SQLite

/*
** Only set the lastErrno if the error code is a real error and not 
** a normal expected return code of SQLITE_BUSY or SQLITE_OK
*/
#define IS_LOCK_ERROR(x)  ((x != SQLITE_OK) && (x != SQLITE_BUSY))

/*
** Are OFD locks supported?
*/
#if defined(F_OFD_SETLK) && defined(F_OFD_GETLK)
# define HAVE_OFD_LOCKS 1
#else
# define HAVE_OFD_LOCKS 0
# define F_OFD_SETLK 0    /* Fake value so we can use the identifier */
# define F_OFD_GETLK 0    /* Fake value so we can use the identifier */
#endif

/* Forward references */
typedef struct unixShm unixShm;               /* Connection shared memory */
typedef struct unixShmNode unixShmNode;       /* Shared memory instance */
typedef struct unixInodeInfo unixInodeInfo;   /* An i-node */
typedef struct UnixUnusedFd UnixUnusedFd;     /* An unused file descriptor */

/*

  unsigned short int ctrlFlags;       /* Behavioral bits.  UNIXFILE_* flags */
  int lastErrno;                      /* The unix errno from last I/O error */
  void *lockingContext;               /* Locking style specific state */
  UnixUnusedFd *pPreallocatedUnused;  /* Pre-allocated UnixUnusedFd */
  const char *zPath;                  /* Name of the file */
  unixShm *pShm;                      /* Shared memory segment information */
  int szChunk;                        /* Configured by FCNTL_CHUNK_SIZE */
  int eGetLk, eSetLk;
#if SQLITE_MAX_MMAP_SIZE>0
  int nFetchOut;                      /* Number of outstanding xFetch refs */
  sqlite3_int64 mmapSize;             /* Usable size of mapping at pMapRegion */
  sqlite3_int64 mmapSizeActual;       /* Actual size of mapping at pMapRegion */
  sqlite3_int64 mmapSizeMax;          /* Configured FCNTL_MMAP_SIZE value */
  void *pMapRegion;                   /* Memory mapped region */
#endif

** command-line option on the compiler.  This code is normally
** turned off.
*/
static int lockTrace(int fd, int op, struct flock *p){
  char *zOpName, *zType;
  int s;
  int savedErrno;
  if( op==F_GETLK || op==F_OFD_GETLK ){
    zOpName = "GETLK";
  }else if( op==F_SETLK || op==F_OFD_SETLK ){
    zOpName = "SETLK";
  }else{
    s = osFcntl(fd, op, p);
    sqlite3DebugPrintf("fcntl unknown %d %d %d\n", fd, op, s);
    return s;
  }
  if( p->l_type==F_RDLCK ){

  }
  assert( p->l_whence==SEEK_SET );
  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,
     (int)p->l_pid, s);
  if( s==(-1)
   && (op==F_SETLK || op==F_OFD_SETLK)
   && (p->l_type==F_RDLCK || p->l_type==F_WRLCK)
  ){
    struct flock l2;
    l2 = *p;
    osFcntl(fd, F_GETLK, &l2);
    if( l2.l_type==F_RDLCK ){
      zType = "RDLCK";
    }else if( l2.l_type==F_WRLCK ){
      zType = "WRLCK";

