object_id && attribute_id == self.attribute_id =>
                {
                    (extent_key, extent_value)
                }
                _ => break,
            };
            if let ExtentValue { device_offset: Some(device_offset) } = extent_value {
                if let Some(overlap) = key.overlap(extent_key) {
                    let range = device_offset + overlap.start - extent_key.range.start
                        ..device_offset + overlap.end - extent_key.range.start;
                    if trace {
                        log::info!(
                            "{}.{} D {:?}",
                            self.store().store_object_id(),
                            self.object_id,
                            range
                        );
                    }
                    allocator.deallocate(transaction, range).await;
                    deallocated += overlap.end - overlap.start;
                } else {
                    break;
                }
            }
            iter.advance().await?;
        }
        Ok(deallocated)
    }

    /// Zeroes the given range.  The range must be aligned.  Returns the amount of data deallocated.
    pub async fn zero(
        &self,
        transaction: &mut Transaction<'_>,
        range: Range<u64>,
    ) -> Result<(), Error> {
        let deallocated = self.deallocate_old_extents(transaction, range.clone()).await?;
        if deallocated > 0 {
            self.update_allocated_size(transaction, 0, deallocated).await?;
            transaction.add(
                self.store().store_object_id,
                Mutation::merge_object(
                    ObjectKey::extent(self.object_id, self.attribute_id, range),
                    ObjectValue::deleted_extent(),
                ),
            );
        }
        Ok(())
    }

    // Within a transaction, the size of the object might have changed, so get the size from there
    // if it exists, otherwise, fall back on the cached size.
    fn txn_get_size(&self, transaction: &Transaction<'_>) -> u64 {
        transaction
            .get_object_mutation(
                self.store().store_object_id,
                ObjectKey::attribute(self.object_id, self.attribute_id),
            )
            .and_then(|m| {
                if let ObjectItem { value: ObjectValue::Attribute { size }, .. } = m.item {
                    Some(size)
                } else {
                    None
                }
            })
            .unwrap_or_else(|| self.get_size())
    }

    #[cfg(test)]
    async fn get_allocated_size(&self) -> Result<u64, Error> {
        if let ObjectItem {
            value: ObjectValue::Object { kind: ObjectKind::File { allocated_size, .. } },
            ..
        } = self
            .store()
            .tree
            .find(&ObjectKey::object(self.object_id))
            .await?
            .expect("Unable to find object record")
        {
            Ok(allocated_size)
        } else {
            panic!("Unexpected object value");
        }
    }

    async fn update_allocated_size(
        &self,
        transaction: &mut Transaction<'_>,
        allocated: u64,
        deallocated: u64,
    ) -> Result<(), Error> {
        if allocated == deallocated {
            return Ok(());
        }
        let mut item = if let Some(ObjectStoreMutation { item, .. }) = transaction
            .get_object_mutation(self.store().store_object_id, ObjectKey::object(self.object_id))
        {
            item.clone()
        } else {
            self.store()
                .tree
                .find(&ObjectKey::object(self.object_id))
                .await?
                .expect("Unable to find object record")
        };
        if let ObjectItem {
            value: ObjectValue::Object { kind: ObjectKind::File { ref mut allocated_size, .. } },
            ..
        } = item
        {
            // The only way for these to fail are if the volume is inconsistent.
            *allocated_size = allocated_size
                .checked_add(allocated)
                .ok_or(FxfsError::Inconsistent)?
                .checked_sub(deallocated)
                .ok_or(FxfsError::Inconsistent)?;
        } else {
            panic!("Unexpceted object value");
        }
        transaction.add(
            self.store().store_object_id,
            Mutation::replace_or_insert_object(item.key, item.value),
        );
        Ok(())
    }
}

impl<S: Send + Sync> AssociatedObject for StoreObjectHandle<S> {
    fn will_apply_mutation(&self, mutation: &Mutation) {
        match mutation {
            Mutation::ObjectStore(ObjectStoreMutation {
                item: ObjectItem { value: ObjectValue::Attribute { size }, .. },
                ..
            }) => *self.size.lock().unwrap() = *size,
            _ => {}
        }
    }
}

// TODO(jfsulliv): Move into utils module or something else.
fn round_down<T: Into<u64>>(offset: u64, block_size: T) -> u64 {
    offset - offset % block_size.into()
}

fn round_up<T: Into<u64>>(offset: u64, block_size: T) -> u64 {
    let block_size = block_size.into();
    round_down(offset + block_size - 1, block_size)
}

