From: drh <drh@noemail.net>
Date: Wed, 2 Mar 2011 15:09:07 +0000 (+0000)
Subject: Proof-of-concept prototype for the proposed xSetSystemCall extension method
X-Git-Tag: version-3.7.6~112^2~3
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=99ab3b120e9667221338a6f0b3c844ec525bc5ed;p=thirdparty%2Fsqlite.git

Proof-of-concept prototype for the proposed xSetSystemCall extension method
on the VFS.

FossilOrigin-Name: 92b5a76abc53290e1bb87b6b55bc64bb1b331dfc
---

diff --git a/manifest b/manifest
index 30c4b431b1..db71d0c060 100644
--- a/manifest
+++ b/manifest
@@ -1,8 +1,8 @@
 -----BEGIN PGP SIGNED MESSAGE-----
 Hash: SHA1
 
-C Log\sall\serror\sfrom\sclose()\sin\sos_unix.c\sto\ssqlite3_log()\sbut\sdo\snot\sattempt\sto\nreport\serrors\sback\sup\sto\sthe\sapplication.\s\sUpdate\sthe\sunix\serror\slogging\sto\nput\sthe\smost\simportant\sinformation\searlier\sin\sthe\smessage.
-D 2011-03-02T02:08:13.207
+C Proof-of-concept\sprototype\sfor\sthe\sproposed\sxSetSystemCall\sextension\smethod\non\sthe\sVFS.
+D 2011-03-02T15:09:07.461
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 27701a1653595a1f2187dc61c8117e00a6c1d50f
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -164,8 +164,8 @@ F src/os.c 22ac61d06e72a0dac900400147333b07b13d8e1d
 F src/os.h 9dbed8c2b9c1f2f2ebabc09e49829d4777c26bf9
 F src/os_common.h a8f95b81eca8a1ab8593d23e94f8a35f35d4078f
 F src/os_os2.c 2e452c9f2ca507623ad351c33a8a8b27849b1863
-F src/os_unix.c 5e2e1187c19cc20798dd9a08bee841fab0929ccf
-F src/os_win.c 9abdcdd925416d854eabb0996c96debd92abfef5
+F src/os_unix.c 34f0341ab45ba2708714c8e3f7bd35c7ccb5e34d
+F src/os_win.c c2df806a8510ec8c2c2c30fb78b3a25bc1b2f325
 F src/pager.c 6aa906b60a59664ba58d3f746164bb010d407ce1
 F src/pager.h 3f8c783de1d4706b40b1ac15b64f5f896bcc78d1
 F src/parse.y 12b7ebd61ea54f0e1b1083ff69cc2c8ce9353d58
@@ -180,7 +180,7 @@ F src/resolve.c 1c0f32b64f8e3f555fe1f732f9d6f501a7f05706
 F src/rowset.c 69afa95a97c524ba6faf3805e717b5b7ae85a697
 F src/select.c d24406c45dd2442eb2eeaac413439066b149c944
 F src/shell.c 649c51979812f77f97507024a4cea480c6862b8b
-F src/sqlite.h.in ccb23cc9378874c7c72682b739f311474a80848d
+F src/sqlite.h.in a2115e725e77ea1284a4df51b39f94121f020ab8
 F src/sqlite3ext.h c90bd5507099f62043832d73f6425d8d5c5da754
 F src/sqliteInt.h 4290fff17fabc6e07fc4338233df0e39e6350ca1
 F src/sqliteLimit.h a17dcd3fb775d63b64a43a55c54cb282f9726f44
@@ -912,14 +912,18 @@ F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
 F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
 F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
 F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
-P 4e50b0362ab6604a4b6c9f4ad849ec1733d6ce1a
-R a9b7ad5c14ea738e4f49c429699cb565
+P 7b6e30e6a712311d4ef275253b085b85e6e17116
+R b432d469c6ed4dca97f566fa093fcbff
+T *bgcolor * #a8d3c0
+T *branch * syscall-override
+T *sym-syscall-override *
+T -sym-trunk *
 U drh
-Z c02292224bfb7c5f15d6a63d1b16838a
+Z 9b09403dc20dd3b2e37d470a4feaa93c
 -----BEGIN PGP SIGNATURE-----
 Version: GnuPG v1.4.6 (GNU/Linux)
 