******************************************************************************/


/******************************************************************************
*************************** Posix Advisory Locking ****************************
**
** POSIX advisory locks are broken by design.  ANSI STD 1003.1 (1996)
** section 6.5.2.2 lines 483 through 490 says that when a process
** sets or clears a lock, that operation overrides any prior locks set
** by the *same process*.  That means that if two different threads
** open the same file using different file descriptors, then POSIX
** advisory locking will not work to coordinate access between those two
** threads.  Consider this test case:
**
**       int fd1 = open("./file1", O_RDWR|O_CREAT, 0644);
**       int fd2 = open("./file2", O_RDWR|O_CREAT, 0644);
**
** Suppose ./file1 and ./file2 are really the same file (because
** one is a hard or symbolic link to the other) then if you set
** an exclusive lock on fd1, then try to get an exclusive lock
** on fd2, it works.  In a reasonable system,  the second lock would
** fail since there was already a lock on the file due to fd1.
** But this is not the case in POSIX advisory locking.  Since both
** locks came from the same process, the second overrides the first,
** even though they were on different file descriptors opened on
** different file names.
**
** This means that we cannot use POSIX locks to synchronize file access
** among competing threads of the same process.  POSIX locks will work fine
** to synchronize access for threads in separate processes, but not
** threads within the same process.
**
** To work around the problem, SQLite has to manage file locks internally
** on its own.  Whenever a new database is opened, we have to find the
** specific inode of the database file (the inode is determined by the
** st_dev and st_ino fields of the stat structure that fstat() fills in)
** and check for locks already existing on that inode.  When locks are
** created or removed, we have to look at our own internal record of the
** locks to see if another thread has previously set a lock on that same
** inode.
**
** (Aside: The use of inode numbers as unique IDs does not work on VxWorks.
** For VxWorks, we have to use the alternative unique ID system based on
** canonical filename and implemented in the previous division.)
**
** The sqlite3_file object for POSIX (a.k.a. the unixFile object) is more
** than just an integer file descriptor.  It also holds  a pointer
** a pointer to another object (unixInodeInfo) that describes the
** internal locks on the corresponding inode.  There is one
** unixInodeInfo object per inode, so if the same inode is opened twice,
** both unixFile objects point to the same lunixInodeInfo. The unixInodeInfo
** keeps a reference count (nRef) so we will know when to delete it.



**
** Any attempt to lock or unlock a unixFile first checks the unixInodeInfo.
** The fcntl() system call is only invoked to set a POSIX lock if the

** unixInodeInfo transitions between a locked and an unlocked state.
**
** But wait:  there are yet more problems with POSIX advisory locks.
**
** If you close a file descriptor that points to a file that has locks,
** all locks on that file that are owned by the current process are
** released.  To work around this problem, each unixInodeInfo object
** maintains a count of the number of pending locks on tha inode.
** When an attempt is made to close an unixFile, if there are other
** unixFile objcts open on the same inode that are holding locks, the call
** to close() the file descriptor is deferred until all of the locks clear.
** The unixInodeInfo structure keeps a list of file descriptors that need to
** be closed and that list is walked (and cleared) when the last lock
** clears.
**
** LinuxThreads:
**
** Many older versions of linux use the LinuxThreads library which is
** not posix compliant.  Under LinuxThreads, a lock created by thread
** A cannot be modified or overridden by a different thread B.
** Only thread A can modify the lock.  Locking behavior is correct
** if the appliation uses the newer Native Posix Thread Library (NPTL)
** on linux - with NPTL a lock created by thread A can override locks
** in thread B.  But there is no way to know at compile-time which
** threading library is being used.  So there is no way to know at
** compile-time whether or not thread A can override locks on thread B.
** One has to do a run-time check to discover the behavior of the
** current process.
**
** SQLite used to support LinuxThreads.  But support for LinuxThreads
** was dropped beginning with version 3.7.0.  SQLite will still work with
** LinuxThreads provided that (1) there is no more than one connection 
** per database file in the same process and (2) database connections
** do not move across threads.
**
** OFD Locks:
**
** Recent unix-like OSes have added support for Open File Description or "OFD"
** locks.  (This is not a typo: the name is "Open File Description" not
** "Open File Descriptor".  "-ion" not "-or".  There is a subtle difference
** between "Discription" and "Descriptor" which is described on the Linux
** fcntl manpage and will not be repeated here.)  The main difference
** between OFD locks and POSIX locks is that OFD locks are associated
** with a single open() system call and do not interfere with with file
** descriptors obtained from different open() system calls in the same
** process.  In other words, OFD locks fix the brokenness of POSIX locks.
**
** As of 2018-06-19, SQLite will use OFD locks if they are available.
** But the older work-arounds for POSIX locks are still here in the code
** since SQLite also needs to work on systems that do not support
** OFD locks.  Someday, perhaps, all unix systems will have reliable
** support for OFD locks, and at that time we can omit the unixInodeInfo
** object and all of its associated complication.  But for now we still
** have to support the older POSIX lock work-around hack.
*/

/*
** An instance of the following structure serves as the key used
** to locate a particular unixInodeInfo object.
*/
struct unixFileId {

