src/journal.c

   1 /*
   2 ** 2007 August 22
   3 **
   4 ** The author disclaims copyright to this source code.  In place of
   5 ** a legal notice, here is a blessing:
   6 **
   7 **    May you do good and not evil.
   8 **    May you find forgiveness for yourself and forgive others.
   9 **    May you share freely, never taking more than you give.
  10 **
  11 *************************************************************************
  12 **
  13 ** This file implements a special kind of sqlite3_file object used
  14 ** by SQLite to create journal files if the atomic-write optimization
  15 ** is enabled.
  16 **
  17 ** The distinctive characteristic of this sqlite3_file is that the
  18 ** actual on disk file is created lazily. When the file is created,
  19 ** the caller specifies a buffer size for an in-memory buffer to
  20 ** be used to service read() and write() requests. The actual file
  21 ** on disk is not created or populated until either:
  22 **
  23 **   1) The in-memory representation grows too large for the allocated
  24 **      buffer, or
  25 **   2) The sqlite3JournalCreate() function is called.
  26 */
  27 #ifdef SQLITE_ENABLE_ATOMIC_WRITE
  28 #include "sqliteInt.h"
  29
  30
  31 /*
  32 ** A JournalFile object is a subclass of sqlite3_file used by
  33 ** as an open file handle for journal files.
  34 */
  35 struct JournalFile {
  36   sqlite3_io_methods *pMethod;    /* I/O methods on journal files */
  37   int nBuf;                       /* Size of zBuf[] in bytes */
  38   char *zBuf;                     /* Space to buffer journal writes */
  39   int iSize;                      /* Amount of zBuf[] currently used */
  40   int flags;                      /* xOpen flags */
  41   sqlite3_vfs *pVfs;              /* The "real" underlying VFS */
  42   sqlite3_file *pReal;            /* The "real" underlying file descriptor */
  43   const char *zJournal;           /* Name of the journal file */
  44 };
  45 typedef struct JournalFile JournalFile;
  46
  47 /*
  48 ** If it does not already exists, create and populate the on-disk file
  49 ** for JournalFile p.
  50 */
  51 static int createFile(JournalFile *p){
  52   int rc = SQLITE_OK;
  53   if( !p->pReal ){
  54     sqlite3_file *pReal = (sqlite3_file *)&p[1];
  55     rc = sqlite3OsOpen(p->pVfs, p->zJournal, pReal, p->flags, 0);
  56     if( rc==SQLITE_OK ){
  57       p->pReal = pReal;
  58       if( p->iSize>0 ){
  59         assert(p->iSize<=p->nBuf);
  60         rc = sqlite3OsWrite(p->pReal, p->zBuf, p->iSize, 0);
  61       }
  62     }
  63   }
  64   return rc;
  65 }
  66
  67 /*
  68 ** Close the file.
  69 */
  70 static int jrnlClose(sqlite3_file *pJfd){
  71   JournalFile *p = (JournalFile *)pJfd;
  72   if( p->pReal ){
  73     sqlite3OsClose(p->pReal);
  74   }
  75   sqlite3_free(p->zBuf);
  76   return SQLITE_OK;
  77 }
  78
  79 /*
  80 ** Read data from the file.
  81 */
  82 static int jrnlRead(
  83   sqlite3_file *pJfd,    /* The journal file from which to read */
  84   void *zBuf,            /* Put the results here */
  85   int iAmt,              /* Number of bytes to read */
  86   sqlite_int64 iOfst     /* Begin reading at this offset */
  87 ){
  88   int rc = SQLITE_OK;
  89   JournalFile *p = (JournalFile *)pJfd;
  90   if( p->pReal ){
  91     rc = sqlite3OsRead(p->pReal, zBuf, iAmt, iOfst);
  92   }else if( (iAmt+iOfst)>p->iSize ){
  93     rc = SQLITE_IOERR_SHORT_READ;
  94   }else{
  95     memcpy(zBuf, &p->zBuf[iOfst], iAmt);
  96   }
  97   return rc;
  98 }
  99
 100 /*
 101 ** Write data to the file.
 102 */
 103 static int jrnlWrite(
 104   sqlite3_file *pJfd,    /* The journal file into which to write */
 105   const void *zBuf,      /* Take data to be written from here */
 106   int iAmt,              /* Number of bytes to write */
 107   sqlite_int64 iOfst     /* Begin writing at this offset into the file */
 108 ){
 109   int rc = SQLITE_OK;
 110   JournalFile *p = (JournalFile *)pJfd;
 111   if( !p->pReal && (iOfst+iAmt)>p->nBuf ){
 112     rc = createFile(p);
 113   }
 114   if( rc==SQLITE_OK ){
 115     if( p->pReal ){
 116       rc = sqlite3OsWrite(p->pReal, zBuf, iAmt, iOfst);
 117     }else{
 118       memcpy(&p->zBuf[iOfst], zBuf, iAmt);
 119       if( p->iSize<(iOfst+iAmt) ){
 120         p->iSize = (iOfst+iAmt);
 121       }
 122     }
 123   }
 124   return rc;
 125 }
 126
 127 /*
 128 ** Truncate the file.
