Tidyup fixes for fcntl spin problem.

[Samba/gbeck.git] / source / locking / posix.c

/* 
   Unix SMB/Netbios implementation.
   Version 3.0
   Locking functions
   Copyright (C) Jeremy Allison 1992-2000
   
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.
   
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
   
   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

   Revision History:

   POSIX locking support. Jeremy Allison (jeremy@valinux.com), Apr. 2000.
*/

#include "includes.h"
extern int DEBUGLEVEL;

/*
 * The POSIX locking database handle.
 */

static TDB_CONTEXT *posix_lock_tdb;

/*
 * The pending close database handle.
 */

static TDB_CONTEXT *posix_pending_close_tdb;

/*
 * The data in POSIX lock records is an unsorted linear array of these
 * records.  It is unnecessary to store the count as tdb provides the
 * size of the record.
 */

struct posix_lock {
        int fd;
        SMB_OFF_T start;
        SMB_OFF_T size;
        int lock_type;
};

/*
 * The data in POSIX pending close records is an unsorted linear array of int
 * records.  It is unnecessary to store the count as tdb provides the
 * size of the record.
 */

/* The key used in both the POSIX databases. */

struct posix_lock_key {
        SMB_DEV_T device;
        SMB_INO_T inode;
}; 

/*******************************************************************
 Form a static locking key for a dev/inode pair.
******************************************************************/

static TDB_DATA locking_key(SMB_DEV_T dev, SMB_INO_T inode)
{
        static struct posix_lock_key key;
        TDB_DATA kbuf;

        memset(&key, '\0', sizeof(key));
        key.device = dev;
        key.inode = inode;
        kbuf.dptr = (char *)&key;
        kbuf.dsize = sizeof(key);
        return kbuf;
}

/*******************************************************************
 Convenience function to get a key from an fsp.
******************************************************************/

static TDB_DATA locking_key_fsp(files_struct *fsp)
{
        return locking_key(fsp->dev, fsp->inode);
}

/****************************************************************************
 Add an fd to the pending close tdb.
****************************************************************************/

static BOOL add_fd_to_close_entry(files_struct *fsp)
{
        TDB_DATA kbuf = locking_key_fsp(fsp);
        TDB_DATA dbuf;
        char *tp;

        dbuf.dptr = NULL;

        dbuf = tdb_fetch(posix_pending_close_tdb, kbuf);

        tp = Realloc(dbuf.dptr, dbuf.dsize + sizeof(int));
        if (!tp) {
                DEBUG(0,("add_fd_to_close_entry: Realloc fail !\n"));
                if (dbuf.dptr) free(dbuf.dptr);
                return False;
        }
        else dbuf.dptr = tp;
        memcpy(dbuf.dptr + dbuf.dsize, &fsp->fd, sizeof(int));
        dbuf.dsize += sizeof(int);

        if (tdb_store(posix_pending_close_tdb, kbuf, dbuf, TDB_REPLACE) == -1) {
                DEBUG(0,("add_fd_to_close_entry: tdb_store fail !\n"));
        }

        free(dbuf.dptr);
        return True;
}

/****************************************************************************
 Remove all fd entries for a specific dev/inode pair from the tdb.
****************************************************************************/

static void delete_close_entries(files_struct *fsp)
{
        TDB_DATA kbuf = locking_key_fsp(fsp);

        if (tdb_delete(posix_pending_close_tdb, kbuf) == -1)
                DEBUG(0,("delete_close_entries: tdb_delete fail !\n"));
}

/****************************************************************************
 Get the array of POSIX pending close records for an open fsp. Caller must
 free. Returns number of entries.
****************************************************************************/

static size_t get_posix_pending_close_entries(files_struct *fsp, int **entries)
{
        TDB_DATA kbuf = locking_key_fsp(fsp);
        TDB_DATA dbuf;
        size_t count = 0;

        *entries = NULL;
        dbuf.dptr = NULL;

        dbuf = tdb_fetch(posix_pending_close_tdb, kbuf);

    if (!dbuf.dptr) {
                return 0;
        }

        *entries = (int *)dbuf.dptr;
        count = (size_t)(dbuf.dsize / sizeof(int));

        return count;
}

/****************************************************************************
 Get the array of POSIX locks for an fsp. Caller must free. Returns
 number of entries.
****************************************************************************/

static size_t get_posix_lock_entries(files_struct *fsp, struct posix_lock **entries)
{
        TDB_DATA kbuf = locking_key_fsp(fsp);
        TDB_DATA dbuf;
        size_t count = 0;