#ifndef __DJGPP__
  if( !reserved && !pFile->pInode->bProcessLock ){
    struct flock lock;
    lock.l_whence = SEEK_SET;
    lock.l_start = RESERVED_BYTE;
    lock.l_len = 1;
    lock.l_type = F_WRLCK;
    lock.l_pid = 0;
    if( osFcntl(pFile->h, pFile->eGetLk, &lock) ){
      rc = SQLITE_IOERR_CHECKRESERVEDLOCK;
      storeLastErrno(pFile, errno);
    } else if( lock.l_type!=F_UNLCK ){
      reserved = 1;
    }
  }
#endif

** failing the lock.  The iBusyTimeout value is always reset back to
** zero on each call.
**
** If SQLITE_ENABLE_SETLK_TIMEOUT is not defined, then do a non-blocking
** attempt to set the lock.
*/
#ifndef SQLITE_ENABLE_SETLK_TIMEOUT
# define osSetAdvisoryLock(h,e,x,t) osFcntl(h,e,x)
#else
static int osSetAdvisoryLock(
  int h,                /* The file descriptor on which to take the lock */
  int eSetLk,           /* ioctl verb for setting the lock */
  struct flock *pLock,  /* The description of the lock */
  unixFile *pFile       /* Structure holding timeout value */
){
  int rc = osFcntl(h,eSetLk,pLock);
  while( rc<0 && pFile->iBusyTimeout>0 ){
    /* On systems that support some kind of blocking file lock with a timeout,
    ** make appropriate changes here to invoke that blocking file lock.  On
    ** generic posix, however, there is no such API.  So we simply try the
    ** lock once every millisecond until either the timeout expires, or until
    ** the lock is obtained. */
    usleep(1000);
    rc = osFcntl(h,eSetLk,pLock);
    pFile->iBusyTimeout--;
  }
  return rc;
}
#endif /* SQLITE_ENABLE_SETLK_TIMEOUT */

    if( pInode->bProcessLock==0 ){
      struct flock lock;
      assert( pInode->nLock==0 );
      lock.l_whence = SEEK_SET;
      lock.l_start = SHARED_FIRST;
      lock.l_len = SHARED_SIZE;
      lock.l_type = F_WRLCK;
      lock.l_pid = 0;
      rc = osSetAdvisoryLock(pFile->h, pFile->eSetLk, &lock, pFile);
      if( rc<0 ) return rc;
      pInode->bProcessLock = 1;
      pInode->nLock++;
    }else{
      rc = 0;
    }
  }else{
    pLock->l_pid = 0;
    rc = osSetAdvisoryLock(pFile->h, pFile->eSetLk, pLock, pFile);
  }
  return rc;
}

/*
** Lock the file with the lock specified by parameter eFileLock - one
** of the following:

    goto end_lock;
  }

  /* If a SHARED lock is requested, and some thread using this PID already
  ** has a SHARED or RESERVED lock, then increment reference counts and
  ** return SQLITE_OK.
  */
  if( eFileLock==SHARED_LOCK
   && pFile->eGetLk==F_GETLK
   && (pInode->eFileLock==SHARED_LOCK || pInode->eFileLock==RESERVED_LOCK)
  ){
    assert( eFileLock==SHARED_LOCK );
    assert( pFile->eFileLock==0 );
    assert( pInode->nShared>0 );
    pFile->eFileLock = SHARED_LOCK;
    pInode->nShared++;
    pInode->nLock++;
    goto end_lock;

    }
#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
    case SQLITE_FCNTL_LOCK_TIMEOUT: {
      pFile->iBusyTimeout = *(int*)pArg;
      return SQLITE_OK;
    }
#endif
    case SQLITE_FCNTL_OFD_LOCKS: {
      int x = *(int*)pArg;
      if( x==0 ){
        pFile->eSetLk = F_SETLK;
        pFile->eGetLk = F_GETLK;
      }
      *(int*)pArg = pFile->eSetLk==F_OFD_SETLK;
      return SQLITE_OK;
    }
#if SQLITE_MAX_MMAP_SIZE>0
    case SQLITE_FCNTL_MMAP_SIZE: {
      i64 newLimit = *(i64*)pArg;
      int rc = SQLITE_OK;
      if( newLimit>sqlite3GlobalConfig.mxMmap ){
        newLimit = sqlite3GlobalConfig.mxMmap;
      }

  if( pShmNode->h>=0 ){
    /* Initialize the locking parameters */
    f.l_type = lockType;
    f.l_whence = SEEK_SET;
    f.l_start = ofst;
    f.l_len = n;
    f.l_pid = 0;
    rc = osSetAdvisoryLock(pShmNode->h, pFile->eSetLk, &f, pFile);
    rc = (rc!=(-1)) ? SQLITE_OK : SQLITE_BUSY;
  }