-iD8DBQFNbaaQoxKgR168RlERAshdAJ4iJDt6I1+oeLfL9JDapg61g0RrTgCfcFyC
-s4eiT7ukCDxc6MYErF6v4VI=
-=AyES
+iD8DBQFNbl2aoxKgR168RlERAnuDAJ9BNtRHzGqMMOlHR9sjdCvks/uYWQCgiUgt
+CkJFrHO5mCcgtbaMpvVY+k0=
+=K2zl
 -----END PGP SIGNATURE-----
diff --git a/manifest.uuid b/manifest.uuid
index 0b4dc2a39e..ee6de5d921 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-7b6e30e6a712311d4ef275253b085b85e6e17116
\ No newline at end of file
+92b5a76abc53290e1bb87b6b55bc64bb1b331dfc
\ No newline at end of file
diff --git a/src/os_unix.c b/src/os_unix.c
index b70e2736bd..d2263addc6 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -270,6 +270,42 @@ struct unixFile {
 # define O_BINARY 0
 #endif
 
+/*
+** The threadid macro resolves to the thread-id or to 0.  Used for
+** testing and debugging only.
+*/
+#if SQLITE_THREADSAFE
+#define threadid pthread_self()
+#else
+#define threadid 0
+#endif
+
+/*
+** Many system calls are accessed through pointer-to-functions so that
+** they may be overridden at runtime to facilitate fault injection during
+** testing and sandboxing.  The following array holds the names and pointers
+** to all overrideable system calls.
+*/
+static struct unix_syscall {
+  const char *zName;      /* Name of the sytem call */
+  void *pCurrent;         /* Current value of the system call */
+  void *pDefault;         /* Default value */
+} aSyscall[] = {
+  { "open",         (void*)open,       0  },
+#define osOpen      ((int(*)(const char*,int,int))aSyscall[0].pCurrent)
+
+  { "close",        (void*)close,      0  },
+#define osClose     ((int(*)(int))aSyscall[1].pCurrent)
+
+  { "access",       (void*)access,     0  },
+#define osAccess    ((int(*)(const char*,int))aSyscall[2].pCurrent)
+
+  { "getcwd",       (void*)getcwd,     0  },
+#define osGetcwd    ((char*(*)(char*,size_t))aSyscall[3].pCurrent)
+
+  { "stat",         (void*)stat,       0  },
+#define osStat      ((int(*)(const char*,struct stat*))aSyscall[4].pCurrent)
+
 /*
 ** The DJGPP compiler environment looks mostly like Unix, but it
 ** lacks the fcntl() system call.  So redefine fcntl() to be something
@@ -277,18 +313,59 @@ struct unixFile {
 ** DJGPP.  But it is DOS - what did you expect?
 */
 #ifdef __DJGPP__
-# define fcntl(A,B,C) 0
+  { "fstat",        0,                 0  },
+#define osFstat(a,b,c)    0
+#else     
+  { "fstat",        (void*)fstat,      0  },
+#define osFstat     ((int(*)(int,struct stat*))aSyscall[5].pCurrent)
 #endif
 
+  { "ftruncate",    (void*)ftruncate,  0  },
+#define osFtruncate ((int(*)(int,off_t))aSyscall[6].pCurrent)
+
+  { "fcntl",        (void*)fcntl,    0  },
+#define osFcntl     ((int(*)(int,int,...))aSyscall[7].pCurrent)
+};
+
 /*
-** The threadid macro resolves to the thread-id or to 0.  Used for
-** testing and debugging only.
+** This is the xSetSystemCall() method of sqlite3_vfs for all of the
+** "unix" VFSes.
 */
-#if SQLITE_THREADSAFE
-#define threadid pthread_self()
-#else
-#define threadid 0
-#endif
+static int unixSetSystemCall(
+  sqlite3_vfs *pNotUsed,     /* The VFS pointer.  Not used */
+  const char *zName,         /* Name of system call to override */
+  void *pNewFunc             /* Pointer to new system call value */
+){
+  int i;
+  int rc = 0;
+  if( zName==0 ){
+    /* If no zName is given, restore all system calls to their default
+    ** settings and return NULL
+    */
+    for(i=0; i<sizeof(aSyscall)/sizeof(aSyscall[0]); i++){
+      if( aSyscall[i].pDefault ){
+        aSyscall[i].pCurrent = aSyscall[i].pDefault;
+        rc = 1;
+      }
+    }
+  }else{
+    /* If zName is specified, operate on only the one system call
+    ** specified.
+    */
+    for(i=0; i<sizeof(aSyscall)/sizeof(aSyscall[0]); i++){
+      if( strcmp(zName, aSyscall[i].zName)==0 ){
+        if( aSyscall[i].pDefault==0 ){
+          aSyscall[i].pDefault = aSyscall[i].pCurrent;
+        }
+        rc = 1;
+        if( pNewFunc==0 ) pNewFunc = aSyscall[i].pDefault;
+        aSyscall[i].pCurrent = pNewFunc;
+        break;
+      }
+    }
+  }
+  return rc;
+}
 
