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Overview
Comment:Add comments describing upcoming changes to crash-test module (test6.c). No code changes. (CVS 4223)
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SHA1: 63631c17376bcb5a7aa305408aaeaf03738d7b95
User & Date: danielk1977 2007-08-14 17:42:06
Context
2007-08-14
18:03
Clarify documentation on sqlite3_interrupt(). (CVS 4224) check-in: 0b5b526c user: drh tags: trunk
17:42
Add comments describing upcoming changes to crash-test module (test6.c). No code changes. (CVS 4223) check-in: 63631c17 user: danielk1977 tags: trunk
01:58
Add a first cut at the new version 3.5 interface definitions to sqlite.h.in. (CVS 4219) check-in: 0a57f3dd user: drh tags: trunk
Changes
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Changes to src/test6.c.

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#if SQLITE_TEST          /* This file is used for the testing only */
#include "sqliteInt.h"
#include "os.h"
#include "tcl.h"

#ifndef SQLITE_OMIT_DISKIO  /* This file is a no-op if disk I/O is disabled */




/*






















































































** crashFile is a subclass of OsFile that is taylored for the
** crash test module.
*/
typedef struct crashFile crashFile;
struct crashFile {
  IoMethod const *pMethod; /* Must be first */
  u8 **apBlk;              /* Array of blocks that have been written to. */
  int nBlk;                /* Size of apBlock. */
  i64 offset;              /* Next character to be read from the file */
  int nMaxWrite;           /* Largest offset written to. */
  char *zName;             /* File name */







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#if SQLITE_TEST          /* This file is used for the testing only */
#include "sqliteInt.h"
#include "os.h"
#include "tcl.h"

#ifndef SQLITE_OMIT_DISKIO  /* This file is a no-op if disk I/O is disabled */

typedef struct crashFile crashFile;
typedef struct WriteBuffer WriteBuffer;

/*
** Method:
**
**   This layer is implemented as a wrapper around the "real" 
**   sqlite3_file object for the host system. Each time data is 
**   written to the file object, instead of being written to the
**   underlying file, the write operation is stored in an in-memory 
**   structure (type WriteBuffer). This structure is placed at the
**   end of a global ordered list (the write-list).
**
**   When data is read from a file object, the requested region is
**   first retrieved from the real file. The write-list is then 
**   traversed and data copied from any overlapping WriteBuffer 
**   structures to the output buffer. i.e. a read() operation following
**   one or more write() operations works as expected, even if no
**   data has actually been written out to the real file.
**
**   When a fsync() operation is performed, an operating system crash 
**   may be simulated, in which case exit(-1) is called (the call to 
**   xSync() never returns). Whether or not a crash is simulated,
**   the data associated with a subset of the WriteBuffer structures 
**   stored in the write-list is written to the real underlying files 
**   and the entries removed from the write-list. If a crash is simulated,
**   a subset of the buffers may be corrupted before the data is written.
**
**   The exact subset of the write-list written and/or corrupted is
**   determined by the simulated device characteristics and sector-size.
**
** "Normal" mode:
**
**   Normal mode is used when the simulated device has none of the
**   SQLITE_IOCAP_XXX flags set.
**
**   In normal mode, if the fsync() is not a simulated crash, the 
**   write-list is traversed from beginning to end. Each WriteBuffer
**   structure associated with the file handle used to call xSync()
**   is written to the real file and removed from the write-list.
**
**   If a crash is simulated, one of the following takes place for 
**   each WriteBuffer in the write-list, regardless of which 
**   file-handle it is associated with:
**
**     1. The buffer is correctly written to the file, just as if
**        a crash were not being simulated.
**
**     2. Nothing is done.
**
**     3. Garbage data is written to all sectors of the file that 
**        overlap the region specified by the WriteBuffer. Or garbage
**        data is written to some contiguous section within the 
**        overlapped sectors.
**
** Device Characteristic flag handling:
**
**   If the IOCAP_ATOMIC flag is set, then option (3) above is 
**   never selected.
**
**   If the IOCAP_ATOMIC512 flag is set, and the WriteBuffer represents
**   an aligned write() of an integer number of 512 byte regions, then
**   option (3) above is never selected. Instead, each 512 byte region
**   is either correctly written or left completely untouched. Similar
**   logic governs the behaviour if any of the other ATOMICXXX flags
**   is set.
**
**   If either the IOCAP_SAFEAPPEND or IOCAP_SEQUENTIAL flags are set
**   and a crash is being simulated, then an entry of the write-list is
**   selected at random. Everything in the list after the selected entry 
**   is discarded before processing begins.
**
**   If IOCAP_SEQUENTIAL is set and a crash is being simulated, option 
**   (1) is selected for all write-list entries except the last. If a 
**   crash is not being simulated, then all entries in the write-list
**   that occur before at least one write() on the file-handle specified
**   as part of the xSync() are written to their associated real files.
**
**   If IOCAP_SAFEAPPEND is set and the first byte written by the write()
**   operation is one byte past the current end of the file, then option
**   (1) is always selected.
*/
struct WriteBuffer {
  i64 iOffset;             /* Byte offset of the start of this write() */
  int nBuf;                /* Number of bytes written */
  u8 *zBuf;                /* Pointer to copy of written data */
  crashFile *pFile;        /* File this write() applies to */
};

/*
** crashFile is a subclass of OsFile that is taylored for 
** the crash test module.
*/

struct crashFile {
  IoMethod const *pMethod; /* Must be first */
  u8 **apBlk;              /* Array of blocks that have been written to. */
  int nBlk;                /* Size of apBlock. */
  i64 offset;              /* Next character to be read from the file */
  int nMaxWrite;           /* Largest offset written to. */
  char *zName;             /* File name */