citra/src/core/file_sys/file_backend.h

// Copyright 2014 Citra Emulator Project
// Licensed under GPLv2 or any later version
// Refer to the license.txt file included.

#pragma once

#include <algorithm>
#include <cstddef>
#include "common/common_types.h"
#include "core/hle/result.h"

////////////////////////////////////////////////////////////////////////////////////////////////////
// FileSys namespace

namespace FileSys {

class FileBackend : NonCopyable {
public:
    FileBackend() {}
    virtual ~FileBackend() {}

    /**
     * Read data from the file
     * @param offset Offset in bytes to start reading data from
     * @param length Length in bytes of data to read from file
     * @param buffer Buffer to read data into
     * @return Number of bytes read, or error code
     */
    virtual ResultVal<size_t> Read(u64 offset, size_t length, u8* buffer) const = 0;

    /**
     * Write data to the file
     * @param offset Offset in bytes to start writing data to
     * @param length Length in bytes of data to write to file
     * @param flush The flush parameters (0 == do not flush)
     * @param buffer Buffer to read data from
     * @return Number of bytes written, or error code
     */
    virtual ResultVal<size_t> Write(u64 offset, size_t length, bool flush, const u8* buffer) = 0;

    /**
     * Get the amount of time a 3ds needs to read those data
     * @param length Length in bytes of data read from file
     * @return Nanoseconds for the delay
     */
    virtual u64 GetReadDelayNs(size_t length) const {
        // Return the default delay for the case that the subclass backend didn't
        // implement one. We take the one measured for romfs reads
        // This should be removed as soon as every subclass backend
        // has one implemented
        LOG_WARNING(Service_FS, "Using default delay for read");
        static constexpr u64 slope(94);
        static constexpr u64 offset(582778);
        static constexpr u64 minimum(663124);
        u64 IPCDelayNanoseconds = std::max<u64>(static_cast<u64>(length) * slope + offset, minimum);
        return IPCDelayNanoseconds;
    }

    /**
     * Get the size of the file in bytes
     * @return Size of the file in bytes
     */
    virtual u64 GetSize() const = 0;

    /**
     * Set the size of the file in bytes
     * @param size New size of the file
     * @return true if successful
     */
    virtual bool SetSize(u64 size) const = 0;

    /**
     * Close the file
     * @return true if the file closed correctly
     */
    virtual bool Close() const = 0;

    /**
     * Flushes the file
     */
    virtual void Flush() const = 0;
};

} // namespace FileSys