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+/*
+** 2010 April 7
+**
+** 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 file implements an example of a simple VFS implementation that
+** omits complex features often not required or not possible on embedded
+** platforms. Code is included to buffer writes to the journal file,
+** which can be a significant performance improvement on some embedded
+** platforms.
+**
+** OVERVIEW
+**
+** The code in this file implements a minimal SQLite VFS that can be
+** used on Linux and other posix-like operating systems. The following
+** system calls are used:
+**
+** File-system: access(), unlink(), getcwd()
+** File IO: open(), read(), write(), fsync(), close(), fstat()
+** Other: sleep(), usleep(), time()
+**
+** The following VFS features are omitted:
+**
+** 1. File locking. The user must ensure that there is at most one
+** connection to each database when using this VFS. Multiple
+** connections to a single shared-cache count as a single connection
+** for the purposes of the previous statement.
+**
+** 2. The loading of dynamic extensions (shared libraries).
+**
+** 3. Temporary files. The user must configure SQLite to use in-memory
+** temp files when using this VFS. The easiest way to do this is to
+** compile with:
+**
+** -DSQLITE_TEMP_STORE=3
+**
+** 4. File truncation. As of version 3.6.24, SQLite may run without
+** a working xTruncate() call, providing the user does not configure
+** SQLite to use "journal_mode=truncate", or use both
+** "journal_mode=persist" and ATTACHed databases.
+**
+** It is assumed that the system uses UNIX-like path-names. Specifically,
+** that '/' characters are used to separate path components and that
+** a path-name is a relative path unless it begins with a '/'. And that
+** no UTF-8 encoded paths are greater than 512 bytes in length.
+**
+** JOURNAL WRITE-BUFFERING
+**
+** To commit a transaction to the database, SQLite first writes rollback
+** information into the journal file. This usually consists of 4 steps:
+**
+** 1. The rollback information is sequentially written into the journal
+** file, starting at the start of the file.
+** 2. The journal file is synced to disk.
+** 3. A modification is made to the first few bytes of the journal file.
+** 4. The journal file is synced to disk again.
+**
+** Most of the data is written in step 1 using a series of calls to the
+** VFS xWrite() method. The buffers passed to the xWrite() calls are of
+** various sizes. For example, as of version 3.6.24, when committing a
+** transaction that modifies 3 pages of a database file that uses 4096
+** byte pages residing on a media with 512 byte sectors, SQLite makes
+** eleven calls to the xWrite() method to create the rollback journal,
+** as follows:
+**
+** Write offset | Bytes written
+** ----------------------------
+** 0 512
+** 512 4
+** 516 4096
+** 4612 4
+** 4616 4
+** 4620 4096
+** 8716 4
+** 8720 4
+** 8724 4096
+** 12820 4
+** ++++++++++++SYNC+++++++++++
+** 0 12
+** ++++++++++++SYNC+++++++++++
+**
+** On many operating systems, this is an efficient way to write to a file.
+** However, on some embedded systems that do not cache writes in OS
+** buffers it is much more efficient to write data in blocks that are
+** an integer multiple of the sector-size in size and aligned at the
+** start of a sector.
+**
+** To work around this, the code in this file allocates a fixed size
+** buffer of SQLITE_DEMOVFS_BUFFERSZ using sqlite3_malloc() whenever a
+** journal file is opened. It uses the buffer to coalesce sequential
+** writes into aligned SQLITE_DEMOVFS_BUFFERSZ blocks. When SQLite
+** invokes the xSync() method to sync the contents of the file to disk,
+** all accumulated data is written out, even if it does not constitute
+** a complete block. This means the actual IO to create the rollback
+** journal for the example transaction above is this:
+**
+** Write offset | Bytes written
+** ----------------------------
+** 0 8192
+** 8192 4632
+** ++++++++++++SYNC+++++++++++
+** 0 12
+** ++++++++++++SYNC+++++++++++
+**
+** Much more efficient if the underlying OS is not caching write
+** operations.