#[async_trait]
impl<S: AsRef<ObjectStore> + Send + Sync + 'static> ObjectHandle for StoreObjectHandle<S> {
    fn set_trace(&self, v: bool) {
        log::info!("{}.{} tracing: {}", self.store().store_object_id, self.object_id(), v);
        self.trace.store(v, atomic::Ordering::Relaxed);
    }

    fn object_id(&self) -> u64 {
        return self.object_id;
    }

    fn allocate_buffer(&self, size: usize) -> Buffer<'_> {
        self.store().device.allocate_buffer(size)
    }

    async fn read(&self, mut offset: u64, mut buf: MutableBufferRef<'_>) -> Result<usize, Error> {
        if buf.len() == 0 {
            return Ok(0);
        }
        let fs = self.store().filesystem();
        let _guard = fs
            .read_lock(&[LockKey::object_attribute(
                self.store().store_object_id,
                self.object_id,
                self.attribute_id,
            )])
            .await;
        let size = self.get_size();
        if offset >= size {
            return Ok(0);
        }
        let tree = &self.store().tree;
        let layer_set = tree.layer_set();
        let mut merger = layer_set.merger();
        let mut iter = merger
            .seek(Bound::Included(&ObjectKey::extent(
                self.object_id,
                self.attribute_id,
                offset..offset + 1,
            )))
            .await?;
        let to_do = min(buf.len() as u64, size - offset) as usize;
        buf = buf.subslice_mut(0..to_do);
        let mut start_align = (offset % self.block_size) as usize;
        let end_align = ((offset + to_do as u64) % self.block_size) as usize;
        let trace = self.trace.load(atomic::Ordering::Relaxed);
        while let Some((object_id, attribute_id, extent_key, extent_value)) =
            iter.get().and_then(Into::into)
        {
            if object_id != self.object_id || attribute_id != self.attribute_id {
                break;
            }
            if extent_key.range.start > offset {
                // Zero everything up to the start of the extent.
                let to_zero = min(extent_key.range.start - offset, buf.len() as u64) as usize;
                for i in &mut buf.as_mut_slice()[..to_zero] {
                    *i = 0;
                }
                buf = buf.subslice_mut(to_zero..);
                if buf.is_empty() {
                    break;
                }
                offset += to_zero as u64;
                start_align = 0;
            }

            if let ExtentValue { device_offset: Some(device_offset) } = extent_value {
                let mut device_offset =
                    device_offset + (offset - start_align as u64 - extent_key.range.start);

                // Deal with starting alignment by reading the existing contents into an alignment
                // buffer.
                if start_align > 0 {
                    let mut align_buf =
                        self.store().device.allocate_buffer(self.block_size as usize);
                    if trace {
                        log::info!(
                            "{}.{} RH {:?}",
                            self.store().store_object_id(),
                            self.object_id,
                            device_offset..device_offset + align_buf.len() as u64
                        );
                    }
                    self.store().device.read(device_offset, align_buf.as_mut()).await?;
                    let to_copy = min(self.block_size as usize - start_align, buf.len());
                    buf.as_mut_slice()[..to_copy].copy_from_slice(
                        &align_buf.as_slice()[start_align..(start_align + to_copy)],
                    );
                    buf = buf.subslice_mut(to_copy..);
                    if buf.is_empty() {
                        break;
                    }
                    offset += to_copy as u64;
                    device_offset += self.block_size;
                    start_align = 0;
                }

                let to_copy = min(buf.len() - end_align, (extent_key.range.end - offset) as usize);
                if to_copy > 0 {
                    if trace {
                        log::info!(
                            "{}.{} R {:?}",
                            self.store().store_object_id(),
                            self.object_id,
                            device_offset..device_offset + to_copy as u64
                        );
                    }
                    self.store()
                        .device
                        .read(device_offset, buf.reborrow().subslice_mut(..to_copy))
                        .await?;
                    buf = buf.subslice_mut(to_copy..);
                    if buf.is_empty() {
                        break;
                    }
                    offset += to_copy as u64;
                    device_offset += to_copy as u64;
                }

                // Deal with end alignment, again by reading the exsting contents into an alignment
                // buffer.
                if offset < extent_key.range.end && end_align > 0 {
                    let mut align_buf =
                        self.store().device.allocate_buffer(self.block_size as usize);
                    if trace {
                        log::info!(
                            "{}.{} RT {:?}",
                            self.store().store_object_id(),
                            self.object_id,
                            device_offset..device_offset + align_buf.len() as u64
                        );
                    }
                    self.store().device.read(device_offset, align_buf.as_mut()).await?;
                    buf.as_mut_slice().copy_from_slice(&align_buf.as_slice()[..end_align]);
                    buf = buf.subslice_mut(0..0);
                    break;
                }
            } else if extent_key.range.end >= offset + buf.len() as u64 {
                // Deleted extent covers remainder, so we're done.
                break;
            }

            iter.advance().await?;
        }
        buf.as_mut_slice().fill(0);
        Ok(to_do)
    }

    async fn txn_write<'a>(
        &'a self,
        transaction: &mut Transaction<'a>,
        offset: u64,
        buf: BufferRef<'_>,
    ) -> Result<(), Error> {
        if buf.is_empty() {
            Ok(())
        } else if self.options.overwrite {
            self.overwrite(offset, buf).await
        } else {
            self.write_cow(transaction, offset, buf).await
        }
    }

