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 /* Maximum pathname length.  Note: FILENAME_MAX defined by stdio.h
  37 */
  38 #ifndef SQLITE_MAX_PATHLEN
  39 # define SQLITE_MAX_PATHLEN FILENAME_MAX
  40 #endif
  41
  42 /* Maximum number of symlinks that will be resolved while trying to
  43 ** expand a filename in xFullPathname() in the VFS.
  44 */
  45 #ifndef SQLITE_MAX_SYMLINK
  46 # define SQLITE_MAX_SYMLINK 200
  47 #endif
  48
  49 /*
  50 ** The default size of a disk sector
  51 */
  52 #ifndef SQLITE_DEFAULT_SECTOR_SIZE
  53 # define SQLITE_DEFAULT_SECTOR_SIZE 4096
  54 #endif
  55
  56 /*
  57 ** Temporary files are named starting with this prefix followed by 16 random
  58 ** alphanumeric characters, and no file extension. They are stored in the
  59 ** OS's standard temporary file directory, and are deleted prior to exit.
  60 ** If sqlite is being embedded in another program, you may wish to change the
  61 ** prefix to reflect your program's name, so that if your program exits
  62 ** prematurely, old temporary files can be easily identified. This can be done
  63 ** using -DSQLITE_TEMP_FILE_PREFIX=myprefix_ on the compiler command line.
  64 **
  65 ** 2006-10-31:  The default prefix used to be "sqlite_".  But then
  66 ** Mcafee started using SQLite in their anti-virus product and it
  67 ** started putting files with the "sqlite" name in the c:/temp folder.
  68 ** This annoyed many windows users.  Those users would then do a
  69 ** Google search for "sqlite", find the telephone numbers of the
  70 ** developers and call to wake them up at night and complain.
  71 ** For this reason, the default name prefix is changed to be "sqlite"
  72 ** spelled backwards.  So the temp files are still identified, but
  73 ** anybody smart enough to figure out the code is also likely smart
  74 ** enough to know that calling the developer will not help get rid
  75 ** of the file.
  76 */
  77 #ifndef SQLITE_TEMP_FILE_PREFIX
  78 # define SQLITE_TEMP_FILE_PREFIX "etilqs_"
  79 #endif
  80
  81 /*
  82 ** The following values may be passed as the second argument to
  83 ** sqlite3OsLock(). The various locks exhibit the following semantics:
  84 **
  85 ** SHARED:    Any number of processes may hold a SHARED lock simultaneously.
  86 ** RESERVED:  A single process may hold a RESERVED lock on a file at
  87 **            any time. Other processes may hold and obtain new SHARED locks.
  88 ** PENDING:   A single process may hold a PENDING lock on a file at
  89 **            any one time. Existing SHARED locks may persist, but no new
  90 **            SHARED locks may be obtained by other processes.
  91 ** EXCLUSIVE: An EXCLUSIVE lock precludes all other locks.
  92 **
  93 ** PENDING_LOCK may not be passed directly to sqlite3OsLock(). Instead, a
  94 ** process that requests an EXCLUSIVE lock may actually obtain a PENDING
  95 ** lock. This can be upgraded to an EXCLUSIVE lock by a subsequent call to
  96 ** sqlite3OsLock().
  97 */
  98 #define NO_LOCK         0
  99 #define SHARED_LOCK     1
 100 #define RESERVED_LOCK   2
 101 #define PENDING_LOCK    3
 102 #define EXCLUSIVE_LOCK  4
 103
 104 /*
 105 ** File Locking Notes:  (Mostly about windows but also some info for Unix)
 106 **
 107 ** We cannot use LockFileEx() or UnlockFileEx() on Win95/98/ME because
 108 ** those functions are not available.  So we use only LockFile() and
 109 ** UnlockFile().
 110 **
 111 ** LockFile() prevents not just writing but also reading by other processes.
 112 ** A SHARED_LOCK is obtained by locking a single randomly-chosen
 113 ** byte out of a specific range of bytes. The lock byte is obtained at
 114 ** random so two separate readers can probably access the file at the
 115 ** same time, unless they are unlucky and choose the same lock byte.
 116 ** An EXCLUSIVE_LOCK is obtained by locking all bytes in the range.
 117 ** There can only be one writer.  A RESERVED_LOCK is obtained by locking
 118 ** a single byte of the file that is designated as the reserved lock byte.
 119 ** A PENDING_LOCK is obtained by locking a designated byte different from
 120 ** the RESERVED_LOCK byte.
 121 **
 122 ** On WinNT/2K/XP systems, LockFileEx() and UnlockFileEx() are available,
 123 ** which means we can use reader/writer locks.  When reader/writer locks
 124 ** are used, the lock is placed on the same range of bytes that is used
 125 ** for probabilistic locking in Win95/98/ME.  Hence, the locking scheme
 126 ** will support two or more Win95 readers or two or more WinNT readers.
 127 ** But a single Win95 reader will lock out all WinNT readers and a single
 128 ** WinNT reader will lock out all other Win95 readers.
 129 **
 130 ** The following #defines specify the range of bytes used for locking.
 131 ** SHARED_SIZE is the number of bytes available in the pool from which
 132 ** a random byte is selected for a shared lock.  The pool of bytes for
 133 ** shared locks begins at SHARED_FIRST.
