// Copyright 2017 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.

#include "src/storage/blobfs/blob.h"

#include <assert.h>
#include <ctype.h>
#include <fuchsia/device/c/fidl.h>
#include <fuchsia/io/llcpp/fidl.h>
#include <lib/sync/completion.h>
#include <lib/zx/status.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <zircon/assert.h>
#include <zircon/device/vfs.h>
#include <zircon/errors.h>
#include <zircon/status.h>
#include <zircon/syscalls.h>

#include <algorithm>
#include <memory>
#include <utility>
#include <vector>

#include <blobfs/blob-layout.h>
#include <blobfs/common.h>
#include <blobfs/compression-settings.h>
#include <blobfs/format.h>
#include <digest/digest.h>
#include <digest/merkle-tree.h>
#include <digest/node-digest.h>
#include <fbl/algorithm.h>
#include <fbl/auto_call.h>
#include <fbl/ref_ptr.h>
#include <fbl/string_buffer.h>
#include <fbl/string_piece.h>
#include <fs/journal/data_streamer.h>
#include <fs/metrics/events.h>
#include <fs/trace.h>
#include <fs/transaction/writeback.h>
#include <fs/vfs_types.h>
#include <safemath/checked_math.h>

#include "src/storage/blobfs/blob-verifier.h"
#include "src/storage/blobfs/blobfs.h"
#include "src/storage/blobfs/compression/chunked.h"
#include "src/storage/blobfs/iterator/allocated-extent-iterator.h"
#include "src/storage/blobfs/iterator/block-iterator.h"
#include "src/storage/blobfs/iterator/extent-iterator.h"
#include "src/storage/blobfs/iterator/node-populator.h"
#include "src/storage/blobfs/iterator/vector-extent-iterator.h"
#include "src/storage/blobfs/metrics.h"

namespace blobfs {
namespace {

using digest::Digest;
using digest::MerkleTreeCreator;

bool SupportsPaging(const Inode& inode) {
  zx::status<CompressionAlgorithm> status = AlgorithmForInode(inode);
  if (status.is_ok() && (status.value() == CompressionAlgorithm::UNCOMPRESSED ||
                         status.value() == CompressionAlgorithm::CHUNKED)) {
    return true;
  }
  return false;
}

}  // namespace

zx_status_t Blob::Verify() const {
  if (inode_.blob_size > 0) {
    ZX_ASSERT(IsDataLoaded());
  }

  auto blob_layout =
      BlobLayout::CreateFromInode(GetBlobLayoutFormat(blobfs_->Info()), inode_, GetBlockSize());
  if (blob_layout.is_error()) {
    FS_TRACE_ERROR("blobfs: Failed to create blob layout: %s\n", blob_layout.status_string());
    return blob_layout.status_value();
  }

  zx_status_t status;
  std::unique_ptr<BlobVerifier> verifier;

  if (blob_layout->MerkleTreeSize() == 0) {
    // No merkle tree is stored for small blobs, because the entire blob can be verified based
    // on its merkle root digest (i.e. the blob's merkle tree is just a single root digest).
    // Still verify the blob's contents in this case.
    if ((status = BlobVerifier::CreateWithoutTree(
             MerkleRoot(), blobfs_->Metrics(), inode_.blob_size, blobfs_->GetCorruptBlobNotifier(),
             &verifier)) != ZX_OK) {
      return status;
    }
  } else {
    ZX_ASSERT(IsMerkleTreeLoaded());
    if ((status = BlobVerifier::Create(
             MerkleRoot(), blobfs_->Metrics(), GetMerkleTreeBuffer(*blob_layout.value()),
             blob_layout->MerkleTreeSize(), blob_layout->Format(), inode_.blob_size,
             blobfs_->GetCorruptBlobNotifier(), &verifier)) != ZX_OK) {
      return status;
    }
  }

  return verifier->Verify(data_mapping_.start(), inode_.blob_size, data_mapping_.size());
}

uint64_t Blob::SizeData() const {
  if (state() == BlobState::kReadable) {
    return inode_.blob_size;
  }
  return 0;
}

Blob::Blob(Blobfs* bs, const Digest& digest)
    : CacheNode(digest), blobfs_(bs), clone_watcher_(this) {}

Blob::Blob(Blobfs* bs, uint32_t node_index, const Inode& inode)
    : CacheNode(Digest(inode.merkle_root_hash)),
      blobfs_(bs),
      state_(BlobState::kReadable),
      syncing_state_(SyncingState::kDone),
      map_index_(node_index),
      clone_watcher_(this),
      inode_(inode) {}

zx_status_t Blob::WriteNullBlob() {
  ZX_DEBUG_ASSERT(inode_.blob_size == 0);
  ZX_DEBUG_ASSERT(inode_.block_count == 0);

  zx_status_t status = Verify();
  if (status != ZX_OK) {
    return status;
  }

  BlobTransaction transaction;
  if (zx_status_t status = WriteMetadata(transaction); status != ZX_OK) {
    return status;
  }
  transaction.Commit(*blobfs_->journal(), {},
                     [blob = fbl::RefPtr(this)]() { blob->CompleteSync(); });
  return ZX_OK;
}

zx_status_t Blob::PrepareWrite(uint64_t size_data) {
  if (state() != BlobState::kEmpty) {
    return ZX_ERR_BAD_STATE;
  }

  memset(inode_.merkle_root_hash, 0, sizeof(inode_.merkle_root_hash));
  inode_.blob_size = size_data;

  auto write_info = std::make_unique<WritebackInfo>();

