MCL/sf/os/persistentdata: comparison persistentstorage/sql/SQLite/os

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+:08ec8eefde2f
+/*
+** 2004 May 22
+**
+** 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 contains code that is specific to Unix systems.
+**
+** $Id: os_unix.c,v 1.195 2008/07/30 17:28:04 drh Exp $
+*/
+#include "sqliteInt.h"
+#if SQLITE_OS_UNIX              /* This file is used on unix only */
+/*
+** If SQLITE_ENABLE_LOCKING_STYLE is defined, then several different
+** locking implementations are provided:
+**
+**   * POSIX locking (the default),
+**   * No locking,
+**   * Dot-file locking,
+**   * flock() locking,
+**   * AFP locking (OSX only).
+*/
+/* #define SQLITE_ENABLE_LOCKING_STYLE 0 */
+/*
+** These #defines should enable >2GB file support on Posix if the
+** underlying operating system supports it.  If the OS lacks
+** large file support, these should be no-ops.
+**
+** Large file support can be disabled using the -DSQLITE_DISABLE_LFS switch
+** on the compiler command line.  This is necessary if you are compiling
+** on a recent machine (ex: RedHat 7.2) but you want your code to work
+** on an older machine (ex: RedHat 6.0).  If you compile on RedHat 7.2
+** without this option, LFS is enable.  But LFS does not exist in the kernel
+** in RedHat 6.0, so the code won't work.  Hence, for maximum binary
+** portability you should omit LFS.
+*/
+#ifndef SQLITE_DISABLE_LFS
+# define _LARGE_FILE       1
+# ifndef _FILE_OFFSET_BITS
+#   define _FILE_OFFSET_BITS 64
+# endif
+# define _LARGEFILE_SOURCE 1
+#endif
+/*
+** standard include files.
+*/
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <time.h>
+#include <sys/time.h>
+#include <errno.h>
+#ifdef SQLITE_ENABLE_LOCKING_STYLE
+#include <sys/ioctl.h>
+#include <sys/param.h>
+#include <sys/mount.h>
+#endif /* SQLITE_ENABLE_LOCKING_STYLE */
+/*
+** If we are to be thread-safe, include the pthreads header and define
+** the SQLITE_UNIX_THREADS macro.
+*/
+#if SQLITE_THREADSAFE
+# include <pthread.h>
+# define SQLITE_UNIX_THREADS 1
+#endif
+/*
+** Default permissions when creating a new file
+*/
+#ifndef SQLITE_DEFAULT_FILE_PERMISSIONS
+# define SQLITE_DEFAULT_FILE_PERMISSIONS 0644
+#endif
+/*
+** Maximum supported path-length.
+*/
+#define MAX_PATHNAME 512
+/*
+** The unixFile structure is subclass of sqlite3_file specific for the unix
+** protability layer.
+*/
+typedef struct unixFile unixFile;
+struct unixFile {
+sqlite3_io_methods const *pMethod;  /* Always the first entry */
+#ifdef SQLITE_TEST
+/* In test mode, increase the size of this structure a bit so that
+** it is larger than the struct CrashFile defined in test6.c.
+*/
+char aPadding[32];
+#endif
+struct openCnt *pOpen;    /* Info about all open fd's on this inode */
+struct lockInfo *pLock;   /* Info about locks on this inode */
+#ifdef SQLITE_ENABLE_LOCKING_STYLE
+void *lockingContext;     /* Locking style specific state */
+#endif
+int h;                    /* The file descriptor */
+unsigned char locktype;   /* The type of lock held on this fd */
+int dirfd;                /* File descriptor for the directory */
+#if SQLITE_THREADSAFE
+pthread_t tid;            /* The thread that "owns" this unixFile */
+#endif
+};
+/*
+** Include code that is common to all os_*.c files
+*/
+#include "os_common.h"
+/*
+** Define various macros that are missing from some systems.
+*/
+#ifndef O_LARGEFILE
+# define O_LARGEFILE 0
+#endif
+#ifdef SQLITE_DISABLE_LFS
+# undef O_LARGEFILE
+# define O_LARGEFILE 0
+#endif
+#ifndef O_NOFOLLOW
+# define O_NOFOLLOW 0
+#endif
+#ifndef O_BINARY
+# define O_BINARY 0
+#endif
+/*
+** The DJGPP compiler environment looks mostly like Unix, but it
+** lacks the fcntl() system call.  So redefine fcntl() to be something
+** that always succeeds.  This means that locking does not occur under
+** DJGPP.  But it is DOS - what did you expect?
+*/
+#ifdef __DJGPP__
+# define fcntl(A,B,C) 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
+/*
+** Set or check the unixFile.tid field.  This field is set when an unixFile
+** is first opened.  All subsequent uses of the unixFile verify that the
+** same thread is operating on the unixFile.  Some operating systems do
+** not allow locks to be overridden by other threads and that restriction
+** means that sqlite3* database handles cannot be moved from one thread
+** to another.  This logic makes sure a user does not try to do that
+** by mistake.
+**
+** Version 3.3.1 (2006-01-15):  unixFile can be moved from one thread to
+** another as long as we are running on a system that supports threads
+** overriding each others locks (which now the most common behavior)
+** or if no locks are held.  But the unixFile.pLock field needs to be
+** recomputed because its key includes the thread-id.  See the
+** transferOwnership() function below for additional information
+*/
+#if SQLITE_THREADSAFE
+# define SET_THREADID(X)   (X)->tid = pthread_self()
+# define CHECK_THREADID(X) (threadsOverrideEachOthersLocks==0 && \
+!pthread_equal((X)->tid, pthread_self()))
+#else
+# define SET_THREADID(X)
+# define CHECK_THREADID(X) 0
+#endif
+/*
+** Here is the dirt on POSIX advisory locks:  ANSI STD 1003.1 (1996)
+** section 6.5.2.2 lines 483 through 490 specify that when a process
+** sets or clears a lock, that operation overrides any prior locks set
+** by the same process.  It does not explicitly say so, but this implies
+** that it overrides locks set by the same process using a different
+** file descriptor.  Consider this test case:
+**       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.  I would have expected the second lock to
+** fail since there was already a lock on the file due to fd1.
+** But not so.  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.
+**
+** Bummer.  If you ask me, this is broken.  Badly broken.  It 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.
+**
+** The sqlite3_file structure for POSIX is no longer just an integer file
+** descriptor.  It is now a structure that holds the integer file
+** descriptor and a pointer to a structure that describes the internal
+** locks on the corresponding inode.  There is one locking structure
+** per inode, so if the same inode is opened twice, both unixFile structures
+** point to the same locking structure.  The locking structure keeps
+** a reference count (so we will know when to delete it) and a "cnt"
+** field that tells us its internal lock status.  cnt==0 means the
+** file is unlocked.  cnt==-1 means the file has an exclusive lock.
+** cnt>0 means there are cnt shared locks on the file.
+**
+** Any attempt to lock or unlock a file first checks the locking
+** structure.  The fcntl() system call is only invoked to set a
+** POSIX lock if the internal lock structure transitions between
+** a locked and an unlocked state.
+**
+** 2004-Jan-11:
+** More recent discoveries about POSIX advisory locks.  (The more
+** I discover, the more I realize the a POSIX advisory locks are
+** an abomination.)
+**
+** 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 unixFile structure contains
+** a pointer to an openCnt structure.  There is one openCnt structure
+** per open inode, which means that multiple unixFile can point to a single
+** openCnt.  When an attempt is made to close an unixFile, if there are
+** other unixFile 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 openCnt structure keeps a list of file descriptors that need to
+** be closed and that list is walked (and cleared) when the last lock
+** clears.
+**
+** First, under Linux threads, because each thread has a separate
+** process ID, lock operations in one thread do not override locks
+** to the same file in other threads.  Linux threads behave like
+** separate processes in this respect.  But, if you close a file
+** descriptor in linux threads, all locks are cleared, even locks
+** on other threads and even though the other threads have different
+** process IDs.  Linux threads is inconsistent in this respect.
+** (I'm beginning to think that linux threads is an abomination too.)
+** The consequence of this all is that the hash table for the lockInfo
+** structure has to include the process id as part of its key because
+** locks in different threads are treated as distinct.  But the
+** openCnt structure should not include the process id in its
+** key because close() clears lock on all threads, not just the current
+** thread.  Were it not for this goofiness in linux threads, we could
+** combine the lockInfo and openCnt structures into a single structure.
+**
+** 2004-Jun-28:
+** On some versions of linux, threads can override each others locks.
+** On others not.  Sometimes you can change the behavior on the same
+** system by setting the LD_ASSUME_KERNEL environment variable.  The
+** POSIX standard is silent as to which behavior is correct, as far
+** as I can tell, so other versions of unix might show the same
+** inconsistency.  There is no little doubt in my mind that posix
+** advisory locks and linux threads are profoundly broken.
+**
+** To work around the inconsistencies, we have to test at runtime
+** whether or not threads can override each others locks.  This test
+** is run once, the first time any lock is attempted.  A static
+** variable is set to record the results of this test for future
+** use.
+*/
+/*
+** An instance of the following structure serves as the key used
+** to locate a particular lockInfo structure given its inode.
+**
+** If threads cannot override each others locks, then we set the
+** lockKey.tid field to the thread ID.  If threads can override
+** each others locks then tid is always set to zero.  tid is omitted
+** if we compile without threading support.
+*/
+struct lockKey {
+dev_t dev;       /* Device number */
+ino_t ino;       /* Inode number */
+#if SQLITE_THREADSAFE
+pthread_t tid;   /* Thread ID or zero if threads can override each other */
+#endif
+};
+/*
+** An instance of the following structure is allocated for each open
+** inode on each thread with a different process ID.  (Threads have
+** different process IDs on linux, but not on most other unixes.)
+**
+** A single inode can have multiple file descriptors, so each unixFile
+** structure contains a pointer to an instance of this object and this
+** object keeps a count of the number of unixFile pointing to it.
+*/
+struct lockInfo {
+struct lockKey key;  /* The lookup key */
+int cnt;             /* Number of SHARED locks held */
+int locktype;        /* One of SHARED_LOCK, RESERVED_LOCK etc. */
+int nRef;            /* Number of pointers to this structure */
+struct lockInfo *pNext, *pPrev;   /* List of all lockInfo objects */
+};
+/*
+** An instance of the following structure serves as the key used
+** to locate a particular openCnt structure given its inode.  This
+** is the same as the lockKey except that the thread ID is omitted.
+*/
+struct openKey {
+dev_t dev;   /* Device number */
+ino_t ino;   /* Inode number */
+};
+/*
+** An instance of the following structure is allocated for each open
+** inode.  This structure keeps track of the number of locks on that
+** inode.  If a close is attempted against an inode that is holding
+** locks, the close is deferred until all locks clear by adding the
+** file descriptor to be closed to the pending list.
+*/
+struct openCnt {
+struct openKey key;   /* The lookup key */
+int nRef;             /* Number of pointers to this structure */
+int nLock;            /* Number of outstanding locks */
+int nPending;         /* Number of pending close() operations */
+int *aPending;        /* Malloced space holding fd's awaiting a close() */
+struct openCnt *pNext, *pPrev;   /* List of all openCnt objects */
+};
+/*
+** List of all lockInfo and openCnt objects.  This used to be a hash
+** table.  But the number of objects is rarely more than a dozen and
+** never exceeds a few thousand.  And lookup is not on a critical
+** path oo a simple linked list will suffice.
+*/
+static struct lockInfo *lockList = 0;
+static struct openCnt *openList = 0;
+/*
+** The locking styles are associated with the different file locking
+** capabilities supported by different file systems.
