src/cobalt/storage/sql_vfs.cc

// Copyright 2015 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "cobalt/storage/sql_vfs.h"

#include "base/logging.h"
#include "base/rand_util.h"
#include "base/string_util.h"
#include "base/synchronization/lock.h"
#include "cobalt/storage/virtual_file.h"
#include "cobalt/storage/virtual_file_system.h"
#include "third_party/sqlite/sqlite3.h"

namespace cobalt {
namespace storage {

namespace {

// A "subclass" of sqlite3_file with our required data structures added.
struct virtual_file {
  sqlite3_file sql_internal_file;
  VirtualFile* file;
  base::Lock* lock;
  int current_lock;
  int shared;
};

int VfsClose(sqlite3_file* file) {
  virtual_file* vfile = reinterpret_cast<virtual_file*>(file);
  delete vfile->lock;
  return SQLITE_OK;
}

int VfsRead(sqlite3_file* file, void* out, int bytes, sqlite_int64 offset) {
  virtual_file* vfile = reinterpret_cast<virtual_file*>(file);
  vfile->file->Read(out, bytes, static_cast<int>(offset));
  return SQLITE_OK;
}

int VfsWrite(sqlite3_file* file, const void* data, int bytes,
             sqlite3_int64 offset) {
  virtual_file* vfile = reinterpret_cast<virtual_file*>(file);
  vfile->file->Write(data, bytes, static_cast<int>(offset));
  return SQLITE_OK;
}

int VfsSync(sqlite3_file* pFile, int flags) {
  UNREFERENCED_PARAMETER(pFile);
  UNREFERENCED_PARAMETER(flags);
  return SQLITE_OK;
}

int VfsFileControl(sqlite3_file* pFile, int op, void* pArg) {
  UNREFERENCED_PARAMETER(pFile);
  UNREFERENCED_PARAMETER(op);
  UNREFERENCED_PARAMETER(pArg);
  return SQLITE_OK;
}

int VfsSectorSize(sqlite3_file* file) {
  // The number of bytes that can be read without disturbing other bytes in the
  // file.
  UNREFERENCED_PARAMETER(file);
  return 1;
}

int VfsLock(sqlite3_file* file, const int mode) {
  virtual_file* vfile = reinterpret_cast<virtual_file*>(file);
  base::AutoLock lock(*vfile->lock);

  // If there is already a lock of this type or more restrictive, do nothing
  if (vfile->current_lock >= mode) {
    return SQLITE_OK;
  }

  if (mode == SQLITE_LOCK_SHARED) {
    DCHECK_EQ(vfile->current_lock, SQLITE_LOCK_NONE);
    vfile->shared++;
    vfile->current_lock = SQLITE_LOCK_SHARED;
  }

  if (mode == SQLITE_LOCK_RESERVED) {
    DCHECK_EQ(vfile->current_lock, SQLITE_LOCK_SHARED);
    vfile->current_lock = SQLITE_LOCK_RESERVED;
  }

  if (mode == SQLITE_LOCK_EXCLUSIVE) {
    if (vfile->current_lock >= SQLITE_LOCK_PENDING) {
      return SQLITE_BUSY;
    }
    vfile->current_lock = SQLITE_LOCK_PENDING;
    if (vfile->shared > 1) {
      // There are some outstanding shared locks (greater than one because the
      // pending lock is an "upgraded" shared lock)
      return SQLITE_BUSY;
    }
    // Acquire the exclusive lock
    vfile->current_lock = SQLITE_LOCK_EXCLUSIVE;
  }

  return SQLITE_OK;
}

int VfsUnlock(sqlite3_file* file, int mode) {
  DCHECK_LE(mode, SQLITE_LOCK_SHARED);
  virtual_file* vfile = reinterpret_cast<virtual_file*>(file);
  base::AutoLock lock(*vfile->lock);

  COMPILE_ASSERT(SQLITE_LOCK_NONE < SQLITE_LOCK_SHARED,
                 sqlite_lock_constants_order_has_changed);
  COMPILE_ASSERT(SQLITE_LOCK_SHARED < SQLITE_LOCK_RESERVED,
                 sqlite_lock_constants_order_has_changed);
  COMPILE_ASSERT(SQLITE_LOCK_RESERVED < SQLITE_LOCK_PENDING,
                 sqlite_lock_constants_order_has_changed);
  COMPILE_ASSERT(SQLITE_LOCK_PENDING < SQLITE_LOCK_EXCLUSIVE,
                 sqlite_lock_constants_order_has_changed);

  if (mode == SQLITE_LOCK_NONE && vfile->current_lock >= SQLITE_LOCK_SHARED) {
    vfile->shared--;
  }

  vfile->current_lock = mode;
  return SQLITE_OK;
}

int VfsCheckReservedLock(sqlite3_file* file, int* result) {
  virtual_file* vfile = reinterpret_cast<virtual_file*>(file);
  base::AutoLock lock(*vfile->lock);