  // Reserve a node for blob's inode. We might need more nodes for extents later.
  zx_status_t status = blobfs_->GetAllocator()->ReserveNodes(1, &write_info->node_indices);
  if (status != ZX_OK) {
    return status;
  }

  // For non-null blobs, initialize the merkle/data VMOs so that we can write into them.
  if (inode_.blob_size != 0) {
    if ((status = PrepareVmosForWriting(write_info->node_indices[0].index(), inode_.blob_size)) !=
        ZX_OK) {
      return status;
    }
  }
  if (blobfs_->ShouldCompress() && inode_.blob_size >= kCompressionSizeThresholdBytes) {
    write_info->compressor =
        BlobCompressor::Create(blobfs_->write_compression_settings(), inode_.blob_size);
    if (!write_info->compressor) {
      FS_TRACE_ERROR("blobfs: Failed to initialize compressor: %d\n", status);
      return status;
    }
  }

  map_index_ = write_info->node_indices[0].index();
  write_info_ = std::move(write_info);
  set_state(BlobState::kDataWrite);

  return ZX_OK;
}

zx_status_t Blob::SpaceAllocate(uint32_t block_count) {
  TRACE_DURATION("blobfs", "Blobfs::SpaceAllocate", "block_count", block_count);
  ZX_ASSERT(block_count != 0);

  fs::Ticker ticker(blobfs_->Metrics()->Collecting());

  // Initialize the inode with known fields. The block count may change if the
  // blob is compressible.
  inode_.block_count = block_count;

  fbl::Vector<ReservedExtent> extents;
  fbl::Vector<ReservedNode> nodes;

  // Reserve space for the blob.
  const uint64_t reserved_blocks = blobfs_->GetAllocator()->ReservedBlockCount();
  zx_status_t status = blobfs_->GetAllocator()->ReserveBlocks(inode_.block_count, &extents);
  if (status == ZX_ERR_NO_SPACE && reserved_blocks > 0) {
    // It's possible that a blob has just been unlinked but has yet to be flushed through the
    // journal, and the blocks are still reserved, so if that looks likely, force a flush and then
    // try again.  This might need to be revisited if/when blobfs becomes multi-threaded.
    sync_completion_t sync;
    blobfs_->Sync([&](zx_status_t) { sync_completion_signal(&sync); });
    sync_completion_wait(&sync, ZX_TIME_INFINITE);
    status = blobfs_->GetAllocator()->ReserveBlocks(inode_.block_count, &extents);
  }
  if (status != ZX_OK) {
    return status;
  }
  if (extents.size() > kMaxBlobExtents) {
    FS_TRACE_ERROR("Error: Block reservation requires too many extents (%zu vs %zu max)\n",
                   extents.size(), kMaxBlobExtents);
    return ZX_ERR_BAD_STATE;
  }
  const ExtentCountType extent_count = static_cast<ExtentCountType>(extents.size());

  // Reserve space for all additional nodes necessary to contain this blob.
  // The inode has already been reserved in Blob::PrepareWrite.
  // Hence, we need to reserve one less node here.
  size_t node_count = NodePopulator::NodeCountForExtents(extent_count) - 1;
  status = blobfs_->GetAllocator()->ReserveNodes(node_count, &nodes);
  if (status != ZX_OK) {
    return status;
  }

  write_info_->extents = std::move(extents);
  while (!nodes.is_empty()) {
    write_info_->node_indices.push_back(nodes.erase(0));
  }
  blobfs_->Metrics()->UpdateAllocation(inode_.blob_size, ticker.End());
  return ZX_OK;
}

bool Blob::IsDataLoaded() const { return data_mapping_.vmo().is_valid(); }
bool Blob::IsMerkleTreeLoaded() const { return merkle_mapping_.vmo().is_valid(); }

void* Blob::GetDataBuffer() const { return data_mapping_.start(); }
void* Blob::GetMerkleTreeBuffer(const BlobLayout& blob_layout) const {
  void* vmo_start = merkle_mapping_.start();
  if (vmo_start == nullptr) {
    return nullptr;
  }
  // In the compact format the Merkle tree doesn't start at the beginning of the VMO.
  return static_cast<uint8_t*>(vmo_start) + blob_layout.MerkleTreeOffsetWithinBlockOffset();
}

bool Blob::IsPagerBacked() const {
  return SupportsPaging(inode_) && state() == BlobState::kReadable;
}

Digest Blob::MerkleRoot() const { return GetKeyAsDigest(); }

zx_status_t Blob::WriteMetadata(BlobTransaction& transaction) {
  TRACE_DURATION("blobfs", "Blobfs::WriteMetadata");
  assert(state() == BlobState::kDataWrite);

  // Update the on-disk hash.
  MerkleRoot().CopyTo(inode_.merkle_root_hash);

  // All data has been written to the containing VMO.
  set_state(BlobState::kReadable);
  if (readable_event_.is_valid()) {
    zx_status_t status = readable_event_.signal(0u, ZX_USER_SIGNAL_0);
    if (status != ZX_OK) {
      set_state(BlobState::kError);
      return status;
    }
  }

  // Currently only the syncing_state needs protection with the lock.
  {
    std::scoped_lock guard(mutex_);
    syncing_state_ = SyncingState::kSyncing;
  }

  if (inode_.block_count) {
    // We utilize the NodePopulator class to take our reserved blocks and nodes and fill the
    // persistent map with an allocated inode / container.