+*/
+
+#if !defined(SQLITE_TEST) || SQLITE_OS_UNIX
+
+#include "sqlite3.h"
+
+#include <assert.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/file.h>
+#include <sys/param.h>
+#include <unistd.h>
+#include <time.h>
+#include <errno.h>
+#include <fcntl.h>
+
+/*
+** Size of the write buffer used by journal files in bytes.
+*/
+#ifndef SQLITE_DEMOVFS_BUFFERSZ
+# define SQLITE_DEMOVFS_BUFFERSZ 8192
+#endif
+
+/*
+** The maximum pathname length supported by this VFS.
+*/
+#define MAXPATHNAME 512
+
+/*
+** When using this VFS, the sqlite3_file* handles that SQLite uses are
+** actually pointers to instances of type DemoFile.
+*/
+typedef struct DemoFile DemoFile;
+struct DemoFile {
+ sqlite3_file base; /* Base class. Must be first. */
+ int fd; /* File descriptor */
+
+ char *aBuffer; /* Pointer to malloc'd buffer */
+ int nBuffer; /* Valid bytes of data in zBuffer */
+ sqlite3_int64 iBufferOfst; /* Offset in file of zBuffer[0] */
+};
+
+/*
+** Write directly to the file passed as the first argument. Even if the
+** file has a write-buffer (DemoFile.aBuffer), ignore it.
+*/
+static int demoDirectWrite(
+ DemoFile *p, /* File handle */
+ const void *zBuf, /* Buffer containing data to write */
+ int iAmt, /* Size of data to write in bytes */
+ sqlite_int64 iOfst /* File offset to write to */
+){
+ off_t ofst; /* Return value from lseek() */
+ size_t nWrite; /* Return value from write() */
+
+ ofst = lseek(p->fd, iOfst, SEEK_SET);
+ if( ofst!=iOfst ){
+ return SQLITE_IOERR_WRITE;
+ }
+
+ nWrite = write(p->fd, zBuf, iAmt);
+ if( nWrite!=iAmt ){
+ return SQLITE_IOERR_WRITE;
+ }
+
+ return SQLITE_OK;
+}
+
+/*
+** Flush the contents of the DemoFile.aBuffer buffer to disk. This is a
+** no-op if this particular file does not have a buffer (i.e. it is not
+** a journal file) or if the buffer is currently empty.
+*/
+static int demoFlushBuffer(DemoFile *p){
+ int rc = SQLITE_OK;
+ if( p->nBuffer ){
+ rc = demoDirectWrite(p, p->aBuffer, p->nBuffer, p->iBufferOfst);
+ p->nBuffer = 0;
+ }
+ return rc;
+}
+
+/*
+** Close a file.
+*/
+static int demoClose(sqlite3_file *pFile){
+ int rc;
+ DemoFile *p = (DemoFile*)pFile;
+ rc = demoFlushBuffer(p);
+ sqlite3_free(p->aBuffer);
+ close(p->fd);
+ return rc;
+}
+
+/*
+** Read data from a file.
+*/
+static int demoRead(
+ sqlite3_file *pFile,
+ void *zBuf,
+ int iAmt,
+ sqlite_int64 iOfst
+){
+ DemoFile *p = (DemoFile*)pFile;
+ off_t ofst; /* Return value from lseek() */
+ int nRead; /* Return value from read() */
+ int rc; /* Return code from demoFlushBuffer() */
+
+ /* Flush any data in the write buffer to disk in case this operation
+ ** is trying to read data the file-region currently cached in the buffer.
+ ** It would be possible to detect this case and possibly save an
+ ** unnecessary write here, but in practice SQLite will rarely read from
+ ** a journal file when there is data cached in the write-buffer.
+ */
+ rc = demoFlushBuffer(p);
+ if( rc!=SQLITE_OK ){
+ return rc;
+ }
+
+ ofst = lseek(p->fd, iOfst, SEEK_SET);
+ if( ofst!=iOfst ){
+ return SQLITE_IOERR_READ;
+ }
+ nRead = read(p->fd, zBuf, iAmt);
+
+ if( nRead==iAmt ){
+ return SQLITE_OK;
+ }else if( nRead>=0 ){
+ if( nRead<iAmt ){
+ memset(&((char*)zBuf)[nRead], 0, iAmt-nRead);
+ }
+ return SQLITE_IOERR_SHORT_READ;
+ }
+
+ return SQLITE_IOERR_READ;
+}
+
+/*
+** Write data to a crash-file.
