SQLite

** The pager is used to access a database disk file.  It implements
** atomic commit and rollback through the use of a journal file that
** is separate from the database file.  The pager also implements file
** locking to prevent two processes from writing the same database
** file simultaneously, or one process from reading the database while
** another is writing.
**
** @(#) $Id: pager.c,v 1.125 2004/06/14 05:10:43 danielk1977 Exp $
*/
#include "os.h"         /* Must be first to enable large file support */
#include "sqliteInt.h"
#include "pager.h"
#include <assert.h>
#include <string.h>

**                       processes may still be reading the on-disk
**                       database file.
**
**   PAGER_EXCLUSIVE     The page cache is writing the database.
**                       Access is exclusive.  No other processes or
**                       threads can be reading or writing while one
**                       process is writing.
**
**   PAGER_SYNCED        The pager moves to this state from PAGER_EXCLUSIVE
**                       after all dirty pages have been written to the
**                       database file and the file has been synced to
**                       disk. All that remains to do is to remove the
**                       journal file and the transaction will be
**                       committed.
**
** The page cache comes up in PAGER_UNLOCK.  The first time a
** sqlite3pager_get() occurs, the state transitions to PAGER_SHARED.
** After all pages have been released using sqlite_page_unref(),
** the state transitions back to PAGER_UNLOCK.  The first time
** that sqlite3pager_write() is called, the state transitions to
** PAGER_RESERVED.  (Note that sqlite_page_write() can only be
** called on an outstanding page which means that the pager must
** be in PAGER_SHARED before it transitions to PAGER_RESERVED.)
** The transition to PAGER_EXCLUSIVE occurs when before any changes
** are made to the database file.  After an sqlite3pager_rollback()
** or sqlite_pager_commit(), the state goes back to PAGER_SHARED.
*/
#define PAGER_UNLOCK      0
#define PAGER_SHARED      1
#define PAGER_RESERVED    2
#define PAGER_EXCLUSIVE   3
#define PAGER_SYNCED      4


/*
** Each in-memory image of a page begins with the following header.
** This header is only visible to this pager module.  The client
** code that calls pager sees only the data that follows the header.
**

  ac[1] = (val>>16) & 0xff;
  ac[2] = (val>>8) & 0xff;
  ac[3] = val & 0xff;
  return sqlite3OsWrite(fd, ac, 4);
}

/*
** Write the 32-bit integer 'val' into the page identified by page header
** 'p' at offset 'offset'.
*/
static void store32bits(u32 val, PgHdr *p, int offset){
  unsigned char *ac;
  ac = &((unsigned char*)PGHDR_TO_DATA(p))[offset];
  ac[0] = (val>>24) & 0xff;
  ac[1] = (val>>16) & 0xff;
  ac[2] = (val>>8) & 0xff;
  ac[3] = val & 0xff;
}

/*
** Read a 32-bit integer at offset 'offset' from the page identified by
** page header 'p'.
*/
static u32 retrieve32bits(PgHdr *p, int offset){
  unsigned char *ac;
  ac = &((unsigned char*)PGHDR_TO_DATA(p))[offset];
  return (ac[0]<<24) | (ac[1]<<16) | (ac[2]<<8) | ac[3];
}


/*
** Convert the bits in the pPager->errMask into an approprate
** return code.
*/
static int pager_errcode(Pager *pPager){

    rc = read32bits(jfd, &cksum);
    if( rc ) return rc;
    if( pager_cksum(pPager, pgno, aData)!=cksum ){
      return SQLITE_DONE;
    }
  }

  assert( pPager->state==PAGER_RESERVED || pPager->state>=PAGER_EXCLUSIVE );

  /* If the pager is in RESERVED state, then there must be a copy of this
  ** page in the pager cache. In this case just update the pager cache,
  ** not the database file. The page is left marked dirty in this case.
  **
  ** FIX ME: Ideally the page would only be left marked dirty when the
  ** pager is in RESERVED state if it was dirty when this statement
  ** transaction was started. 
  **
  ** If in EXCLUSIVE state, then we update the pager cache if it exists
  ** and the main file. The page is then marked not dirty.
  */
  pPg = pager_lookup(pPager, pgno);
  assert( pPager->state>=PAGER_EXCLUSIVE || pPg );
  TRACE2("PLAYBACK page %d\n", pgno);
  if( pPager->state>=PAGER_EXCLUSIVE ){
    sqlite3OsSeek(&pPager->fd, (pgno-1)*(off_t)SQLITE_PAGE_SIZE);
    rc = sqlite3OsWrite(&pPager->fd, aData, SQLITE_PAGE_SIZE);
  }
  if( pPg ){
    /* No page should ever be rolled back that is in use, except for page
    ** 1 which is held in use in order to keep the lock on the database
    ** active.
    */
    void *pData;
    assert( pPg->nRef==0 || pPg->pgno==1 );
    pData = PGHDR_TO_DATA(pPg);
    memcpy(pData, aData, pPager->pageSize);
    if( pPager->xDestructor ){  /*** FIX ME:  Should this be xReinit? ***/
      pPager->xDestructor(pData, pPager->pageSize);
    }
    if( pPager->state>=PAGER_EXCLUSIVE ){
      pPg->dirty = 0;
      pPg->needSync = 0;
    }
    CODEC(pPager, pData, pPg->pgno, 3);
  }
  return rc;
}