    // If |on_node| is invoked on a node, it means that node was necessary to represent this
    // blob. Persist the node back to durable storge.
    auto on_node = [this, &transaction](const ReservedNode& node) {
      blobfs_->PersistNode(node.index(), transaction);
    };

    // If |on_extent| is invoked on an extent, it was necessary to represent this blob. Persist
    // the allocation of these blocks back to durable storage.
    //
    // Additionally, because of the compression feature of blobfs, it is possible we reserved
    // more extents than this blob ended up using. Decrement |remaining_blocks| to track if we
    // should exit early.
    size_t remaining_blocks = inode_.block_count;
    auto on_extent = [this, &transaction, &remaining_blocks](ReservedExtent& extent) {
      ZX_DEBUG_ASSERT(remaining_blocks > 0);
      if (remaining_blocks >= extent.extent().Length()) {
        // Consume the entire extent.
        remaining_blocks -= extent.extent().Length();
      } else {
        // Consume only part of the extent; we're done iterating.
        extent.SplitAt(static_cast<BlockCountType>(remaining_blocks));
        remaining_blocks = 0;
      }
      blobfs_->PersistBlocks(extent, transaction);
      if (remaining_blocks == 0) {
        return NodePopulator::IterationCommand::Stop;
      }
      return NodePopulator::IterationCommand::Continue;
    };

    InodePtr mapped_inode = blobfs_->GetNode(map_index_);
    *mapped_inode = inode_;
    NodePopulator populator(blobfs_->GetAllocator(), std::move(write_info_->extents),
                            std::move(write_info_->node_indices));
    ZX_ASSERT(populator.Walk(on_node, on_extent) == ZX_OK);

    // Ensure all non-allocation flags are propagated to the inode.
    const uint16_t non_allocation_flags = kBlobFlagMaskAnyCompression;
    {
      const uint16_t compression_flags = inode_.header.flags & kBlobFlagMaskAnyCompression;
      // Kernighan's algorithm for bit counting, returns 0 when zero or one bits are set.
      ZX_DEBUG_ASSERT((compression_flags & (compression_flags - 1)) == 0);
    }
    mapped_inode->header.flags &= ~non_allocation_flags;  // Clear any existing flags first.
    mapped_inode->header.flags |= (inode_.header.flags & non_allocation_flags);
  } else {
    // Special case: Empty node.
    ZX_DEBUG_ASSERT(write_info_->node_indices.size() == 1);
    *(blobfs_->GetNode(map_index_)) = inode_;
    const ReservedNode& node = write_info_->node_indices[0];
    blobfs_->GetAllocator()->MarkInodeAllocated(node);
    blobfs_->PersistNode(node.index(), transaction);
  }
  write_info_.reset();
  return ZX_OK;
}

[[nodiscard]] static zx_status_t ZeroTail(zx_handle_t vmo, uint64_t end) {
  uint64_t vmo_size;
  zx_status_t status = zx_vmo_get_size(vmo, &vmo_size);
  if (status != ZX_OK) {
    return status;
  }
  const uint64_t tail_len = safemath::CheckSub(vmo_size, end).ValueOrDie();
  return tail_len > 0 ? zx_vmo_op_range(vmo, ZX_VMO_OP_ZERO, end, tail_len, nullptr, 0) : ZX_OK;
}

zx_status_t Blob::WriteInternal(const void* data, size_t len, size_t* actual) {
  TRACE_DURATION("blobfs", "Blobfs::WriteInternal", "data", data, "len", len);

  *actual = 0;
  if (len == 0) {
    return ZX_OK;
  }

  if (state() != BlobState::kDataWrite) {
    if (state() == BlobState::kError && write_info_ && write_info_->write_error != ZX_OK) {
      return write_info_->write_error;
    }
    return ZX_ERR_BAD_STATE;
  }

  const size_t to_write = std::min(len, inode_.blob_size - write_info_->bytes_written);
  const size_t offset = write_info_->bytes_written;

  zx_status_t status;
  if ((status = data_mapping_.vmo().write(data, offset, to_write)) != ZX_OK) {
    FS_TRACE_ERROR("blob: VMO write failed: %s\n", zx_status_get_string(status));
    return status;
  }

  *actual = to_write;
  write_info_->bytes_written += to_write;

  if (write_info_->compressor) {
    if ((status = write_info_->compressor->Update(data, to_write)) != ZX_OK) {
      return status;
    }
    ConsiderCompressionAbort();
  }

  // More data to write.
  if (write_info_->bytes_written < inode_.blob_size) {
    return ZX_OK;
  }

  status = Commit();
  if (status != ZX_OK) {
    // Record the status so that if called again, we return the same status again.  This is done
    // because it's possible that the end-user managed to partially write some data to this blob in
    // which case the error could be dropped (by zxio or some other layer) and a short write
    // returned instead.  If this happens, the end-user will retry at which point it's helpful if we
    // return the same error rather than ZX_ERR_BAD_STATE (see above).
    write_info_->write_error = status;
    set_state(BlobState::kError);
  }

  return status;
}

zx_status_t Blob::Commit() {
  zx_status_t status;