+*/
+static int demoWrite(
+ sqlite3_file *pFile,
+ const void *zBuf,
+ int iAmt,
+ sqlite_int64 iOfst
+){
+ DemoFile *p = (DemoFile*)pFile;
+
+ if( p->aBuffer ){
+ char *z = (char *)zBuf; /* Pointer to remaining data to write */
+ int n = iAmt; /* Number of bytes at z */
+ sqlite3_int64 i = iOfst; /* File offset to write to */
+
+ while( n>0 ){
+ int nCopy; /* Number of bytes to copy into buffer */
+
+ /* If the buffer is full, or if this data is not being written directly
+ ** following the data already buffered, flush the buffer. Flushing
+ ** the buffer is a no-op if it is empty.
+ */
+ if( p->nBuffer==SQLITE_DEMOVFS_BUFFERSZ || p->iBufferOfst+p->nBuffer!=i ){
+ int rc = demoFlushBuffer(p);
+ if( rc!=SQLITE_OK ){
+ return rc;
+ }
+ }
+ assert( p->nBuffer==0 || p->iBufferOfst+p->nBuffer==i );
+ p->iBufferOfst = i - p->nBuffer;
+
+ /* Copy as much data as possible into the buffer. */
+ nCopy = SQLITE_DEMOVFS_BUFFERSZ - p->nBuffer;
+ if( nCopy>n ){
+ nCopy = n;
+ }
+ memcpy(&p->aBuffer[p->nBuffer], z, nCopy);
+ p->nBuffer += nCopy;
+
+ n -= nCopy;
+ i += nCopy;
+ z += nCopy;
+ }
+ }else{
+ return demoDirectWrite(p, zBuf, iAmt, iOfst);
+ }
+
+ return SQLITE_OK;
+}
+
+/*
+** Truncate a file. This is a no-op for this VFS (see header comments at
+** the top of the file).
+*/
+static int demoTruncate(sqlite3_file *pFile, sqlite_int64 size){
+#if 0
+ if( ftruncate(((DemoFile *)pFile)->fd, size) ) return SQLITE_IOERR_TRUNCATE;
+#endif
+ return SQLITE_OK;
+}
+
+/*
+** Sync the contents of the file to the persistent media.
+*/
+static int demoSync(sqlite3_file *pFile, int flags){
+ DemoFile *p = (DemoFile*)pFile;
+ int rc;
+
+ rc = demoFlushBuffer(p);
+ if( rc!=SQLITE_OK ){
+ return rc;
+ }
+
+ rc = fsync(p->fd);
+ return (rc==0 ? SQLITE_OK : SQLITE_IOERR_FSYNC);
+}
+
+/*
+** Write the size of the file in bytes to *pSize.
+*/
+static int demoFileSize(sqlite3_file *pFile, sqlite_int64 *pSize){
+ DemoFile *p = (DemoFile*)pFile;
+ int rc; /* Return code from fstat() call */
+ struct stat sStat; /* Output of fstat() call */
+
+ /* Flush the contents of the buffer to disk. As with the flush in the
+ ** demoRead() method, it would be possible to avoid this and save a write
+ ** here and there. But in practice this comes up so infrequently it is
+ ** not worth the trouble.
+ */
+ rc = demoFlushBuffer(p);
+ if( rc!=SQLITE_OK ){
+ return rc;
+ }
+
+ rc = fstat(p->fd, &sStat);
+ if( rc!=0 ) return SQLITE_IOERR_FSTAT;
+ *pSize = sStat.st_size;
+ return SQLITE_OK;
+}
+
+/*
+** Locking functions. The xLock() and xUnlock() methods are both no-ops.
+** The xCheckReservedLock() always indicates that no other process holds
+** a reserved lock on the database file. This ensures that if a hot-journal
+** file is found in the file-system it is rolled back.