    fn get_size(&self) -> u64 {
        *self.size.lock().unwrap()
    }

    async fn truncate<'a>(
        &'a self,
        transaction: &mut Transaction<'a>,
        size: u64,
    ) -> Result<(), Error> {
        let old_size = self.txn_get_size(transaction);
        if size < old_size {
            self.zero(
                transaction,
                round_up(size, self.block_size)..round_up(old_size, self.block_size),
            )
            .await?;
            let to_zero = round_up(size, self.block_size) - size;
            if to_zero > 0 {
                assert!(to_zero < self.block_size);
                // We intentionally use the COW write path even if we're in overwrite mode. There's
                // no need to support overwrite mode here, and it would be difficult since we'd need
                // to transactionalize zeroing the tail of the last block with the other metadata
                // changes, which we don't currently have a way to do.
                // TODO(csuter): This is allocating a small buffer that we'll just end up copying.
                // Is there a better way?
                let mut buf = self.allocate_buffer(to_zero as usize);
                buf.as_mut_slice().fill(0);
                self.write_cow(transaction, size, buf.as_ref()).await?;
            }
        }
        transaction.add_with_object(
            self.store().store_object_id,
            Mutation::replace_or_insert_object(
                ObjectKey::attribute(self.object_id, self.attribute_id),
                ObjectValue::attribute(size),
            ),
            self,
        );
        Ok(())
    }

    // Must be multiple of block size.
    async fn preallocate_range<'a>(
        &'a self,
        transaction: &mut Transaction<'a>,
        mut file_range: Range<u64>,
    ) -> Result<Vec<Range<u64>>, Error> {
        let mut ranges = Vec::new();
        let tree = &self.store().tree;
        let layer_set = tree.layer_set();
        let mut merger = layer_set.merger();
        let mut iter = merger
            .seek(Bound::Included(&ObjectKey::with_extent_key(
                self.object_id,
                self.attribute_id,
                ExtentKey::new(file_range.clone()).search_key(),
            )))
            .await?;
        let mut allocated = 0;
        'outer: while file_range.start < file_range.end {
            let allocate_end = loop {
                match iter.get().and_then(Into::into) {
                    Some((
                        oid,
                        attribute_id,
                        extent_key,
                        ExtentValue { device_offset: Some(device_offset) },
                    )) if oid == self.object_id
                        && attribute_id == self.attribute_id
                        && extent_key.range.start < file_range.end =>
                    {
                        if extent_key.range.start <= file_range.start {
                            // Record the existing extent and move on.
                            let device_range = device_offset + file_range.start
                                - extent_key.range.start
                                ..device_offset + min(extent_key.range.end, file_range.end)
                                    - extent_key.range.start;
                            file_range.start += device_range.end - device_range.start;
                            ranges.push(device_range);
                            if file_range.start >= file_range.end {
                                break 'outer;
                            }
                            iter.advance().await?;
                            continue;
                        } else {
                            // There's nothing allocated between file_range.start and the beginning
                            // of this extent.
                            break extent_key.range.start;
                        }
                    }
                    Some((oid, attribute_id, extent_key, ExtentValue { device_offset: None }))
                        if oid == self.object_id
                            && attribute_id == self.attribute_id
                            && extent_key.range.end < file_range.end =>
                    {
                        iter.advance().await?;
                    }
                    _ => {
                        // We can just preallocate the rest.
                        break file_range.end;
                    }
                }
            };
            let device_range = self
                .store()
                .allocator()
                .allocate(transaction, allocate_end - file_range.start)
                .await
                .context("allocation failed")?;
            allocated += device_range.end - device_range.start;
            let this_file_range =
                file_range.start..file_range.start + device_range.end - device_range.start;
            file_range.start = this_file_range.end;
            transaction.add(
                self.store().store_object_id,
                Mutation::merge_object(
                    ObjectKey::extent(self.object_id, self.attribute_id, this_file_range),
                    ObjectValue::extent(device_range.start),
                ),
            );
            ranges.push(device_range);
            // If we didn't allocate all that we requested, we'll loop around and try again.
        }
        // Update the file size if it changed.
        if file_range.end > self.txn_get_size(transaction) {
            transaction.add_with_object(
                self.store().store_object_id,
                Mutation::replace_or_insert_object(
                    ObjectKey::attribute(self.object_id, self.attribute_id),
                    ObjectValue::attribute(file_range.end),
                ),
                self,
            );
        }
        self.update_allocated_size(transaction, allocated, 0).await?;
        Ok(ranges)
    }

    async fn new_transaction<'a>(&self) -> Result<Transaction<'a>, Error> {
        Ok(self
            .store()
            .filesystem()
            .new_transaction(&[LockKey::object_attribute(
                self.store().store_object_id,
                self.object_id,
                self.attribute_id,
            )])
            .await?)
    }
}