  // Only write data to disk once we've buffered the file into memory.
  // This gives us a chance to try compressing the blob before we write it back.
  if (write_info_->compressor) {
    if ((status = write_info_->compressor->End()) != ZX_OK) {
      return status;
    }
    ConsiderCompressionAbort();
  }

  fs::Duration generation_time;
  fs::DataStreamer streamer(blobfs_->journal(), blobfs_->WritebackCapacity());

  const zx::vmo& data_vmo =
      write_info_->compressor ? write_info_->compressor->Vmo() : data_mapping_.vmo();
  uint64_t data_size = write_info_->compressor ? write_info_->compressor->Size() : inode_.blob_size;

  auto blob_layout = BlobLayout::CreateFromSizes(GetBlobLayoutFormat(blobfs_->Info()),
                                                 inode_.blob_size, data_size, GetBlockSize());
  if (blob_layout.is_error()) {
    FS_TRACE_ERROR("blobfs: Failed to create blob layout: %s\n", blob_layout.status_string());
    return blob_layout.status_value();
  }

  uint32_t total_block_count = blob_layout->TotalBlockCount();
  if ((status = SpaceAllocate(total_block_count)) != ZX_OK) {
    FS_TRACE_ERROR("blobfs: Failed to allocate %u blocks for the blob: %s\n", total_block_count,
                   zx_status_get_string(status));
    return status;
  }

  uint32_t merkle_tree_block_count = blob_layout->MerkleTreeBlockCount();

  if (blob_layout->MerkleTreeSize() > 0) {
    // Tracking generation time.
    fs::Ticker ticker(blobfs_->Metrics()->Collecting());

    // TODO(smklein): As an optimization, use the Append method to create the merkle tree as we
    // write data, rather than waiting until the data is fully downloaded to create the tree.
    MerkleTreeCreator mtc;
    mtc.SetUseCompactFormat(ShouldUseCompactMerkleTreeFormat(blob_layout->Format()));
    uint8_t root[digest::kSha256Length];
    if ((status = mtc.SetDataLength(inode_.blob_size)) != ZX_OK ||
        (status = mtc.SetTree(GetMerkleTreeBuffer(*blob_layout.value()),
                              blob_layout->MerkleTreeSize(), root, sizeof(root))) != ZX_OK ||
        (status = mtc.Append(GetDataBuffer(), inode_.blob_size)) != ZX_OK) {
      FS_TRACE_ERROR("blob: Failed to create merkle: %s\n", zx_status_get_string(status));
      return status;
    }

    if (MerkleRoot() != root) {
      // Downloaded blob did not match provided digest.
      return ZX_ERR_IO_DATA_INTEGRITY;
    }

    // If the Merkle tree and data share a block then copy the data from the last block of the data
    // VMO to the start of the Merkle tree VMO.  The end of the data will be written along with the
    // Merkle tree.
    if (blob_layout->HasMerkleTreeAndDataSharedBlock()) {
      uint64_t data_size_in_last_block = data_size % GetBlockSize();
      if ((status = zx_vmo_read(data_vmo.get(), merkle_mapping_.start(),
                                data_size - data_size_in_last_block, data_size_in_last_block)) !=
          ZX_OK) {
        FS_TRACE_ERROR("blobfs: Failed to copy the end of the data to the Merkle tree vmo: %s\n",
                       zx_status_get_string(status));
        return status;
      }
    }
    if ((status = WriteBlocks(merkle_mapping_.vmo(), merkle_tree_block_count,
                              blob_layout->MerkleTreeBlockOffset(), streamer)) != ZX_OK) {
      FS_TRACE_ERROR("blobfs: Failed to write the Merkle tree to the block device: %s\n",
                     zx_status_get_string(status));
      return status;
    }
    generation_time = ticker.End();
  } else if ((status = Verify()) != ZX_OK) {
    // Small blobs may not have associated Merkle Trees, and will
    // require validation, since we are not regenerating and checking
    // the digest.
    return status;
  }

  // This shouldn't be necessary because it should already be zeroed, but just in case:
  if ((status = ZeroTail(data_vmo.get(), data_size)) != ZX_OK) {
    FS_TRACE_ERROR("blob: Failed to zero out the end of the data vmo: %s\n",
                   zx_status_get_string(status));
    return status;
  }

  // If the Merkle tree and data don't share a block then |total_block_count| -
  // |merkle_tree_block_count| = the data block count.
  // If the Merkle tree and data do share a block then |data_blocks_to_write| will be 1 less than
  // the data block count.  The last data block was written along with the Merkle tree so
  // there's 1 less data block that needs to be written.
  int32_t data_blocks_to_write = total_block_count - merkle_tree_block_count;
  if ((status = WriteBlocks(data_vmo, data_blocks_to_write, blob_layout->DataBlockOffset(),
                            streamer)) != ZX_OK) {
    FS_TRACE_ERROR("blob: Failed to write the data to the block device: %s\n",
                   zx_status_get_string(status));
    return status;
  }

  if (write_info_->compressor) {
    // By compressing, we used less blocks than we originally reserved.
    ZX_DEBUG_ASSERT(blob_layout->DataBlockAlignedSize() < blob_layout->FileBlockAlignedSize());
    SetCompressionAlgorithm(&inode_, blobfs_->write_compression_settings().compression_algorithm);
  }

  // Enqueue the blob's final data work. Metadata must be enqueued separately.
  fs::Journal::Promise write_all_data = streamer.Flush();

  // No more data to write. Flush to disk.
  fs::Ticker ticker(blobfs_->Metrics()->Collecting());  // Tracking enqueue time.

