2 ** 2001 September 16
4 ** The author disclaims copyright to this source code. In place of
5 ** a legal notice, here is a blessing:
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.
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.
17 ** This header file is #include-ed by sqliteInt.h and thus ends up
18 ** being included by every source file.
20 #ifndef _SQLITE_OS_H_
21 #define _SQLITE_OS_H_
24 ** Attempt to automatically detect the operating system and setup the
25 ** necessary pre-processor macros for it.
27 #include "os_setup.h"
29 /* If the SET_FULLSYNC macro is not defined above, then make it
30 ** a no-op
32 #ifndef SET_FULLSYNC
33 # define SET_FULLSYNC(x,y)
37 ** The default size of a disk sector
39 #ifndef SQLITE_DEFAULT_SECTOR_SIZE
40 # define SQLITE_DEFAULT_SECTOR_SIZE 4096
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.
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.
64 #ifndef SQLITE_TEMP_FILE_PREFIX
65 # define SQLITE_TEMP_FILE_PREFIX "etilqs_"
66 #endif 67
69 ** The following values may be passed as the second argument to
70 ** sqlite3OsLock(). The various locks exhibit the following semantics:
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.
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().
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
92 ** File Locking Notes: (Mostly about windows but also some info for Unix)
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().
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.
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.
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.
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.
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.
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.
146 #ifdef SQLITE_OMIT_WSD
147 # define PENDING_BYTE (0x40000000)
149 # define PENDING_BYTE sqlite3PendingByte
151 #define RESERVED_BYTE (PENDING_BYTE+1)
152 #define SHARED_FIRST (PENDING_BYTE+2)
153 #define SHARED_SIZE 510
156 ** Wrapper around OS specific sqlite3_os_init() function.
158 int sqlite3OsInit(void);
161 ** Functions for accessing sqlite3_file methods
163 int 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 int sqlite3OsShmMap(sqlite3_file *,int,int,int,void volatile **);
178 int sqlite3OsShmLock(sqlite3_file *id, int, int, int);
179 void sqlite3OsShmBarrier(sqlite3_file *id);
180 int sqlite3OsShmUnmap(sqlite3_file *id, int);
181 int sqlite3OsFetch(sqlite3_file *id, i64, int, void **);
182 int sqlite3OsUnfetch(sqlite3_file *, i64, void *);
186 ** Functions for accessing sqlite3_vfs methods
188 int sqlite3OsOpen(sqlite3_vfs *, const char *, sqlite3_file*, int, int *);
189 int sqlite3OsDelete(sqlite3_vfs *, const char *, int);
190 int sqlite3OsAccess(sqlite3_vfs *, const char *, int, int *pResOut);
191 int sqlite3OsFullPathname(sqlite3_vfs *, const char *, int, char *);
192 #ifndef SQLITE_OMIT_LOAD_EXTENSION
193 void *sqlite3OsDlOpen(sqlite3_vfs *, const char *);
194 void sqlite3OsDlError(sqlite3_vfs *, int, char *);
195 void (*sqlite3OsDlSym(sqlite3_vfs *, void *, const char *))(void);
196 void sqlite3OsDlClose(sqlite3_vfs *, void *);
197 #endif /* SQLITE_OMIT_LOAD_EXTENSION */
198 int sqlite3OsRandomness(sqlite3_vfs *, int, char *);
199 int sqlite3OsSleep(sqlite3_vfs *, int);
200 int sqlite3OsCurrentTimeInt64(sqlite3_vfs *, sqlite3_int64*);
203 ** Convenience functions for opening and closing files using
204 ** sqlite3_malloc() to obtain space for the file-handle structure.
206 int sqlite3OsOpenMalloc(sqlite3_vfs *, const char *, sqlite3_file **, int,int*);
207 int sqlite3OsCloseFree(sqlite3_file *);
209 #endif /* _SQLITE_OS_H_ */