 129 */
 130 static int jrnlTruncate(sqlite3_file *pJfd, sqlite_int64 size){
 131   int rc = SQLITE_OK;
 132   JournalFile *p = (JournalFile *)pJfd;
 133   if( p->pReal ){
 134     rc = sqlite3OsTruncate(p->pReal, size);
 135   }else if( size<p->iSize ){
 136     p->iSize = size;
 137   }
 138   return rc;
 139 }
 140
 141 /*
 142 ** Sync the file.
 143 */
 144 static int jrnlSync(sqlite3_file *pJfd, int flags){
 145   int rc;
 146   JournalFile *p = (JournalFile *)pJfd;
 147   if( p->pReal ){
 148     rc = sqlite3OsSync(p->pReal, flags);
 149   }else{
 150     rc = SQLITE_OK;
 151   }
 152   return rc;
 153 }
 154
 155 /*
 156 ** Query the size of the file in bytes.
 157 */
 158 static int jrnlFileSize(sqlite3_file *pJfd, sqlite_int64 *pSize){
 159   int rc = SQLITE_OK;
 160   JournalFile *p = (JournalFile *)pJfd;
 161   if( p->pReal ){
 162     rc = sqlite3OsFileSize(p->pReal, pSize);
 163   }else{
 164     *pSize = (sqlite_int64) p->iSize;
 165   }
 166   return rc;
 167 }
 168
 169 /*
 170 ** Table of methods for JournalFile sqlite3_file object.
 171 */
 172 static struct sqlite3_io_methods JournalFileMethods = {
 173   1,             /* iVersion */
 174   jrnlClose,     /* xClose */
 175   jrnlRead,      /* xRead */
 176   jrnlWrite,     /* xWrite */
 177   jrnlTruncate,  /* xTruncate */
 178   jrnlSync,      /* xSync */
 179   jrnlFileSize,  /* xFileSize */
 180   0,             /* xLock */
 181   0,             /* xUnlock */
 182   0,             /* xCheckReservedLock */
 183   0,             /* xFileControl */
 184   0,             /* xSectorSize */
 185   0,             /* xDeviceCharacteristics */
 186   0,             /* xShmMap */
 187   0,             /* xShmLock */
 188   0,             /* xShmBarrier */
 189   0              /* xShmUnmap */
 190 };
 191
 192 /*
 193 ** Open a journal file.
 194 */
 195 int sqlite3JournalOpen(
 196   sqlite3_vfs *pVfs,         /* The VFS to use for actual file I/O */
 197   const char *zName,         /* Name of the journal file */
 198   sqlite3_file *pJfd,        /* Preallocated, blank file handle */
 199   int flags,                 /* Opening flags */
 200   int nBuf                   /* Bytes buffered before opening the file */
 201 ){
 202   JournalFile *p = (JournalFile *)pJfd;
 203   memset(p, 0, sqlite3JournalSize(pVfs));
 204   if( nBuf>0 ){
 205     p->zBuf = sqlite3MallocZero(nBuf);
 206     if( !p->zBuf ){
 207       return SQLITE_NOMEM;
 208     }
 209   }else{
 210     return sqlite3OsOpen(pVfs, zName, pJfd, flags, 0);
 211   }
 212   p->pMethod = &JournalFileMethods;
 213   p->nBuf = nBuf;
 214   p->flags = flags;
 215   p->zJournal = zName;
 216   p->pVfs = pVfs;
 217   return SQLITE_OK;
 218 }
 219
 220 /*
 221 ** If the argument p points to a JournalFile structure, and the underlying
 222 ** file has not yet been created, create it now.
 223 */
 224 int sqlite3JournalCreate(sqlite3_file *p){
 225   if( p->pMethods!=&JournalFileMethods ){
 226     return SQLITE_OK;
 227   }
 228   return createFile((JournalFile *)p);
 229 }
 230
 231 /*
 232 ** Return the number of bytes required to store a JournalFile that uses vfs
 233 ** pVfs to create the underlying on-disk files.
 234 */
 235 int sqlite3JournalSize(sqlite3_vfs *pVfs){
 236   return (pVfs->szOsFile+sizeof(JournalFile));
 237 }
 238 #endif