  // Wrap all pending writes with a strong reference to this Blob, so that it stays
  // alive while there are writes in progress acting on it.
  BlobTransaction transaction;
  if (zx_status_t status = WriteMetadata(transaction); status != ZX_OK) {
    return status;
  }
  transaction.Commit(*blobfs_->journal(), std::move(write_all_data),
                     [self = fbl::RefPtr(this)]() {});
  blobfs_->Metrics()->UpdateClientWrite(data_size, blob_layout->MerkleTreeSize(), ticker.End(),
                                        generation_time);
  return ZX_OK;
}

zx_status_t Blob::WriteBlocks(const zx::vmo& vmo, uint32_t block_count, uint32_t blob_block_offset,
                              fs::DataStreamer& streamer) {
  const uint64_t blobfs_data_start = DataStartBlock(blobfs_->Info());
  zx_status_t status;
  BlockIterator block_iter(std::make_unique<VectorExtentIterator>(write_info_->extents));
  if ((status = IterateToBlock(&block_iter, blob_block_offset)) != ZX_OK) {
    FS_TRACE_ERROR("blobfs: Failed to iterate to the starting block: %s\n",
                   zx_status_get_string(status));
    return status;
  }
  return StreamBlocks(
      &block_iter, block_count, [&](uint64_t block_offset, uint64_t dev_offset, uint32_t length) {
        ZX_DEBUG_ASSERT(block_offset >= blob_block_offset);
        storage::UnbufferedOperation op = {.vmo = zx::unowned_vmo(vmo.get()),
                                           .op = {
                                               .type = storage::OperationType::kWrite,
                                               .vmo_offset = block_offset - blob_block_offset,
                                               .dev_offset = dev_offset + blobfs_data_start,
                                               .length = length,
                                           }};
        streamer.StreamData(std::move(op));
        return ZX_OK;
      });
}

void Blob::ConsiderCompressionAbort() {
  // There's no point compressing if we're not going to actually save any disk space.
  // TODO(fxbug.dev/36663): In the compact layout if the uncompressed data is larger than the
  // compressed data and they both use same number of blocks this might waste a block if the
  // compressed data could have shared a block with the Merkle tree where the uncompressed data
  // couldn't.
  if (fbl::round_up(write_info_->compressor->Size(), kBlobfsBlockSize) >=
      fbl::round_up(inode_.blob_size, kBlobfsBlockSize)) {
    write_info_->compressor.reset();
  }
}

zx_status_t Blob::GetReadableEvent(zx::event* out) {
  TRACE_DURATION("blobfs", "Blobfs::GetReadableEvent");
  zx_status_t status;
  // This is the first 'wait until read event' request received.
  if (!readable_event_.is_valid()) {
    status = zx::event::create(0, &readable_event_);
    if (status != ZX_OK) {
      return status;
    } else if (state() == BlobState::kReadable) {
      readable_event_.signal(0u, ZX_USER_SIGNAL_0);
    }
  }
  zx::event out_event;
  status = readable_event_.duplicate(ZX_RIGHTS_BASIC, &out_event);
  if (status != ZX_OK) {
    return status;
  }

  *out = std::move(out_event);
  return ZX_OK;
}

zx_status_t Blob::CloneDataVmo(zx_rights_t rights, zx::vmo* out_vmo, size_t* out_size) {
  TRACE_DURATION("blobfs", "Blobfs::CloneVmo", "rights", rights);
  if (state() != BlobState::kReadable) {
    return ZX_ERR_BAD_STATE;
  }
  if (inode_.blob_size == 0) {
    return ZX_ERR_BAD_STATE;
  }

  auto status = LoadVmosFromDisk();
  if (status != ZX_OK) {
    return status;
  }
  const zx::vmo& data_vmo = data_mapping_.vmo();

  zx::vmo clone;
  status = data_vmo.create_child(ZX_VMO_CHILD_COPY_ON_WRITE, 0, inode_.blob_size, &clone);
  if (status != ZX_OK) {
    FS_TRACE_ERROR("blobfs: Failed to create child VMO: %s\n", zx_status_get_string(status));
    return status;
  }

  // Only add exec right to VMO if explictly requested.  (Saves a syscall if
  // we're just going to drop the right back again in replace() call below.)
  if (rights & ZX_RIGHT_EXECUTE) {
    // Check if the VMEX resource held by Blobfs is valid and fail if it isn't. We do this to make
    // sure that we aren't implicitly relying on the ZX_POL_AMBIENT_MARK_VMO_EXEC job policy.
    const zx::resource& vmex = blobfs_->vmex_resource();
    if (!vmex.is_valid()) {
      FS_TRACE_ERROR("blobfs: No VMEX resource available, executable blobs unsupported\n");
      return ZX_ERR_NOT_SUPPORTED;
    }
    if ((status = clone.replace_as_executable(vmex, &clone)) != ZX_OK) {
      return status;
    }
  }

  // Narrow rights to those requested.
  if ((status = clone.replace(rights, &clone)) != ZX_OK) {
    return status;
  }
  *out_vmo = std::move(clone);
  *out_size = inode_.blob_size;

  if (clone_watcher_.object() == ZX_HANDLE_INVALID) {
    clone_watcher_.set_object(data_vmo.get());
    clone_watcher_.set_trigger(ZX_VMO_ZERO_CHILDREN);

