src/os.h

   1 /*
   2 ** 2001 September 16
   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 header file (together with is companion C source-code file
  14 ** "os.c") attempt to abstract the underlying operating system so that
  15 ** the SQLite library will work on both POSIX and windows systems.
  16 **
  17 ** This header file is #include-ed by sqliteInt.h and thus ends up
  18 ** being included by every source file.
  19 */
  20 #ifndef _SQLITE_OS_H_
  21 #define _SQLITE_OS_H_
  22
  23 /*
  24 ** Attempt to automatically detect the operating system and setup the
  25 ** necessary pre-processor macros for it.
  26 */
  27 #include "os_setup.h"
  28
  29 /* If the SET_FULLSYNC macro is not defined above, then make it
  30 ** a no-op
  31 */
  32 #ifndef SET_FULLSYNC
  33 # define SET_FULLSYNC(x,y)
  34 #endif
  35
  36 /*
  37 ** The default size of a disk sector
  38 */
  39 #ifndef SQLITE_DEFAULT_SECTOR_SIZE
  40 # define SQLITE_DEFAULT_SECTOR_SIZE 4096
  41 #endif
  42
  43 /*
  44 ** Temporary files are named starting with this prefix followed by 16 random
  45 ** alphanumeric characters, and no file extension. They are stored in the
  46 ** OS's standard temporary file directory, and are deleted prior to exit.
  47 ** If sqlite is being embedded in another program, you may wish to change the
  48 ** prefix to reflect your program's name, so that if your program exits
  49 ** prematurely, old temporary files can be easily identified. This can be done
  50 ** using -DSQLITE_TEMP_FILE_PREFIX=myprefix_ on the compiler command line.
  51 **
  52 ** 2006-10-31:  The default prefix used to be "sqlite_".  But then
  53 ** Mcafee started using SQLite in their anti-virus product and it
  54 ** started putting files with the "sqlite" name in the c:/temp folder.
  55 ** This annoyed many windows users.  Those users would then do a
  56 ** Google search for "sqlite", find the telephone numbers of the
  57 ** developers and call to wake them up at night and complain.
  58 ** For this reason, the default name prefix is changed to be "sqlite"
  59 ** spelled backwards.  So the temp files are still identified, but
  60 ** anybody smart enough to figure out the code is also likely smart
  61 ** enough to know that calling the developer will not help get rid
  62 ** of the file.
  63 */
  64 #ifndef SQLITE_TEMP_FILE_PREFIX
  65 # define SQLITE_TEMP_FILE_PREFIX "etilqs_"
  66 #endif
  67
  68 /*
  69 ** The following values may be passed as the second argument to
  70 ** sqlite3OsLock(). The various locks exhibit the following semantics:
  71 **
  72 ** SHARED:    Any number of processes may hold a SHARED lock simultaneously.
  73 ** RESERVED:  A single process may hold a RESERVED lock on a file at
  74 **            any time. Other processes may hold and obtain new SHARED locks.
  75 ** PENDING:   A single process may hold a PENDING lock on a file at
  76 **            any one time. Existing SHARED locks may persist, but no new
  77 **            SHARED locks may be obtained by other processes.
  78 ** EXCLUSIVE: An EXCLUSIVE lock precludes all other locks.
  79 **
  80 ** PENDING_LOCK may not be passed directly to sqlite3OsLock(). Instead, a
  81 ** process that requests an EXCLUSIVE lock may actually obtain a PENDING
  82 ** lock. This can be upgraded to an EXCLUSIVE lock by a subsequent call to
  83 ** sqlite3OsLock().
  84 */
  85 #define NO_LOCK         0
  86 #define SHARED_LOCK     1
  87 #define RESERVED_LOCK   2
  88 #define PENDING_LOCK    3
  89 #define EXCLUSIVE_LOCK  4
  90
  91 /*
  92 ** File Locking Notes:  (Mostly about windows but also some info for Unix)
  93 **
  94 ** We cannot use LockFileEx() or UnlockFileEx() on Win95/98/ME because
  95 ** those functions are not available.  So we use only LockFile() and
  96 ** UnlockFile().
  97 **
  98 ** LockFile() prevents not just writing but also reading by other processes.
  99 ** A SHARED_LOCK is obtained by locking a single randomly-chosen
 100 ** byte out of a specific range of bytes. The lock byte is obtained at
 101 ** random so two separate readers can probably access the file at the
 102 ** same time, unless they are unlucky and choose the same lock byte.
 103 ** An EXCLUSIVE_LOCK is obtained by locking all bytes in the range.
 104 ** There can only be one writer.  A RESERVED_LOCK is obtained by locking
 105 ** a single byte of the file that is designated as the reserved lock byte.
 106 ** A PENDING_LOCK is obtained by locking a designated byte different from
 107 ** the RESERVED_LOCK byte.
 108 **
 109 ** On WinNT/2K/XP systems, LockFileEx() and UnlockFileEx() are available,
 110 ** which means we can use reader/writer locks.  When reader/writer locks
 111 ** are used, the lock is placed on the same range of bytes that is used
 112 ** for probabilistic locking in Win95/98/ME.  Hence, the locking scheme
 113 ** will support two or more Win95 readers or two or more WinNT readers.
 114 ** But a single Win95 reader will lock out all WinNT readers and a single
 115 ** WinNT reader will lock out all other Win95 readers.
 116 **
 117 ** The following #defines specify the range of bytes used for locking.
 118 ** SHARED_SIZE is the number of bytes available in the pool from which
 119 ** a random byte is selected for a shared lock.  The pool of bytes for
 120 ** shared locks begins at SHARED_FIRST.