+*/
+static int demoLock(sqlite3_file *pFile, int eLock){
+ return SQLITE_OK;
+}
+static int demoUnlock(sqlite3_file *pFile, int eLock){
+ return SQLITE_OK;
+}
+static int demoCheckReservedLock(sqlite3_file *pFile, int *pResOut){
+ *pResOut = 0;
+ return SQLITE_OK;
+}
+
+/*
+** No xFileControl() verbs are implemented by this VFS.
+*/
+static int demoFileControl(sqlite3_file *pFile, int op, void *pArg){
+ return SQLITE_NOTFOUND;
+}
+
+/*
+** The xSectorSize() and xDeviceCharacteristics() methods. These two
+** may return special values allowing SQLite to optimize file-system
+** access to some extent. But it is also safe to simply return 0.
+*/
+static int demoSectorSize(sqlite3_file *pFile){
+ return 0;
+}
+static int demoDeviceCharacteristics(sqlite3_file *pFile){
+ return 0;
+}
+
+/*
+** Open a file handle.
+*/
+static int demoOpen(
+ sqlite3_vfs *pVfs, /* VFS */
+ const char *zName, /* File to open, or 0 for a temp file */
+ sqlite3_file *pFile, /* Pointer to DemoFile struct to populate */
+ int flags, /* Input SQLITE_OPEN_XXX flags */
+ int *pOutFlags /* Output SQLITE_OPEN_XXX flags (or NULL) */
+){
+ static const sqlite3_io_methods demoio = {
+ 1, /* iVersion */
+ demoClose, /* xClose */
+ demoRead, /* xRead */
+ demoWrite, /* xWrite */
+ demoTruncate, /* xTruncate */
+ demoSync, /* xSync */
+ demoFileSize, /* xFileSize */
+ demoLock, /* xLock */
+ demoUnlock, /* xUnlock */
+ demoCheckReservedLock, /* xCheckReservedLock */
+ demoFileControl, /* xFileControl */
+ demoSectorSize, /* xSectorSize */
+ demoDeviceCharacteristics /* xDeviceCharacteristics */
+ };
+
+ DemoFile *p = (DemoFile*)pFile; /* Populate this structure */
+ int oflags = 0; /* flags to pass to open() call */
+ char *aBuf = 0;
+
+ if( zName==0 ){
+ return SQLITE_IOERR;
+ }
+
+ if( flags&SQLITE_OPEN_MAIN_JOURNAL ){
+ aBuf = (char *)sqlite3_malloc(SQLITE_DEMOVFS_BUFFERSZ);
+ if( !aBuf ){
+ return SQLITE_NOMEM;
+ }
+ }
+
+ if( flags&SQLITE_OPEN_EXCLUSIVE ) oflags |= O_EXCL;
+ if( flags&SQLITE_OPEN_CREATE ) oflags |= O_CREAT;
+ if( flags&SQLITE_OPEN_READONLY ) oflags |= O_RDONLY;
+ if( flags&SQLITE_OPEN_READWRITE ) oflags |= O_RDWR;
+
+ memset(p, 0, sizeof(DemoFile));
+ p->fd = open(zName, oflags, 0600);
+ if( p->fd<0 ){
+ sqlite3_free(aBuf);
+ return SQLITE_CANTOPEN;
+ }
+ p->aBuffer = aBuf;
+
+ if( pOutFlags ){
+ *pOutFlags = flags;
+ }
+ p->base.pMethods = &demoio;
+ return SQLITE_OK;
+}
+
+/*
+** Delete the file identified by argument zPath. If the dirSync parameter
+** is non-zero, then ensure the file-system modification to delete the
+** file has been synced to disk before returning.