+**
+** POSIX locking style fully supports shared and exclusive byte-range locks
+** AFP locking only supports exclusive byte-range locks
+** FLOCK only supports a single file-global exclusive lock
+** DOTLOCK isn't a true locking style, it refers to the use of a special
+**   file named the same as the database file with a '.lock' extension, this
+**   can be used on file systems that do not offer any reliable file locking
+** NO locking means that no locking will be attempted, this is only used for
+**   read-only file systems currently
+** UNSUPPORTED means that no locking will be attempted, this is only used for
+**   file systems that are known to be unsupported
+*/
+#define LOCKING_STYLE_POSIX        1
+#define LOCKING_STYLE_NONE         2
+#define LOCKING_STYLE_DOTFILE      3
+#define LOCKING_STYLE_FLOCK        4
+#define LOCKING_STYLE_AFP          5
+/*
+** Helper functions to obtain and relinquish the global mutex.
+*/
+static void enterMutex(){
+sqlite3_mutex_enter(sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER));
+}
+static void leaveMutex(){
+sqlite3_mutex_leave(sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER));
+}
+#if SQLITE_THREADSAFE
+/*
+** This variable records whether or not threads can override each others
+** locks.
+**
+**    0:  No.  Threads cannot override each others locks.
+**    1:  Yes.  Threads can override each others locks.
+**   -1:  We don't know yet.
+**
+** On some systems, we know at compile-time if threads can override each
+** others locks.  On those systems, the SQLITE_THREAD_OVERRIDE_LOCK macro
+** will be set appropriately.  On other systems, we have to check at
+** runtime.  On these latter systems, SQLTIE_THREAD_OVERRIDE_LOCK is
+** undefined.
+**
+** This variable normally has file scope only.  But during testing, we make
+** it a global so that the test code can change its value in order to verify
+** that the right stuff happens in either case.
+*/
+#ifndef SQLITE_THREAD_OVERRIDE_LOCK
+# define SQLITE_THREAD_OVERRIDE_LOCK -1
+#endif
+#ifdef SQLITE_TEST
+int threadsOverrideEachOthersLocks = SQLITE_THREAD_OVERRIDE_LOCK;
+#else
+static int threadsOverrideEachOthersLocks = SQLITE_THREAD_OVERRIDE_LOCK;
+#endif
+/*
+** This structure holds information passed into individual test
+** threads by the testThreadLockingBehavior() routine.
+*/
+struct threadTestData {
+int fd;                /* File to be locked */
+struct flock lock;     /* The locking operation */
+int result;            /* Result of the locking operation */
+};
+#ifdef SQLITE_LOCK_TRACE
+/*
+** Print out information about all locking operations.
+**
+** This routine is used for troubleshooting locks on multithreaded
+** platforms.  Enable by compiling with the -DSQLITE_LOCK_TRACE
+** 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 ){
+zOpName = "GETLK";
+}else if( op==F_SETLK ){
+zOpName = "SETLK";
+}else{
+s = fcntl(fd, op, p);
+sqlite3DebugPrintf("fcntl unknown %d %d %d\n", fd, op, s);
+return s;
+}
+if( p->l_type==F_RDLCK ){
+zType = "RDLCK";
+}else if( p->l_type==F_WRLCK ){
+zType = "WRLCK";
+}else if( p->l_type==F_UNLCK ){
+zType = "UNLCK";
+}else{
+assert( 0 );
+}
+assert( p->l_whence==SEEK_SET );
+s = fcntl(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 && (p->l_type==F_RDLCK || p->l_type==F_WRLCK) ){
+struct flock l2;
+l2 = *p;
+fcntl(fd, F_GETLK, &l2);
+if( l2.l_type==F_RDLCK ){
+zType = "RDLCK";
+}else if( l2.l_type==F_WRLCK ){
+zType = "WRLCK";
+}else if( l2.l_type==F_UNLCK ){
+zType = "UNLCK";
+}else{
+assert( 0 );
+}
+sqlite3DebugPrintf("fcntl-failure-reason: %s %d %d %d\n",
+zType, (int)l2.l_start, (int)l2.l_len, (int)l2.l_pid);
+}
+errno = savedErrno;
+return s;
+}
+#define fcntl lockTrace
+#endif /* SQLITE_LOCK_TRACE */
+/*
+** The testThreadLockingBehavior() routine launches two separate
+** threads on this routine.  This routine attempts to lock a file
+** descriptor then returns.  The success or failure of that attempt
+** allows the testThreadLockingBehavior() procedure to determine
+** whether or not threads can override each others locks.
+*/
+static void *threadLockingTest(void *pArg){
+struct threadTestData *pData = (struct threadTestData*)pArg;
+pData->result = fcntl(pData->fd, F_SETLK, &pData->lock);
+return pArg;
+}
+/*
+** This procedure attempts to determine whether or not threads
+** can override each others locks then sets the
+** threadsOverrideEachOthersLocks variable appropriately.
+*/
+static void testThreadLockingBehavior(int fd_orig){
+int fd;
+struct threadTestData d[2];
+pthread_t t[2];
+fd = dup(fd_orig);
+if( fd<0 ) return;
+memset(d, 0, sizeof(d));
+d[0].fd = fd;
+d[0].lock.l_type = F_RDLCK;
+d[0].lock.l_len = 1;
+d[0].lock.l_start = 0;
+d[0].lock.l_whence = SEEK_SET;
+d[1] = d[0];
+d[1].lock.l_type = F_WRLCK;
+pthread_create(&t[0], 0, threadLockingTest, &d[0]);
+pthread_create(&t[1], 0, threadLockingTest, &d[1]);
+pthread_join(t[0], 0);
+pthread_join(t[1], 0);
+close(fd);
+threadsOverrideEachOthersLocks =  d[0].result==0 && d[1].result==0;
+}
+#endif /* SQLITE_THREADSAFE */
+/*
+** Release a lockInfo structure previously allocated by findLockInfo().
+*/
+static void releaseLockInfo(struct lockInfo *pLock){
+if( pLock ){
+pLock->nRef--;
+if( pLock->nRef==0 ){
+if( pLock->pPrev ){
+assert( pLock->pPrev->pNext==pLock );
+pLock->pPrev->pNext = pLock->pNext;
+}else{
+assert( lockList==pLock );
+lockList = pLock->pNext;
+}
+if( pLock->pNext ){
+assert( pLock->pNext->pPrev==pLock );
+pLock->pNext->pPrev = pLock->pPrev;
+}
+sqlite3_free(pLock);
+}
+}
+}
+/*
+** Release a openCnt structure previously allocated by findLockInfo().
+*/
+static void releaseOpenCnt(struct openCnt *pOpen){
+if( pOpen ){
+pOpen->nRef--;
+if( pOpen->nRef==0 ){
+if( pOpen->pPrev ){
+assert( pOpen->pPrev->pNext==pOpen );
+pOpen->pPrev->pNext = pOpen->pNext;
+}else{
+assert( openList==pOpen );
+openList = pOpen->pNext;
+}
+if( pOpen->pNext ){
+assert( pOpen->pNext->pPrev==pOpen );
+pOpen->pNext->pPrev = pOpen->pPrev;
+}
+sqlite3_free(pOpen->aPending);
+sqlite3_free(pOpen);
+}
+}
+}
+#ifdef SQLITE_ENABLE_LOCKING_STYLE
+/*
+** Tests a byte-range locking query to see if byte range locks are
+** supported, if not we fall back to dotlockLockingStyle.
+*/
+static int testLockingStyle(int fd){
+struct flock lockInfo;
+/* Test byte-range lock using fcntl(). If the call succeeds,
+** assume that the file-system supports POSIX style locks.
+*/
+lockInfo.l_len = 1;
+lockInfo.l_start = 0;
+lockInfo.l_whence = SEEK_SET;
+lockInfo.l_type = F_RDLCK;
+if( fcntl(fd, F_GETLK, &lockInfo)!=-1 ) {
+return LOCKING_STYLE_POSIX;
+}
+/* Testing for flock() can give false positives.  So if if the above
+** test fails, then we fall back to using dot-file style locking.
+*/
+return LOCKING_STYLE_DOTFILE;
+}
+#endif
+/*
+** If SQLITE_ENABLE_LOCKING_STYLE is defined, this function Examines the
+** f_fstypename entry in the statfs structure as returned by stat() for
+** the file system hosting the database file and selects  the appropriate
+** locking style based on its value.  These values and assignments are
+** based on Darwin/OSX behavior and have not been thoroughly tested on
+** other systems.
+**
+** If SQLITE_ENABLE_LOCKING_STYLE is not defined, this function always
+** returns LOCKING_STYLE_POSIX.
+*/
+static int detectLockingStyle(
+sqlite3_vfs *pVfs,
+const char *filePath,
+int fd
+){
+#ifdef SQLITE_ENABLE_LOCKING_STYLE
+struct Mapping {
+const char *zFilesystem;
+int eLockingStyle;
+} aMap[] = {
+{ "hfs",    LOCKING_STYLE_POSIX },
+{ "ufs",    LOCKING_STYLE_POSIX },
+{ "afpfs",  LOCKING_STYLE_AFP },
+{ "smbfs",  LOCKING_STYLE_FLOCK },
+{ "msdos",  LOCKING_STYLE_DOTFILE },
+{ "webdav", LOCKING_STYLE_NONE },
+{ 0, 0 }
+};
+int i;
+struct statfs fsInfo;
+if( !filePath ){
+return LOCKING_STYLE_NONE;
+}
+if( pVfs->pAppData ){
+return (int)pVfs->pAppData;
+}
+if( statfs(filePath, &fsInfo) != -1 ){
+if( fsInfo.f_flags & MNT_RDONLY ){
+return LOCKING_STYLE_NONE;
+}
+for(i=0; aMap[i].zFilesystem; i++){
+if( strcmp(fsInfo.f_fstypename, aMap[i].zFilesystem)==0 ){
+return aMap[i].eLockingStyle;
+}
+}
+}
+/* Default case. Handles, amongst others, "nfs". */
+return testLockingStyle(fd);
+#endif
+return LOCKING_STYLE_POSIX;
+}
+/*
+** Given a file descriptor, locate lockInfo and openCnt structures that
+** describes that file descriptor.  Create new ones if necessary.  The
+** return values might be uninitialized if an error occurs.
+**
+** Return an appropriate error code.
+*/
+static int findLockInfo(
+int fd,                      /* The file descriptor used in the key */
+struct lockInfo **ppLock,    /* Return the lockInfo structure here */
+struct openCnt **ppOpen      /* Return the openCnt structure here */
+){
+int rc;
+struct lockKey key1;
+struct openKey key2;
+struct stat statbuf;
+struct lockInfo *pLock;
+struct openCnt *pOpen;
+rc = fstat(fd, &statbuf);
+if( rc!=0 ){
+#ifdef EOVERFLOW
+if( errno==EOVERFLOW ) return SQLITE_NOLFS;
+#endif
+return SQLITE_IOERR;
+}
+/* On OS X on an msdos filesystem, the inode number is reported
+** incorrectly for zero-size files.  See ticket #3260.  To work
+** around this problem (we consider it a bug in OS X, not SQLite)
+** we always increase the file size to 1 by writing a single byte
+** prior to accessing the inode number.  The one byte written is
+** an ASCII 'S' character which also happens to be the first byte
+** in the header of every SQLite database.  In this way, if there
+** is a race condition such that another thread has already populated
+** the first page of the database, no damage is done.
