logfile.h

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// @file logfile.h simple file log writing / journaling

#pragma once

#include <string>


namespace mongo {

class LogFile {
public:
    LogFile(const std::string& name, bool readwrite = false);

    ~LogFile();

    void synchronousAppend(const void* buf, size_t len);

    void writeAt(unsigned long long offset, const void* _bug, size_t _len);

    void readAt(unsigned long long offset, void* _buf, size_t _len);

    const std::string _name;

    void truncate();  // Removes extra data after current position

private:
    // Originally disks had a sector size of 512 bytes, after Advanced Format disks were deployed in
    // 2011, the default minimium size became 4096.
    // The direct io size is based on the physical disk sector, not the VM page size.
    const size_t minDirectIOSizeBytes = 4096;

private:
#if defined(_WIN32)
    typedef HANDLE fd_type;
#else
    typedef int fd_type;
#endif
    fd_type _fd;
    bool _direct;  // are we using direct I/O

    // Block size, in case of direct I/O we need to test alignment against the page size,
    // which can be different than 4kB.
    size_t _blkSize;
};
}