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// Copyright 2019 The Chromium 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 "base/files/file.h"
#include "base/files/file_path.h"
#include "third_party/sqlite/sqlite3.h"
namespace sql {
class SandboxedVfs;
// SQLite VFS file implementation that works in a sandboxed process.
// An instance is created when SQLite calls into SandboxedVfs::Open(). The
// instance is deleted by a call to SandboxedVfsFile::Close().
// The SQLite VFS API includes a complex locking strategy documented in
// This implementation uses a simplified locking strategy, where we grab an
// exclusive lock when entering any of the modes that prepare for a transition
// to EXCLUSIVE. (These modes are RESERVED and PENDING). This approach is easy
// to implement on top of base::File's locking primitives, at the cost of some
// false contention, which makes us slower under high concurrency.
// SQLite's built-in VFSes use the OS support for locking a range of bytes in
// the file, rather locking than the whole file.
class SandboxedVfsFile {
// Creates an instance in the given buffer. Note that `vfs` MUST outlive the
// returned sqlite3_file object.
static void Create(base::File file,
base::FilePath file_path,
SandboxedVfs* vfs,
sqlite3_file& buffer);
// Extracts the instance bridged to the given SQLite VFS file.
static SandboxedVfsFile& FromSqliteFile(sqlite3_file& sqlite_file);
// sqlite3_file implementation.
int Close();
int Read(void* buffer, int size, sqlite3_int64 offset);
int Write(const void* buffer, int size, sqlite3_int64 offset);
int Truncate(sqlite3_int64 size);
int Sync(int flags);
int FileSize(sqlite3_int64* result_size);
int Lock(int mode);
int Unlock(int mode);
int CheckReservedLock(int* has_reserved_lock);
int FileControl(int opcode, void* data);
int SectorSize();
int DeviceCharacteristics();
int ShmMap(int page_index,
int page_size,
int extend_file_if_needed,
void volatile** result);
int ShmLock(int offset, int size, int flags);
void ShmBarrier();
int ShmUnmap(int also_delete_file);
int Fetch(sqlite3_int64 offset, int size, void** result);
int Unfetch(sqlite3_int64 offset, void* fetch_result);
SandboxedVfsFile(base::File file,
base::FilePath file_path,
SandboxedVfs* vfs);
// Constructed from a file handle passed from the browser process.
base::File file_;
// One of the SQLite locking mode constants.
int sqlite_lock_mode_;
// The SandboxedVfs that created this instance.
SandboxedVfs* const vfs_;
// Used to identify the file in IPCs to the browser process.
const base::FilePath file_path_;
// sqlite3_file "subclass" that bridges to a SandboxedVfsFile instance.
struct SandboxedVfsFileSqliteBridge {
sqlite3_file sqlite_file;
SandboxedVfsFile* sandboxed_vfs_file;
static SandboxedVfsFileSqliteBridge& FromSqliteFile(
sqlite3_file& sqlite_file);
} // namespace sql