+*/
+static int demoDelete(sqlite3_vfs *pVfs, const char *zPath, int dirSync){
+ int rc; /* Return code */
+
+ rc = unlink(zPath);
+ if( rc!=0 && errno==ENOENT ) return SQLITE_OK;
+
+ if( rc==0 && dirSync ){
+ int dfd; /* File descriptor open on directory */
+ int i; /* Iterator variable */
+ char *zSlash;
+ char zDir[MAXPATHNAME+1]; /* Name of directory containing file zPath */
+
+ /* Figure out the directory name from the path of the file deleted. */
+ sqlite3_snprintf(MAXPATHNAME, zDir, "%s", zPath);
+ zDir[MAXPATHNAME] = '\0';
+ zSlash = strrchr(zDir,'/');
+ if( zSlash ){
+ /* Open a file-descriptor on the directory. Sync. Close. */
+ zSlash[0] = 0;
+ dfd = open(zDir, O_RDONLY, 0);
+ if( dfd<0 ){
+ rc = -1;
+ }else{
+ rc = fsync(dfd);
+ close(dfd);
+ }
+ }
+ }
+ return (rc==0 ? SQLITE_OK : SQLITE_IOERR_DELETE);
+}
+
+#ifndef F_OK
+# define F_OK 0
+#endif
+#ifndef R_OK
+# define R_OK 4
+#endif
+#ifndef W_OK
+# define W_OK 2
+#endif
+
+/*
+** Query the file-system to see if the named file exists, is readable or
+** is both readable and writable.
+*/
+static int demoAccess(
+ sqlite3_vfs *pVfs,
+ const char *zPath,
+ int flags,
+ int *pResOut
+){
+ int rc; /* access() return code */
+ int eAccess = F_OK; /* Second argument to access() */
+
+ assert( flags==SQLITE_ACCESS_EXISTS /* access(zPath, F_OK) */
+ || flags==SQLITE_ACCESS_READ /* access(zPath, R_OK) */
+ || flags==SQLITE_ACCESS_READWRITE /* access(zPath, R_OK|W_OK) */
+ );
+
+ if( flags==SQLITE_ACCESS_READWRITE ) eAccess = R_OK|W_OK;
+ if( flags==SQLITE_ACCESS_READ ) eAccess = R_OK;
+
+ rc = access(zPath, eAccess);
+ *pResOut = (rc==0);
+ return SQLITE_OK;
+}
+
+/*
+** Argument zPath points to a nul-terminated string containing a file path.
+** If zPath is an absolute path, then it is copied as is into the output
+** buffer. Otherwise, if it is a relative path, then the equivalent full
+** path is written to the output buffer.
+**
+** This function assumes that paths are UNIX style. Specifically, that:
+**
+** 1. Path components are separated by a '/'. and
+** 2. Full paths begin with a '/' character.
+*/
+static int demoFullPathname(
+ sqlite3_vfs *pVfs, /* VFS */
+ const char *zPath, /* Input path (possibly a relative path) */
+ int nPathOut, /* Size of output buffer in bytes */
+ char *zPathOut /* Pointer to output buffer */
+){
+ char zDir[MAXPATHNAME+1];
+ if( zPath[0]=='/' ){
+ zDir[0] = '\0';
+ }else{
+ if( getcwd(zDir, sizeof(zDir))==0 ) return SQLITE_IOERR;
+ }
+ zDir[MAXPATHNAME] = '\0';
+
+ sqlite3_snprintf(nPathOut, zPathOut, "%s/%s", zDir, zPath);
+ zPathOut[nPathOut-1] = '\0';
+
+ return SQLITE_OK;
+}
+
+/*
+** The following four VFS methods:
+**
+** xDlOpen
+** xDlError
+** xDlSym
+** xDlClose
+**
+** are supposed to implement the functionality needed by SQLite to load
+** extensions compiled as shared objects. This simple VFS does not support
+** this functionality, so the following functions are no-ops.
+*/
+static void *demoDlOpen(sqlite3_vfs *pVfs, const char *zPath){
+ return 0;
+}
+static void demoDlError(sqlite3_vfs *pVfs, int nByte, char *zErrMsg){
+ sqlite3_snprintf(nByte, zErrMsg, "Loadable extensions are not supported");
+ zErrMsg[nByte-1] = '\0';
+}
+static void (*demoDlSym(sqlite3_vfs *pVfs, void *pH, const char *z))(void){
+ return 0;
+}
+static void demoDlClose(sqlite3_vfs *pVfs, void *pHandle){
+ return;
+}
+
+/*
+** Parameter zByte points to a buffer nByte bytes in size. Populate this
+** buffer with pseudo-random data.