        *entries = NULL;

        dbuf.dptr = NULL;

        dbuf = tdb_fetch(posix_lock_tdb, kbuf);

    if (!dbuf.dptr) {
                return 0;
        }

        *entries = (struct posix_lock *)dbuf.dptr;
        count = (size_t)(dbuf.dsize / sizeof(struct posix_lock));

        return count;
}

/****************************************************************************
 Deal with pending closes needed by POSIX locking support.
 Note that posix_locking_close_file() is expected to have been called
 to delete all locks on this fsp before this function is called.
****************************************************************************/

int fd_close_posix(struct connection_struct *conn, files_struct *fsp)
{
        int saved_errno = 0;
        int ret;
        size_t count, i;
        struct posix_lock *entries = NULL;
        int *fd_array = NULL;
        BOOL locks_on_other_fds = False;

        if (!lp_posix_locking(SNUM(conn))) {
                /*
                 * No POSIX to worry about, just close.
                 */
                ret = conn->vfs_ops.close(fsp,fsp->fd);
                fsp->fd = -1;
                return ret;
        }

        /*
         * Get the number of outstanding POSIX locks on this dev/inode pair.
         */

        count = get_posix_lock_entries(fsp, &entries);

        /*
         * Check if there are any outstanding locks belonging to
         * other fd's. This should never be the case if posix_locking_close_file()
         * has been called first, but it never hurts to be *sure*.
         */

        for (i = 0; i < count; i++) {
                if (entries[i].fd != fsp->fd) {
                        locks_on_other_fds = True;
                        break;
                }
        }

        if (locks_on_other_fds) {

                /*
                 * There are outstanding locks on this dev/inode pair on other fds.
                 * Add our fd to the pending close tdb and set fsp->fd to -1.
                 */

                if (!add_fd_to_close_entry(fsp)) {
                        free((char *)entries);
                        return False;
                }

                free((char *)entries);
                fsp->fd = -1;
                return 0;
        }

        if(entries)
                free((char *)entries);

        /*
         * No outstanding POSIX locks. Get the pending close fd's
         * from the tdb and close them all.
         */

        count = get_posix_pending_close_entries(fsp, &fd_array);

        if (count) {
                DEBUG(10,("fd_close_posix: doing close on %u fd's.\n", (unsigned int)count ));

                for(i = 0; i < count; i++) {
                        if (conn->vfs_ops.close(fsp,fd_array[i]) == -1) {
                                saved_errno = errno;
                        }
                }

                /*
                 * Delete all fd's stored in the tdb
                 * for this dev/inode pair.
                 */

                delete_close_entries(fsp);
        }

        if (fd_array)
                free((char *)fd_array);

        /*
         * Finally close the fd associated with this fsp.
         */

        ret = conn->vfs_ops.close(fsp,fsp->fd);

        if (saved_errno != 0) {
        errno = saved_errno;
                ret = -1;
    } 

        fsp->fd = -1;

        return ret;
}

/****************************************************************************
 Debugging aid :-).
****************************************************************************/

static const char *posix_lock_type_name(int lock_type)
{
        return (lock_type == F_RDLCK) ? "READ" : "WRITE";
}

/****************************************************************************
 Delete a POSIX lock entry by index number. Used if the tdb add succeeds, but
 then the POSIX fcntl lock fails.
****************************************************************************/

static BOOL delete_posix_lock_entry_by_index(files_struct *fsp, size_t entry)
{
        TDB_DATA kbuf = locking_key_fsp(fsp);
        TDB_DATA dbuf;
        struct posix_lock *locks;
        size_t count;

        dbuf.dptr = NULL;
        
        dbuf = tdb_fetch(posix_lock_tdb, kbuf);

        if (!dbuf.dptr) {
                DEBUG(10,("delete_posix_lock_entry_by_index: tdb_fetch failed !\n"));
                goto fail;
        }

        count = (size_t)(dbuf.dsize / sizeof(struct posix_lock));
        locks = (struct posix_lock *)dbuf.dptr;

        if (count == 1) {
                tdb_delete(posix_lock_tdb, kbuf);
        } else {
                if (entry < count-1) {
                        memmove(&locks[entry], &locks[entry+1], sizeof(*locks)*((count-1) - entry));
                }
                dbuf.dsize -= sizeof(*locks);
                tdb_store(posix_lock_tdb, kbuf, dbuf, TDB_REPLACE);
        }