#[cfg(test)]
mod tests {
    use {
        crate::{
            device::DeviceHolder,
            lsm_tree::types::{ItemRef, LayerIterator},
            object_handle::{ObjectHandle, ObjectHandleExt},
            object_store::{
                filesystem::{Filesystem, Mutations},
                graveyard::Graveyard,
                record::{ObjectKey, ObjectKeyData},
                round_up,
                testing::{fake_allocator::FakeAllocator, fake_filesystem::FakeFilesystem},
                transaction::TransactionHandler,
                HandleOptions, ObjectStore, StoreObjectHandle,
            },
            testing::fake_device::FakeDevice,
        },
        fuchsia_async as fasync,
        futures::{channel::oneshot::channel, join},
        rand::Rng,
        std::{
            ops::Bound,
            sync::{Arc, Mutex},
            time::Duration,
        },
    };

    const TEST_DEVICE_BLOCK_SIZE: u32 = 512;

    // Some tests (the preallocate_range ones) currently assume that the data only occupies a single
    // device block.
    const TEST_DATA_OFFSET: u64 = 600;
    const TEST_DATA: &[u8] = b"hello";
    const TEST_OBJECT_SIZE: u64 = 913;

    async fn test_filesystem_and_store(
    ) -> (Arc<FakeFilesystem>, Arc<FakeAllocator>, Arc<ObjectStore>) {
        let device = DeviceHolder::new(FakeDevice::new(1024, TEST_DEVICE_BLOCK_SIZE));
        let fs = FakeFilesystem::new(device);
        let allocator = Arc::new(FakeAllocator::new());
        fs.object_manager().set_allocator(allocator.clone());
        let parent_store = ObjectStore::new_empty(None, 2, fs.clone());
        let mut transaction =
            fs.clone().new_transaction(&[]).await.expect("new_transaction failed");
        let store = parent_store
            .create_child_store_with_id(&mut transaction, 3)
            .await
            .expect("create_child_store failed");
        let graveyard =
            Arc::new(Graveyard::create(&mut transaction, &store).await.expect("create failed"));
        fs.object_manager().register_graveyard(graveyard);
        transaction.commit().await;
        (fs.clone(), allocator, store)
    }

    async fn test_filesystem_and_object(
    ) -> (Arc<FakeFilesystem>, Arc<FakeAllocator>, StoreObjectHandle<ObjectStore>) {
        let (fs, allocator, store) = test_filesystem_and_store().await;
        let object;
        let mut transaction =
            fs.clone().new_transaction(&[]).await.expect("new_transaction failed");
        object = ObjectStore::create_object(&store, &mut transaction, HandleOptions::default())
            .await
            .expect("create_object failed");
        {
            let mut buf = object.allocate_buffer(TEST_DATA.len());
            buf.as_mut_slice().copy_from_slice(TEST_DATA);
            object
                .txn_write(&mut transaction, TEST_DATA_OFFSET, buf.as_ref())
                .await
                .expect("write failed");
        }
        object.truncate(&mut transaction, TEST_OBJECT_SIZE).await.expect("truncate failed");
        transaction.commit().await;
        (fs, allocator, object)
    }

    #[fasync::run_singlethreaded(test)]
    async fn test_zero_buf_len_read() {
        let (_fs, _, object) = test_filesystem_and_object().await;
        let mut buf = object.allocate_buffer(0);
        assert_eq!(object.read(0u64, buf.as_mut()).await.expect("read failed"), 0);
    }

    #[fasync::run_singlethreaded(test)]
    async fn test_beyond_eof_read() {
        let (_fs, _, object) = test_filesystem_and_object().await;
        let mut buf = object.allocate_buffer(TEST_DATA.len() * 2);
        buf.as_mut_slice().fill(123u8);
        assert_eq!(object.read(TEST_OBJECT_SIZE, buf.as_mut()).await.expect("read failed"), 0);
        assert_eq!(object.read(TEST_OBJECT_SIZE - 2, buf.as_mut()).await.expect("read failed"), 2);
        assert_eq!(&buf.as_slice()[0..2], &[0, 0]);
    }

    #[fasync::run_singlethreaded(test)]
    async fn test_read_sparse() {
        let (_fs, _, object) = test_filesystem_and_object().await;
        // Deliberately read 1 byte into the object and not right to eof.
        let len = TEST_OBJECT_SIZE as usize - 2;
        let mut buf = object.allocate_buffer(len);
        buf.as_mut_slice().fill(123u8);
        assert_eq!(object.read(1u64, buf.as_mut()).await.expect("read failed"), len);
        let mut expected = vec![0; len];
        let offset = TEST_DATA_OFFSET as usize - 1;
        &mut expected[offset..offset + TEST_DATA.len()].copy_from_slice(TEST_DATA);
        assert_eq!(buf.as_slice()[..len], expected[..]);
    }