+*/
+if( statbuf.st_size==0 ){
+write(fd, "S", 1);
+rc = fstat(fd, &statbuf);
+if( rc!=0 ){
+return SQLITE_IOERR;
+}
+}
+memset(&key1, 0, sizeof(key1));
+key1.dev = statbuf.st_dev;
+key1.ino = statbuf.st_ino;
+#if SQLITE_THREADSAFE
+if( threadsOverrideEachOthersLocks<0 ){
+testThreadLockingBehavior(fd);
+}
+key1.tid = threadsOverrideEachOthersLocks ? 0 : pthread_self();
+#endif
+memset(&key2, 0, sizeof(key2));
+key2.dev = statbuf.st_dev;
+key2.ino = statbuf.st_ino;
+pLock = lockList;
+while( pLock && memcmp(&key1, &pLock->key, sizeof(key1)) ){
+pLock = pLock->pNext;
+}
+if( pLock==0 ){
+pLock = sqlite3_malloc( sizeof(*pLock) );
+if( pLock==0 ){
+rc = SQLITE_NOMEM;
+goto exit_findlockinfo;
+}
+pLock->key = key1;
+pLock->nRef = 1;
+pLock->cnt = 0;
+pLock->locktype = 0;
+pLock->pNext = lockList;
+pLock->pPrev = 0;
+if( lockList ) lockList->pPrev = pLock;
+lockList = pLock;
+}else{
+pLock->nRef++;
+}
+*ppLock = pLock;
+if( ppOpen!=0 ){
+pOpen = openList;
+while( pOpen && memcmp(&key2, &pOpen->key, sizeof(key2)) ){
+pOpen = pOpen->pNext;
+}
+if( pOpen==0 ){
+pOpen = sqlite3_malloc( sizeof(*pOpen) );
+if( pOpen==0 ){
+releaseLockInfo(pLock);
+rc = SQLITE_NOMEM;
+goto exit_findlockinfo;
+}
+pOpen->key = key2;
+pOpen->nRef = 1;
+pOpen->nLock = 0;
+pOpen->nPending = 0;
+pOpen->aPending = 0;
+pOpen->pNext = openList;
+pOpen->pPrev = 0;
+if( openList ) openList->pPrev = pOpen;
+openList = pOpen;
+}else{
+pOpen->nRef++;
+}
+*ppOpen = pOpen;
+}
+exit_findlockinfo:
+return rc;
+}
+#ifdef SQLITE_DEBUG
+/*
+** Helper function for printing out trace information from debugging
+** binaries. This returns the string represetation of the supplied
+** integer lock-type.
+*/
+static const char *locktypeName(int locktype){
+switch( locktype ){
+case NO_LOCK: return "NONE";
+case SHARED_LOCK: return "SHARED";
+case RESERVED_LOCK: return "RESERVED";
+case PENDING_LOCK: return "PENDING";
+case EXCLUSIVE_LOCK: return "EXCLUSIVE";
+}
+return "ERROR";
+}
+#endif
+/*
+** If we are currently in a different thread than the thread that the
+** unixFile argument belongs to, then transfer ownership of the unixFile
+** over to the current thread.
+**
+** A unixFile is only owned by a thread on systems where one thread is
+** unable to override locks created by a different thread.  RedHat9 is
+** an example of such a system.
+**
+** Ownership transfer is only allowed if the unixFile is currently unlocked.
+** If the unixFile is locked and an ownership is wrong, then return
+** SQLITE_MISUSE.  SQLITE_OK is returned if everything works.
+*/
+#if SQLITE_THREADSAFE
+static int transferOwnership(unixFile *pFile){
+int rc;
+pthread_t hSelf;
+if( threadsOverrideEachOthersLocks ){
+/* Ownership transfers not needed on this system */
+return SQLITE_OK;
+}
+hSelf = pthread_self();
+if( pthread_equal(pFile->tid, hSelf) ){
+/* We are still in the same thread */
+OSTRACE1("No-transfer, same thread\n");
+return SQLITE_OK;
+}
+if( pFile->locktype!=NO_LOCK ){
+/* We cannot change ownership while we are holding a lock! */
+return SQLITE_MISUSE;
+}
+OSTRACE4("Transfer ownership of %d from %d to %d\n",
+pFile->h, pFile->tid, hSelf);
+pFile->tid = hSelf;
+if (pFile->pLock != NULL) {
+releaseLockInfo(pFile->pLock);
+rc = findLockInfo(pFile->h, &pFile->pLock, 0);
+OSTRACE5("LOCK    %d is now %s(%s,%d)\n", pFile->h,
+locktypeName(pFile->locktype),
+locktypeName(pFile->pLock->locktype), pFile->pLock->cnt);
+return rc;
+} else {
+return SQLITE_OK;
+}
+}
+#else
+/* On single-threaded builds, ownership transfer is a no-op */
+# define transferOwnership(X) SQLITE_OK
+#endif
+/*
+** Seek to the offset passed as the second argument, then read cnt
+** bytes into pBuf. Return the number of bytes actually read.
+**
+** NB:  If you define USE_PREAD or USE_PREAD64, then it might also
+** be necessary to define _XOPEN_SOURCE to be 500.  This varies from
+** one system to another.  Since SQLite does not define USE_PREAD
+** any any form by default, we will not attempt to define _XOPEN_SOURCE.
+** See tickets #2741 and #2681.
+*/
+static int seekAndRead(unixFile *id, sqlite3_int64 offset, void *pBuf, int cnt){
+int got;
+i64 newOffset;
+TIMER_START;
+#if defined(USE_PREAD)
+got = pread(id->h, pBuf, cnt, offset);
+SimulateIOError( got = -1 );
+#elif defined(USE_PREAD64)
+got = pread64(id->h, pBuf, cnt, offset);
+SimulateIOError( got = -1 );
+#else
+newOffset = lseek(id->h, offset, SEEK_SET);
+SimulateIOError( newOffset-- );
+if( newOffset!=offset ){
+return -1;
+}
+got = read(id->h, pBuf, cnt);
+#endif
+TIMER_END;
+OSTRACE5("READ    %-3d %5d %7lld %llu\n", id->h, got, offset, TIMER_ELAPSED);
+return got;
+}
+/*
+** Read data from a file into a buffer.  Return SQLITE_OK if all
+** bytes were read successfully and SQLITE_IOERR if anything goes
+** wrong.
+*/
+static int unixRead(
+sqlite3_file *id,
+void *pBuf,
+int amt,
+sqlite3_int64 offset
+){
+int got;
+assert( id );
+got = seekAndRead((unixFile*)id, offset, pBuf, amt);
+if( got==amt ){
+return SQLITE_OK;
+}else if( got<0 ){
+return SQLITE_IOERR_READ;
+}else{
+memset(&((char*)pBuf)[got], 0, amt-got);
+return SQLITE_IOERR_SHORT_READ;
+}
+}
+/*
+** Seek to the offset in id->offset then read cnt bytes into pBuf.
+** Return the number of bytes actually read.  Update the offset.
+*/
+static int seekAndWrite(unixFile *id, i64 offset, const void *pBuf, int cnt){
+int got;
+i64 newOffset;
+TIMER_START;
+#if defined(USE_PREAD)
+got = pwrite(id->h, pBuf, cnt, offset);
+#elif defined(USE_PREAD64)
+got = pwrite64(id->h, pBuf, cnt, offset);
+#else
+newOffset = lseek(id->h, offset, SEEK_SET);
+if( newOffset!=offset ){
+return -1;
+}
+got = write(id->h, pBuf, cnt);
+#endif
+TIMER_END;
+OSTRACE5("WRITE   %-3d %5d %7lld %llu\n", id->h, got, offset, TIMER_ELAPSED);
+return got;
+}
+/*
+** Write data from a buffer into a file.  Return SQLITE_OK on success
+** or some other error code on failure.
+*/
+static int unixWrite(
+sqlite3_file *id,
+const void *pBuf,
+int amt,
+sqlite3_int64 offset
+){
+int wrote = 0;
+assert( id );
+assert( amt>0 );
+while( amt>0 && (wrote = seekAndWrite((unixFile*)id, offset, pBuf, amt))>0 ){
+amt -= wrote;
+offset += wrote;
+pBuf = &((char*)pBuf)[wrote];
+}
+SimulateIOError(( wrote=(-1), amt=1 ));
+SimulateDiskfullError(( wrote=0, amt=1 ));
+if( amt>0 ){
+if( wrote<0 ){
+return SQLITE_IOERR_WRITE;
+}else{
+return SQLITE_FULL;
+}
+}
+return SQLITE_OK;
+}
+#ifdef SQLITE_TEST
+/*
+** Count the number of fullsyncs and normal syncs.  This is used to test
+** that syncs and fullsyncs are occuring at the right times.
+*/
+int sqlite3_sync_count = 0;
+int sqlite3_fullsync_count = 0;
+#endif
+/*
+** Use the fdatasync() API only if the HAVE_FDATASYNC macro is defined.
+** Otherwise use fsync() in its place.
+*/
+#ifndef HAVE_FDATASYNC
+# define fdatasync fsync
+#endif
+/*
+** Define HAVE_FULLFSYNC to 0 or 1 depending on whether or not
+** the F_FULLFSYNC macro is defined.  F_FULLFSYNC is currently
+** only available on Mac OS X.  But that could change.
+*/
+#ifdef F_FULLFSYNC
+# define HAVE_FULLFSYNC 1
+#else
+# define HAVE_FULLFSYNC 0
+#endif
+/*
+** The fsync() system call does not work as advertised on many
+** unix systems.  The following procedure is an attempt to make
+** it work better.
+**
+** The SQLITE_NO_SYNC macro disables all fsync()s.  This is useful
+** for testing when we want to run through the test suite quickly.
+** You are strongly advised *not* to deploy with SQLITE_NO_SYNC
+** enabled, however, since with SQLITE_NO_SYNC enabled, an OS crash
+** or power failure will likely corrupt the database file.
+*/
+static int full_fsync(int fd, int fullSync, int dataOnly){
+int rc;
+/* Record the number of times that we do a normal fsync() and
+** FULLSYNC.  This is used during testing to verify that this procedure
+** gets called with the correct arguments.
+*/
+#ifdef SQLITE_TEST
+if( fullSync ) sqlite3_fullsync_count++;
+sqlite3_sync_count++;
+#endif
+/* If we compiled with the SQLITE_NO_SYNC flag, then syncing is a
+** no-op
+*/
+#ifdef SQLITE_NO_SYNC
+rc = SQLITE_OK;
+#else
+#if HAVE_FULLFSYNC
+if( fullSync ){
+rc = fcntl(fd, F_FULLFSYNC, 0);
+}else{
+rc = 1;
+}
+/* If the FULLFSYNC failed, fall back to attempting an fsync().
+* It shouldn't be possible for fullfsync to fail on the local
+* file system (on OSX), so failure indicates that FULLFSYNC
+* isn't supported for this file system. So, attempt an fsync
+* and (for now) ignore the overhead of a superfluous fcntl call.
+* It'd be better to detect fullfsync support once and avoid
+* the fcntl call every time sync is called.
+*/
+if( rc ) rc = fsync(fd);
+#else
+if( dataOnly ){
+rc = fdatasync(fd);
+}else{
+rc = fsync(fd);
+}
+#endif /* HAVE_FULLFSYNC */
+#endif /* defined(SQLITE_NO_SYNC) */
+return rc;
+}
+/*
+** Make sure all writes to a particular file are committed to disk.
+**
+** If dataOnly==0 then both the file itself and its metadata (file
+** size, access time, etc) are synced.  If dataOnly!=0 then only the
+** file data is synced.
+**
+** Under Unix, also make sure that the directory entry for the file
+** has been created by fsync-ing the directory that contains the file.
+** If we do not do this and we encounter a power failure, the directory
+** entry for the journal might not exist after we reboot.  The next
+** SQLite to access the file will not know that the journal exists (because
+** the directory entry for the journal was never created) and the transaction
+** will not roll back - possibly leading to database corruption.