 
 /*
@@ -354,7 +431,7 @@ static int lockTrace(int fd, int op, struct flock *p){
   }else if( op==F_SETLK ){
     zOpName = "SETLK";
   }else{
-    s = fcntl(fd, op, p);
+    s = osFcntl(fd, op, p);
     sqlite3DebugPrintf("fcntl unknown %d %d %d\n", fd, op, s);
     return s;
   }
@@ -368,7 +445,7 @@ static int lockTrace(int fd, int op, struct flock *p){
     assert( 0 );
   }
   assert( p->l_whence==SEEK_SET );
-  s = fcntl(fd, op, p);
+  s = osFcntl(fd, op, p);
   savedErrno = errno;
   sqlite3DebugPrintf("fcntl %d %d %s %s %d %d %d %d\n",
      threadid, fd, zOpName, zType, (int)p->l_start, (int)p->l_len,
@@ -376,7 +453,7 @@ static int lockTrace(int fd, int op, struct flock *p){
   if( s==(-1) && op==F_SETLK && (p->l_type==F_RDLCK || p->l_type==F_WRLCK) ){
     struct flock l2;
     l2 = *p;
-    fcntl(fd, F_GETLK, &l2);
+    osFcntl(fd, F_GETLK, &l2);
     if( l2.l_type==F_RDLCK ){
       zType = "RDLCK";
     }else if( l2.l_type==F_WRLCK ){
@@ -392,7 +469,8 @@ static int lockTrace(int fd, int op, struct flock *p){
   errno = savedErrno;
   return s;
 }
-#define fcntl lockTrace
+#undef osFcntl
+#define osFcntl lockTrace
 #endif /* SQLITE_LOCK_TRACE */
 
 
@@ -402,11 +480,11 @@ static int lockTrace(int fd, int op, struct flock *p){
 #ifdef EINTR
 static int robust_ftruncate(int h, sqlite3_int64 sz){
   int rc;
-  do{ rc = ftruncate(h,sz); }while( rc<0 && errno==EINTR );
+  do{ rc = osFtruncate(h,sz); }while( rc<0 && errno==EINTR );
   return rc;
 }
 #else
-# define robust_ftruncate(a,b) ftruncate(a,b)
+# define robust_ftruncate(a,b) osFtruncate(a,b)
 #endif 
 