    #[fasync::run_singlethreaded(test)]
    async fn test_read_after_writes_interspersed_with_flush() {
        let (_fs, _, object) = test_filesystem_and_object().await;

        object.owner().flush().await.expect("flush failed");

        // Write more test data to the first block fo the file.
        let mut buf = object.allocate_buffer(TEST_DATA.len());
        buf.as_mut_slice().copy_from_slice(TEST_DATA);
        object.write(0u64, buf.as_ref()).await.expect("write failed");

        let len = TEST_OBJECT_SIZE as usize - 2;
        let mut buf = object.allocate_buffer(len);
        buf.as_mut_slice().fill(123u8);
        assert_eq!(object.read(1u64, buf.as_mut()).await.expect("read failed"), len);

        let mut expected = vec![0u8; len];
        let offset = TEST_DATA_OFFSET as usize - 1;
        &mut expected[offset..offset + TEST_DATA.len()].copy_from_slice(TEST_DATA);
        &mut expected[..TEST_DATA.len() - 1].copy_from_slice(&TEST_DATA[1..]);
        assert_eq!(buf.as_slice()[..len], expected[..]);
    }

    #[fasync::run_singlethreaded(test)]
    async fn test_read_after_truncate_and_extend() {
        let (fs, _, object) = test_filesystem_and_object().await;

        // Arrange for there to be <extent><deleted-extent><extent>.
        let mut buf = object.allocate_buffer(TEST_DATA.len());
        buf.as_mut_slice().copy_from_slice(TEST_DATA);
        object.write(0, buf.as_ref()).await.expect("write failed"); // This adds an extent at 0..512.
        let mut transaction =
            fs.clone().new_transaction(&[]).await.expect("new_transaction failed");
        object.truncate(&mut transaction, 3).await.expect("truncate failed"); // This deletes 512..1024.
        transaction.commit().await;
        let data = b"foo";
        let mut buf = object.allocate_buffer(data.len());
        buf.as_mut_slice().copy_from_slice(data);
        object.write(1500, buf.as_ref()).await.expect("write failed"); // This adds 1024..1536.

        const LEN1: usize = 1501;
        let mut buf = object.allocate_buffer(LEN1);
        buf.as_mut_slice().fill(123u8);
        assert_eq!(object.read(1u64, buf.as_mut()).await.expect("read failed"), LEN1);
        let mut expected = [0; LEN1];
        &mut expected[0..2].copy_from_slice(&TEST_DATA[1..3]);
        &mut expected[1499..].copy_from_slice(b"fo");
        assert_eq!(buf.as_slice(), expected);

        // Also test a read that ends midway through the deleted extent.
        const LEN2: usize = 600;
        let mut buf = object.allocate_buffer(LEN2);
        buf.as_mut_slice().fill(123u8);
        assert_eq!(object.read(1u64, buf.as_mut()).await.expect("read failed"), LEN2);
        assert_eq!(buf.as_slice(), &expected[..LEN2]);
    }

    #[fasync::run_singlethreaded(test)]
    async fn test_read_whole_blocks_with_multiple_objects() {
        let (fs, _, object) = test_filesystem_and_object().await;
        let mut buffer = object.allocate_buffer(512);
        buffer.as_mut_slice().fill(0xaf);
        object.write(0, buffer.as_ref()).await.expect("write failed");

        let store = object.owner();
        let mut transaction =
            fs.clone().new_transaction(&[]).await.expect("new_transaction failed");
        let object2 =
            ObjectStore::create_object(&store, &mut transaction, HandleOptions::default())
                .await
                .expect("create_object failed");
        transaction.commit().await;
        let mut ef_buffer = object.allocate_buffer(512);
        ef_buffer.as_mut_slice().fill(0xef);
        object2.write(0, ef_buffer.as_ref()).await.expect("write failed");

        let mut buffer = object.allocate_buffer(512);
        buffer.as_mut_slice().fill(0xaf);
        object.write(512, buffer.as_ref()).await.expect("write failed");
        let mut transaction = object.new_transaction().await.expect("new_transaction failed");
        object.truncate(&mut transaction, 1536).await.expect("truncate failed");
        transaction.commit().await;
        object2.write(512, ef_buffer.as_ref()).await.expect("write failed");

        let mut buffer = object.allocate_buffer(2048);
        buffer.as_mut_slice().fill(123);
        assert_eq!(object.read(0, buffer.as_mut()).await.expect("read failed"), 1536);
        assert_eq!(&buffer.as_slice()[..1024], &[0xaf; 1024]);
        assert_eq!(&buffer.as_slice()[1024..1536], &[0; 512]);
        assert_eq!(object2.read(0, buffer.as_mut()).await.expect("read failed"), 1024);
        assert_eq!(&buffer.as_slice()[..1024], &[0xef; 1024]);
    }

