dur_journalformat.h

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// @file dur_journalformat.h The format of our journal files.

#pragma once

#include "../util/md5.hpp"

namespace mongo {

    namespace dur {

#pragma pack(1)

        struct JHeader {
            JHeader() { }
            JHeader(string fname);

            char magic[2]; // "j\n". j means journal, then a linefeed, fwiw if you were to run "less" on the file or something...

            // x4142 is asci--readable if you look at the file with head/less -- thus the starting values were near
            // that.  simply incrementing the version # is safe on a fwd basis.
            enum { CurrentVersion = 0x4147 };
            unsigned short _version;

            // these are just for diagnostic ease (make header more useful as plain text)
            char n1;          // '\n'
            char ts[20];      // ascii timestamp of file generation.  for user reading, not used by code.
            char n2;          // '\n'
            char dbpath[128]; // path/filename of this file for human reading and diagnostics.  not used by code.
            char n3, n4;      // '\n', '\n'

            unsigned long long fileId; // unique identifier that will be in each JSectHeader. important as we recycle prealloced files

            char reserved3[8026]; // 8KB total for the file header
            char txt2[2];         // "\n\n" at the end

            bool versionOk() const { return _version == CurrentVersion; }
            bool valid() const { return magic[0] == 'j' && txt2[1] == '\n' && fileId; }
        };

        struct JSectHeader {
            unsigned len;                  // length in bytes of the whole section
            unsigned long long seqNumber;  // sequence number that can be used on recovery to not do too much work
            unsigned long long fileId;     // matches JHeader::fileId
        };

        struct JEntry {
            enum OpCodes {
                OpCode_Footer      = 0xffffffff,
                OpCode_DbContext   = 0xfffffffe,
                OpCode_FileCreated = 0xfffffffd,
                OpCode_DropDb      = 0xfffffffc,
                OpCode_Min         = 0xfffff000
            };
            union {
                unsigned len;    // length in bytes of the data of the JEntry. does not include the JEntry header
                OpCodes opcode;
            };

            unsigned ofs;  // offset in file

            // sentinel and masks for _fileNo
            enum {
                DotNsSuffix = 0x7fffffff, // ".ns" file
                LocalDbBit  = 0x80000000  // assuming "local" db instead of using the JDbContext
            };
            int _fileNo;   // high bit is set to indicate it should be the <dbpath>/local database
            // char data[len] follows

            const char * srcData() const {
                const int *i = &_fileNo;
                return (const char *) (i+1);
            }

            int getFileNo() const { return _fileNo & (~LocalDbBit); }
            void setFileNo(int f) { _fileNo = f; }
            bool isNsSuffix() const { return getFileNo() == DotNsSuffix; }

            void setLocalDbContextBit() { _fileNo |= LocalDbBit; }
            bool isLocalDbContext() const { return _fileNo & LocalDbBit; }
            void clearLocalDbContextBit() { _fileNo = getFileNo(); }

            static string suffix(int fileno) {
                if( fileno == DotNsSuffix ) return "ns";
                stringstream ss;
                ss << fileno;
                return ss.str();
            }
        };

        struct JSectFooter {
            JSectFooter(const void* begin, int len) { // needs buffer to compute hash
                sentinel = JEntry::OpCode_Footer;
                reserved = 0;
                magic[0] = magic[1] = magic[2] = magic[3] = '\n';

                // skip section header since size modified after hashing
                (const char*&)begin += sizeof(JSectHeader);
                len                 -= sizeof(JSectHeader);

                md5(begin, len, hash);
            }
            unsigned sentinel;
            md5digest hash; // unsigned char[16]
            unsigned long long reserved;
            char magic[4]; // "\n\n\n\n"

            bool checkHash(const void* begin, int len) const {
                // skip section header since size modified after hashing
                (const char*&)begin += sizeof(JSectHeader);
                len                 -= sizeof(JSectHeader);
                md5digest current;
                md5(begin, len, current);
                DEV log() << "checkHash len:" << len << " hash:" << toHex(hash, 16) << " current:" << toHex(current, 16) << endl;
                return (memcmp(hash, current, sizeof(hash)) == 0);
            }
        };

        struct JDbContext {
            JDbContext() : sentinel(JEntry::OpCode_DbContext) { }
            const unsigned sentinel;   // compare to JEntry::len -- zero is our sentinel
            //char dbname[];
        };

        struct LSNFile {
            unsigned ver;
            unsigned reserved2;
            unsigned long long lsn;
            unsigned long long checkbytes;
            unsigned long long reserved[8];

            void set(unsigned long long lsn);
            unsigned long long get();
        };

#pragma pack()

    }

}

---

mongodb
Author(s): Nate Koenig
autogenerated on Fri Jan 11 12:15:18 2013