    // Keep a reference to "this" alive, preventing the blob
    // from being closed while someone may still be using the
    // underlying memory.
    //
    // We'll release it when no client-held VMOs are in use.
    clone_ref_ = fbl::RefPtr<Blob>(this);
    clone_watcher_.Begin(blobfs_->dispatcher());
  }

  return ZX_OK;
}

void Blob::HandleNoClones(async_dispatcher_t* dispatcher, async::WaitBase* wait, zx_status_t status,
                          const zx_packet_signal_t* signal) {
  const zx::vmo& vmo = data_mapping_.vmo();
  if (vmo.is_valid()) {
    zx_info_vmo_t info;
    zx_status_t info_status = vmo.get_info(ZX_INFO_VMO, &info, sizeof(info), nullptr, nullptr);
    if (info_status == ZX_OK) {
      if (info.num_children > 0) {
        // A clone was added at some point since the asynchronous HandleNoClones call was enqueued.
        // Re-arm the watcher, and return.
        //
        // clone_watcher_ is level triggered, so even if there are no clones now (since the call to
        // get_info), HandleNoClones will still be enqueued.
        //
        // No new clones can be added during this function, since clones are added on the main
        // dispatch thread which is currently running this function. If blobfs becomes
        // multi-threaded, locking will be necessary here.
        clone_watcher_.set_object(vmo.get());
        clone_watcher_.set_trigger(ZX_VMO_ZERO_CHILDREN);
        clone_watcher_.Begin(blobfs_->dispatcher());
        return;
      }
    } else {
      FS_TRACE_WARN("Failed to get_info for vmo (%s); unable to verify VMO has no clones.\n",
                    zx_status_get_string(info_status));
    }
  }
  if (!tearing_down_) {
    ZX_DEBUG_ASSERT(status == ZX_OK);
    ZX_DEBUG_ASSERT((signal->observed & ZX_VMO_ZERO_CHILDREN) != 0);
    ZX_DEBUG_ASSERT(clone_watcher_.object() != ZX_HANDLE_INVALID);
  }
  clone_watcher_.set_object(ZX_HANDLE_INVALID);
  clone_ref_ = nullptr;
}

zx_status_t Blob::ReadInternal(void* data, size_t len, size_t off, size_t* actual) {
  TRACE_DURATION("blobfs", "Blobfs::ReadInternal", "len", len, "off", off);

  if (state() != BlobState::kReadable) {
    return ZX_ERR_BAD_STATE;
  }

  auto status = LoadVmosFromDisk();
  if (status != ZX_OK) {
    return status;
  }

  if (inode_.blob_size == 0) {
    *actual = 0;
    return ZX_OK;
  }
  if (off >= inode_.blob_size) {
    *actual = 0;
    return ZX_OK;
  }
  if (len > (inode_.blob_size - off)) {
    len = inode_.blob_size - off;
  }

  status = data_mapping_.vmo().read(data, off, len);
  if (status == ZX_OK) {
    *actual = len;
  }
  return status;
}

zx_status_t Blob::LoadVmosFromDisk() {
  if (IsDataLoaded()) {
    return ZX_OK;
  }
  BlobLoader& loader = blobfs_->loader();

  zx_status_t status;
  if (IsPagerBacked()) {
    // If there is an overriden cache policy for pager-backed blobs, apply it now.
    // Otherwise the system-wide default will be used.
    std::optional<CachePolicy> cache_policy = blobfs_->pager_backed_cache_policy();
    if (cache_policy) {
      set_overridden_cache_policy(*cache_policy);
    }
    status = loader.LoadBlobPaged(map_index_, blobfs_->GetCorruptBlobNotifier(), &page_watcher_,
                                  &data_mapping_, &merkle_mapping_);
  } else {
    status = loader.LoadBlob(map_index_, blobfs_->GetCorruptBlobNotifier(), &data_mapping_,
                             &merkle_mapping_);
  }

  std::scoped_lock guard(mutex_);
  syncing_state_ = SyncingState::kDone;  // Nothing to sync when blob was loaded from the device.
  return status;
}

zx_status_t Blob::PrepareVmosForWriting(uint32_t node_index, size_t data_size) {
  if (IsDataLoaded()) {
    return ZX_OK;
  }
  // Assume the blob is uncompressed for creating the uncompressed VMOs.
  auto blob_layout = BlobLayout::CreateFromSizes(GetBlobLayoutFormat(blobfs_->Info()), data_size,
                                                 data_size, GetBlockSize());
  if (blob_layout.is_error()) {
    FS_TRACE_ERROR("blobfs: Failed to create blob layout: %s\n", blob_layout.status_string());
    return blob_layout.status_value();
  }

  zx_status_t status;

  fzl::OwnedVmoMapper merkle_mapping;
  fzl::OwnedVmoMapper data_mapping;

  uint64_t merkle_vmo_size = blob_layout->MerkleTreeBlockAlignedSize();
  // For small blobs, no merkle tree is stored, so we leave the merkle mapping uninitialized.
  if (merkle_vmo_size > 0) {
    fbl::StringBuffer<ZX_MAX_NAME_LEN> merkle_vmo_name;
    FormatBlobMerkleVmoName(node_index, &merkle_vmo_name);
    if ((status = merkle_mapping.CreateAndMap(merkle_vmo_size, merkle_vmo_name.c_str())) != ZX_OK) {
      FS_TRACE_ERROR("blobfs: Failed to map merkle vmo: %s\n", zx_status_get_string(status));
      return status;
    }
  }