  /* Update the global lock state and do debug tracing */
#ifdef SQLITE_DEBUG
  { u16 mask;
  OSTRACE(("SHM-LOCK "));

  ** process might open and use the *-shm file without truncating it.
  ** And if the *-shm file has been corrupted by a power failure or
  ** system crash, the database itself may also become corrupt.  */
  lock.l_whence = SEEK_SET;
  lock.l_start = UNIX_SHM_DMS;
  lock.l_len = 1;
  lock.l_type = F_WRLCK;
  if( osFcntl(pShmNode->h, pDbFd->eGetLk, &lock)!=0 ) {
    rc = SQLITE_IOERR_LOCK;
  }else if( lock.l_type==F_UNLCK ){
    if( pShmNode->isReadonly ){
      pShmNode->isUnlocked = 1;
      rc = SQLITE_READONLY_CANTINIT;
    }else{
      rc = unixShmSystemLock(pDbFd, F_WRLCK, UNIX_SHM_DMS, 1);

  assert( pNew->pInode==NULL );

  /* No locking occurs in temporary files */
  assert( zFilename!=0 || (ctrlFlags & UNIXFILE_NOLOCK)!=0 );

  OSTRACE(("OPEN    %-3d %s\n", h, zFilename));
  pNew->h = h;
  pNew->eSetLk = F_SETLK;
  pNew->eGetLk = F_GETLK;
#if HAVE_OFD_LOCKS
  {
    struct flock lock;
    lock.l_whence = SEEK_SET;
    lock.l_start = RESERVED_BYTE;
    lock.l_len = 1;
    lock.l_type = F_WRLCK;
    lock.l_pid = 0;
    if( osFcntl(h, F_OFD_GETLK, &lock)==0 ){
      pNew->eSetLk = F_OFD_SETLK;
      pNew->eGetLk = F_OFD_GETLK;
    }
  }
#endif
  pNew->pVfs = pVfs;
  pNew->zPath = zFilename;
  pNew->ctrlFlags = (u8)ctrlFlags;
#if SQLITE_MAX_MMAP_SIZE>0
  pNew->mmapSizeMax = sqlite3GlobalConfig.szMmap;
#endif
  if( sqlite3_uri_boolean(((ctrlFlags & UNIXFILE_URI) ? zFilename : 0),

** a prior successful call to [SQLITE_FCNTL_BEGIN_ATOMIC_WRITE].
**
** <li>[[SQLITE_FCNTL_LOCK_TIMEOUT]]
** The [SQLITE_FCNTL_LOCK_TIMEOUT] opcode causes attempts to obtain
** a file lock using the xLock or xShmLock methods of the VFS to wait
** for up to M milliseconds before failing, where M is the single 
** unsigned integer parameter.
**
** <li>[[SQLITE_FCNTL_OFD_LOCKS]]
** The [SQLITE_FCNTL_OFD_LOCKS] opcode will query whether or not OFD
** locking is currently being used for an open file, or disable the use
** of OFD locking on the file.  The argument is a pointer to an integer
** in the callers context.  If that integer is initially -1, then it is
** set to 1 or 0 if the system is or is not using OFD locks for the file.
** If the integer is initially 0, then OFD locks are disabled for the file.
** This file-control is intended for testing and validation use only.
** Applications that strive for correctness and error-free operation should
** not mess with this file-control.
** </ul>
*/
#define SQLITE_FCNTL_LOCKSTATE               1
#define SQLITE_FCNTL_GET_LOCKPROXYFILE       2
#define SQLITE_FCNTL_SET_LOCKPROXYFILE       3
#define SQLITE_FCNTL_LAST_ERRNO              4
#define SQLITE_FCNTL_SIZE_HINT               5