    async fn test_preallocate_common(
        allocator: &FakeAllocator,
        object: StoreObjectHandle<ObjectStore>,
    ) {
        let allocated_before = allocator.allocated();
        let mut transaction = object.new_transaction().await.expect("new_transaction failed");
        object.preallocate_range(&mut transaction, 0..512).await.expect("preallocate_range failed");
        transaction.commit().await;
        assert!(object.get_size() < 1048576);
        let mut transaction = object.new_transaction().await.expect("new_transaction failed");
        object
            .preallocate_range(&mut transaction, 0..1048576)
            .await
            .expect("preallocate_range failed");
        transaction.commit().await;
        assert_eq!(object.get_size(), 1048576);
        // Check that it didn't reallocate the space for the existing extent
        let allocated_after = allocator.allocated();
        assert_eq!(allocated_after - allocated_before, 1048576 - TEST_DEVICE_BLOCK_SIZE as usize);

        // Reopen the object in overwrite mode.
        let object = ObjectStore::open_object(
            &object.owner,
            object.object_id(),
            HandleOptions { overwrite: true, ..Default::default() },
        )
        .await
        .expect("open_object failed");
        let mut buf = object.allocate_buffer(2048);
        buf.as_mut_slice().fill(47);
        object.write(0, buf.subslice(..TEST_DATA_OFFSET as usize)).await.expect("write failed");
        buf.as_mut_slice().fill(95);
        let offset = round_up(TEST_OBJECT_SIZE, TEST_DEVICE_BLOCK_SIZE);
        object.write(offset, buf.as_ref()).await.expect("write failed");

        // Make sure there were no more allocations.
        assert_eq!(allocator.allocated(), allocated_after);

        // Read back the data and make sure it is what we expect.
        let mut buf = object.allocate_buffer(104876);
        assert_eq!(object.read(0, buf.as_mut()).await.expect("read failed"), buf.len());
        assert_eq!(&buf.as_slice()[..TEST_DATA_OFFSET as usize], &[47; TEST_DATA_OFFSET as usize]);
        assert_eq!(
            &buf.as_slice()[TEST_DATA_OFFSET as usize..TEST_DATA_OFFSET as usize + TEST_DATA.len()],
            TEST_DATA
        );
        assert_eq!(&buf.as_slice()[offset as usize..offset as usize + 2048], &[95; 2048]);
    }

    #[fasync::run_singlethreaded(test)]
    async fn test_preallocate_range() {
        let (_fs, allocator, object) = test_filesystem_and_object().await;
        test_preallocate_common(&allocator, object).await;
    }

    // This is identical to the previous test except that we flush so that extents end up in
    // different layers.
    #[fasync::run_singlethreaded(test)]
    async fn test_preallocate_suceeds_when_extents_are_in_different_layers() {
        let (_fs, allocator, object) = test_filesystem_and_object().await;
        object.owner().flush().await.expect("flush failed");
        test_preallocate_common(&allocator, object).await;
    }

    #[fasync::run_singlethreaded(test)]
    async fn test_already_preallocated() {
        let (_fs, allocator, object) = test_filesystem_and_object().await;
        let allocated_before = allocator.allocated();
        let mut transaction = object.new_transaction().await.expect("new_transaction failed");
        let offset = TEST_DATA_OFFSET - TEST_DATA_OFFSET % TEST_DEVICE_BLOCK_SIZE as u64;
        object
            .preallocate_range(&mut transaction, offset..offset + 512)
            .await
            .expect("preallocate_range failed");
        transaction.commit().await;
        // Check that it didn't reallocate any new space.
        assert_eq!(allocator.allocated(), allocated_before);
    }

    #[fasync::run_singlethreaded(test)]
    async fn test_overwrite_fails_if_not_preallocated() {
        let (_fs, _, object) = test_filesystem_and_object().await;

        let object = ObjectStore::open_object(
            &object.owner,
            object.object_id(),
            HandleOptions { overwrite: true, ..Default::default() },
        )
        .await
        .expect("open_object failed");
        let mut buf = object.allocate_buffer(2048);
        buf.as_mut_slice().fill(95);
        let offset = round_up(TEST_OBJECT_SIZE, TEST_DEVICE_BLOCK_SIZE);
        object.write(offset, buf.as_ref()).await.expect_err("write suceceded");
    }

