Initial commit

Signed-off-by: Mavridis Philippe <[email protected]>

1 files changed, 1345 insertions, 0 deletions

diff --git a/src/sqlite/os_unix.c b/src/sqlite/os_unix.c
new file mode 100644
index 0000000..9c361a1
--- /dev/null
+++ b/src/sqlite/os_unix.c
@@ -0,0 +1,1345 @@
+/*
+** 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.
+*/
+#include "sqliteInt.h"
+#include "os.h"
+#if OS_UNIX              /* This file is used on unix only */
+
+
+#include <time.h>
+#include <errno.h>
+#include <unistd.h>
+
+/*
+** Do not include any of the File I/O interface procedures if the
+** SQLITE_OMIT_DISKIO macro is defined (indicating that there database
+** will be in-memory only)
+*/
+#ifndef SQLITE_OMIT_DISKIO
+
+
+/*
+** 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 its DOS - what did you expect?
+*/
+#ifdef __DJGPP__
+# define fcntl(A,B,C) 0
+#endif
+
+/*
+** Macros used to determine whether or not to use threads.  The
+** SQLITE_UNIX_THREADS macro is defined if we are synchronizing for
+** Posix threads and SQLITE_W32_THREADS is defined if we are
+** synchronizing using Win32 threads.
+*/
+#if defined(THREADSAFE) && THREADSAFE
+# include <pthread.h>
+# define SQLITE_UNIX_THREADS 1
+#endif
+
+
+/*
+** Include code that is common to all os_*.c files
+*/
+#include "os_common.h"
+
+#if defined(THREADSAFE) && THREADSAFE && defined(__linux__)
+#define getpid pthread_self
+#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 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.  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 OsFile 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 OsFile 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 OsFile structure contains
+** a pointer to an openCnt structure.  There is one openCnt structure
+** per open inode, which means that multiple OsFiles can point to a single
+** openCnt.  When an attempt is made to close an OsFile, if there are
+** other OsFiles 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 also
+** set to zero if we compile without threading support.
+*/
+struct lockKey {
+  dev_t dev;       /* Device number */
+  ino_t ino;       /* Inode number */
+#ifdef SQLITE_UNIX_THREADS
+  pthread_t tid;   /* Thread ID or zero if threads cannot 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 OsFile
+** structure contains a pointer to an instance of this object and this
+** object keeps a count of the number of OsFiles 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 */
+};
+
+/*
+** 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() */
+};
+
+/* 
+** These hash table maps inodes and process IDs into lockInfo and openCnt
+** structures.  Access to these hash tables must be protected by a mutex.
+*/
+static Hash lockHash = { SQLITE_HASH_BINARY, 0, 0, 0, 0, 0 };
+static Hash openHash = { SQLITE_HASH_BINARY, 0, 0, 0, 0, 0 };
+
+
+#ifdef SQLITE_UNIX_THREADS
+/*
+** 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.
+*/
+static int threadsOverrideEachOthersLocks = -1;
+
+/*
+** 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 */
+};
+
+/*
+** 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(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_UNIX_THREADS */
+
+/*
+** Release a lockInfo structure previously allocated by findLockInfo().
+*/
+static void releaseLockInfo(struct lockInfo *pLock){
+  pLock->nRef--;
+  if( pLock->nRef==0 ){
+    sqlite3HashInsert(&lockHash, &pLock->key, sizeof(pLock->key), 0);
+    sqliteFree(pLock);
+  }
+}
+
+/*
+** Release a openCnt structure previously allocated by findLockInfo().
+*/
+static void releaseOpenCnt(struct openCnt *pOpen){
+  pOpen->nRef--;
+  if( pOpen->nRef==0 ){
+    sqlite3HashInsert(&openHash, &pOpen->key, sizeof(pOpen->key), 0);
+    sqliteFree(pOpen->aPending);
+    sqliteFree(pOpen);
+  }
+}
+
+/*
+** Given a file descriptor, locate lockInfo and openCnt structures that
+** describes that file descriptor.  Create a new ones if necessary.  The
+** return values might be unset if an error occurs.