        free(dbuf.dptr);

        return True;

 fail:
    if (dbuf.dptr)
                free(dbuf.dptr);
    return False;
}

/****************************************************************************
 Add an entry into the POSIX locking tdb. We return the index number of the
 added lock (used in case we need to delete *exactly* this entry). Returns
 False on fail, True on success.
****************************************************************************/

static BOOL add_posix_lock_entry(files_struct *fsp, SMB_OFF_T start, SMB_OFF_T size, int lock_type, size_t *pentry_num)
{
        TDB_DATA kbuf = locking_key_fsp(fsp);
        TDB_DATA dbuf;
        struct posix_lock pl;
        char *tp;

        dbuf.dptr = NULL;

        dbuf = tdb_fetch(posix_lock_tdb, kbuf);

        *pentry_num = (size_t)(dbuf.dsize / sizeof(pl));

        /*
         * Add new record.
         */

        pl.fd = fsp->fd;
        pl.start = start;
        pl.size = size;
        pl.lock_type = lock_type;

        tp = Realloc(dbuf.dptr, dbuf.dsize + sizeof(pl));
        if (!tp) {
                DEBUG(0,("add_posix_lock_entry: Realloc fail !\n"));
                goto fail;
        }
        else dbuf.dptr = tp;

        memcpy(dbuf.dptr + dbuf.dsize, &pl, sizeof(pl));
        dbuf.dsize += sizeof(pl);

        if (tdb_store(posix_lock_tdb, kbuf, dbuf, TDB_REPLACE) == -1) {
                DEBUG(0,("add_posix_lock: Failed to add lock entry on file %s\n", fsp->fsp_name));
                goto fail;
        }

    free(dbuf.dptr);

        DEBUG(10,("add_posix_lock: File %s: type = %s: start=%.0f size=%.0f: dev=%.0f inode=%.0f\n",
                        fsp->fsp_name, posix_lock_type_name(lock_type), (double)start, (double)size,
                        (double)fsp->dev, (double)fsp->inode ));

    return True;

 fail:
    if (dbuf.dptr)
                free(dbuf.dptr);
    return False;
}

/****************************************************************************
 Calculate if locks have any overlap at all.
****************************************************************************/

static BOOL does_lock_overlap(SMB_OFF_T start1, SMB_OFF_T size1, SMB_OFF_T start2, SMB_OFF_T size2)
{
        if (start1 >= start2 && start1 <= start2 + size2)
                return True;

        if (start1 < start2 && start1 + size1 > start2)
                return True;

        return False;
}

/****************************************************************************
 Delete an entry from the POSIX locking tdb. Returns a copy of the entry being
 deleted and the number of records that are overlapped by this one, or -1 on error.
****************************************************************************/

static int delete_posix_lock_entry(files_struct *fsp, SMB_OFF_T start, SMB_OFF_T size, struct posix_lock *pl)
{
        TDB_DATA kbuf = locking_key_fsp(fsp);
        TDB_DATA dbuf;
        struct posix_lock *locks;
        size_t i, count;
        BOOL found = False;
        int num_overlapping_records = 0;

        dbuf.dptr = NULL;
        
        dbuf = tdb_fetch(posix_lock_tdb, kbuf);

        if (!dbuf.dptr) {
                DEBUG(10,("delete_posix_lock_entry: tdb_fetch failed !\n"));
                goto fail;
        }

        /* There are existing locks - find a match. */
        locks = (struct posix_lock *)dbuf.dptr;
        count = (size_t)(dbuf.dsize / sizeof(*locks));

        /*
         * Search for and delete the first record that matches the
         * unlock criteria.
         */

        for (i=0; i<count; i++) { 
                struct posix_lock *entry = &locks[i];

                if (entry->fd == fsp->fd &&
                        entry->start == start &&
                        entry->size == size) {

                        /* Make a copy if requested. */
                        if (pl)
                                *pl = *entry;

                        /* Found it - delete it. */
                        if (count == 1) {
                                tdb_delete(posix_lock_tdb, kbuf);
                        } else {
                                if (i < count-1) {
                                        memmove(&locks[i], &locks[i+1], sizeof(*locks)*((count-1) - i));
                                }
                                dbuf.dsize -= sizeof(*locks);
                                tdb_store(posix_lock_tdb, kbuf, dbuf, TDB_REPLACE);
                        }
                        count--;
                        found = True;
                        break;
                }
        }

        if (!found)
                goto fail;

