/*

 ** 2001 September 16

 **

 ** The author disclaims copyright to this source code.  In place of

 ** a legal notice, here is a blessing:

 **

 **    May you do good and not evil.

 **    May you find forgiveness for yourself and forgive others.

 **    May you share freely, never taking more than you give.

 **

 ******************************************************************************

 **

 ** This header file (together with is companion C source-code file

 ** "os.c") attempt to abstract the underlying operating system so that

 ** the SQLite library will work on both POSIX and windows systems.

 **

 ** This header file is #include-ed by sqliteInt.h and thus ends up

 ** being included by every source file.

 */

 #ifndef _SQLITE_OS_H_

 #define _SQLITE_OS_H_

 /*

 ** Figure out if we are dealing with Unix, Windows, or some other

 ** operating system.  After the following block of preprocess macros,

 ** all of OS_UNIX, OS_WIN, OS_OS2, and OS_OTHER will defined to either

 ** 1 or 0.  One of the four will be 1.  The other three will be 0.

 */

 #if defined(OS_OTHER)

 # if OS_OTHER==1

 #   undef OS_UNIX

 #   define OS_UNIX 0

 #   undef OS_WIN

 #   define OS_WIN 0

 #   undef OS_OS2

 #   define OS_OS2 0

 # else

 #   undef OS_OTHER

 # endif

 #endif

 #if !defined(OS_UNIX) && !defined(OS_OTHER)