+**
+** Return the number of errors.
+*/
+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 ) return 1;
+  memset(&key1, 0, sizeof(key1));
+  key1.dev = statbuf.st_dev;
+  key1.ino = statbuf.st_ino;
+#ifdef SQLITE_UNIX_THREADS
+  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 = (struct lockInfo*)sqlite3HashFind(&lockHash, &key1, sizeof(key1));
+  if( pLock==0 ){
+    struct lockInfo *pOld;
+    pLock = sqliteMallocRaw( sizeof(*pLock) );
+    if( pLock==0 ) return 1;
+    pLock->key = key1;
+    pLock->nRef = 1;
+    pLock->cnt = 0;
+    pLock->locktype = 0;
+    pOld = sqlite3HashInsert(&lockHash, &pLock->key, sizeof(key1), pLock);
+    if( pOld!=0 ){
+      assert( pOld==pLock );
+      sqliteFree(pLock);
+      return 1;
+    }
+  }else{
+    pLock->nRef++;
+  }
+  *ppLock = pLock;
+  pOpen = (struct openCnt*)sqlite3HashFind(&openHash, &key2, sizeof(key2));
+  if( pOpen==0 ){
+    struct openCnt *pOld;
+    pOpen = sqliteMallocRaw( sizeof(*pOpen) );
+    if( pOpen==0 ){
+      releaseLockInfo(pLock);
+      return 1;
+    }
+    pOpen->key = key2;
+    pOpen->nRef = 1;
+    pOpen->nLock = 0;
+    pOpen->nPending = 0;
+    pOpen->aPending = 0;
+    pOld = sqlite3HashInsert(&openHash, &pOpen->key, sizeof(key2), pOpen);
+    if( pOld!=0 ){
+      assert( pOld==pOpen );
+      sqliteFree(pOpen);
+      releaseLockInfo(pLock);
+      return 1;
+    }
+  }else{
+    pOpen->nRef++;
+  }
+  *ppOpen = pOpen;
+  return 0;
+}
+
+/*
+** Delete the named file
+*/
+int sqlite3OsDelete(const char *zFilename){
+  unlink(zFilename);
+  return SQLITE_OK;
+}
+
+/*
+** Return TRUE if the named file exists.
+*/
+int sqlite3OsFileExists(const char *zFilename){
+  return access(zFilename, 0)==0;
+}
+
+/*
+** Attempt to open a file for both reading and writing.  If that
+** fails, try opening it read-only.  If the file does not exist,
+** try to create it.
+**
+** On success, a handle for the open file is written to *id
+** and *pReadonly is set to 0 if the file was opened for reading and
+** writing or 1 if the file was opened read-only.  The function returns
+** SQLITE_OK.
+**
+** On failure, the function returns SQLITE_CANTOPEN and leaves
+** *id and *pReadonly unchanged.
+*/
+int sqlite3OsOpenReadWrite(
+  const char *zFilename,
+  OsFile *id,
+  int *pReadonly
+){
+  int rc;
+  assert( !id->isOpen );
+  id->dirfd = -1;
+  id->h = open(zFilename, O_RDWR|O_CREAT|O_LARGEFILE|O_BINARY,
+                          SQLITE_DEFAULT_FILE_PERMISSIONS);
+  if( id->h<0 ){
+#ifdef EISDIR
+    if( errno==EISDIR ){
+      return SQLITE_CANTOPEN;
+    }
+#endif
+    id->h = open(zFilename, O_RDONLY|O_LARGEFILE|O_BINARY);
+    if( id->h<0 ){
+      return SQLITE_CANTOPEN; 
+    }
+    *pReadonly = 1;
+  }else{
+    *pReadonly = 0;
+  }
+  sqlite3OsEnterMutex();
+  rc = findLockInfo(id->h, &id->pLock, &id->pOpen);
+  sqlite3OsLeaveMutex();
+  if( rc ){
+    close(id->h);
+    return SQLITE_NOMEM;
+  }
+  id->locktype = 0;
+  id->isOpen = 1;
+  TRACE3("OPEN    %-3d %s\n", id->h, zFilename);
+  OpenCounter(+1);
+  return SQLITE_OK;
+}
+
+
+/*
+** Attempt to open a new file for exclusive access by this process.