+*/
+static int unixSync(sqlite3_file *id, int flags){
+int rc;
+unixFile *pFile = (unixFile*)id;
+int isDataOnly = (flags&SQLITE_SYNC_DATAONLY);
+int isFullsync = (flags&0x0F)==SQLITE_SYNC_FULL;
+/* Check that one of SQLITE_SYNC_NORMAL or FULL was passed */
+assert((flags&0x0F)==SQLITE_SYNC_NORMAL
+|| (flags&0x0F)==SQLITE_SYNC_FULL
+);
+assert( pFile );
+OSTRACE2("SYNC    %-3d\n", pFile->h);
+rc = full_fsync(pFile->h, isFullsync, isDataOnly);
+SimulateIOError( rc=1 );
+if( rc ){
+return SQLITE_IOERR_FSYNC;
+}
+if( pFile->dirfd>=0 ){
+OSTRACE4("DIRSYNC %-3d (have_fullfsync=%d fullsync=%d)\n", pFile->dirfd,
+HAVE_FULLFSYNC, isFullsync);
+#ifndef SQLITE_DISABLE_DIRSYNC
+/* The directory sync is only attempted if full_fsync is
+** turned off or unavailable.  If a full_fsync occurred above,
+** then the directory sync is superfluous.
+*/
+if( (!HAVE_FULLFSYNC || !isFullsync) && full_fsync(pFile->dirfd,0,0) ){
+/*
+** We have received multiple reports of fsync() returning
+** errors when applied to directories on certain file systems.
+** A failed directory sync is not a big deal.  So it seems
+** better to ignore the error.  Ticket #1657
+*/
+/* return SQLITE_IOERR; */
+}
+#endif
+close(pFile->dirfd);  /* Only need to sync once, so close the directory */
+pFile->dirfd = -1;    /* when we are done. */
+}
+return SQLITE_OK;
+}
+/*
+** Truncate an open file to a specified size
+*/
+static int unixTruncate(sqlite3_file *id, i64 nByte){
+int rc;
+assert( id );
+SimulateIOError( return SQLITE_IOERR_TRUNCATE );
+rc = ftruncate(((unixFile*)id)->h, (off_t)nByte);
+if( rc ){
+return SQLITE_IOERR_TRUNCATE;
+}else{
+return SQLITE_OK;
+}
+}
+/*
+** Determine the current size of a file in bytes
+*/
+static int unixFileSize(sqlite3_file *id, i64 *pSize){
+int rc;
+struct stat buf;
+assert( id );
+rc = fstat(((unixFile*)id)->h, &buf);
+SimulateIOError( rc=1 );
+if( rc!=0 ){
+return SQLITE_IOERR_FSTAT;
+}
+*pSize = buf.st_size;
+/* When opening a zero-size database, the findLockInfo() procedure
+** writes a single byte into that file in order to work around a bug
+** in the OS-X msdos filesystem.  In order to avoid problems with upper
+** layers, we need to report this file size as zero even though it is
+** really 1.   Ticket #3260.
+*/
+if( *pSize==1 ) *pSize = 0;
+return SQLITE_OK;
+}
+/*
+** This routine checks if there is a RESERVED lock held on the specified
+** file by this or any other process. If such a lock is held, return
+** non-zero.  If the file is unlocked or holds only SHARED locks, then
+** return zero.
+*/
+static int unixCheckReservedLock(sqlite3_file *id, int *pResOut){
+int r = 0;
+unixFile *pFile = (unixFile*)id;
+SimulateIOError( return SQLITE_IOERR_CHECKRESERVEDLOCK; );
+assert( pFile );
+enterMutex(); /* Because pFile->pLock is shared across threads */
+/* Check if a thread in this process holds such a lock */
+if( pFile->pLock->locktype>SHARED_LOCK ){
+r = 1;
+}
+/* Otherwise see if some other process holds it.
+*/
+if( !r ){
+struct flock lock;
+lock.l_whence = SEEK_SET;
+lock.l_start = RESERVED_BYTE;
+lock.l_len = 1;
+lock.l_type = F_WRLCK;
+fcntl(pFile->h, F_GETLK, &lock);
+if( lock.l_type!=F_UNLCK ){
+r = 1;
+}
+}
+leaveMutex();
+OSTRACE3("TEST WR-LOCK %d %d\n", pFile->h, r);
+*pResOut = r;
+return SQLITE_OK;
+}
+/*
+** Lock the file with the lock specified by parameter locktype - one
+** of the following:
+**
+**     (1) SHARED_LOCK
+**     (2) RESERVED_LOCK
+**     (3) PENDING_LOCK
+**     (4) EXCLUSIVE_LOCK
+**
+** Sometimes when requesting one lock state, additional lock states
+** are inserted in between.  The locking might fail on one of the later
+** transitions leaving the lock state different from what it started but
+** still short of its goal.  The following chart shows the allowed
+** transitions and the inserted intermediate states:
+**
+**    UNLOCKED -> SHARED
+**    SHARED -> RESERVED
+**    SHARED -> (PENDING) -> EXCLUSIVE
+**    RESERVED -> (PENDING) -> EXCLUSIVE
+**    PENDING -> EXCLUSIVE
+**
+** This routine will only increase a lock.  Use the sqlite3OsUnlock()
+** routine to lower a locking level.
+*/
+static int unixLock(sqlite3_file *id, int locktype){
+/* The following describes the implementation of the various locks and
+** lock transitions in terms of the POSIX advisory shared and exclusive
+** lock primitives (called read-locks and write-locks below, to avoid
+** confusion with SQLite lock names). The algorithms are complicated
+** slightly in order to be compatible with windows systems simultaneously
+** accessing the same database file, in case that is ever required.
+**
+** Symbols defined in os.h indentify the 'pending byte' and the 'reserved
+** byte', each single bytes at well known offsets, and the 'shared byte
+** range', a range of 510 bytes at a well known offset.
+**
+** To obtain a SHARED lock, a read-lock is obtained on the 'pending
+** byte'.  If this is successful, a random byte from the 'shared byte
+** range' is read-locked and the lock on the 'pending byte' released.
+**
+** A process may only obtain a RESERVED lock after it has a SHARED lock.
+** A RESERVED lock is implemented by grabbing a write-lock on the
+** 'reserved byte'.
+**
+** A process may only obtain a PENDING lock after it has obtained a
+** SHARED lock. A PENDING lock is implemented by obtaining a write-lock
+** on the 'pending byte'. This ensures that no new SHARED locks can be
+** obtained, but existing SHARED locks are allowed to persist. A process
+** does not have to obtain a RESERVED lock on the way to a PENDING lock.
+** This property is used by the algorithm for rolling back a journal file
+** after a crash.
+**
+** An EXCLUSIVE lock, obtained after a PENDING lock is held, is
+** implemented by obtaining a write-lock on the entire 'shared byte
+** range'. Since all other locks require a read-lock on one of the bytes
+** within this range, this ensures that no other locks are held on the
+** database.
+**
+** The reason a single byte cannot be used instead of the 'shared byte
+** range' is that some versions of windows do not support read-locks. By
+** locking a random byte from a range, concurrent SHARED locks may exist
+** even if the locking primitive used is always a write-lock.
+*/
+int rc = SQLITE_OK;
+unixFile *pFile = (unixFile*)id;
+struct lockInfo *pLock = pFile->pLock;
+struct flock lock;
+int s;
+assert( pFile );
+OSTRACE7("LOCK    %d %s was %s(%s,%d) pid=%d\n", pFile->h,
+locktypeName(locktype), locktypeName(pFile->locktype),
+locktypeName(pLock->locktype), pLock->cnt , getpid());
+/* If there is already a lock of this type or more restrictive on the
+** unixFile, do nothing. Don't use the end_lock: exit path, as
+** enterMutex() hasn't been called yet.
+*/
+if( pFile->locktype>=locktype ){
+OSTRACE3("LOCK    %d %s ok (already held)\n", pFile->h,
+locktypeName(locktype));
+return SQLITE_OK;
+}
+/* Make sure the locking sequence is correct
+*/
+assert( pFile->locktype!=NO_LOCK || locktype==SHARED_LOCK );
+assert( locktype!=PENDING_LOCK );
+assert( locktype!=RESERVED_LOCK || pFile->locktype==SHARED_LOCK );
+/* This mutex is needed because pFile->pLock is shared across threads
+*/
+enterMutex();
+/* Make sure the current thread owns the pFile.
+*/
+rc = transferOwnership(pFile);
+if( rc!=SQLITE_OK ){
+leaveMutex();
+return rc;
+}
+pLock = pFile->pLock;
+/* If some thread using this PID has a lock via a different unixFile*
+** handle that precludes the requested lock, return BUSY.
+*/
+if( (pFile->locktype!=pLock->locktype &&
+(pLock->locktype>=PENDING_LOCK || locktype>SHARED_LOCK))
+){
+rc = SQLITE_BUSY;
+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( locktype==SHARED_LOCK &&
+(pLock->locktype==SHARED_LOCK || pLock->locktype==RESERVED_LOCK) ){
+assert( locktype==SHARED_LOCK );
+assert( pFile->locktype==0 );
+assert( pLock->cnt>0 );
+pFile->locktype = SHARED_LOCK;
+pLock->cnt++;
+pFile->pOpen->nLock++;
+goto end_lock;
+}
+lock.l_len = 1L;
+lock.l_whence = SEEK_SET;
+/* A PENDING lock is needed before acquiring a SHARED lock and before
+** acquiring an EXCLUSIVE lock.  For the SHARED lock, the PENDING will
+** be released.
+*/
+if( locktype==SHARED_LOCK
+|| (locktype==EXCLUSIVE_LOCK && pFile->locktype<PENDING_LOCK)
+){
+lock.l_type = (locktype==SHARED_LOCK?F_RDLCK:F_WRLCK);
+lock.l_start = PENDING_BYTE;
+s = fcntl(pFile->h, F_SETLK, &lock);
+if( s==(-1) ){
+rc = (errno==EINVAL) ? SQLITE_NOLFS : SQLITE_BUSY;
+goto end_lock;
+}
+}
+/* If control gets to this point, then actually go ahead and make
+** operating system calls for the specified lock.
+*/
+if( locktype==SHARED_LOCK ){
+assert( pLock->cnt==0 );
+assert( pLock->locktype==0 );
+/* Now get the read-lock */
+lock.l_start = SHARED_FIRST;
+lock.l_len = SHARED_SIZE;
+s = fcntl(pFile->h, F_SETLK, &lock);
+/* 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 ){
+rc = SQLITE_IOERR_UNLOCK;  /* This should never happen */
+goto end_lock;
+}
+if( s==(-1) ){
+rc = (errno==EINVAL) ? SQLITE_NOLFS : SQLITE_BUSY;
+}else{
+pFile->locktype = SHARED_LOCK;
+pFile->pOpen->nLock++;
+pLock->cnt = 1;
+}
+}else if( locktype==EXCLUSIVE_LOCK && pLock->cnt>1 ){
+/* We are trying for an exclusive lock but another thread in this
+** same process is still holding a shared lock. */
+rc = SQLITE_BUSY;
+}else{
+/* The request was for a RESERVED or EXCLUSIVE lock.  It is
+** assumed that there is a SHARED or greater lock on the file
+** already.
+*/
+assert( 0!=pFile->locktype );
+lock.l_type = F_WRLCK;
+switch( locktype ){
+case RESERVED_LOCK:
+lock.l_start = RESERVED_BYTE;
+break;
+case EXCLUSIVE_LOCK:
+lock.l_start = SHARED_FIRST;
+lock.l_len = SHARED_SIZE;
+break;
+default:
+assert(0);
+}
+s = fcntl(pFile->h, F_SETLK, &lock);
+if( s==(-1) ){
+rc = (errno==EINVAL) ? SQLITE_NOLFS : SQLITE_BUSY;
+}
+}
+if( rc==SQLITE_OK ){
+pFile->locktype = locktype;
+pLock->locktype = locktype;
+}else if( locktype==EXCLUSIVE_LOCK ){
+pFile->locktype = PENDING_LOCK;
+pLock->locktype = PENDING_LOCK;
+}
+end_lock:
+leaveMutex();
+OSTRACE4("LOCK    %d %s %s\n", pFile->h, locktypeName(locktype),
+rc==SQLITE_OK ? "ok" : "failed");
+return rc;
+}
+/*
+** Lower the locking level on file descriptor pFile to locktype.  locktype
+** must be either NO_LOCK or SHARED_LOCK.