    #[fasync::run_singlethreaded(test)]
    async fn test_extend() {
        let (fs, _allocator, store) = test_filesystem_and_store().await;
        let handle;
        let mut transaction =
            fs.clone().new_transaction(&[]).await.expect("new_transaction failed");
        handle = ObjectStore::create_object(
            &store,
            &mut transaction,
            HandleOptions { overwrite: true, ..Default::default() },
        )
        .await
        .expect("create_object failed");
        handle
            .extend(&mut transaction, 0..5 * TEST_DEVICE_BLOCK_SIZE as u64)
            .await
            .expect("extend failed");
        transaction.commit().await;
        let mut buf = handle.allocate_buffer(5 * TEST_DEVICE_BLOCK_SIZE as usize);
        buf.as_mut_slice().fill(123);
        handle.write(0, buf.as_ref()).await.expect("write failed");
        buf.as_mut_slice().fill(67);
        handle.read(0, buf.as_mut()).await.expect("read failed");
        assert_eq!(buf.as_slice(), [123; 5 * TEST_DEVICE_BLOCK_SIZE as usize]);
    }

    #[fasync::run_singlethreaded(test)]
    async fn test_truncate_deallocates_old_extents() {
        let (fs, allocator, object) = test_filesystem_and_object().await;
        let mut buf = object.allocate_buffer(5 * TEST_DEVICE_BLOCK_SIZE as usize);
        buf.as_mut_slice().fill(0xaa);
        object.write(0, buf.as_ref()).await.expect("write failed");

        let deallocated_before = allocator.deallocated();
        let mut transaction =
            fs.clone().new_transaction(&[]).await.expect("new_transaction failed");
        object
            .truncate(&mut transaction, TEST_DEVICE_BLOCK_SIZE as u64)
            .await
            .expect("truncate failed");
        transaction.commit().await;
        let deallocated_after = allocator.deallocated();
        assert!(
            deallocated_before < deallocated_after,
            "before = {} after = {}",
            deallocated_before,
            deallocated_after
        );
    }

    #[fasync::run_singlethreaded(test)]
    async fn test_adjust_refs() {
        let (fs, allocator, object) = test_filesystem_and_object().await;
        let mut transaction =
            fs.clone().new_transaction(&[]).await.expect("new_transaction failed");
        let store = object.owner();
        store
            .adjust_refs(&mut transaction, object.object_id(), 1)
            .await
            .expect("adjust_refs failed");
        transaction.commit().await;

        let deallocated_before = allocator.deallocated();
        let mut transaction =
            fs.clone().new_transaction(&[]).await.expect("new_transaction failed");
        store
            .adjust_refs(&mut transaction, object.object_id(), -2)
            .await
            .expect("adjust_refs failed");
        transaction.commit().await;
        assert_eq!(allocator.deallocated() - deallocated_before, TEST_DEVICE_BLOCK_SIZE as usize);

        let layer_set = store.tree.layer_set();
        let mut merger = layer_set.merger();
        let mut iter = merger.seek(Bound::Unbounded).await.expect("seek failed");
        let mut found = false;
        while let Some(ItemRef { key: ObjectKey { object_id, data }, .. }) = iter.get() {
            if let ObjectKeyData::Tombstone = data {
                assert!(!found);
                found = true;
            } else {
                assert!(*object_id != object.object_id(), "{:?}", iter.get());
            }
            iter.advance().await.expect("advance failed");
        }
        assert!(found);
    }

    #[fasync::run_singlethreaded(test)]
    async fn test_locks() {
        let (_fs, _allocator, object) = test_filesystem_and_object().await;
        let (send1, recv1) = channel();
        let (send2, recv2) = channel();
        let (send3, recv3) = channel();
        let done = Mutex::new(false);
        join!(
            async {
                let mut t = object.new_transaction().await.expect("new_transaction failed");
                send1.send(()).unwrap(); // Tell the next future to continue.
                send3.send(()).unwrap(); // Tell the last future to continue.
                recv2.await.unwrap();
                let mut buf = object.allocate_buffer(5);
                buf.as_mut_slice().copy_from_slice(b"hello");
                object.txn_write(&mut t, 0, buf.as_ref()).await.expect("write failed");
                // This is a halting problem so all we can do is sleep.
                fasync::Timer::new(Duration::from_millis(100)).await;
                assert!(!*done.lock().unwrap());
                t.commit().await;
            },
            async {
                recv1.await.unwrap();
                // Reads should not block.
                let mut buf = object.allocate_buffer(TEST_DATA.len());
                assert_eq!(
                    object.read(TEST_DATA_OFFSET, buf.as_mut()).await.expect("read failed"),
                    TEST_DATA.len()
                );
                assert_eq!(buf.as_slice(), TEST_DATA);
                // Tell the first future to continue.
                send2.send(()).unwrap();
            },
            async {
                // This should block until the first future has completed.
                recv3.await.unwrap();
                let _t = object.new_transaction().await.expect("new_transaction failed");
                let mut buf = object.allocate_buffer(5);
                assert_eq!(object.read(0, buf.as_mut()).await.expect("read failed"), 5);
                assert_eq!(buf.as_slice(), b"hello");
            }
        );
    }