  // The function expects a result is 1 if the lock is reserved, pending, or
  // exclusive; 0 otherwise.
  *result = vfile->current_lock >= SQLITE_LOCK_RESERVED ? 1 : 0;
  return SQLITE_OK;
}

int VfsFileSize(sqlite3_file* file, sqlite3_int64* out_size) {
  virtual_file* vfile = reinterpret_cast<virtual_file*>(file);
  *out_size = vfile->file->Size();
  return SQLITE_OK;
}

int VfsTruncate(sqlite3_file* file, sqlite3_int64 size) {
  virtual_file* vfile = reinterpret_cast<virtual_file*>(file);
  vfile->file->Truncate(static_cast<int>(size));
  return SQLITE_OK;
}

int VfsDeviceCharacteristics(sqlite3_file* file) {
  UNREFERENCED_PARAMETER(file);
  return 0;
}

const sqlite3_io_methods s_cobalt_vfs_io = {
    1,                        // Structure version number
    VfsClose,                 // xClose
    VfsRead,                  // xRead
    VfsWrite,                 // xWrite
    VfsTruncate,              // xTruncate
    VfsSync,                  // xSync
    VfsFileSize,              // xFileSize
    VfsLock,                  // xLock
    VfsUnlock,                // xUnlock
    VfsCheckReservedLock,     // xCheckReservedLock
    VfsFileControl,           // xFileControl
    VfsSectorSize,            // xSectorSize
    VfsDeviceCharacteristics  // xDeviceCharacteristics
};

int VfsOpen(sqlite3_vfs* sql_vfs, const char* path, sqlite3_file* file,
            int flags, int* out_flags) {
  UNREFERENCED_PARAMETER(flags);
  UNREFERENCED_PARAMETER(out_flags);
  DCHECK(path) << "NULL filename not supported.";
  virtual_file* vfile = reinterpret_cast<virtual_file*>(file);
  vfile->lock = new base::Lock;
  file->pMethods = &s_cobalt_vfs_io;

  VirtualFileSystem* vfs =
      reinterpret_cast<VirtualFileSystem*>(sql_vfs->pAppData);
  vfile->file = vfs->Open(path);
  return SQLITE_OK;
}

int VfsDelete(sqlite3_vfs* sql_vfs, const char* path, int sync_dir) {
  UNREFERENCED_PARAMETER(sync_dir);
  VirtualFileSystem* vfs =
      reinterpret_cast<VirtualFileSystem*>(sql_vfs->pAppData);
  vfs->Delete(path);
  return SQLITE_OK;
}

int VfsFullPathname(sqlite3_vfs* sql_vfs, const char* path, int out_size,
                    char* out_path) {
  UNREFERENCED_PARAMETER(sql_vfs);
  size_t path_size = static_cast<size_t>(out_size);
  if (base::strlcpy(out_path, path, path_size) < path_size) {
    return SQLITE_OK;
  }
  return SQLITE_ERROR;
}

int VfsAccess(sqlite3_vfs* sql_vfs, const char* name, int flags, int* result) {
  UNREFERENCED_PARAMETER(name);
  UNREFERENCED_PARAMETER(sql_vfs);
  UNREFERENCED_PARAMETER(flags);
  // We should always have a valid, readable/writable file.
  *result |= SQLITE_ACCESS_EXISTS | SQLITE_ACCESS_READWRITE;
  return SQLITE_OK;
}

int VfsRandomness(sqlite3_vfs* sql_vfs, int bytes, char* out) {
  UNREFERENCED_PARAMETER(sql_vfs);
  base::RandBytes(out, static_cast<size_t>(bytes));
  return SQLITE_OK;
}

}  // namespace

SqlVfs::SqlVfs(const std::string& name, VirtualFileSystem* vfs)
    : sql_vfs_(new sqlite3_vfs()) {
  memset(sql_vfs_.get(), 0, sizeof(sqlite3_vfs));
  sql_vfs_->iVersion = 1;
  sql_vfs_->szOsFile = sizeof(virtual_file);
  sql_vfs_->mxPathname = VirtualFile::kMaxVfsPathname;
  sql_vfs_->pNext = NULL;
  sql_vfs_->zName = name.c_str();
  sql_vfs_->pAppData = vfs;
  sql_vfs_->xOpen = VfsOpen;
  sql_vfs_->xDelete = VfsDelete;
  sql_vfs_->xAccess = VfsAccess;
  sql_vfs_->xFullPathname = VfsFullPathname;
  sql_vfs_->xRandomness = VfsRandomness;

  // Ensure we are not registering multiple of these with the same name.
  // Behavior is undefined in that case.
  DCHECK(sqlite3_vfs_find(name.c_str()) == NULL);

  int ret = sqlite3_vfs_register(sql_vfs_.get(), 1 /* make_default */);
  DCHECK_EQ(ret, SQLITE_OK);
}

SqlVfs::~SqlVfs() {
  int ret = sqlite3_vfs_unregister(sql_vfs_.get());
  DCHECK_EQ(ret, SQLITE_OK);
}

}  // namespace storage
}  // namespace cobalt