+**
+** If the locking level of the file descriptor is already at or below
+** the requested locking level, this routine is a no-op.
+*/
+static int unixUnlock(sqlite3_file *id, int locktype){
+struct lockInfo *pLock;
+struct flock lock;
+int rc = SQLITE_OK;
+unixFile *pFile = (unixFile*)id;
+int h;
+assert( pFile );
+OSTRACE7("UNLOCK  %d %d was %d(%d,%d) pid=%d\n", pFile->h, locktype,
+pFile->locktype, pFile->pLock->locktype, pFile->pLock->cnt, getpid());
+assert( locktype<=SHARED_LOCK );
+if( pFile->locktype<=locktype ){
+return SQLITE_OK;
+}
+if( CHECK_THREADID(pFile) ){
+return SQLITE_MISUSE;
+}
+enterMutex();
+h = pFile->h;
+pLock = pFile->pLock;
+assert( pLock->cnt!=0 );
+if( pFile->locktype>SHARED_LOCK ){
+assert( pLock->locktype==pFile->locktype );
+SimulateIOErrorBenign(1);
+SimulateIOError( h=(-1) )
+SimulateIOErrorBenign(0);
+if( locktype==SHARED_LOCK ){
+lock.l_type = F_RDLCK;
+lock.l_whence = SEEK_SET;
+lock.l_start = SHARED_FIRST;
+lock.l_len = SHARED_SIZE;
+if( fcntl(h, F_SETLK, &lock)==(-1) ){
+rc = SQLITE_IOERR_RDLOCK;
+}
+}
+lock.l_type = F_UNLCK;
+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) ){
+pLock->locktype = SHARED_LOCK;
+}else{
+rc = SQLITE_IOERR_UNLOCK;
+}
+}
+if( locktype==NO_LOCK ){
+struct openCnt *pOpen;
+/* Decrement the shared lock counter.  Release the lock using an
+** OS call only when all threads in this same process have released
+** the lock.
+*/
+pLock->cnt--;
+if( pLock->cnt==0 ){
+lock.l_type = F_UNLCK;
+lock.l_whence = SEEK_SET;
+lock.l_start = lock.l_len = 0L;
+SimulateIOErrorBenign(1);
+SimulateIOError( h=(-1) )
+SimulateIOErrorBenign(0);
+if( fcntl(h, F_SETLK, &lock)!=(-1) ){
+pLock->locktype = NO_LOCK;
+}else{
+rc = SQLITE_IOERR_UNLOCK;
+pLock->cnt = 1;
+}
+}
+/* Decrement the count of locks against this same file.  When the
+** count reaches zero, close any other file descriptors whose close
+** was deferred because of outstanding locks.
+*/
+if( rc==SQLITE_OK ){
+pOpen = pFile->pOpen;
+pOpen->nLock--;
+assert( pOpen->nLock>=0 );
+if( pOpen->nLock==0 && pOpen->nPending>0 ){
+int i;
+for(i=0; i<pOpen->nPending; i++){
+close(pOpen->aPending[i]);
+}
+sqlite3_free(pOpen->aPending);
+pOpen->nPending = 0;
+pOpen->aPending = 0;
+}
+}
+}
+leaveMutex();
+if( rc==SQLITE_OK ) pFile->locktype = locktype;
+return rc;
+}
+/*
+** This function performs the parts of the "close file" operation
+** common to all locking schemes. It closes the directory and file
+** handles, if they are valid, and sets all fields of the unixFile
+** structure to 0.
+*/
+static int closeUnixFile(sqlite3_file *id){
+unixFile *pFile = (unixFile*)id;
+if( pFile ){
+if( pFile->dirfd>=0 ){
+close(pFile->dirfd);
+}
+if( pFile->h>=0 ){
+close(pFile->h);
+}
+OSTRACE2("CLOSE   %-3d\n", pFile->h);
+OpenCounter(-1);
+memset(pFile, 0, sizeof(unixFile));
+}
+return SQLITE_OK;
+}
+/*
+** Close a file.
+*/
+static int unixClose(sqlite3_file *id){
+if( id ){
+unixFile *pFile = (unixFile *)id;
+unixUnlock(id, NO_LOCK);
+enterMutex();
+if( pFile->pOpen && pFile->pOpen->nLock ){
+/* If there are outstanding locks, do not actually close the file just
+** yet because that would clear those locks.  Instead, add the file
+** descriptor to pOpen->aPending.  It will be automatically closed when
+** the last lock is cleared.
+*/
+int *aNew;
+struct openCnt *pOpen = pFile->pOpen;
+aNew = sqlite3_realloc(pOpen->aPending, (pOpen->nPending+1)*sizeof(int) );
+if( aNew==0 ){
+/* If a malloc fails, just leak the file descriptor */
+}else{
+pOpen->aPending = aNew;
+pOpen->aPending[pOpen->nPending] = pFile->h;
+pOpen->nPending++;
+pFile->h = -1;
+}
+}
+releaseLockInfo(pFile->pLock);
+releaseOpenCnt(pFile->pOpen);
+closeUnixFile(id);
+leaveMutex();
+}
+return SQLITE_OK;
+}
+#ifdef SQLITE_ENABLE_LOCKING_STYLE
+#pragma mark AFP Support
+/*
+** The afpLockingContext structure contains all afp lock specific state
+*/
+typedef struct afpLockingContext afpLockingContext;
+struct afpLockingContext {
+unsigned long long sharedLockByte;
+const char *filePath;
+};
+struct ByteRangeLockPB2
+{
+unsigned long long offset;        /* offset to first byte to lock */
+unsigned long long length;        /* nbr of bytes to lock */
+unsigned long long retRangeStart; /* nbr of 1st byte locked if successful */
+unsigned char unLockFlag;         /* 1 = unlock, 0 = lock */
+unsigned char startEndFlag;       /* 1=rel to end of fork, 0=rel to start */
+int fd;                           /* file desc to assoc this lock with */
+};
+#define afpfsByteRangeLock2FSCTL        _IOWR('z', 23, struct ByteRangeLockPB2)
+/*
+** Return 0 on success, 1 on failure.  To match the behavior of the
+** normal posix file locking (used in unixLock for example), we should
+** provide 'richer' return codes - specifically to differentiate between
+** 'file busy' and 'file system error' results.
+*/
+static int _AFPFSSetLock(
+const char *path,
+int fd,
+unsigned long long offset,
+unsigned long long length,
+int setLockFlag
+){
+struct ByteRangeLockPB2       pb;
+int                     err;
+pb.unLockFlag = setLockFlag ? 0 : 1;
+pb.startEndFlag = 0;
+pb.offset = offset;
+pb.length = length;
+pb.fd = fd;
+OSTRACE5("AFPLOCK setting lock %s for %d in range %llx:%llx\n",
+(setLockFlag?"ON":"OFF"), fd, offset, length);
+err = fsctl(path, afpfsByteRangeLock2FSCTL, &pb, 0);
+if ( err==-1 ) {
+OSTRACE4("AFPLOCK failed to fsctl() '%s' %d %s\n", path, errno,
+strerror(errno));
+return 1; /* error */
+} else {
+return 0;
+}
+}
+/*
+** This routine checks if there is a RESERVED lock held on the specified
+** file by this or any other process. If such a lock is held, return
+** non-zero.  If the file is unlocked or holds only SHARED locks, then
+** return zero.
+*/
+static int afpCheckReservedLock(sqlite3_file *id, int *pResOut){
+int r = 0;
+unixFile *pFile = (unixFile*)id;
+assert( pFile );
+afpLockingContext *context = (afpLockingContext *) pFile->lockingContext;
+/* Check if a thread in this process holds such a lock */
+if( pFile->locktype>SHARED_LOCK ){
+r = 1;
+}
+/* Otherwise see if some other process holds it.
+*/
+if ( !r ) {
+/* lock the byte */
+int failed = _AFPFSSetLock(context->filePath, pFile->h, RESERVED_BYTE, 1,1);
+if (failed) {
+/* if we failed to get the lock then someone else must have it */
+r = 1;
+} else {
+/* if we succeeded in taking the reserved lock, unlock it to restore
+** the original state */
+_AFPFSSetLock(context->filePath, pFile->h, RESERVED_BYTE, 1, 0);
+}
+}
+OSTRACE3("TEST WR-LOCK %d %d\n", pFile->h, r);
+*pResOut = r;
+return SQLITE_OK;
+}
+/* AFP-style locking following the behavior of unixLock, see the unixLock
+** function comments for details of lock management. */
+static int afpLock(sqlite3_file *id, int locktype){
+int rc = SQLITE_OK;
+unixFile *pFile = (unixFile*)id;
+afpLockingContext *context = (afpLockingContext *) pFile->lockingContext;
+assert( pFile );
+OSTRACE5("LOCK    %d %s was %s pid=%d\n", pFile->h,
+locktypeName(locktype), locktypeName(pFile->locktype), getpid());
+/* If there is already a lock of this type or more restrictive on the
+** unixFile, do nothing. Don't use the afp_end_lock: exit path, as
+** enterMutex() hasn't been called yet.
+*/
+if( pFile->locktype>=locktype ){
+OSTRACE3("LOCK    %d %s ok (already held)\n", pFile->h,
+locktypeName(locktype));
+return SQLITE_OK;
+}
+/* Make sure the locking sequence is correct
+*/
+assert( pFile->locktype!=NO_LOCK || locktype==SHARED_LOCK );
+assert( locktype!=PENDING_LOCK );
+assert( locktype!=RESERVED_LOCK || pFile->locktype==SHARED_LOCK );
+/* This mutex is needed because pFile->pLock is shared across threads
+*/
+enterMutex();
+/* Make sure the current thread owns the pFile.
+*/
+rc = transferOwnership(pFile);
+if( rc!=SQLITE_OK ){
+leaveMutex();
+return rc;
+}
+/* A PENDING lock is needed before acquiring a SHARED lock and before
+** acquiring an EXCLUSIVE lock.  For the SHARED lock, the PENDING will
+** be released.
+*/
+if( locktype==SHARED_LOCK
+|| (locktype==EXCLUSIVE_LOCK && pFile->locktype<PENDING_LOCK)
+){
+int failed;
+failed = _AFPFSSetLock(context->filePath, pFile->h, PENDING_BYTE, 1, 1);
+if (failed) {
+rc = SQLITE_BUSY;
+goto afp_end_lock;
+}
+}
+/* If control gets to this point, then actually go ahead and make
+** operating system calls for the specified lock.
+*/
+if( locktype==SHARED_LOCK ){
+int lk, failed;
+/* Now get the read-lock */
+/* note that the quality of the randomness doesn't matter that much */
+lk = random();
+context->sharedLockByte = (lk & 0x7fffffff)%(SHARED_SIZE - 1);
+failed = _AFPFSSetLock(context->filePath, pFile->h,
+SHARED_FIRST+context->sharedLockByte, 1, 1);
+/* Drop the temporary PENDING lock */
+if (_AFPFSSetLock(context->filePath, pFile->h, PENDING_BYTE, 1, 0)) {
+rc = SQLITE_IOERR_UNLOCK;  /* This should never happen */
+goto afp_end_lock;
+}
+if( failed ){
+rc = SQLITE_BUSY;
+} else {
+pFile->locktype = SHARED_LOCK;
+}
+}else{
+/* The request was for a RESERVED or EXCLUSIVE lock.  It is
+** assumed that there is a SHARED or greater lock on the file
+** already.