 134 **
 135 ** The same locking strategy and
 136 ** byte ranges are used for Unix.  This leaves open the possibility of having
 137 ** clients on win95, winNT, and unix all talking to the same shared file
 138 ** and all locking correctly.  To do so would require that samba (or whatever
 139 ** tool is being used for file sharing) implements locks correctly between
 140 ** windows and unix.  I'm guessing that isn't likely to happen, but by
 141 ** using the same locking range we are at least open to the possibility.
 142 **
 143 ** Locking in windows is manditory.  For this reason, we cannot store
 144 ** actual data in the bytes used for locking.  The pager never allocates
 145 ** the pages involved in locking therefore.  SHARED_SIZE is selected so
 146 ** that all locks will fit on a single page even at the minimum page size.
 147 ** PENDING_BYTE defines the beginning of the locks.  By default PENDING_BYTE
 148 ** is set high so that we don't have to allocate an unused page except
 149 ** for very large databases.  But one should test the page skipping logic
 150 ** by setting PENDING_BYTE low and running the entire regression suite.
 151 **
 152 ** Changing the value of PENDING_BYTE results in a subtly incompatible
 153 ** file format.  Depending on how it is changed, you might not notice
 154 ** the incompatibility right away, even running a full regression test.
 155 ** The default location of PENDING_BYTE is the first byte past the
 156 ** 1GB boundary.
 157 **
 158 */
 159 #ifdef SQLITE_OMIT_WSD
 160 # define PENDING_BYTE     (0x40000000)
 161 #else
 162 # define PENDING_BYTE      sqlite3PendingByte
 163 #endif
 164 #define RESERVED_BYTE     (PENDING_BYTE+1)
 165 #define SHARED_FIRST      (PENDING_BYTE+2)
 166 #define SHARED_SIZE       510
 167
 168 /*
 169 ** Wrapper around OS specific sqlite3_os_init() function.
 170 */
 171 int sqlite3OsInit(void);
 172
 173 /*
 174 ** Functions for accessing sqlite3_file methods
 175 */
 176 void sqlite3OsClose(sqlite3_file*);
 177 int sqlite3OsRead(sqlite3_file*, void*, int amt, i64 offset);
 178 int sqlite3OsWrite(sqlite3_file*, const void*, int amt, i64 offset);
 179 int sqlite3OsTruncate(sqlite3_file*, i64 size);
 180 int sqlite3OsSync(sqlite3_file*, int);
 181 int sqlite3OsFileSize(sqlite3_file*, i64 *pSize);
 182 int sqlite3OsLock(sqlite3_file*, int);
 183 int sqlite3OsUnlock(sqlite3_file*, int);
 184 int sqlite3OsCheckReservedLock(sqlite3_file *id, int *pResOut);
 185 int sqlite3OsFileControl(sqlite3_file*,int,void*);
 186 void sqlite3OsFileControlHint(sqlite3_file*,int,void*);
 187 #define SQLITE_FCNTL_DB_UNCHANGED 0xca093fa0
 188 int sqlite3OsSectorSize(sqlite3_file *id);
 189 int sqlite3OsDeviceCharacteristics(sqlite3_file *id);
 190 #ifndef SQLITE_OMIT_WAL
 191 int sqlite3OsShmMap(sqlite3_file *,int,int,int,void volatile **);
 192 int sqlite3OsShmLock(sqlite3_file *id, int, int, int);
 193 void sqlite3OsShmBarrier(sqlite3_file *id);
 194 int sqlite3OsShmUnmap(sqlite3_file *id, int);
 195 #endif /* SQLITE_OMIT_WAL */
 196 int sqlite3OsFetch(sqlite3_file *id, i64, int, void **);
 197 int sqlite3OsUnfetch(sqlite3_file *, i64, void *);
 198
 199
 200 /*
 201 ** Functions for accessing sqlite3_vfs methods
 202 */
 203 int sqlite3OsOpen(sqlite3_vfs *, const char *, sqlite3_file*, int, int *);
 204 int sqlite3OsDelete(sqlite3_vfs *, const char *, int);
 205 int sqlite3OsAccess(sqlite3_vfs *, const char *, int, int *pResOut);
 206 int sqlite3OsFullPathname(sqlite3_vfs *, const char *, int, char *);
 207 #ifndef SQLITE_OMIT_LOAD_EXTENSION
 208 void *sqlite3OsDlOpen(sqlite3_vfs *, const char *);
 209 void sqlite3OsDlError(sqlite3_vfs *, int, char *);
 210 void (*sqlite3OsDlSym(sqlite3_vfs *, void *, const char *))(void);
 211 void sqlite3OsDlClose(sqlite3_vfs *, void *);
 212 #endif /* SQLITE_OMIT_LOAD_EXTENSION */
 213 int sqlite3OsRandomness(sqlite3_vfs *, int, char *);
 214 int sqlite3OsSleep(sqlite3_vfs *, int);
 215 int sqlite3OsGetLastError(sqlite3_vfs*);
 216 int sqlite3OsCurrentTimeInt64(sqlite3_vfs *, sqlite3_int64*);
 217
 218 /*
 219 ** Convenience functions for opening and closing files using
 220 ** sqlite3_malloc() to obtain space for the file-handle structure.
 221 */
 222 int sqlite3OsOpenMalloc(sqlite3_vfs *, const char *, sqlite3_file **, int,int*);
 223 void sqlite3OsCloseFree(sqlite3_file *);
 224
 225 #endif /* _SQLITE_OS_H_ */