** with this page cache after this function returns will likely
** result in a coredump.
*/
int sqlite3pager_close(Pager *pPager){
  PgHdr *pPg, *pNext;
  switch( pPager->state ){
    case PAGER_RESERVED:
    case PAGER_SYNCED: 
    case PAGER_EXCLUSIVE: {
      sqlite3pager_rollback(pPager);
      if( !pPager->memDb ){
        sqlite3OsUnlock(&pPager->fd, NO_LOCK);
      }
      assert( pPager->journalOpen==0 );
      break;

  Pager *pPager,
  void (*xCodec)(void*,void*,Pgno,int),
  void *pCodecArg
){
  pPager->xCodec = xCodec;
  pPager->pCodecArg = pCodecArg;
}

/*
** This routine is called to increment the database file change-counter,
** stored at byte 24 of the pager file.
*/
static int pager_incr_changecounter(Pager *pPager){
  void *pPage;
  PgHdr *pPgHdr;
  u32 change_counter;
  int rc;

  /* Open page 1 of the file for writing. */
  rc = sqlite3pager_get(pPager, 1, &pPage);
  if( rc!=SQLITE_OK ) return rc;
  rc = sqlite3pager_write(pPage);
  if( rc!=SQLITE_OK ) return rc;

  /* Read the current value at byte 24. */
  pPgHdr = DATA_TO_PGHDR(pPage);
  change_counter = retrieve32bits(pPgHdr, 24);

  /* Increment the value just read and write it back to byte 24. */
  change_counter++;
  store32bits(change_counter, pPgHdr, 24);

  /* Release the page reference. */
  sqlite3pager_unref(pPage);
  return SQLITE_OK;
}

/*
** Sync the database file for the pager pPager. zMaster points to the name
** of a master journal file that should be written into the individual
** journal file. zMaster may be NULL, which is interpreted as no master
** journal (a single database transaction).
**
** This routine ensures that the journal is synced, all dirty pages written
** to the database file and the database file synced. The only thing that
** remains to commit the transaction is to delete the journal file (or
** master journal file if specified).
**
** Note that if zMaster==NULL, this does not overwrite a previous value
** passed to an sqlite3pager_sync() call.
*/
int sqlite3pager_sync(Pager *pPager, const char *zMaster){
  int rc = SQLITE_OK;

  /* If this is an in-memory db, or no pages have been written to, or this
  ** function has already been called, it is a no-op.
  */
  if( pPager->state!=PAGER_SYNCED && !pPager->memDb && pPager->dirtyCache ){
    PgHdr *pPg;
    assert( pPager->journalOpen );

    rc = pager_incr_changecounter(pPager);
    if( rc!=SQLITE_OK ) goto sync_exit;

    /* Sync the journal file */
    rc = syncJournal(pPager, zMaster);
    if( rc!=SQLITE_OK ) goto sync_exit;

    /* Write all dirty pages to the database file */
    pPg = pager_get_all_dirty_pages(pPager);
    rc = pager_write_pagelist(pPg);
    if( rc!=SQLITE_OK ) goto sync_exit;

    /* Sync the database file. */
    if( !pPager->noSync ){
      rc = sqlite3OsSync(&pPager->fd);
    }

    pPager->state = PAGER_SYNCED;
  }

sync_exit:
  return rc;
}

#ifdef SQLITE_DEBUG

**
** Various scripts scan this source file in order to generate HTML
** documentation, headers files, or other derived files.  The formatting
** of the code in this file is, therefore, important.  See other comments
** in this file for details.  If in doubt, do not deviate from existing
** commenting and indentation practices when changing or adding code.
**
** $Id: vdbe.c,v 1.371 2004/06/14 05:10:43 danielk1977 Exp $
*/
#include "sqliteInt.h"
#include "os.h"
#include <ctype.h>
#include "vdbeInt.h"

/*

**  Character      Column affinity
**  ------------------------------
**  'n'            NUMERIC
**  'i'            INTEGER
**  't'            TEXT
**  'o'            NONE
**
** If P3 is NULL then no datatype coercion occurs.
*/
/* Opcode MakeRecord P1 * P3
**
** Convert the top P1 entries of the stack into a single entry
** suitable for use as a data record in a database table.  The
** details of the format are irrelavant as long as the OP_Column
** opcode can decode the record later.  Refer to source code