 
@@ -835,7 +913,7 @@ static int unixLogErrorAtLine(
 ** and move on.
 */
 static void robust_close(unixFile *pFile, int h, int lineno){
-  if( close(h) ){
+  if( osClose(h) ){
     unixLogErrorAtLine(SQLITE_IOERR_CLOSE, "close",
                        pFile ? pFile->zPath : 0, lineno);
   }
@@ -912,7 +990,7 @@ static int findInodeInfo(
   ** create a unique name for the file.
   */
   fd = pFile->h;
-  rc = fstat(fd, &statbuf);
+  rc = osFstat(fd, &statbuf);
   if( rc!=0 ){
     pFile->lastErrno = errno;
 #ifdef EOVERFLOW
@@ -938,7 +1016,7 @@ static int findInodeInfo(
       pFile->lastErrno = errno;
       return SQLITE_IOERR;
     }
-    rc = fstat(fd, &statbuf);
+    rc = osFstat(fd, &statbuf);
     if( rc!=0 ){
       pFile->lastErrno = errno;
       return SQLITE_IOERR;
@@ -1007,7 +1085,7 @@ static int unixCheckReservedLock(sqlite3_file *id, int *pResOut){
     lock.l_start = RESERVED_BYTE;
     lock.l_len = 1;
     lock.l_type = F_WRLCK;
-    if (-1 == fcntl(pFile->h, F_GETLK, &lock)) {
+    if (-1 == osFcntl(pFile->h, F_GETLK, &lock)) {
       int tErrno = errno;
       rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_CHECKRESERVEDLOCK);
       pFile->lastErrno = tErrno;
@@ -1160,7 +1238,7 @@ static int unixLock(sqlite3_file *id, int eFileLock){
   ){
     lock.l_type = (eFileLock==SHARED_LOCK?F_RDLCK:F_WRLCK);
     lock.l_start = PENDING_BYTE;
-    s = fcntl(pFile->h, F_SETLK, &lock);
+    s = osFcntl(pFile->h, F_SETLK, &lock);
     if( s==(-1) ){
       tErrno = errno;
       rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_LOCK);
@@ -1182,14 +1260,14 @@ static int unixLock(sqlite3_file *id, int eFileLock){
     /* Now get the read-lock */
     lock.l_start = SHARED_FIRST;
     lock.l_len = SHARED_SIZE;
-    if( (s = fcntl(pFile->h, F_SETLK, &lock))==(-1) ){
+    if( (s = osFcntl(pFile->h, F_SETLK, &lock))==(-1) ){
       tErrno = errno;
     }
     /* Drop the temporary PENDING lock */
     lock.l_start = PENDING_BYTE;
     lock.l_len = 1L;
     lock.l_type = F_UNLCK;
-    if( fcntl(pFile->h, F_SETLK, &lock)!=0 ){
+    if( osFcntl(pFile->h, F_SETLK, &lock)!=0 ){
       if( s != -1 ){
         /* This could happen with a network mount */
         tErrno = errno; 
@@ -1232,7 +1310,7 @@ static int unixLock(sqlite3_file *id, int eFileLock){
       default:
         assert(0);
     }
-    s = fcntl(pFile->h, F_SETLK, &lock);
+    s = osFcntl(pFile->h, F_SETLK, &lock);
     if( s==(-1) ){
       tErrno = errno;
       rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_LOCK);
@@ -1367,7 +1445,7 @@ static int _posixUnlock(sqlite3_file *id, int eFileLock, int handleNFSUnlock){
         lock.l_whence = SEEK_SET;
         lock.l_start = SHARED_FIRST;
         lock.l_len = divSize;
-        if( fcntl(h, F_SETLK, &lock)==(-1) ){
+        if( osFcntl(h, F_SETLK, &lock)==(-1) ){
           tErrno = errno;
           rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_UNLOCK);
           if( IS_LOCK_ERROR(rc) ){
@@ -1379,7 +1457,7 @@ static int _posixUnlock(sqlite3_file *id, int eFileLock, int handleNFSUnlock){
         lock.l_whence = SEEK_SET;
         lock.l_start = SHARED_FIRST;
         lock.l_len = divSize;
-        if( fcntl(h, F_SETLK, &lock)==(-1) ){
+        if( osFcntl(h, F_SETLK, &lock)==(-1) ){
           tErrno = errno;
           rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_RDLOCK);
           if( IS_LOCK_ERROR(rc) ){
@@ -1391,7 +1469,7 @@ static int _posixUnlock(sqlite3_file *id, int eFileLock, int handleNFSUnlock){
         lock.l_whence = SEEK_SET;
         lock.l_start = SHARED_FIRST+divSize;
         lock.l_len = SHARED_SIZE-divSize;
-        if( fcntl(h, F_SETLK, &lock)==(-1) ){
+        if( osFcntl(h, F_SETLK, &lock)==(-1) ){
           tErrno = errno;
           rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_UNLOCK);
           if( IS_LOCK_ERROR(rc) ){
@@ -1406,7 +1484,7 @@ static int _posixUnlock(sqlite3_file *id, int eFileLock, int handleNFSUnlock){
         lock.l_whence = SEEK_SET;
         lock.l_start = SHARED_FIRST;
         lock.l_len = SHARED_SIZE;
-        if( fcntl(h, F_SETLK, &lock)==(-1) ){
+        if( osFcntl(h, F_SETLK, &lock)==(-1) ){
           tErrno = errno;
           rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_RDLOCK);
           if( IS_LOCK_ERROR(rc) ){
@@ -1420,7 +1498,7 @@ static int _posixUnlock(sqlite3_file *id, int eFileLock, int handleNFSUnlock){
     lock.l_whence = SEEK_SET;
     lock.l_start = PENDING_BYTE;
     lock.l_len = 2L;  assert( PENDING_BYTE+1==RESERVED_BYTE );
-    if( fcntl(h, F_SETLK, &lock)!=(-1) ){
+    if( osFcntl(h, F_SETLK, &lock)!=(-1) ){
       pInode->eFileLock = SHARED_LOCK;
     }else{
       tErrno = errno;
@@ -1444,7 +1522,7 @@ static int _posixUnlock(sqlite3_file *id, int eFileLock, int handleNFSUnlock){
       SimulateIOErrorBenign(1);
       SimulateIOError( h=(-1) )
       SimulateIOErrorBenign(0);
-      if( fcntl(h, F_SETLK, &lock)!=(-1) ){
+      if( osFcntl(h, F_SETLK, &lock)!=(-1) ){
         pInode->eFileLock = NO_LOCK;
       }else{
         tErrno = errno;
@@ -1646,7 +1724,7 @@ static int dotlockCheckReservedLock(sqlite3_file *id, int *pResOut) {
   }else{
     /* The lock is held if and only if the lockfile exists */
     const char *zLockFile = (const char*)pFile->lockingContext;
-    reserved = access(zLockFile, 0)==0;
+    reserved = osAccess(zLockFile, 0)==0;
   }
   OSTRACE(("TEST WR-LOCK %d %d %d (dotlock)\n", pFile->h, rc, reserved));
   *pResOut = reserved;
@@ -1700,7 +1778,7 @@ static int dotlockLock(sqlite3_file *id, int eFileLock) {
   }
   