 121 **
 122 ** The same locking strategy and
 123 ** byte ranges are used for Unix.  This leaves open the possibility of having
 124 ** clients on win95, winNT, and unix all talking to the same shared file
 125 ** and all locking correctly.  To do so would require that samba (or whatever
 126 ** tool is being used for file sharing) implements locks correctly between
 127 ** windows and unix.  I'm guessing that isn't likely to happen, but by
 128 ** using the same locking range we are at least open to the possibility.
 129 **
 130 ** Locking in windows is manditory.  For this reason, we cannot store
 131 ** actual data in the bytes used for locking.  The pager never allocates
 132 ** the pages involved in locking therefore.  SHARED_SIZE is selected so
 133 ** that all locks will fit on a single page even at the minimum page size.
 134 ** PENDING_BYTE defines the beginning of the locks.  By default PENDING_BYTE
 135 ** is set high so that we don't have to allocate an unused page except
 136 ** for very large databases.  But one should test the page skipping logic
 137 ** by setting PENDING_BYTE low and running the entire regression suite.
 138 **
 139 ** Changing the value of PENDING_BYTE results in a subtly incompatible
 140 ** file format.  Depending on how it is changed, you might not notice
 141 ** the incompatibility right away, even running a full regression test.
 142 ** The default location of PENDING_BYTE is the first byte past the
 143 ** 1GB boundary.
 144 **
 145 */
 146 #ifdef SQLITE_OMIT_WSD
 147 # define PENDING_BYTE     (0x40000000)
 148 #else
 149 # define PENDING_BYTE      sqlite3PendingByte
 150 #endif
 151 #define RESERVED_BYTE     (PENDING_BYTE+1)
 152 #define SHARED_FIRST      (PENDING_BYTE+2)
 153 #define SHARED_SIZE       510
 154
 155 /*
 156 ** Wrapper around OS specific sqlite3_os_init() function.
 157 */
 158 int sqlite3OsInit(void);
 159
 160 /*
 161 ** Functions for accessing sqlite3_file methods
 162 */
 163 void sqlite3OsClose(sqlite3_file*);
 164 int sqlite3OsRead(sqlite3_file*, void*, int amt, i64 offset);
 165 int sqlite3OsWrite(sqlite3_file*, const void*, int amt, i64 offset);
 166 int sqlite3OsTruncate(sqlite3_file*, i64 size);
 167 int sqlite3OsSync(sqlite3_file*, int);
 168 int sqlite3OsFileSize(sqlite3_file*, i64 *pSize);
 169 int sqlite3OsLock(sqlite3_file*, int);
 170 int sqlite3OsUnlock(sqlite3_file*, int);
 171 int sqlite3OsCheckReservedLock(sqlite3_file *id, int *pResOut);
 172 int sqlite3OsFileControl(sqlite3_file*,int,void*);
 173 void sqlite3OsFileControlHint(sqlite3_file*,int,void*);
 174 #define SQLITE_FCNTL_DB_UNCHANGED 0xca093fa0
 175 int sqlite3OsSectorSize(sqlite3_file *id);
 176 int sqlite3OsDeviceCharacteristics(sqlite3_file *id);
 177 #ifndef SQLITE_OMIT_WAL
 178 int sqlite3OsShmMap(sqlite3_file *,int,int,int,void volatile **);
 179 int sqlite3OsShmLock(sqlite3_file *id, int, int, int);
 180 void sqlite3OsShmBarrier(sqlite3_file *id);
 181 int sqlite3OsShmUnmap(sqlite3_file *id, int);
 182 #endif /* SQLITE_OMIT_WAL */
 183 int sqlite3OsFetch(sqlite3_file *id, i64, int, void **);
 184 int sqlite3OsUnfetch(sqlite3_file *, i64, void *);
 185
 186
 187 /*
 188 ** Functions for accessing sqlite3_vfs methods
 189 */
 190 int sqlite3OsOpen(sqlite3_vfs *, const char *, sqlite3_file*, int, int *);
 191 int sqlite3OsDelete(sqlite3_vfs *, const char *, int);
 192 int sqlite3OsAccess(sqlite3_vfs *, const char *, int, int *pResOut);
 193 int sqlite3OsFullPathname(sqlite3_vfs *, const char *, int, char *);
 194 #ifndef SQLITE_OMIT_LOAD_EXTENSION
 195 void *sqlite3OsDlOpen(sqlite3_vfs *, const char *);
 196 void sqlite3OsDlError(sqlite3_vfs *, int, char *);
 197 void (*sqlite3OsDlSym(sqlite3_vfs *, void *, const char *))(void);
 198 void sqlite3OsDlClose(sqlite3_vfs *, void *);
 199 #endif /* SQLITE_OMIT_LOAD_EXTENSION */
 200 int sqlite3OsRandomness(sqlite3_vfs *, int, char *);
 201 int sqlite3OsSleep(sqlite3_vfs *, int);
 202 int sqlite3OsGetLastError(sqlite3_vfs*);
 203 int sqlite3OsCurrentTimeInt64(sqlite3_vfs *, sqlite3_int64*);
 204
 205 /*
 206 ** Convenience functions for opening and closing files using
 207 ** sqlite3_malloc() to obtain space for the file-handle structure.
 208 */
 209 int sqlite3OsOpenMalloc(sqlite3_vfs *, const char *, sqlite3_file **, int,int*);
 210 void sqlite3OsCloseFree(sqlite3_file *);
 211
 212 #endif /* _SQLITE_OS_H_ */