+** The file will be opened for both reading and writing.  To avoid
+** a potential security problem, we do not allow the file to have
+** previously existed.  Nor do we allow the file to be a symbolic
+** link.
+**
+** If delFlag is true, then make arrangements to automatically delete
+** the file when it is closed.
+**
+** On success, write the file handle into *id and return SQLITE_OK.
+**
+** On failure, return SQLITE_CANTOPEN.
+*/
+int sqlite3OsOpenExclusive(const char *zFilename, OsFile *id, int delFlag){
+  int rc;
+  assert( !id->isOpen );
+  if( access(zFilename, 0)==0 ){
+    return SQLITE_CANTOPEN;
+  }
+  id->dirfd = -1;
+  id->h = open(zFilename,
+                O_RDWR|O_CREAT|O_EXCL|O_NOFOLLOW|O_LARGEFILE|O_BINARY, 0600);
+  if( id->h<0 ){
+    return SQLITE_CANTOPEN;
+  }
+  sqlite3OsEnterMutex();
+  rc = findLockInfo(id->h, &id->pLock, &id->pOpen);
+  sqlite3OsLeaveMutex();
+  if( rc ){
+    close(id->h);
+    unlink(zFilename);
+    return SQLITE_NOMEM;
+  }
+  id->locktype = 0;
+  id->isOpen = 1;
+  if( delFlag ){
+    unlink(zFilename);
+  }
+  TRACE3("OPEN-EX %-3d %s\n", id->h, zFilename);
+  OpenCounter(+1);
+  return SQLITE_OK;
+}
+
+/*
+** Attempt to open a new file for read-only access.
+**
+** On success, write the file handle into *id and return SQLITE_OK.
+**
+** On failure, return SQLITE_CANTOPEN.
+*/
+int sqlite3OsOpenReadOnly(const char *zFilename, OsFile *id){
+  int rc;
+  assert( !id->isOpen );
+  id->dirfd = -1;
+  id->h = open(zFilename, O_RDONLY|O_LARGEFILE|O_BINARY);
+  if( id->h<0 ){
+    return SQLITE_CANTOPEN;
+  }
+  sqlite3OsEnterMutex();
+  rc = findLockInfo(id->h, &id->pLock, &id->pOpen);
+  sqlite3OsLeaveMutex();
+  if( rc ){
+    close(id->h);
+    return SQLITE_NOMEM;
+  }
+  id->locktype = 0;
+  id->isOpen = 1;
+  TRACE3("OPEN-RO %-3d %s\n", id->h, zFilename);
+  OpenCounter(+1);
+  return SQLITE_OK;
+}
+
+/*
+** Attempt to open a file descriptor for the directory that contains a
+** file.  This file descriptor can be used to fsync() the directory
+** in order to make sure the creation of a new file is actually written
+** to disk.
+**
+** This routine is only meaningful for Unix.  It is a no-op under
+** windows since windows does not support hard links.
+**
+** On success, a handle for a previously open file is at *id is
+** updated with the new directory file descriptor and SQLITE_OK is
+** returned.
+**
+** On failure, the function returns SQLITE_CANTOPEN and leaves
+** *id unchanged.
+*/
+int sqlite3OsOpenDirectory(
+  const char *zDirname,
+  OsFile *id
+){
+  if( !id->isOpen ){
+    /* Do not open the directory if the corresponding file is not already
+    ** open. */
+    return SQLITE_CANTOPEN;
+  }
+  assert( id->dirfd<0 );
+  id->dirfd = open(zDirname, O_RDONLY|O_BINARY, 0);
+  if( id->dirfd<0 ){
+    return SQLITE_CANTOPEN; 
+  }
+  TRACE3("OPENDIR %-3d %s\n", id->dirfd, zDirname);
+  return SQLITE_OK;
+}
+
+/*
+** If the following global variable points to a string which is the
+** name of a directory, then that directory will be used to store
+** temporary files.