   /* grab an exclusive lock */
-  fd = open(zLockFile,O_RDONLY|O_CREAT|O_EXCL,0600);
+  fd = osOpen(zLockFile,O_RDONLY|O_CREAT|O_EXCL,0600);
   if( fd<0 ){
     /* failed to open/create the file, someone else may have stolen the lock */
     int tErrno = errno;
@@ -2964,7 +3042,7 @@ static int full_fsync(int fd, int fullSync, int dataOnly){
   rc = SQLITE_OK;
 #elif HAVE_FULLFSYNC
   if( fullSync ){
-    rc = fcntl(fd, F_FULLFSYNC, 0);
+    rc = osFcntl(fd, F_FULLFSYNC, 0);
   }else{
     rc = 1;
   }
@@ -3111,7 +3189,7 @@ static int unixFileSize(sqlite3_file *id, i64 *pSize){
   int rc;
   struct stat buf;
   assert( id );
-  rc = fstat(((unixFile*)id)->h, &buf);
+  rc = osFstat(((unixFile*)id)->h, &buf);
   SimulateIOError( rc=1 );
   if( rc!=0 ){
     ((unixFile*)id)->lastErrno = errno;
@@ -3152,7 +3230,7 @@ static int fcntlSizeHint(unixFile *pFile, i64 nByte){
     i64 nSize;                    /* Required file size */
     struct stat buf;              /* Used to hold return values of fstat() */
    
-    if( fstat(pFile->h, &buf) ) return SQLITE_IOERR_FSTAT;
+    if( osFstat(pFile->h, &buf) ) return SQLITE_IOERR_FSTAT;
 
     nSize = ((nByte+pFile->szChunk-1) / pFile->szChunk) * pFile->szChunk;
     if( nSize>(i64)buf.st_size ){
@@ -3367,7 +3445,7 @@ static int unixShmSystemLock(
   f.l_start = ofst;
   f.l_len = n;
 
-  rc = fcntl(pShmNode->h, F_SETLK, &f);
+  rc = osFcntl(pShmNode->h, F_SETLK, &f);
   rc = (rc!=(-1)) ? SQLITE_OK : SQLITE_BUSY;
 
   /* Update the global lock state and do debug tracing */
@@ -3492,7 +3570,7 @@ static int unixOpenSharedMemory(unixFile *pDbFd){
     ** with the same permissions. The actual permissions the file is created
     ** with are subject to the current umask setting.
     */
-    if( fstat(pDbFd->h, &sStat) ){
+    if( osFstat(pDbFd->h, &sStat) ){
       rc = SQLITE_IOERR_FSTAT;
       goto shm_open_err;
     }
@@ -3525,7 +3603,7 @@ static int unixOpenSharedMemory(unixFile *pDbFd){
       goto shm_open_err;
     }
 