 # define OS_OTHER 0

 # ifndef OS_WIN

 #   if defined(_WIN32) || defined(WIN32) || defined(__CYGWIN__) || defined(__MINGW32__) || defined(__BORLANDC__)

 #     define OS_WIN 1

 #     define OS_UNIX 0

 #     define OS_OS2 0

 #   elif defined(__EMX__) || defined(_OS2) || defined(OS2) || defined(_OS2_) || defined(__OS2__)

 #     define OS_WIN 0

 #     define OS_UNIX 0

 #     define OS_OS2 1

 #   else

 #     define OS_WIN 0

 #     define OS_UNIX 1

 #     define OS_OS2 0

 #  endif

 # else

 #  define OS_UNIX 0

 #  define OS_OS2 0

 # endif

 #else

 # ifndef OS_WIN

 #  define OS_WIN 0

 # endif

 #endif

 /*

 ** Define the maximum size of a temporary filename

 */

 #if OS_WIN

 # include <windows.h>

 # define SQLITE_TEMPNAME_SIZE (MAX_PATH+50)

 #elif OS_OS2

 # if (__GNUC__ > 3 || __GNUC__ == 3 && __GNUC_MINOR__ >= 3) && defined(OS2_HIGH_MEMORY)

 #  include <os2safe.h> /* has to be included before os2.h for linking to work */

 # endif

 # define INCL_DOSDATETIME

 # define INCL_DOSFILEMGR

 # define INCL_DOSERRORS

 # define INCL_DOSMISC

 # define INCL_DOSPROCESS

 # define INCL_DOSMODULEMGR

 # include <os2.h>

 # define SQLITE_TEMPNAME_SIZE (CCHMAXPATHCOMP)

 #else

 # define SQLITE_TEMPNAME_SIZE 200

 #endif

 /* If the SET_FULLSYNC macro is not defined above, then make it

 ** a no-op

 */

 #ifndef SET_FULLSYNC

 # define SET_FULLSYNC(x,y)

 #endif

 /*

 ** The default size of a disk sector

 */

 #ifndef SQLITE_DEFAULT_SECTOR_SIZE

 # define SQLITE_DEFAULT_SECTOR_SIZE 512

 #endif

 /*

 ** Temporary files are named starting with this prefix followed by 16 random

 ** alphanumeric characters, and no file extension. They are stored in the

 ** OS's standard temporary file directory, and are deleted prior to exit.

 ** If sqlite is being embedded in another program, you may wish to change the

 ** prefix to reflect your program's name, so that if your program exits

 ** prematurely, old temporary files can be easily identified. This can be done

 ** using -DSQLITE_TEMP_FILE_PREFIX=myprefix_ on the compiler command line.

 **

 ** 2006-10-31:  The default prefix used to be "sqlite_".  But then

 ** Mcafee started using SQLite in their anti-virus product and it

 ** started putting files with the "sqlite" name in the c:/temp folder.

 ** This annoyed many windows users.  Those users would then do a 

 ** Google search for "sqlite", find the telephone numbers of the

 ** developers and call to wake them up at night and complain.

 ** For this reason, the default name prefix is changed to be "sqlite" 

 ** spelled backwards.  So the temp files are still identified, but

 ** anybody smart enough to figure out the code is also likely smart

 ** enough to know that calling the developer will not help get rid

 ** of the file.

 */

 #ifndef SQLITE_TEMP_FILE_PREFIX

 # define SQLITE_TEMP_FILE_PREFIX "etilqs_"

 #endif

 /*

 ** If using an alternative OS interface, then we must have an "os_other.h"

 ** header file available for that interface.  Presumably the "os_other.h"

 ** header file contains #defines similar to those above.

 */

 #if OS_OTHER

 # include "os_other.h"

 #endif

 /*

 ** The following values may be passed as the second argument to

 ** sqlite3OsLock(). The various locks exhibit the following semantics:

 **

 ** SHARED:    Any number of processes may hold a SHARED lock simultaneously.

 ** RESERVED:  A single process may hold a RESERVED lock on a file at

 **            any time. Other processes may hold and obtain new SHARED locks.

 ** PENDING:   A single process may hold a PENDING lock on a file at

 **            any one time. Existing SHARED locks may persist, but no new

 **            SHARED locks may be obtained by other processes.

 ** EXCLUSIVE: An EXCLUSIVE lock precludes all other locks.

 **

 ** PENDING_LOCK may not be passed directly to sqlite3OsLock(). Instead, a

 ** process that requests an EXCLUSIVE lock may actually obtain a PENDING

 ** lock. This can be upgraded to an EXCLUSIVE lock by a subsequent call to

 ** sqlite3OsLock().

 */

 #define NO_LOCK         0

 #define SHARED_LOCK     1

 #define RESERVED_LOCK   2

 #define PENDING_LOCK    3

 #define EXCLUSIVE_LOCK  4

 /*

 ** File Locking Notes:  (Mostly about windows but also some info for Unix)

 **

 ** We cannot use LockFileEx() or UnlockFileEx() on Win95/98/ME because

 ** those functions are not available.  So we use only LockFile() and

 ** UnlockFile().

 **

 ** LockFile() prevents not just writing but also reading by other processes.

 ** A SHARED_LOCK is obtained by locking a single randomly-chosen 

 ** byte out of a specific range of bytes. The lock byte is obtained at 

 ** random so two separate readers can probably access the file at the 

 ** same time, unless they are unlucky and choose the same lock byte.

 ** An EXCLUSIVE_LOCK is obtained by locking all bytes in the range.

 ** There can only be one writer.  A RESERVED_LOCK is obtained by locking

 ** a single byte of the file that is designated as the reserved lock byte.

 ** A PENDING_LOCK is obtained by locking a designated byte different from

 ** the RESERVED_LOCK byte.

 **

 ** On WinNT/2K/XP systems, LockFileEx() and UnlockFileEx() are available,

 ** which means we can use reader/writer locks.  When reader/writer locks

 ** are used, the lock is placed on the same range of bytes that is used

 ** for probabilistic locking in Win95/98/ME.  Hence, the locking scheme

 ** will support two or more Win95 readers or two or more WinNT readers.

 ** But a single Win95 reader will lock out all WinNT readers and a single

 ** WinNT reader will lock out all other Win95 readers.

 **

 ** The following #defines specify the range of bytes used for locking.

 ** SHARED_SIZE is the number of bytes available in the pool from which

 ** a random byte is selected for a shared lock.  The pool of bytes for

 ** shared locks begins at SHARED_FIRST. 

 **

 ** These #defines are available in sqlite_aux.h so that adaptors for

 ** connecting SQLite to other operating systems can use the same byte

 ** ranges for locking.  In particular, the same locking strategy and

 ** byte ranges are used for Unix.  This leaves open the possiblity of having

 ** clients on win95, winNT, and unix all talking to the same shared file

 ** and all locking correctly.  To do so would require that samba (or whatever

 ** tool is being used for file sharing) implements locks correctly between

 ** windows and unix.  I'm guessing that isn't likely to happen, but by

 ** using the same locking range we are at least open to the possibility.

 **

 ** Locking in windows is manditory.  For this reason, we cannot store

 ** actual data in the bytes used for locking.  The pager never allocates

 ** the pages involved in locking therefore.  SHARED_SIZE is selected so

 ** that all locks will fit on a single page even at the minimum page size.

 ** PENDING_BYTE defines the beginning of the locks.  By default PENDING_BYTE

 ** is set high so that we don't have to allocate an unused page except

 ** for very large databases.  But one should test the page skipping logic 

 ** by setting PENDING_BYTE low and running the entire regression suite.

 **

 ** Changing the value of PENDING_BYTE results in a subtly incompatible

 ** file format.  Depending on how it is changed, you might not notice

 ** the incompatibility right away, even running a full regression test.

 ** The default location of PENDING_BYTE is the first byte past the

 ** 1GB boundary.

 **

 */

 #ifndef SQLITE_TEST

 #define PENDING_BYTE      0x40000000  /* First byte past the 1GB boundary */

 #else

 extern unsigned int sqlite3_pending_byte;

 #define PENDING_BYTE sqlite3_pending_byte

 #endif

 #define RESERVED_BYTE     (PENDING_BYTE+1)

 #define SHARED_FIRST      (PENDING_BYTE+2)

 #define SHARED_SIZE       510

 /* 

 ** Functions for accessing sqlite3_file methods 

 */

 int sqlite3OsClose(sqlite3_file*);

 int sqlite3OsRead(sqlite3_file*, void*, int amt, i64 offset);

 int sqlite3OsWrite(sqlite3_file*, const void*, int amt, i64 offset);

 int sqlite3OsTruncate(sqlite3_file*, i64 size);

 int sqlite3OsSync(sqlite3_file*, int);

 int sqlite3OsFileSize(sqlite3_file*, i64 *pSize);

 int sqlite3OsLock(sqlite3_file*, int);

 int sqlite3OsUnlock(sqlite3_file*, int);

 int sqlite3OsCheckReservedLock(sqlite3_file *id);

 int sqlite3OsFileControl(sqlite3_file*,int,void*);

 int sqlite3OsSectorSize(sqlite3_file *id);

 int sqlite3OsDeviceCharacteristics(sqlite3_file *id);

 /* 

 ** Functions for accessing sqlite3_vfs methods 

 */

 int sqlite3OsOpen(sqlite3_vfs *, const char *, sqlite3_file*, int, int *);

 int sqlite3OsDelete(sqlite3_vfs *, const char *, int);

 int sqlite3OsAccess(sqlite3_vfs *, const char *, int);

 int sqlite3OsGetTempname(sqlite3_vfs *, int, char *);

 int sqlite3OsFullPathname(sqlite3_vfs *, const char *, int, char *);

 void *sqlite3OsDlOpen(sqlite3_vfs *, const char *);

 void sqlite3OsDlError(sqlite3_vfs *, int, char *);

 void *sqlite3OsDlSym(sqlite3_vfs *, void *, const char *);

 void sqlite3OsDlClose(sqlite3_vfs *, void *);

 int sqlite3OsRandomness(sqlite3_vfs *, int, char *);

 int sqlite3OsSleep(sqlite3_vfs *, int);

 int sqlite3OsCurrentTime(sqlite3_vfs *, double*);

 /*

 ** Convenience functions for opening and closing files using 

 ** sqlite3_malloc() to obtain space for the file-handle structure.

 */

 int sqlite3OsOpenMalloc(sqlite3_vfs *, const char *, sqlite3_file **, int,int*);

 int sqlite3OsCloseFree(sqlite3_file *);

 /*

 ** Each OS-specific backend defines an instance of the following

 ** structure for returning a pointer to its sqlite3_vfs.  If OS_OTHER

 ** is defined (meaning that the application-defined OS interface layer

 ** is used) then there is no default VFS.   The application must

 ** register one or more VFS structures using sqlite3_vfs_register()

 ** before attempting to use SQLite.

 */

 #if OS_UNIX || OS_WIN || OS_OS2

 sqlite3_vfs *sqlite3OsDefaultVfs(void);

 #else

 # define sqlite3OsDefaultVfs(X) 0

 #endif

 #endif /* _SQLITE_OS_H_ */