+*/
+char *sqlite3_temp_directory = 0;
+
+/*
+** Create a temporary file name in zBuf.  zBuf must be big enough to
+** hold at least SQLITE_TEMPNAME_SIZE characters.
+*/
+int sqlite3OsTempFileName(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 = ".";
+  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;
+  }
+  do{
+    sprintf(zBuf, "%s/"TEMP_FILE_PREFIX, zDir);
+    j = strlen(zBuf);
+    sqlite3Randomness(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; 
+}
+
+#ifndef SQLITE_OMIT_PAGER_PRAGMAS
+/*
+** Check that a given pathname is a directory and is writable 
+**
+*/
+int sqlite3OsIsDirWritable(char *zBuf){
+  struct stat buf;
+  if( zBuf==0 ) return 0;
+  if( zBuf[0]==0 ) return 0;
+  if( stat(zBuf, &buf) ) return 0;
+  if( !S_ISDIR(buf.st_mode) ) return 0;
+  if( access(zBuf, 07) ) return 0;
+  return 1;
+}
+#endif /* SQLITE_OMIT_PAGER_PRAGMAS */
+
+/*
+** Read data from a file into a buffer.  Return SQLITE_OK if all
+** bytes were read successfully and SQLITE_IOERR if anything goes
+** wrong.
+*/
+int sqlite3OsRead(OsFile *id, void *pBuf, int amt){
+  int got;
+  assert( id->isOpen );
+  SimulateIOError(SQLITE_IOERR);
+  TIMER_START;
+  got = read(id->h, pBuf, amt);
+  TIMER_END;
+  TRACE5("READ    %-3d %5d %7d %d\n", id->h, got, last_page, TIMER_ELAPSED);
+  SEEK(0);
+  /* if( got<0 ) got = 0; */
+  if( got==amt ){
+    return SQLITE_OK;
+  }else{
+    return SQLITE_IOERR;
+  }
+}
+
+/*
+** Write data from a buffer into a file.  Return SQLITE_OK on success
+** or some other error code on failure.
+*/
+int sqlite3OsWrite(OsFile *id, const void *pBuf, int amt){
+  int wrote = 0;
+  assert( id->isOpen );
+  assert( amt>0 );
+  SimulateIOError(SQLITE_IOERR);
+  SimulateDiskfullError;
+  TIMER_START;
+  while( amt>0 && (wrote = write(id->h, pBuf, amt))>0 ){
+    amt -= wrote;
+    pBuf = &((char*)pBuf)[wrote];
+  }
+  TIMER_END;
+  TRACE5("WRITE   %-3d %5d %7d %d\n", id->h, wrote, last_page, TIMER_ELAPSED);
+  SEEK(0);
+  if( amt>0 ){
+    return SQLITE_FULL;
+  }
+  return SQLITE_OK;
+}
+
+/*
+** Move the read/write pointer in a file.
+*/
+int sqlite3OsSeek(OsFile *id, i64 offset){
+  assert( id->isOpen );
+  SEEK(offset/1024 + 1);
+  lseek(id->h, offset, SEEK_SET);
+  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
+
+
+/*
+** 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 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
+
+#ifdef F_FULLFSYNC
+  if( fullSync ){
+    rc = fcntl(fd, F_FULLFSYNC, 0);
+  }else{
+    rc = 1;
+  }
+  /* If the FULLSYNC failed, try to do a normal fsync() */
+  if( rc ) rc = fsync(fd);
+
+#else
+  rc = fsync(fd);
+#endif /* defined(F_FULLFSYNC) */
+#endif /* defined(SQLITE_NO_SYNC) */
+
+  return rc;
+}
+
+/*
+** Make sure all writes to a particular file are committed to disk.
+**
+** 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.