-    pShmNode->h = open(zShmFilename, O_RDWR|O_CREAT, (sStat.st_mode & 0777));
+    pShmNode->h = osOpen(zShmFilename, O_RDWR|O_CREAT, (sStat.st_mode & 0777));
     if( pShmNode->h<0 ){
       rc = unixLogError(SQLITE_CANTOPEN_BKPT, "open", zShmFilename);
       goto shm_open_err;
@@ -3629,7 +3707,7 @@ static int unixShmMap(
     ** Check to see if it has been allocated (i.e. if the wal-index file is
     ** large enough to contain the requested region).
     */
-    if( fstat(pShmNode->h, &sStat) ){
+    if( osFstat(pShmNode->h, &sStat) ){
       rc = SQLITE_IOERR_SHMSIZE;
       goto shmpage_out;
     }
@@ -4088,7 +4166,7 @@ static const sqlite3_io_methods *autolockIoFinderImpl(
   lockInfo.l_start = 0;
   lockInfo.l_whence = SEEK_SET;
   lockInfo.l_type = F_RDLCK;
-  if( fcntl(pNew->h, F_GETLK, &lockInfo)!=-1 ) {
+  if( osFcntl(pNew->h, F_GETLK, &lockInfo)!=-1 ) {
     if( strcmp(fsInfo.f_fstypename, "nfs")==0 ){
       return &nfsIoMethods;
     } else {
@@ -4130,7 +4208,7 @@ static const sqlite3_io_methods *autolockIoFinderImpl(
   lockInfo.l_start = 0;
   lockInfo.l_whence = SEEK_SET;
   lockInfo.l_type = F_RDLCK;
-  if( fcntl(pNew->h, F_GETLK, &lockInfo)!=-1 ) {
+  if( osFcntl(pNew->h, F_GETLK, &lockInfo)!=-1 ) {
     return &posixIoMethods;
   }else{
     return &semIoMethods;
@@ -4353,10 +4431,10 @@ static int openDirectory(const char *zFilename, int *pFd){
   for(ii=(int)strlen(zDirname); ii>1 && zDirname[ii]!='/'; ii--);
   if( ii>0 ){
     zDirname[ii] = '\0';
-    fd = open(zDirname, O_RDONLY|O_BINARY, 0);
+    fd = osOpen(zDirname, O_RDONLY|O_BINARY, 0);
     if( fd>=0 ){
 #ifdef FD_CLOEXEC
-      fcntl(fd, F_SETFD, fcntl(fd, F_GETFD, 0) | FD_CLOEXEC);
+      osFcntl(fd, F_SETFD, osFcntl(fd, F_GETFD, 0) | FD_CLOEXEC);
 #endif
       OSTRACE(("OPENDIR %-3d %s\n", fd, zDirname));
     }
@@ -4386,9 +4464,9 @@ static const char *unixTempFileDir(void){
   if( !azDirs[1] ) azDirs[1] = getenv("TMPDIR");
   for(i=0; i<sizeof(azDirs)/sizeof(azDirs[0]); zDir=azDirs[i++]){
     if( zDir==0 ) continue;
-    if( stat(zDir, &buf) ) continue;
+    if( osStat(zDir, &buf) ) continue;
     if( !S_ISDIR(buf.st_mode) ) continue;
-    if( access(zDir, 07) ) continue;
+    if( osAccess(zDir, 07) ) continue;
     break;
   }
   return zDir;
@@ -4431,7 +4509,7 @@ static int unixGetTempname(int nBuf, char *zBuf){
       zBuf[j] = (char)zChars[ ((unsigned char)zBuf[j])%(sizeof(zChars)-1) ];
     }
     zBuf[j] = 0;
-  }while( access(zBuf,0)==0 );
+  }while( osAccess(zBuf,0)==0 );
   return SQLITE_OK;
 }
 
@@ -4692,7 +4770,7 @@ static int unixOpen(
       assert( eType==SQLITE_OPEN_WAL || eType==SQLITE_OPEN_MAIN_JOURNAL );
       return rc;
     }
-    fd = open(zName, openFlags, openMode);
+    fd = osOpen(zName, openFlags, openMode);
     OSTRACE(("OPENX   %-3d %s 0%o\n", fd, zName, openFlags));
     if( fd<0 && errno!=EISDIR && isReadWrite && !isExclusive ){
       /* Failed to open the file for read/write access. Try read-only. */
@@ -4700,7 +4778,7 @@ static int unixOpen(
       openFlags &= ~(O_RDWR|O_CREAT);
       flags |= SQLITE_OPEN_READONLY;
       openFlags |= O_RDONLY;
-      fd = open(zName, openFlags, openMode);
+      fd = osOpen(zName, openFlags, openMode);
     }
     if( fd<0 ){
       rc = unixLogError(SQLITE_CANTOPEN_BKPT, "open", zName);
@@ -4744,7 +4822,7 @@ static int unixOpen(
   }
 