+*/
+int failed = 0;
+assert( 0!=pFile->locktype );
+if (locktype >= RESERVED_LOCK && pFile->locktype < RESERVED_LOCK) {
+/* Acquire a RESERVED lock */
+failed = _AFPFSSetLock(context->filePath, pFile->h, RESERVED_BYTE, 1,1);
+}
+if (!failed && locktype == EXCLUSIVE_LOCK) {
+/* Acquire an EXCLUSIVE lock */
+/* Remove the shared lock before trying the range.  we'll need to
+** reestablish the shared lock if we can't get the  afpUnlock
+*/
+if (!_AFPFSSetLock(context->filePath, pFile->h, SHARED_FIRST +
+context->sharedLockByte, 1, 0)) {
+/* now attemmpt to get the exclusive lock range */
+failed = _AFPFSSetLock(context->filePath, pFile->h, SHARED_FIRST,
+SHARED_SIZE, 1);
+if (failed && _AFPFSSetLock(context->filePath, pFile->h, SHARED_FIRST +
+context->sharedLockByte, 1, 1)) {
+rc = SQLITE_IOERR_RDLOCK; /* this should never happen */
+}
+} else {
+/* */
+rc = SQLITE_IOERR_UNLOCK; /* this should never happen */
+}
+}
+if( failed && rc == SQLITE_OK){
+rc = SQLITE_BUSY;
+}
+}
+if( rc==SQLITE_OK ){
+pFile->locktype = locktype;
+}else if( locktype==EXCLUSIVE_LOCK ){
+pFile->locktype = PENDING_LOCK;
+}
+afp_end_lock:
+leaveMutex();
+OSTRACE4("LOCK    %d %s %s\n", pFile->h, locktypeName(locktype),
+rc==SQLITE_OK ? "ok" : "failed");
+return rc;
+}
+/*
+** Lower the locking level on file descriptor pFile to locktype.  locktype
+** must be either NO_LOCK or SHARED_LOCK.
+**
+** If the locking level of the file descriptor is already at or below
+** the requested locking level, this routine is a no-op.
+*/
+static int afpUnlock(sqlite3_file *id, int locktype) {
+int rc = SQLITE_OK;
+unixFile *pFile = (unixFile*)id;
+afpLockingContext *context = (afpLockingContext *) pFile->lockingContext;
+assert( pFile );
+OSTRACE5("UNLOCK  %d %d was %d pid=%d\n", pFile->h, locktype,
+pFile->locktype, getpid());
+assert( locktype<=SHARED_LOCK );
+if( pFile->locktype<=locktype ){
+return SQLITE_OK;
+}
+if( CHECK_THREADID(pFile) ){
+return SQLITE_MISUSE;
+}
+enterMutex();
+if( pFile->locktype>SHARED_LOCK ){
+if( locktype==SHARED_LOCK ){
+int failed = 0;
+/* unlock the exclusive range - then re-establish the shared lock */
+if (pFile->locktype==EXCLUSIVE_LOCK) {
+failed = _AFPFSSetLock(context->filePath, pFile->h, SHARED_FIRST,
+SHARED_SIZE, 0);
+if (!failed) {
+/* successfully removed the exclusive lock */
+if (_AFPFSSetLock(context->filePath, pFile->h, SHARED_FIRST+
+context->sharedLockByte, 1, 1)) {
+/* failed to re-establish our shared lock */
+rc = SQLITE_IOERR_RDLOCK; /* This should never happen */
+}
+} else {
+/* This should never happen - failed to unlock the exclusive range */
+rc = SQLITE_IOERR_UNLOCK;
+}
+}
+}
+if (rc == SQLITE_OK && pFile->locktype>=PENDING_LOCK) {
+if (_AFPFSSetLock(context->filePath, pFile->h, PENDING_BYTE, 1, 0)){
+/* failed to release the pending lock */
+rc = SQLITE_IOERR_UNLOCK; /* This should never happen */
+}
+}
+if (rc == SQLITE_OK && pFile->locktype>=RESERVED_LOCK) {
+if (_AFPFSSetLock(context->filePath, pFile->h, RESERVED_BYTE, 1, 0)) {
+/* failed to release the reserved lock */
+rc = SQLITE_IOERR_UNLOCK;  /* This should never happen */
+}
+}
+}
+if( locktype==NO_LOCK ){
+int failed = _AFPFSSetLock(context->filePath, pFile->h,
+SHARED_FIRST + context->sharedLockByte, 1, 0);
+if (failed) {
+rc = SQLITE_IOERR_UNLOCK;  /* This should never happen */
+}
+}
+if (rc == SQLITE_OK)
+pFile->locktype = locktype;
+leaveMutex();
+return rc;
+}
+/*
+** Close a file & cleanup AFP specific locking context
+*/
+static int afpClose(sqlite3_file *id) {
+if( id ){
+unixFile *pFile = (unixFile*)id;
+afpUnlock(id, NO_LOCK);
+sqlite3_free(pFile->lockingContext);
+}
+return closeUnixFile(id);
+}
+#pragma mark flock() style locking
+/*
+** The flockLockingContext is not used
+*/
+typedef void flockLockingContext;
+static int flockCheckReservedLock(sqlite3_file *id, int *pResOut){
+int r = 1;
+unixFile *pFile = (unixFile*)id;
+if (pFile->locktype != RESERVED_LOCK) {
+/* attempt to get the lock */
+int rc = flock(pFile->h, LOCK_EX | LOCK_NB);
+if (!rc) {
+/* got the lock, unlock it */
+flock(pFile->h, LOCK_UN);
+r = 0;  /* no one has it reserved */
+}
+}
+*pResOut = r;
+return SQLITE_OK;
+}
+static int flockLock(sqlite3_file *id, int locktype) {
+unixFile *pFile = (unixFile*)id;
+/* if we already have a lock, it is exclusive.
+** Just adjust level and punt on outta here. */
+if (pFile->locktype > NO_LOCK) {
+pFile->locktype = locktype;
+return SQLITE_OK;
+}
+/* grab an exclusive lock */
+int rc = flock(pFile->h, LOCK_EX | LOCK_NB);
+if (rc) {
+/* didn't get, must be busy */
+return SQLITE_BUSY;
+} else {
+/* got it, set the type and return ok */
+pFile->locktype = locktype;
+return SQLITE_OK;
+}
+}
+static int flockUnlock(sqlite3_file *id, int locktype) {
+unixFile *pFile = (unixFile*)id;
+assert( locktype<=SHARED_LOCK );
+/* no-op if possible */
+if( pFile->locktype==locktype ){
+return SQLITE_OK;
+}
+/* shared can just be set because we always have an exclusive */
+if (locktype==SHARED_LOCK) {
+pFile->locktype = locktype;
+return SQLITE_OK;
+}
+/* no, really, unlock. */
+int rc = flock(pFile->h, LOCK_UN);
+if (rc)
+return SQLITE_IOERR_UNLOCK;
+else {
+pFile->locktype = NO_LOCK;
+return SQLITE_OK;
+}
+}
+/*
+** Close a file.
+*/
+static int flockClose(sqlite3_file *id) {
+if( id ){
+flockUnlock(id, NO_LOCK);
+}
+return closeUnixFile(id);
+}
+#pragma mark Old-School .lock file based locking
+static int dotlockCheckReservedLock(sqlite3_file *id, int *pResOut) {
+int r = 1;
+unixFile *pFile = (unixFile*)id;
+char *zLockFile = (char *)pFile->lockingContext;
+if (pFile->locktype != RESERVED_LOCK) {
+struct stat statBuf;
+if (lstat(zLockFile, &statBuf) != 0){
+/* file does not exist, we could have it if we want it */
+r = 0;
+}
+}
+*pResOut = r;
+return SQLITE_OK;
+}
+static int dotlockLock(sqlite3_file *id, int locktype) {
+unixFile *pFile = (unixFile*)id;
+int fd;
+char *zLockFile = (char *)pFile->lockingContext;
+/* if we already have a lock, it is exclusive.
+** Just adjust level and punt on outta here. */
+if (pFile->locktype > NO_LOCK) {
+pFile->locktype = locktype;
+/* Always update the timestamp on the old file */
+utimes(zLockFile, NULL);
+return SQLITE_OK;
+}
+/* check to see if lock file already exists */
+struct stat statBuf;
+if (lstat(zLockFile,&statBuf) == 0){
+return SQLITE_BUSY; /* it does, busy */
+}
+/* grab an exclusive lock */
+fd = open(zLockFile,O_RDONLY|O_CREAT|O_EXCL,0600);
+if( fd<0 ){
+/* failed to open/create the file, someone else may have stolen the lock */
+return SQLITE_BUSY;
+}
+close(fd);
+/* got it, set the type and return ok */
+pFile->locktype = locktype;
+return SQLITE_OK;
+}
+static int dotlockUnlock(sqlite3_file *id, int locktype) {
+unixFile *pFile = (unixFile*)id;
+char *zLockFile = (char *)pFile->lockingContext;
+assert( locktype<=SHARED_LOCK );
+/* no-op if possible */
+if( pFile->locktype==locktype ){
+return SQLITE_OK;
+}
+/* shared can just be set because we always have an exclusive */
+if (locktype==SHARED_LOCK) {
+pFile->locktype = locktype;
+return SQLITE_OK;
+}
+/* no, really, unlock. */
+unlink(zLockFile);
+pFile->locktype = NO_LOCK;
+return SQLITE_OK;
+}
+/*
+** Close a file.
+*/
+static int dotlockClose(sqlite3_file *id) {
+if( id ){
+unixFile *pFile = (unixFile*)id;
+dotlockUnlock(id, NO_LOCK);
+sqlite3_free(pFile->lockingContext);
+}
+return closeUnixFile(id);
+}
+#endif /* SQLITE_ENABLE_LOCKING_STYLE */
+/*
+** The nolockLockingContext is void
+*/
+typedef void nolockLockingContext;
+static int nolockCheckReservedLock(sqlite3_file *id, int *pResOut) {
+*pResOut = 0;
+return SQLITE_OK;
+}
+static int nolockLock(sqlite3_file *id, int locktype) {
+return SQLITE_OK;
+}
+static int nolockUnlock(sqlite3_file *id, int locktype) {
+return SQLITE_OK;
+}
+/*
+** Close a file.
+*/
+static int nolockClose(sqlite3_file *id) {
+return closeUnixFile(id);
+}
+/*
+** Information and control of an open file handle.
+*/
+static int unixFileControl(sqlite3_file *id, int op, void *pArg){
+switch( op ){
+case SQLITE_FCNTL_LOCKSTATE: {
+*(int*)pArg = ((unixFile*)id)->locktype;
+return SQLITE_OK;
+}
+}
+return SQLITE_ERROR;
+}
+/*
+** Return the sector size in bytes of the underlying block device for
+** the specified file. This is almost always 512 bytes, but may be
+** larger for some devices.
+**
+** SQLite code assumes this function cannot fail. It also assumes that
+** if two files are created in the same file-system directory (i.e.
+** a database and its journal file) that the sector size will be the
+** same for both.
+*/
+static int unixSectorSize(sqlite3_file *id){
+return SQLITE_DEFAULT_SECTOR_SIZE;
+}
+/*
+** Return the device characteristics for the file. This is always 0.
+*/
+static int unixDeviceCharacteristics(sqlite3_file *id){
+return 0;
+}
+/*
+** Initialize the contents of the unixFile structure pointed to by pId.
+**
+** When locking extensions are enabled, the filepath and locking style
+** are needed to determine the unixFile pMethod to use for locking operations.
+** The locking-style specific lockingContext data structure is created
+** and assigned here also.
+*/
+static int fillInUnixFile(
+sqlite3_vfs *pVfs,      /* Pointer to vfs object */
+int h,                  /* Open file descriptor of file being opened */
+int dirfd,              /* Directory file descriptor */
+sqlite3_file *pId,      /* Write to the unixFile structure here */
+const char *zFilename,  /* Name of the file being opened */
+int noLock              /* Omit locking if true */
+){
+int eLockingStyle;
+unixFile *pNew = (unixFile *)pId;
+int rc = SQLITE_OK;
+/* Macro to define the static contents of an sqlite3_io_methods
+** structure for a unix backend file. Different locking methods
+** require different functions for the xClose, xLock, xUnlock and
+** xCheckReservedLock methods.