+*/
+int sqlite3OsSync(OsFile *id){
+  assert( id->isOpen );
+  SimulateIOError(SQLITE_IOERR);
+  TRACE2("SYNC    %-3d\n", id->h);
+  if( full_fsync(id->h, id->fullSync) ){
+    return SQLITE_IOERR;
+  }
+  if( id->dirfd>=0 ){
+    TRACE2("DIRSYNC %-3d\n", id->dirfd);
+    full_fsync(id->dirfd, id->fullSync);
+    close(id->dirfd);  /* Only need to sync once, so close the directory */
+    id->dirfd = -1;    /* when we are done. */
+  }
+  return SQLITE_OK;
+}
+
+/*
+** Sync the directory zDirname. This is a no-op on operating systems other
+** than UNIX.
+**
+** This is used to make sure the master journal file has truely been deleted
+** before making changes to individual journals on a multi-database commit.
+** The F_FULLFSYNC option is not needed here.
+*/
+int sqlite3OsSyncDirectory(const char *zDirname){
+  int fd;
+  int r;
+  SimulateIOError(SQLITE_IOERR);
+  fd = open(zDirname, O_RDONLY|O_BINARY, 0);
+  TRACE3("DIRSYNC %-3d (%s)\n", fd, zDirname);
+  if( fd<0 ){
+    return SQLITE_CANTOPEN; 
+  }
+  r = fsync(fd);
+  close(fd);
+  return ((r==0)?SQLITE_OK:SQLITE_IOERR);
+}
+
+/*
+** Truncate an open file to a specified size
+*/
+int sqlite3OsTruncate(OsFile *id, i64 nByte){
+  assert( id->isOpen );
+  SimulateIOError(SQLITE_IOERR);
+  return ftruncate(id->h, nByte)==0 ? SQLITE_OK : SQLITE_IOERR;
+}
+
+/*
+** Determine the current size of a file in bytes
+*/
+int sqlite3OsFileSize(OsFile *id, i64 *pSize){
+  struct stat buf;
+  assert( id->isOpen );
+  SimulateIOError(SQLITE_IOERR);
+  if( fstat(id->h, &buf)!=0 ){
+    return SQLITE_IOERR;
+  }
+  *pSize = buf.st_size;
+  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.
+*/
+int sqlite3OsCheckReservedLock(OsFile *id){
+  int r = 0;
+
+  assert( id->isOpen );
+  sqlite3OsEnterMutex(); /* Needed because id->pLock is shared across threads */
+
+  /* Check if a thread in this process holds such a lock */
+  if( id->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(id->h, F_GETLK, &lock);
+    if( lock.l_type!=F_UNLCK ){
+      r = 1;
+    }
+  }
+  
+  sqlite3OsLeaveMutex();
+  TRACE3("TEST WR-LOCK %d %d\n", id->h, r);
+
+  return r;
+}
+
+#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
+
+/*
+** 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.
+*/
+int sqlite3OsLock(OsFile *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;
+  struct lockInfo *pLock = id->pLock;
+  struct flock lock;
+  int s;
+
+  assert( id->isOpen );
+  TRACE7("LOCK    %d %s was %s(%s,%d) pid=%d\n", id->h, locktypeName(locktype), 
+      locktypeName(id->locktype), locktypeName(pLock->locktype), pLock->cnt
+      ,getpid() );
+
+  /* If there is already a lock of this type or more restrictive on the
+  ** OsFile, do nothing. Don't use the end_lock: exit path, as
+  ** sqlite3OsEnterMutex() hasn't been called yet.
+  */
+  if( id->locktype>=locktype ){
+    TRACE3("LOCK    %d %s ok (already held)\n", id->h, locktypeName(locktype));
+    return SQLITE_OK;
+  }
+
+  /* Make sure the locking sequence is correct
+  */
+  assert( id->locktype!=NO_LOCK || locktype==SHARED_LOCK );
+  assert( locktype!=PENDING_LOCK );
+  assert( locktype!=RESERVED_LOCK || id->locktype==SHARED_LOCK );
+
+  /* This mutex is needed because id->pLock is shared across threads
+  */
+  sqlite3OsEnterMutex();
+
+  /* If some thread using this PID has a lock via a different OsFile*
+  ** handle that precludes the requested lock, return BUSY.