 #ifdef FD_CLOEXEC
-  fcntl(fd, F_SETFD, fcntl(fd, F_GETFD, 0) | FD_CLOEXEC);
+  osFcntl(fd, F_SETFD, osFcntl(fd, F_GETFD, 0) | FD_CLOEXEC);
 #endif
 
   noLock = eType!=SQLITE_OPEN_MAIN_DB;
@@ -4890,7 +4968,7 @@ static int unixAccess(
     default:
       assert(!"Invalid flags argument");
   }
-  *pResOut = (access(zPath, amode)==0);
+  *pResOut = (osAccess(zPath, amode)==0);
   if( flags==SQLITE_ACCESS_EXISTS && *pResOut ){
     struct stat buf;
     if( 0==stat(zPath, &buf) && buf.st_size==0 ){
@@ -4932,7 +5010,7 @@ static int unixFullPathname(
     sqlite3_snprintf(nOut, zOut, "%s", zPath);
   }else{
     int nCwd;
-    if( getcwd(zOut, nOut-1)==0 ){
+    if( osGetcwd(zOut, nOut-1)==0 ){
       return unixLogError(SQLITE_CANTOPEN_BKPT, "getcwd", zPath);
     }
     nCwd = (int)strlen(zOut);
@@ -5027,7 +5105,7 @@ static int unixRandomness(sqlite3_vfs *NotUsed, int nBuf, char *zBuf){
 #if !defined(SQLITE_TEST)
   {
     int pid, fd;
-    fd = open("/dev/urandom", O_RDONLY);
+    fd = osOpen("/dev/urandom", O_RDONLY, 0);
     if( fd<0 ){
       time_t t;
       time(&t);
@@ -5436,17 +5514,17 @@ static int proxyCreateUnixFile(
     }
   }
   if( fd<0 ){
-    fd = open(path, openFlags, SQLITE_DEFAULT_FILE_PERMISSIONS);
+    fd = osOpen(path, openFlags, SQLITE_DEFAULT_FILE_PERMISSIONS);
     terrno = errno;
     if( fd<0 && errno==ENOENT && islockfile ){
       if( proxyCreateLockPath(path) == SQLITE_OK ){
-        fd = open(path, openFlags, SQLITE_DEFAULT_FILE_PERMISSIONS);
+        fd = osOpen(path, openFlags, SQLITE_DEFAULT_FILE_PERMISSIONS);
       }
     }
   }
   if( fd<0 ){
     openFlags = O_RDONLY;
-    fd = open(path, openFlags, SQLITE_DEFAULT_FILE_PERMISSIONS);
+    fd = osOpen(path, openFlags, SQLITE_DEFAULT_FILE_PERMISSIONS);
     terrno = errno;
   }
   if( fd<0 ){
@@ -5566,7 +5644,7 @@ static int proxyBreakConchLock(unixFile *pFile, uuid_t myHostID){
     goto end_breaklock;
   }
   /* write it out to the temporary break file */
-  fd = open(tPath, (O_RDWR|O_CREAT|O_EXCL), SQLITE_DEFAULT_FILE_PERMISSIONS);
+  fd = osOpen(tPath, (O_RDWR|O_CREAT|O_EXCL), SQLITE_DEFAULT_FILE_PERMISSIONS);
   if( fd<0 ){
     sqlite3_snprintf(sizeof(errmsg), errmsg, "create failed (%d)", errno);
     goto end_breaklock;
@@ -5617,7 +5695,7 @@ static int proxyConchLock(unixFile *pFile, uuid_t myHostID, int lockType){
        * 3rd try: break the lock unless the mod time has changed.
        */
       struct stat buf;
-      if( fstat(conchFile->h, &buf) ){
+      if( osFstat(conchFile->h, &buf) ){
         pFile->lastErrno = errno;
         return SQLITE_IOERR_LOCK;
       }
@@ -5807,7 +5885,7 @@ static int proxyTakeConch(unixFile *pFile){
         if( rc==SQLITE_OK && createConch ){
           struct stat buf;
           int rc;
-          int err = fstat(pFile->h, &buf);
+          int err = osFstat(pFile->h, &buf);
           if( err==0 ){
             mode_t cmode = buf.st_mode&(S_IRUSR|S_IWUSR | S_IRGRP|S_IWGRP |
                                         S_IROTH|S_IWOTH);
@@ -5842,7 +5920,7 @@ static int proxyTakeConch(unixFile *pFile){
           robust_close(pFile, pFile->h, __LINE__) ){
         }
         pFile->h = -1;
-        int fd = open(pCtx->dbPath, pFile->openFlags,
+        int fd = osOpen(pCtx->dbPath, pFile->openFlags,
                       SQLITE_DEFAULT_FILE_PERMISSIONS);
         OSTRACE(("TRANSPROXY: OPEN  %d\n", fd));
         if( fd>=0 ){
@@ -6068,7 +6146,7 @@ static int proxyTransformUnixFile(unixFile *pFile, const char *path) {
       struct stat conchInfo;
       int goLockless = 0;
 