+*/
+#define IOMETHODS(xClose, xLock, xUnlock, xCheckReservedLock) {    \
+1,                          /* iVersion */                           \
+xClose,                     /* xClose */                             \
+unixRead,                   /* xRead */                              \
+unixWrite,                  /* xWrite */                             \
+unixTruncate,               /* xTruncate */                          \
+unixSync,                   /* xSync */                              \
+unixFileSize,               /* xFileSize */                          \
+xLock,                      /* xLock */                              \
+xUnlock,                    /* xUnlock */                            \
+xCheckReservedLock,         /* xCheckReservedLock */                 \
+unixFileControl,            /* xFileControl */                       \
+unixSectorSize,             /* xSectorSize */                        \
+unixDeviceCharacteristics   /* xDeviceCapabilities */                \
+}
+static sqlite3_io_methods aIoMethod[] = {
+IOMETHODS(unixClose, unixLock, unixUnlock, unixCheckReservedLock)
+,IOMETHODS(nolockClose, nolockLock, nolockUnlock, nolockCheckReservedLock)
+#ifdef SQLITE_ENABLE_LOCKING_STYLE
+,IOMETHODS(dotlockClose, dotlockLock, dotlockUnlock,dotlockCheckReservedLock)
+,IOMETHODS(flockClose, flockLock, flockUnlock, flockCheckReservedLock)
+,IOMETHODS(afpClose, afpLock, afpUnlock, afpCheckReservedLock)
+#endif
+};
+/* The order of the IOMETHODS macros above is important.  It must be the
+** same order as the LOCKING_STYLE numbers
+*/
+assert(LOCKING_STYLE_POSIX==1);
+assert(LOCKING_STYLE_NONE==2);
+assert(LOCKING_STYLE_DOTFILE==3);
+assert(LOCKING_STYLE_FLOCK==4);
+assert(LOCKING_STYLE_AFP==5);
+assert( pNew->pLock==NULL );
+assert( pNew->pOpen==NULL );
+OSTRACE3("OPEN    %-3d %s\n", h, zFilename);
+pNew->h = h;
+pNew->dirfd = dirfd;
+SET_THREADID(pNew);
+if( noLock ){
+eLockingStyle = LOCKING_STYLE_NONE;
+}else{
+eLockingStyle = detectLockingStyle(pVfs, zFilename, h);
+}
+switch( eLockingStyle ){
+case LOCKING_STYLE_POSIX: {
+enterMutex();
+rc = findLockInfo(h, &pNew->pLock, &pNew->pOpen);
+leaveMutex();
+break;
+}
+#ifdef SQLITE_ENABLE_LOCKING_STYLE
+case LOCKING_STYLE_AFP: {
+/* AFP locking uses the file path so it needs to be included in
+** the afpLockingContext.
+*/
+afpLockingContext *pCtx;
+pNew->lockingContext = pCtx = sqlite3_malloc( sizeof(*pCtx) );
+if( pCtx==0 ){
+rc = SQLITE_NOMEM;
+}else{
+/* NB: zFilename exists and remains valid until the file is closed
+** according to requirement F11141.  So we do not need to make a
+** copy of the filename. */
+pCtx->filePath = zFilename;
+srandomdev();
+}
+break;
+}
+case LOCKING_STYLE_DOTFILE: {
+/* Dotfile locking uses the file path so it needs to be included in
+** the dotlockLockingContext
+*/
+char *zLockFile;
+int nFilename;
+nFilename = strlen(zFilename) + 6;
+zLockFile = (char *)sqlite3_malloc(nFilename);
+if( zLockFile==0 ){
+rc = SQLITE_NOMEM;
+}else{
+sqlite3_snprintf(nFilename, zLockFile, "%s.lock", zFilename);
+}
+pNew->lockingContext = zLockFile;
+break;
+}
+case LOCKING_STYLE_FLOCK:
+case LOCKING_STYLE_NONE:
+break;
+#endif
+}
+if( rc!=SQLITE_OK ){
+if( dirfd>=0 ) close(dirfd);
+close(h);
+}else{
+pNew->pMethod = &aIoMethod[eLockingStyle-1];
+OpenCounter(+1);
+}
+return rc;
+}
+/*
+** Open a file descriptor to the directory containing file zFilename.
+** If successful, *pFd is set to the opened file descriptor and
+** SQLITE_OK is returned. If an error occurs, either SQLITE_NOMEM
+** or SQLITE_CANTOPEN is returned and *pFd is set to an undefined
+** value.
+**
+** If SQLITE_OK is returned, the caller is responsible for closing
+** the file descriptor *pFd using close().
+*/
+static int openDirectory(const char *zFilename, int *pFd){
+int ii;
+int fd = -1;
+char zDirname[MAX_PATHNAME+1];
+sqlite3_snprintf(MAX_PATHNAME, zDirname, "%s", zFilename);
+for(ii=strlen(zDirname); ii>=0 && zDirname[ii]!='/'; ii--);
+if( ii>0 ){
+zDirname[ii] = '\0';
+fd = open(zDirname, O_RDONLY|O_BINARY, 0);
+if( fd>=0 ){
+#ifdef FD_CLOEXEC
+fcntl(fd, F_SETFD, fcntl(fd, F_GETFD, 0) | FD_CLOEXEC);
+#endif
+OSTRACE3("OPENDIR %-3d %s\n", fd, zDirname);
+}
+}
+*pFd = fd;
+return (fd>=0?SQLITE_OK:SQLITE_CANTOPEN);
+}
+/*
+** Create a temporary file name in zBuf.  zBuf must be allocated
+** by the calling process and must be big enough to hold at least
+** pVfs->mxPathname bytes.
+*/
+static int getTempname(int nBuf, char *zBuf){
+static const char *azDirs[] = {
+0,
+"/var/tmp",
+"/usr/tmp",
+"/tmp",
+".",
+};
+static const unsigned char zChars[] =
+"abcdefghijklmnopqrstuvwxyz"
+"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+"0123456789";
+int i, j;
+struct stat buf;
+const char *zDir = ".";
+/* It's odd to simulate an io-error here, but really this is just
+** using the io-error infrastructure to test that SQLite handles this
+** function failing.
+*/
+SimulateIOError( return SQLITE_IOERR );
+azDirs[0] = sqlite3_temp_directory;
+for(i=0; i<sizeof(azDirs)/sizeof(azDirs[0]); i++){
+if( azDirs[i]==0 ) continue;
+if( stat(azDirs[i], &buf) ) continue;
+if( !S_ISDIR(buf.st_mode) ) continue;
+if( access(azDirs[i], 07) ) continue;
+zDir = azDirs[i];
+break;
+}
+/* Check that the output buffer is large enough for the temporary file
+** name. If it is not, return SQLITE_ERROR.
+*/
+if( (strlen(zDir) + strlen(SQLITE_TEMP_FILE_PREFIX) + 17) >= nBuf ){
+return SQLITE_ERROR;
+}
+do{
+sqlite3_snprintf(nBuf-17, zBuf, "%s/"SQLITE_TEMP_FILE_PREFIX, zDir);
+j = strlen(zBuf);
+sqlite3_randomness(15, &zBuf[j]);
+for(i=0; i<15; i++, j++){
+zBuf[j] = (char)zChars[ ((unsigned char)zBuf[j])%(sizeof(zChars)-1) ];
+}
+zBuf[j] = 0;
+}while( access(zBuf,0)==0 );
+return SQLITE_OK;
+}
+/*
+** Open the file zPath.
+**
+** Previously, the SQLite OS layer used three functions in place of this
+** one:
+**
+**     sqlite3OsOpenReadWrite();
+**     sqlite3OsOpenReadOnly();
+**     sqlite3OsOpenExclusive();
+**
+** These calls correspond to the following combinations of flags:
+**
+**     ReadWrite() ->     (READWRITE | CREATE)
+**     ReadOnly()  ->     (READONLY)
+**     OpenExclusive() -> (READWRITE | CREATE | EXCLUSIVE)
+**
+** The old OpenExclusive() accepted a boolean argument - "delFlag". If
+** true, the file was configured to be automatically deleted when the
+** file handle closed. To achieve the same effect using this new
+** interface, add the DELETEONCLOSE flag to those specified above for
+** OpenExclusive().
+*/
+static int unixOpen(
+sqlite3_vfs *pVfs,
+const char *zPath,
+sqlite3_file *pFile,
+int flags,
+int *pOutFlags
+){
+int fd = 0;                    /* File descriptor returned by open() */
+int dirfd = -1;                /* Directory file descriptor */
+int oflags = 0;                /* Flags to pass to open() */
+int eType = flags&0xFFFFFF00;  /* Type of file to open */
+int noLock;                    /* True to omit locking primitives */
+int isExclusive  = (flags & SQLITE_OPEN_EXCLUSIVE);
+int isDelete     = (flags & SQLITE_OPEN_DELETEONCLOSE);
+int isCreate     = (flags & SQLITE_OPEN_CREATE);
+int isReadonly   = (flags & SQLITE_OPEN_READONLY);
+int isReadWrite  = (flags & SQLITE_OPEN_READWRITE);
+/* If creating a master or main-file journal, this function will open
+** a file-descriptor on the directory too. The first time unixSync()
+** is called the directory file descriptor will be fsync()ed and close()d.
+*/
+int isOpenDirectory = (isCreate &&
+(eType==SQLITE_OPEN_MASTER_JOURNAL || eType==SQLITE_OPEN_MAIN_JOURNAL)
+);
+/* If argument zPath is a NULL pointer, this function is required to open
+** a temporary file. Use this buffer to store the file name in.
+*/
+char zTmpname[MAX_PATHNAME+1];
+const char *zName = zPath;
+/* Check the following statements are true:
+**
+**   (a) Exactly one of the READWRITE and READONLY flags must be set, and
+**   (b) if CREATE is set, then READWRITE must also be set, and
+**   (c) if EXCLUSIVE is set, then CREATE must also be set.
+**   (d) if DELETEONCLOSE is set, then CREATE must also be set.
+*/
+assert((isReadonly==0 || isReadWrite==0) && (isReadWrite || isReadonly));
+assert(isCreate==0 || isReadWrite);
+assert(isExclusive==0 || isCreate);
+assert(isDelete==0 || isCreate);
+/* The main DB, main journal, and master journal are never automatically
+** deleted
+*/
+assert( eType!=SQLITE_OPEN_MAIN_DB || !isDelete );
+assert( eType!=SQLITE_OPEN_MAIN_JOURNAL || !isDelete );
+assert( eType!=SQLITE_OPEN_MASTER_JOURNAL || !isDelete );
+/* Assert that the upper layer has set one of the "file-type" flags. */
+assert( eType==SQLITE_OPEN_MAIN_DB      || eType==SQLITE_OPEN_TEMP_DB
+|| eType==SQLITE_OPEN_MAIN_JOURNAL || eType==SQLITE_OPEN_TEMP_JOURNAL
+|| eType==SQLITE_OPEN_SUBJOURNAL   || eType==SQLITE_OPEN_MASTER_JOURNAL
+|| eType==SQLITE_OPEN_TRANSIENT_DB
+);
+memset(pFile, 0, sizeof(unixFile));
+if( !zName ){
+int rc;
+assert(isDelete && !isOpenDirectory);
+rc = getTempname(MAX_PATHNAME+1, zTmpname);
+if( rc!=SQLITE_OK ){
+return rc;
+}
+zName = zTmpname;
+}
+if( isReadonly )  oflags |= O_RDONLY;
+if( isReadWrite ) oflags |= O_RDWR;
+if( isCreate )    oflags |= O_CREAT;
+if( isExclusive ) oflags |= (O_EXCL|O_NOFOLLOW);
+oflags |= (O_LARGEFILE|O_BINARY);
+fd = open(zName, oflags, isDelete?0600:SQLITE_DEFAULT_FILE_PERMISSIONS);
+if( fd<0 && errno!=EISDIR && isReadWrite && !isExclusive ){
+/* Failed to open the file for read/write access. Try read-only. */
+flags &= ~(SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE);
+flags |= SQLITE_OPEN_READONLY;
+return unixOpen(pVfs, zPath, pFile, flags, pOutFlags);
+}
+if( fd<0 ){
+return SQLITE_CANTOPEN;
+}
+if( isDelete ){
+unlink(zName);
+}
+if( pOutFlags ){
+*pOutFlags = flags;
+}
+assert(fd!=0);
+if( isOpenDirectory ){
+int rc = openDirectory(zPath, &dirfd);
+if( rc!=SQLITE_OK ){
+close(fd);
+return rc;
+}
+}
+#ifdef FD_CLOEXEC
+fcntl(fd, F_SETFD, fcntl(fd, F_GETFD, 0) | FD_CLOEXEC);
+#endif
+noLock = eType!=SQLITE_OPEN_MAIN_DB;
+return fillInUnixFile(pVfs, fd, dirfd, pFile, zPath, noLock);
+}
+/*
+** Delete the file at zPath. If the dirSync argument is true, fsync()
+** the directory after deleting the file.