+*/
+static int demoRandomness(sqlite3_vfs *pVfs, int nByte, char *zByte){
+ return SQLITE_OK;
+}
+
+/*
+** Sleep for at least nMicro microseconds. Return the (approximate) number
+** of microseconds slept for.
+*/
+static int demoSleep(sqlite3_vfs *pVfs, int nMicro){
+ sleep(nMicro / 1000000);
+ usleep(nMicro % 1000000);
+ return nMicro;
+}
+
+/*
+** Set *pTime to the current UTC time expressed as a Julian day. Return
+** SQLITE_OK if successful, or an error code otherwise.
+**
+** http://en.wikipedia.org/wiki/Julian_day
+**
+** This implementation is not very good. The current time is rounded to
+** an integer number of seconds. Also, assuming time_t is a signed 32-bit
+** value, it will stop working some time in the year 2038 AD (the so-called
+** "year 2038" problem that afflicts systems that store time this way).
+*/
+static int demoCurrentTime(sqlite3_vfs *pVfs, double *pTime){
+ time_t t = time(0);
+ *pTime = t/86400.0 + 2440587.5;
+ return SQLITE_OK;
+}
+
+/*
+** This function returns a pointer to the VFS implemented in this file.
+** To make the VFS available to SQLite:
+**
+** sqlite3_vfs_register(sqlite3_demovfs(), 0);
+*/
+sqlite3_vfs *sqlite3_demovfs(void){
+ static sqlite3_vfs demovfs = {
+ 1, /* iVersion */
+ sizeof(DemoFile), /* szOsFile */
+ MAXPATHNAME, /* mxPathname */
+ 0, /* pNext */
+ "demo", /* zName */
+ 0, /* pAppData */
+ demoOpen, /* xOpen */
+ demoDelete, /* xDelete */
+ demoAccess, /* xAccess */
+ demoFullPathname, /* xFullPathname */
+ demoDlOpen, /* xDlOpen */
+ demoDlError, /* xDlError */
+ demoDlSym, /* xDlSym */
+ demoDlClose, /* xDlClose */
+ demoRandomness, /* xRandomness */
+ demoSleep, /* xSleep */
+ demoCurrentTime, /* xCurrentTime */
+ };
+ return &demovfs;
+}
+
+#endif /* !defined(SQLITE_TEST) || SQLITE_OS_UNIX */
+
+
+#ifdef SQLITE_TEST
+
+#if defined(INCLUDE_SQLITE_TCL_H)
+# include "sqlite_tcl.h"
+#else
+# include "tcl.h"
+# ifndef SQLITE_TCLAPI
+# define SQLITE_TCLAPI
+# endif
+#endif
+
+#if SQLITE_OS_UNIX
+static int SQLITE_TCLAPI register_demovfs(
+ ClientData clientData, /* Pointer to sqlite3_enable_XXX function */
+ Tcl_Interp *interp, /* The TCL interpreter that invoked this command */
+ int objc, /* Number of arguments */
+ Tcl_Obj *CONST objv[] /* Command arguments */
+){
+ sqlite3_vfs_register(sqlite3_demovfs(), 1);
+ return TCL_OK;
+}
+static int SQLITE_TCLAPI unregister_demovfs(
+ ClientData clientData, /* Pointer to sqlite3_enable_XXX function */
+ Tcl_Interp *interp, /* The TCL interpreter that invoked this command */
+ int objc, /* Number of arguments */
+ Tcl_Obj *CONST objv[] /* Command arguments */
+){
+ sqlite3_vfs_unregister(sqlite3_demovfs());
+ return TCL_OK;
+}
+
+/*
+** Register commands with the TCL interpreter.
+*/
+int Sqlitetest_demovfs_Init(Tcl_Interp *interp){
+ Tcl_CreateObjCommand(interp, "register_demovfs", register_demovfs, 0, 0);
+ Tcl_CreateObjCommand(interp, "unregister_demovfs", unregister_demovfs, 0, 0);
+ return TCL_OK;
+}
+
+#else
+int Sqlitetest_demovfs_Init(Tcl_Interp *interp){ return TCL_OK; }
+#endif
+
+#endif /* SQLITE_TEST */
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