-      if( stat(pCtx->conchFilePath, &conchInfo) == -1 ) {
+      if( osStat(pCtx->conchFilePath, &conchInfo) == -1 ) {
         int err = errno;
         if( (err==ENOENT) && (statfs(dbPath, &fsInfo) != -1) ){
           goLockless = (fsInfo.f_flags&MNT_RDONLY) == MNT_RDONLY;
@@ -6353,7 +6431,7 @@ int sqlite3_os_init(void){
   ** that filesystem time.
   */
   #define UNIXVFS(VFSNAME, FINDER) {                        \
-    2,                    /* iVersion */                    \
+    3,                    /* iVersion */                    \
     sizeof(unixFile),     /* szOsFile */                    \
     MAX_PATHNAME,         /* mxPathname */                  \
     0,                    /* pNext */                       \
@@ -6372,6 +6450,7 @@ int sqlite3_os_init(void){
     unixCurrentTime,      /* xCurrentTime */                \
     unixGetLastError,     /* xGetLastError */               \
     unixCurrentTimeInt64, /* xCurrentTimeInt64 */           \
+    unixSetSystemCall,    /* xSetSystemCall */              \
   }
 
   /*
diff --git a/src/os_win.c b/src/os_win.c
index 70425178e8..4d19e57a36 100644
--- a/src/os_win.c
+++ b/src/os_win.c
@@ -2746,7 +2746,7 @@ static int winGetLastError(sqlite3_vfs *pVfs, int nBuf, char *zBuf){
 */
 int sqlite3_os_init(void){
   static sqlite3_vfs winVfs = {
-    2,                   /* iVersion */
+    3,                   /* iVersion */
     sizeof(winFile),     /* szOsFile */
     MAX_PATH,            /* mxPathname */
     0,                   /* pNext */
@@ -2765,6 +2765,7 @@ int sqlite3_os_init(void){
     winCurrentTime,      /* xCurrentTime */
     winGetLastError,     /* xGetLastError */
     winCurrentTimeInt64, /* xCurrentTimeInt64 */
+    0,                   /* xSetSystemCall */
   };
 
 #ifndef SQLITE_OMIT_WAL
diff --git a/src/sqlite.h.in b/src/sqlite.h.in
index 3400c6c916..5c07b8d96a 100644
--- a/src/sqlite.h.in
+++ b/src/sqlite.h.in
@@ -896,7 +896,7 @@ typedef struct sqlite3_mutex sqlite3_mutex;
 */
 typedef struct sqlite3_vfs sqlite3_vfs;
 struct sqlite3_vfs {
-  int iVersion;            /* Structure version number (currently 2) */
+  int iVersion;            /* Structure version number (currently 3) */
   int szOsFile;            /* Size of subclassed sqlite3_file */
   int mxPathname;          /* Maximum file pathname length */
   sqlite3_vfs *pNext;      /* Next registered VFS */
@@ -922,6 +922,11 @@ struct sqlite3_vfs {
   int (*xCurrentTimeInt64)(sqlite3_vfs*, sqlite3_int64*);
   /*
   ** The methods above are in versions 1 and 2 of the sqlite_vfs object.
+  ** Those below are for version 3 and greater.
+  */
+  int (*xSetSystemCall)(sqlite3_vfs*, const char *zName, void *pFunc);
+  /*
+  ** The methods above are in versions 1 through 3 of the sqlite_vfs object.
   ** New fields may be appended in figure versions.  The iVersion
   ** value will increment whenever this happens. 
   */