  fbl::StringBuffer<ZX_MAX_NAME_LEN> data_vmo_name;
  FormatBlobDataVmoName(node_index, &data_vmo_name);
  if ((status = data_mapping.CreateAndMap(blob_layout->FileBlockAlignedSize(),
                                          data_vmo_name.c_str())) != ZX_OK) {
    FS_TRACE_ERROR("blobfs: Failed to map data vmo: %s\n", zx_status_get_string(status));
    return status;
  }

  merkle_mapping_ = std::move(merkle_mapping);
  data_mapping_ = std::move(data_mapping);
  return ZX_OK;
}

zx_status_t Blob::QueueUnlink() {
  deletable_ = true;
  // Attempt to purge in case the blob has been unlinked with no open fds
  return TryPurge();
}

zx_status_t Blob::CommitDataBuffer() {
  if (inode_.blob_size == 0) {
    // It's the null blob, so just verify.
    return Verify();
  } else {
    return data_mapping_.vmo().op_range(ZX_VMO_OP_COMMIT, 0, inode_.blob_size, nullptr, 0);
  }
}

zx_status_t Blob::LoadAndVerifyBlob(Blobfs* bs, uint32_t node_index) {
  fbl::RefPtr<Blob> vn = fbl::MakeRefCounted<Blob>(bs, node_index, *bs->GetNode(node_index));

  auto status = vn->LoadVmosFromDisk();
  if (status != ZX_OK) {
    return status;
  }

  // Blobs that are not pager-backed are already verified when they are loaded.
  // For pager-backed blobs, commit the entire blob in memory. This will cause all of the pages to
  // be verified as they are read in. Note that a separate call to Verify() is not required. If the
  // commit operation fails due to a verification failure, we do propagate the error back via the
  // return status.
  if (vn->IsPagerBacked()) {
    return vn->CommitDataBuffer();
  }
  return ZX_OK;
}

BlobCache& Blob::Cache() { return blobfs_->Cache(); }

bool Blob::ShouldCache() const {
  switch (state()) {
    // All "Valid", cacheable states, where the blob still exists on storage.
    case BlobState::kReadable:
      return true;
    default:
      return false;
  }
}

void Blob::ActivateLowMemory() {
  // We shouldn't be putting the blob into a low-memory state while it is still mapped.
  ZX_ASSERT(clone_watcher_.object() == ZX_HANDLE_INVALID);
  page_watcher_.reset();
  data_mapping_.Reset();
  merkle_mapping_.Reset();
}

Blob::~Blob() { ActivateLowMemory(); }

fs::VnodeProtocolSet Blob::GetProtocols() const { return fs::VnodeProtocol::kFile; }

bool Blob::ValidateRights(fs::Rights rights) {
  // To acquire write access to a blob, it must be empty.
  return !rights.write || state() == BlobState::kEmpty;
}

zx_status_t Blob::GetNodeInfoForProtocol([[maybe_unused]] fs::VnodeProtocol protocol,
                                         [[maybe_unused]] fs::Rights rights,
                                         fs::VnodeRepresentation* info) {
  zx::event observer;
  zx_status_t status = GetReadableEvent(&observer);
  if (status != ZX_OK) {
    return status;
  }
  *info = fs::VnodeRepresentation::File{.observer = std::move(observer)};
  return ZX_OK;
}

zx_status_t Blob::Read(void* data, size_t len, size_t off, size_t* out_actual) {
  TRACE_DURATION("blobfs", "Blob::Read", "len", len, "off", off);
  auto event = blobfs_->Metrics()->NewLatencyEvent(fs_metrics::Event::kRead);

  return ReadInternal(data, len, off, out_actual);
}

zx_status_t Blob::Write(const void* data, size_t len, size_t offset, size_t* out_actual) {
  TRACE_DURATION("blobfs", "Blob::Write", "len", len, "off", offset);
  auto event = blobfs_->Metrics()->NewLatencyEvent(fs_metrics::Event::kWrite);
  return WriteInternal(data, len, out_actual);
}

zx_status_t Blob::Append(const void* data, size_t len, size_t* out_end, size_t* out_actual) {
  auto event = blobfs_->Metrics()->NewLatencyEvent(fs_metrics::Event::kAppend);
  zx_status_t status = WriteInternal(data, len, out_actual);
  if (state() == BlobState::kDataWrite) {
    ZX_DEBUG_ASSERT(write_info_ != nullptr);
    *out_actual = write_info_->bytes_written;
  } else {
    *out_actual = inode_.blob_size;
  }
  return status;
}

zx_status_t Blob::GetAttributes(fs::VnodeAttributes* a) {
  auto event = blobfs_->Metrics()->NewLatencyEvent(fs_metrics::Event::kGetAttr);
  *a = fs::VnodeAttributes();
  a->mode = V_TYPE_FILE | V_IRUSR;
  a->inode = Ino();
  a->content_size = SizeData();
  a->storage_size = inode_.block_count * kBlobfsBlockSize;
  a->link_count = 1;
  a->creation_time = 0;
  a->modification_time = 0;
  return ZX_OK;
}

zx_status_t Blob::Truncate(size_t len) {
  TRACE_DURATION("blobfs", "Blob::Truncate", "len", len);
  auto event = blobfs_->Metrics()->NewLatencyEvent(fs_metrics::Event::kTruncate);
  if (len > 0 && fbl::round_up(len, kBlobfsBlockSize) == 0) {
    // Fail early if |len| would overflow when rounded up to block size.
    return ZX_ERR_OUT_OF_RANGE;
  }
  zx_status_t status = PrepareWrite(len);
  if (status != ZX_OK) {
    return status;
  }

