src/os.h

/*
** 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
# define INCL_DOSSEMAPHORES
# 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_ */