+  */
+  if( (id->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( id->locktype==0 );
+    assert( pLock->cnt>0 );
+    id->locktype = SHARED_LOCK;
+    pLock->cnt++;
+    id->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 && id->locktype<PENDING_LOCK)
+  ){
+    lock.l_type = (locktype==SHARED_LOCK?F_RDLCK:F_WRLCK);
+    lock.l_start = PENDING_BYTE;
+    s = fcntl(id->h, F_SETLK, &lock);
+    if( s ){
+      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(id->h, F_SETLK, &lock);
+
+    /* Drop the temporary PENDING lock */
+    lock.l_start = PENDING_BYTE;
+    lock.l_len = 1L;
+    lock.l_type = F_UNLCK;
+    fcntl(id->h, F_SETLK, &lock);
+    if( s ){
+      rc = (errno==EINVAL) ? SQLITE_NOLFS : SQLITE_BUSY;
+    }else{
+      id->locktype = SHARED_LOCK;
+      id->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!=id->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(id->h, F_SETLK, &lock);
+    if( s ){
+      rc = (errno==EINVAL) ? SQLITE_NOLFS : SQLITE_BUSY;
+    }
+  }
+  
+  if( rc==SQLITE_OK ){
+    id->locktype = locktype;
+    pLock->locktype = locktype;
+  }else if( locktype==EXCLUSIVE_LOCK ){
+    id->locktype = PENDING_LOCK;
+    pLock->locktype = PENDING_LOCK;
+  }
+
+end_lock:
+  sqlite3OsLeaveMutex();
+  TRACE4("LOCK    %d %s %s\n", id->h, locktypeName(locktype), 
+      rc==SQLITE_OK ? "ok" : "failed");
+  return rc;
+}
+
+/*
+** Lower the locking level on file descriptor id 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.
+**
+** It is not possible for this routine to fail if the second argument
+** is NO_LOCK.  If the second argument is SHARED_LOCK, this routine
+** might return SQLITE_IOERR instead of SQLITE_OK.
+*/
+int sqlite3OsUnlock(OsFile *id, int locktype){
+  struct lockInfo *pLock;
+  struct flock lock;
+  int rc = SQLITE_OK;
+
+  assert( id->isOpen );
+  TRACE7("UNLOCK  %d %d was %d(%d,%d) pid=%d\n", id->h, locktype, id->locktype, 
+      id->pLock->locktype, id->pLock->cnt, getpid());
+
+  assert( locktype<=SHARED_LOCK );
+  if( id->locktype<=locktype ){
+    return SQLITE_OK;
+  }
+  sqlite3OsEnterMutex();
+  pLock = id->pLock;
+  assert( pLock->cnt!=0 );
+  if( id->locktype>SHARED_LOCK ){
+    assert( pLock->locktype==id->locktype );
+    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(id->h, F_SETLK, &lock)!=0 ){
+        /* This should never happen */
+        rc = SQLITE_IOERR;
+      }
+    }
+    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 );
+    fcntl(id->h, F_SETLK, &lock);
+    pLock->locktype = SHARED_LOCK;
+  }
+  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;
+      fcntl(id->h, F_SETLK, &lock);
+      pLock->locktype = NO_LOCK;
+    }
+
+    /* 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.
+    */
+    pOpen = id->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]);
+      }
+      sqliteFree(pOpen->aPending);
+      pOpen->nPending = 0;
+      pOpen->aPending = 0;
+    }
+  }
+  sqlite3OsLeaveMutex();
+  id->locktype = locktype;
+  return rc;
+}
+
+/*
+** Close a file.