+*/
+static int unixDelete(sqlite3_vfs *pVfs, const char *zPath, int dirSync){
+int rc = SQLITE_OK;
+SimulateIOError(return SQLITE_IOERR_DELETE);
+unlink(zPath);
+if( dirSync ){
+int fd;
+rc = openDirectory(zPath, &fd);
+if( rc==SQLITE_OK ){
+if( fsync(fd) ){
+rc = SQLITE_IOERR_DIR_FSYNC;
+}
+close(fd);
+}
+}
+return rc;
+}
+/*
+** Test the existance of or access permissions of file zPath. The
+** test performed depends on the value of flags:
+**
+**     SQLITE_ACCESS_EXISTS: Return 1 if the file exists
+**     SQLITE_ACCESS_READWRITE: Return 1 if the file is read and writable.
+**     SQLITE_ACCESS_READONLY: Return 1 if the file is readable.
+**
+** Otherwise return 0.
+*/
+static int unixAccess(
+sqlite3_vfs *pVfs,
+const char *zPath,
+int flags,
+int *pResOut
+){
+int amode = 0;
+SimulateIOError( return SQLITE_IOERR_ACCESS; );
+switch( flags ){
+case SQLITE_ACCESS_EXISTS:
+amode = F_OK;
+break;
+case SQLITE_ACCESS_READWRITE:
+amode = W_OK|R_OK;
+break;
+case SQLITE_ACCESS_READ:
+amode = R_OK;
+break;
+default:
+assert(!"Invalid flags argument");
+}
+*pResOut = (access(zPath, amode)==0);
+return SQLITE_OK;
+}
+/*
+** Turn a relative pathname into a full pathname. The relative path
+** is stored as a nul-terminated string in the buffer pointed to by
+** zPath.
+**
+** zOut points to a buffer of at least sqlite3_vfs.mxPathname bytes
+** (in this case, MAX_PATHNAME bytes). The full-path is written to
+** this buffer before returning.
+*/
+static int unixFullPathname(
+sqlite3_vfs *pVfs,            /* Pointer to vfs object */
+const char *zPath,            /* Possibly relative input path */
+int nOut,                     /* Size of output buffer in bytes */
+char *zOut                    /* Output buffer */
+){
+/* It's odd to simulate an io-error here, but really this is just
+** using the io-error infrastructure to test that SQLite handles this
+** function failing. This function could fail if, for example, the
+** current working directly has been unlinked.
+*/
+SimulateIOError( return SQLITE_ERROR );
+assert( pVfs->mxPathname==MAX_PATHNAME );
+zOut[nOut-1] = '\0';
+if( zPath[0]=='/' ){
+sqlite3_snprintf(nOut, zOut, "%s", zPath);
+}else{
+int nCwd;
+if( getcwd(zOut, nOut-1)==0 ){
+return SQLITE_CANTOPEN;
+}
+nCwd = strlen(zOut);
+sqlite3_snprintf(nOut-nCwd, &zOut[nCwd], "/%s", zPath);
+}
+return SQLITE_OK;
+#if 0
+/*
+** Remove "/./" path elements and convert "/A/./" path elements
+** to just "/".
+*/
+if( zFull ){
+int i, j;
+for(i=j=0; zFull[i]; i++){
+if( zFull[i]=='/' ){
+if( zFull[i+1]=='/' ) continue;
+if( zFull[i+1]=='.' && zFull[i+2]=='/' ){
+i += 1;
+continue;
+}
+if( zFull[i+1]=='.' && zFull[i+2]=='.' && zFull[i+3]=='/' ){
+while( j>0 && zFull[j-1]!='/' ){ j--; }
+i += 3;
+continue;
+}
+}
+zFull[j++] = zFull[i];
+}
+zFull[j] = 0;
+}
+#endif
+}
+#ifndef SQLITE_OMIT_LOAD_EXTENSION
+/*
+** Interfaces for opening a shared library, finding entry points
+** within the shared library, and closing the shared library.
+*/
+#include <dlfcn.h>
+static void *unixDlOpen(sqlite3_vfs *pVfs, const char *zFilename){
+return dlopen(zFilename, RTLD_NOW | RTLD_GLOBAL);
+}
+/*
+** SQLite calls this function immediately after a call to unixDlSym() or
+** unixDlOpen() fails (returns a null pointer). If a more detailed error
+** message is available, it is written to zBufOut. If no error message
+** is available, zBufOut is left unmodified and SQLite uses a default
+** error message.
+*/
+static void unixDlError(sqlite3_vfs *pVfs, int nBuf, char *zBufOut){
+char *zErr;
+enterMutex();
+zErr = dlerror();
+if( zErr ){
+sqlite3_snprintf(nBuf, zBufOut, "%s", zErr);
+}
+leaveMutex();
+}
+static void *unixDlSym(sqlite3_vfs *pVfs, void *pHandle, const char *zSymbol){
+return dlsym(pHandle, zSymbol);
+}
+static void unixDlClose(sqlite3_vfs *pVfs, void *pHandle){
+dlclose(pHandle);
+}
+#else /* if SQLITE_OMIT_LOAD_EXTENSION is defined: */
+#define unixDlOpen  0
+#define unixDlError 0
+#define unixDlSym   0
+#define unixDlClose 0
+#endif
+/*
+** Write nBuf bytes of random data to the supplied buffer zBuf.
+*/
+static int unixRandomness(sqlite3_vfs *pVfs, int nBuf, char *zBuf){
+assert(nBuf>=(sizeof(time_t)+sizeof(int)));
+/* We have to initialize zBuf to prevent valgrind from reporting
+** errors.  The reports issued by valgrind are incorrect - we would
+** prefer that the randomness be increased by making use of the
+** uninitialized space in zBuf - but valgrind errors tend to worry
+** some users.  Rather than argue, it seems easier just to initialize
+** the whole array and silence valgrind, even if that means less randomness
+** in the random seed.
+**
+** When testing, initializing zBuf[] to zero is all we do.  That means
+** that we always use the same random number sequence.  This makes the
+** tests repeatable.
+*/
+memset(zBuf, 0, nBuf);
+#if !defined(SQLITE_TEST)
+{
+int pid, fd;
+fd = open("/dev/urandom", O_RDONLY);
+if( fd<0 ){
+time_t t;
+time(&t);
+memcpy(zBuf, &t, sizeof(t));
+pid = getpid();
+memcpy(&zBuf[sizeof(t)], &pid, sizeof(pid));
+}else{
+read(fd, zBuf, nBuf);
+close(fd);
+}
+}
+#endif
+return SQLITE_OK;
+}
+/*
+** Sleep for a little while.  Return the amount of time slept.
+** The argument is the number of microseconds we want to sleep.
+** The return value is the number of microseconds of sleep actually
+** requested from the underlying operating system, a number which
+** might be greater than or equal to the argument, but not less
+** than the argument.
+*/
+static int unixSleep(sqlite3_vfs *pVfs, int microseconds){
+#if defined(HAVE_USLEEP) && HAVE_USLEEP
+usleep(microseconds);
+return microseconds;
+#else
+int seconds = (microseconds+999999)/1000000;
+sleep(seconds);
+return seconds*1000000;
+#endif
+}
+/*
+** The following variable, if set to a non-zero value, becomes the result
+** returned from sqlite3OsCurrentTime().  This is used for testing.
+*/
+#ifdef SQLITE_TEST
+int sqlite3_current_time = 0;
+#endif
+/*
+** Find the current time (in Universal Coordinated Time).  Write the
+** current time and date as a Julian Day number into *prNow and
+** return 0.  Return 1 if the time and date cannot be found.
+*/
+static int unixCurrentTime(sqlite3_vfs *pVfs, double *prNow){
+#ifdef NO_GETTOD
+time_t t;
+time(&t);
+*prNow = t/86400.0 + 2440587.5;
+#else
+struct timeval sNow;
+gettimeofday(&sNow, 0);
+*prNow = 2440587.5 + sNow.tv_sec/86400.0 + sNow.tv_usec/86400000000.0;
+#endif
+#ifdef SQLITE_TEST
+if( sqlite3_current_time ){
+*prNow = sqlite3_current_time/86400.0 + 2440587.5;
+}
+#endif
+return 0;
+}
+static int unixGetLastError(sqlite3_vfs *pVfs, int nBuf, char *zBuf){
+return 0;
+}
+/*
+** Initialize the operating system interface.
+*/
+int sqlite3_os_init(void){
+/* Macro to define the static contents of an sqlite3_vfs structure for
+** the unix backend. The two parameters are the values to use for
+** the sqlite3_vfs.zName and sqlite3_vfs.pAppData fields, respectively.
+**
+*/
+#define UNIXVFS(zVfsName, pVfsAppData) {                  \
+1,                    /* iVersion */                    \
+sizeof(unixFile),     /* szOsFile */                    \
+MAX_PATHNAME,         /* mxPathname */                  \
+0,                    /* pNext */                       \
+zVfsName,             /* zName */                       \
+(void *)pVfsAppData,  /* pAppData */                    \
+unixOpen,             /* xOpen */                       \
+unixDelete,           /* xDelete */                     \
+unixAccess,           /* xAccess */                     \
+unixFullPathname,     /* xFullPathname */               \
+unixDlOpen,           /* xDlOpen */                     \
+unixDlError,          /* xDlError */                    \
+unixDlSym,            /* xDlSym */                      \
+unixDlClose,          /* xDlClose */                    \
+unixRandomness,       /* xRandomness */                 \
+unixSleep,            /* xSleep */                      \
+unixCurrentTime,      /* xCurrentTime */                \
+unixGetLastError      /* xGetLastError */               \
+}
+static sqlite3_vfs unixVfs = UNIXVFS("unix", 0);
+#ifdef SQLITE_ENABLE_LOCKING_STYLE
+#if 0
+int i;
+static sqlite3_vfs aVfs[] = {
+UNIXVFS("unix-posix",   LOCKING_STYLE_POSIX),
+UNIXVFS("unix-afp",     LOCKING_STYLE_AFP),
+UNIXVFS("unix-flock",   LOCKING_STYLE_FLOCK),
+UNIXVFS("unix-dotfile", LOCKING_STYLE_DOTFILE),
+UNIXVFS("unix-none",    LOCKING_STYLE_NONE)
+};
+for(i=0; i<(sizeof(aVfs)/sizeof(sqlite3_vfs)); i++){
+sqlite3_vfs_register(&aVfs[i], 0);
+}
+#endif
+#endif
+sqlite3_vfs_register(&unixVfs, 1);
+return SQLITE_OK;
+}
+/*
+** Shutdown the operating system interface. This is a no-op for unix.
+*/
+int sqlite3_os_end(void){
+return SQLITE_OK;
+}
+#endif /* SQLITE_OS_UNIX */