Support wasm32-wasi target

libsqlite3-sys/build.rs

@@ -58,7 +58,8 @@ mod build_bundled {
             fs::copy("sqlite3/bindgen_bundled_version.rs", out_path)
                 .expect("Could not copy bindings to output directory");
         }
-
+        println!("cargo:rerun-if-changed=sqlite3/sqlite3.c");
+        println!("cargo:rerun-if-changed=sqlite3/wasm32-wasi-vfs.c");
         let mut cfg = cc::Build::new();
         cfg.file("sqlite3/sqlite3.c")
             .flag("-DSQLITE_CORE")
@@ -108,6 +109,13 @@ mod build_bundled {
         if cfg!(not(target_os = "windows")) {
             cfg.flag("-DHAVE_LOCALTIME_R");
         }
+        // Target wasm32-wasi can't compile the default VFS
+        if env::var("TARGET") == Ok("wasm32-wasi".to_string()) {
+            cfg.file("sqlite3/wasm32-wasi-vfs.c")
+                .flag("-DSQLITE_OS_OTHER")
+                // https://github.com/rust-lang/rust/issues/74393
+                .flag("-DLONGDOUBLE_TYPE=double");
+        }
         if cfg!(feature = "unlock_notify") {
             cfg.flag("-DSQLITE_ENABLE_UNLOCK_NOTIFY");
         }

libsqlite3-sys/sqlite3/wasm32-wasi-vfs.c

@@ -0,0 +1,690 @@
+/*
+** 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 ){
+    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_OK;
+}
+
+/*
+** 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 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';
+    for(i=strlen(zDir); i>1 && zDir[i]!='/'; i++);
+    zDir[i] = '\0';
+
+    /* Open a file-descriptor on the directory. Sync. Close. */
+    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 */
+){
+  sqlite3_snprintf(nPathOut, zPathOut, "%s", 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 */
+
+// Register sqlite3_demovfs
+int sqlite3_os_init()
+{
+    sqlite3_vfs_register(sqlite3_demovfs(), 0);
+    return 0;
+}
+
+int sqlite3_os_end()
+{
+    return 0;
+}