  // Special case for the null blob: We skip the write phase.
  if (len == 0) {
    return WriteNullBlob();
  }
  return status;
}

#ifdef __Fuchsia__

zx_status_t Blob::QueryFilesystem(::llcpp::fuchsia::io::FilesystemInfo* info) {
  blobfs_->GetFilesystemInfo(info);
  return ZX_OK;
}

zx_status_t Blob::GetDevicePath(size_t buffer_len, char* out_name, size_t* out_len) {
  return blobfs_->Device()->GetDevicePath(buffer_len, out_name, out_len);
}

zx_status_t Blob::GetVmo(int flags, zx::vmo* out_vmo, size_t* out_size) {
  TRACE_DURATION("blobfs", "Blob::GetVmo", "flags", flags);

  if (flags & ::llcpp::fuchsia::io::VMO_FLAG_WRITE) {
    return ZX_ERR_NOT_SUPPORTED;
  } else if (flags & ::llcpp::fuchsia::io::VMO_FLAG_EXACT) {
    return ZX_ERR_NOT_SUPPORTED;
  }

  // Let clients map and set the names of their VMOs.
  zx_rights_t rights = ZX_RIGHTS_BASIC | ZX_RIGHT_MAP | ZX_RIGHTS_PROPERTY;
  // We can ignore fuchsia_io_VMO_FLAG_PRIVATE, since private / shared access
  // to the underlying VMO can both be satisfied with a clone due to
  // the immutability of blobfs blobs.
  rights |= (flags & ::llcpp::fuchsia::io::VMO_FLAG_READ) ? ZX_RIGHT_READ : 0;
  rights |= (flags & ::llcpp::fuchsia::io::VMO_FLAG_EXEC) ? ZX_RIGHT_EXECUTE : 0;
  return CloneDataVmo(rights, out_vmo, out_size);
}

#endif

void Blob::Sync(SyncCallback on_complete) {
  // This function will issue its callbacks on either the current thread or the journal thread. The
  // vnode interface says this is OK.
  TRACE_DURATION("blobfs", "Blob::Sync");
  auto event = blobfs_->Metrics()->NewLatencyEvent(fs_metrics::Event::kSync);

  SyncingState state;
  {
    std::scoped_lock guard(mutex_);
    state = syncing_state_;
  }

  switch (state) {
    case SyncingState::kDataIncomplete: {
      // It doesn't make sense to sync a partial blob since it can't have its proper
      // content-addressed name without all the data.
      on_complete(ZX_ERR_BAD_STATE);
      break;
    }
    case SyncingState::kSyncing: {
      // The blob data is complete. When this happens the Blob object will automatically write its
      // metadata, but it may not get flushed for some time. This call both encourages the sync to
      // happen "soon" and provides a way to get notified when it does.
      auto trace_id = TRACE_NONCE();
      TRACE_FLOW_BEGIN("blobfs", "Blob.sync", trace_id);
      blobfs_->Sync([evt = std::move(event),
                     on_complete = std::move(on_complete)](zx_status_t status) mutable {
        // Note: this may be executed on an arbitrary thread.
        on_complete(status);
      });
      break;
    }
    case SyncingState::kDone: {
      // All metadata has already been synced. Calling Sync() is a no-op.
      on_complete(ZX_OK);
      break;
    }
  }
}

void Blob::CompleteSync() {
  // Called on the journal thread when the syncing is complete.
  {
    std::scoped_lock guard(mutex_);
    syncing_state_ = SyncingState::kDone;
  }

  // Drop the write info, since we no longer need it.
  write_info_.reset();
}

fbl::RefPtr<Blob> Blob::CloneWatcherTeardown() {
  if (clone_watcher_.is_pending()) {
    clone_watcher_.Cancel();
    clone_watcher_.set_object(ZX_HANDLE_INVALID);
    tearing_down_ = true;
    return std::move(clone_ref_);
  }
  return nullptr;
}

zx_status_t Blob::Open([[maybe_unused]] ValidatedOptions options,
                       fbl::RefPtr<Vnode>* out_redirect) {
  fd_count_++;
  return ZX_OK;
}

zx_status_t Blob::Close() {
  auto event = blobfs_->Metrics()->NewLatencyEvent(fs_metrics::Event::kClose);
  ZX_DEBUG_ASSERT_MSG(fd_count_ > 0, "Closing blob with no fds open");
  fd_count_--;
  // Attempt purge in case blob was unlinked prior to close
  return TryPurge();
}

zx_status_t Blob::TryPurge() {
  if (Purgeable()) {
    return Purge();
  }
  return ZX_OK;
}

zx_status_t Blob::Purge() {
  ZX_DEBUG_ASSERT(fd_count_ == 0);
  ZX_DEBUG_ASSERT(Purgeable());

  if (state() == BlobState::kReadable) {
    // A readable blob should only be purged if it has been unlinked.
    ZX_ASSERT(DeletionQueued());
    BlobTransaction transaction;
    blobfs_->FreeInode(GetMapIndex(), transaction);
    transaction.Commit(*blobfs_->journal());
  }
  ZX_ASSERT(Cache().Evict(fbl::RefPtr(this)) == ZX_OK);
  set_state(BlobState::kPurged);
  return ZX_OK;
}

uint32_t Blob::GetBlockSize() const { return blobfs_->Info().block_size; }

}  // namespace blobfs