+*/
+int sqlite3OsClose(OsFile *id){
+  if( !id->isOpen ) return SQLITE_OK;
+  sqlite3OsUnlock(id, NO_LOCK);
+  if( id->dirfd>=0 ) close(id->dirfd);
+  id->dirfd = -1;
+  sqlite3OsEnterMutex();
+  if( id->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 = id->pOpen;
+    pOpen->nPending++;
+    aNew = sqliteRealloc( pOpen->aPending, pOpen->nPending*sizeof(int) );
+    if( aNew==0 ){
+      /* If a malloc fails, just leak the file descriptor */
+    }else{
+      pOpen->aPending = aNew;
+      pOpen->aPending[pOpen->nPending-1] = id->h;
+    }
+  }else{
+    /* There are no outstanding locks so we can close the file immediately */
+    close(id->h);
+  }
+  releaseLockInfo(id->pLock);
+  releaseOpenCnt(id->pOpen);
+  sqlite3OsLeaveMutex();
+  id->isOpen = 0;
+  TRACE2("CLOSE   %-3d\n", id->h);
+  OpenCounter(-1);
+  return SQLITE_OK;
+}
+
+/*
+** Turn a relative pathname into a full pathname.  Return a pointer
+** to the full pathname stored in space obtained from sqliteMalloc().
+** The calling function is responsible for freeing this space once it
+** is no longer needed.
+*/
+char *sqlite3OsFullPathname(const char *zRelative){
+  char *zFull = 0;
+  if( zRelative[0]=='/' ){
+    sqlite3SetString(&zFull, zRelative, (char*)0);
+  }else{
+    char zBuf[5000];
+    zBuf[0] = 0;
+    sqlite3SetString(&zFull, getcwd(zBuf, sizeof(zBuf)), "/", zRelative,
+                    (char*)0);
+  }
+  return zFull;
+}
+
+
+#endif /* SQLITE_OMIT_DISKIO */
+/***************************************************************************
+** Everything above deals with file I/O.  Everything that follows deals
+** with other miscellanous aspects of the operating system interface
+****************************************************************************/
+
+
+/*
+** Get information to seed the random number generator.  The seed
+** is written into the buffer zBuf[256].  The calling function must
+** supply a sufficiently large buffer.
+*/
+int sqlite3OsRandomSeed(char *zBuf){
+  /* 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, 256);
+#if !defined(SQLITE_TEST)
+  {
+    int pid, fd;
+    fd = open("/dev/urandom", O_RDONLY);
+    if( fd<0 ){
+      time((time_t*)zBuf);
+      pid = getpid();
+      memcpy(&zBuf[sizeof(time_t)], &pid, sizeof(pid));
+    }else{
+      read(fd, zBuf, 256);
+      close(fd);
+    }
+  }
+#endif
+  return SQLITE_OK;
+}
+
+/*
+** Sleep for a little while.  Return the amount of time slept.
+*/
+int sqlite3OsSleep(int ms){
+#if defined(HAVE_USLEEP) && HAVE_USLEEP
+  usleep(ms*1000);
+  return ms;
+#else
+  sleep((ms+999)/1000);
+  return 1000*((ms+999)/1000);
+#endif
+}
+
+/*
+** Static variables used for thread synchronization
+*/
+static int inMutex = 0;
+#ifdef SQLITE_UNIX_THREADS
+static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
+#endif
+
+/*
+** The following pair of routine implement mutual exclusion for
+** multi-threaded processes.  Only a single thread is allowed to
+** executed code that is surrounded by EnterMutex() and LeaveMutex().
+**
+** SQLite uses only a single Mutex.  There is not much critical
+** code and what little there is executes quickly and without blocking.
+*/
+void sqlite3OsEnterMutex(){
+#ifdef SQLITE_UNIX_THREADS
+  pthread_mutex_lock(&mutex);
+#endif
+  assert( !inMutex );
+  inMutex = 1;
+}
+void sqlite3OsLeaveMutex(){
+  assert( inMutex );
+  inMutex = 0;
+#ifdef SQLITE_UNIX_THREADS
+  pthread_mutex_unlock(&mutex);
+#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.
+*/
+int sqlite3OsCurrentTime(double *prNow){
+  time_t t;
+  time(&t);
+  *prNow = t/86400.0 + 2440587.5;
+#ifdef SQLITE_TEST
+  if( sqlite3_current_time ){
+    *prNow = sqlite3_current_time/86400.0 + 2440587.5;
+  }
+#endif
+  return 0;
+}
+
+#endif /* OS_UNIX */