#define SQLITE_FCNTL_JOURNAL_POINTER        28
#define SQLITE_FCNTL_WIN32_GET_HANDLE       29
#define SQLITE_FCNTL_PDB                    30
#define SQLITE_FCNTL_BEGIN_ATOMIC_WRITE     31
#define SQLITE_FCNTL_COMMIT_ATOMIC_WRITE    32
#define SQLITE_FCNTL_ROLLBACK_ATOMIC_WRITE  33
#define SQLITE_FCNTL_LOCK_TIMEOUT           34
#define SQLITE_FCNTL_OFD_LOCKS              35

/* deprecated names */
#define SQLITE_GET_LOCKPROXYFILE      SQLITE_FCNTL_GET_LOCKPROXYFILE
#define SQLITE_SET_LOCKPROXYFILE      SQLITE_FCNTL_SET_LOCKPROXYFILE
#define SQLITE_LAST_ERRNO             SQLITE_FCNTL_LAST_ERRNO

  }
  if( Tcl_GetIntFromObj(interp, objv[2], &bPersist) ) return TCL_ERROR;
  rc = sqlite3_file_control(db, NULL, SQLITE_FCNTL_PERSIST_WAL, (void*)&bPersist);
  sqlite3_snprintf(sizeof(z), z, "%d %d", rc, bPersist);
  Tcl_AppendResult(interp, z, (char*)0);
  return TCL_OK;  
}

/*
** tclcmd:   file_control_ofd_locks DB ?DISABLE?
**
** Run sqlite3_file_control() to query the OFD lock capability.  Return
** true if OFD locks are available and false if not.
**
** If the DISABLE argument is true, then disable OFD locking, if it is
** enabled.  The returned value will show that OFD locks are disabled.
*/
static int SQLITE_TCLAPI file_control_ofd_locks(
  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 *db;
  int rc;
  int b = 0;

  if( objc!=2 && objc!=3 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"",
        Tcl_GetStringFromObj(objv[0], 0), " DB ?DISABLE?", 0);
    return TCL_ERROR;
  }
  if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ){
    return TCL_ERROR;
  }
  if( objc==3 && Tcl_GetIntFromObj(interp, objv[2], &b) ) return TCL_ERROR;
  b = b ? 0 : -1;
  rc = sqlite3_file_control(db,NULL,SQLITE_FCNTL_OFD_LOCKS,(void*)&b);
  Tcl_AppendResult(interp, (rc==SQLITE_OK && b) ? "1" : "0", (char*)0);
  return TCL_OK;  
}

/*
** tclcmd:   file_control_powersafe_overwrite DB PSOW-FLAG
**
** This TCL command runs the sqlite3_file_control interface with
** the SQLITE_FCNTL_POWERSAFE_OVERWRITE opcode.
*/

  }
  if( Tcl_GetIntFromObj(interp, objv[2], &b) ) return TCL_ERROR;
  rc = sqlite3_file_control(db,NULL,SQLITE_FCNTL_POWERSAFE_OVERWRITE,(void*)&b);
  sqlite3_snprintf(sizeof(z), z, "%d %d", rc, b);
  Tcl_AppendResult(interp, z, (char*)0);
  return TCL_OK;  
}


/*
** tclcmd:   file_control_vfsname DB ?AUXDB?
**
** Return a string that describes the stack of VFSes.
*/
static int SQLITE_TCLAPI file_control_vfsname(

     { "file_control_sizehint_test",  file_control_sizehint_test,   0   },
#if SQLITE_OS_WIN
     { "file_control_win32_av_retry", file_control_win32_av_retry,  0   },
     { "file_control_win32_get_handle", file_control_win32_get_handle, 0  },
     { "file_control_win32_set_handle", file_control_win32_set_handle, 0  },
#endif
     { "file_control_persist_wal",    file_control_persist_wal,     0   },
     { "file_control_ofd_locks",      file_control_ofd_locks,       0   },
     { "file_control_powersafe_overwrite",file_control_powersafe_overwrite,0},
     { "file_control_vfsname",        file_control_vfsname,         0   },
     { "file_control_tempfilename",   file_control_tempfilename,    0   },
     { "sqlite3_vfs_list",           vfs_list,     0   },
     { "sqlite3_create_function_v2", test_create_function_v2, 0 },

     /* Functions from os.h */