    #[fasync::run(10, test)]
    async fn test_racy_reads() {
        let (fs, _allocator, store) = test_filesystem_and_store().await;
        let object;
        let mut transaction =
            fs.clone().new_transaction(&[]).await.expect("new_transaction failed");
        object = Arc::new(
            ObjectStore::create_object(&store, &mut transaction, HandleOptions::default())
                .await
                .expect("create_object failed"),
        );
        transaction.commit().await;
        for _ in 0..100 {
            let cloned_object = object.clone();
            let writer = fasync::Task::spawn(async move {
                let mut buf = cloned_object.allocate_buffer(10);
                buf.as_mut_slice().fill(123);
                cloned_object.write(0, buf.as_ref()).await.expect("write failed");
            });
            let cloned_object = object.clone();
            let reader = fasync::Task::spawn(async move {
                let wait_time = rand::thread_rng().gen_range(0, 5);
                fasync::Timer::new(Duration::from_millis(wait_time)).await;
                let mut buf = cloned_object.allocate_buffer(10);
                buf.as_mut_slice().fill(23);
                let amount = cloned_object.read(0, buf.as_mut()).await.expect("write failed");
                // If we succeed in reading data, it must include the write; i.e. if we see the size
                // change, we should see the data too.  For this to succeed it requires locking on
                // the read size to ensure that when we read the size, we get the extents changed in
                // that same transaction.
                if amount != 0 {
                    assert_eq!(amount, 10);
                    assert_eq!(buf.as_slice(), &[123; 10]);
                }
            });
            writer.await;
            reader.await;
            let mut transaction = object.new_transaction().await.expect("new_transaction failed");
            object.truncate(&mut transaction, 0).await.expect("truncate failed");
            transaction.commit().await;
        }
    }

    #[fasync::run_singlethreaded(test)]
    async fn test_allocated_size() {
        let (_fs, _allocator, object) = test_filesystem_and_object().await;

        let before = object.get_allocated_size().await.expect("get_allocated_size failed");
        let mut buf = object.allocate_buffer(5);
        buf.as_mut_slice().copy_from_slice(b"hello");
        object.write(0, buf.as_ref()).await.expect("write failed");
        let after = object.get_allocated_size().await.expect("get_allocated_size failed");
        assert_eq!(after, before + TEST_DEVICE_BLOCK_SIZE as u64);

        // Do the same write again and there should be no change.
        object.write(0, buf.as_ref()).await.expect("write failed");
        assert_eq!(object.get_allocated_size().await.expect("get_allocated_size failed"), after);

        // extend...
        let mut transaction = object.new_transaction().await.expect("new_transaction failed");
        let offset = 1000 * TEST_DEVICE_BLOCK_SIZE as u64;
        let before = after;
        object
            .extend(&mut transaction, offset..offset + TEST_DEVICE_BLOCK_SIZE as u64)
            .await
            .expect("extend failed");
        transaction.commit().await;
        let after = object.get_allocated_size().await.expect("get_allocated_size failed");
        assert_eq!(after, before + TEST_DEVICE_BLOCK_SIZE as u64);

        // truncate...
        let mut transaction = object.new_transaction().await.expect("new_transaction failed");
        let before = after;
        let size = object.get_size();
        object
            .truncate(&mut transaction, size - TEST_DEVICE_BLOCK_SIZE as u64)
            .await
            .expect("extend failed");
        transaction.commit().await;
        let after = object.get_allocated_size().await.expect("get_allocated_size failed");
        assert_eq!(after, before - TEST_DEVICE_BLOCK_SIZE as u64);

        // preallocate_range...
        let mut transaction = object.new_transaction().await.expect("new_transaction failed");
        let before = after;
        object
            .preallocate_range(&mut transaction, offset..offset + TEST_DEVICE_BLOCK_SIZE as u64)
            .await
            .expect("extend failed");
        transaction.commit().await;
        let after = object.get_allocated_size().await.expect("get_allocated_size failed");
        assert_eq!(after, before + TEST_DEVICE_BLOCK_SIZE as u64);
    }

    #[fasync::run(10, test)]
    async fn test_zero() {
        let (_fs, _allocator, object) = test_filesystem_and_object().await;
        let expected_size = object.get_size();
        let mut transaction = object.new_transaction().await.expect("new_transaction failed");
        object
            .zero(&mut transaction, 0..TEST_DEVICE_BLOCK_SIZE as u64 * 10)
            .await
            .expect("zero failed");
        transaction.commit().await;
        assert_eq!(object.get_size(), expected_size);
        let mut buf = object.allocate_buffer(TEST_DEVICE_BLOCK_SIZE as usize * 10);
        assert_eq!(object.read(0, buf.as_mut()).await.expect("read failed") as u64, expected_size);
        assert_eq!(
            &buf.as_slice()[0..expected_size as usize],
            vec![0u8; expected_size as usize].as_slice()
        );
    }
}

// TODO(csuter): validation of all deserialized structs.
// TODO(csuter): check all panic! calls.