        /*
         * Count the number of entries that are
         * overlapped by this unlock request.
         */

        for (i = 0; i < count; i++) {
                struct posix_lock *entry = &locks[i];

                if (fsp->fd == entry->fd &&
                        does_lock_overlap( start, size, entry->start, entry->size))
                                num_overlapping_records++;
        }

        DEBUG(10,("delete_posix_lock_entry: type = %s: start=%.0f size=%.0f, num_records = %d\n",
                        posix_lock_type_name(pl->lock_type), (double)pl->start, (double)pl->size,
                                (unsigned int)num_overlapping_records ));

    if (dbuf.dptr)
                free(dbuf.dptr);

        return num_overlapping_records;

 fail:
    if (dbuf.dptr)
                free(dbuf.dptr);
    return -1;
}

/****************************************************************************
 Utility function to map a lock type correctly depending on the open
 mode of a file.
****************************************************************************/

static int map_posix_lock_type( files_struct *fsp, enum brl_type lock_type)
{
        if((lock_type == WRITE_LOCK) && !fsp->can_write) {
                /*
                 * Many UNIX's cannot get a write lock on a file opened read-only.
                 * Win32 locking semantics allow this.
                 * Do the best we can and attempt a read-only lock.
                 */
                DEBUG(10,("map_posix_lock_type: Downgrading write lock to read due to read-only file.\n"));
                return F_RDLCK;
        } else if((lock_type == READ_LOCK) && !fsp->can_read) {
                /*
                 * Ditto for read locks on write only files.
                 */
                DEBUG(10,("map_posix_lock_type: Changing read lock to write due to write-only file.\n"));
                return F_WRLCK;
        }

  /*
   * This return should be the most normal, as we attempt
   * to always open files read/write.
   */

  return (lock_type == READ_LOCK) ? F_RDLCK : F_WRLCK;
}

/****************************************************************************
 Check to see if the given unsigned lock range is within the possible POSIX
 range. Modifies the given args to be in range if possible, just returns
 False if not.
****************************************************************************/

static BOOL posix_lock_in_range(SMB_OFF_T *offset_out, SMB_OFF_T *count_out,
                                                                SMB_BIG_UINT u_offset, SMB_BIG_UINT u_count)
{
        SMB_OFF_T offset = (SMB_OFF_T)u_offset;
        SMB_OFF_T count = (SMB_OFF_T)u_count;

        /*
         * For the type of system we are, attempt to
         * find the maximum positive lock offset as an SMB_OFF_T.
         */

#if defined(LARGE_SMB_OFF_T) && !defined(HAVE_BROKEN_FCNTL64_LOCKS)

        /*
         * In this case SMB_OFF_T is 64 bits,
         * and the underlying system can handle 64 bit signed locks.
         */

    SMB_OFF_T mask2 = ((SMB_OFF_T)0x4) << (SMB_OFF_T_BITS-4);
    SMB_OFF_T mask = (mask2<<1);
    SMB_OFF_T max_positive_lock_offset = ~mask;

#else /* !LARGE_SMB_OFF_T || HAVE_BROKEN_FCNTL64_LOCKS */

        /*
         * In this case either SMB_OFF_T is 32 bits,
         * or the underlying system cannot handle 64 bit signed locks.
         * All offsets & counts must be 2^31 or less.
         */

    SMB_OFF_T max_positive_lock_offset = 0x7FFFFFFF;

#endif /* !LARGE_SMB_OFF_T || HAVE_BROKEN_FCNTL64_LOCKS */

        /*
         * If the given offset was > max_positive_lock_offset then we cannot map this at all
         * ignore this lock.
         */

        if (u_offset & ~((SMB_BIG_UINT)max_positive_lock_offset)) {
                DEBUG(10,("posix_lock_in_range: (offset = %.0f) offset > %.0f and we cannot handle this. Ignoring lock.\n",
                                (double)u_offset, (double)((SMB_BIG_UINT)max_positive_lock_offset) ));
                return False;
        }

        /*
         * We must truncate the offset and count to less than max_positive_lock_offset.
         */

        offset &= max_positive_lock_offset;
        count &= max_positive_lock_offset;


        /*
         * Deal with a very common case of count of all ones.
         * (lock entire file).
         */

        if(count == (SMB_OFF_T)-1)
                count = max_positive_lock_offset;

        /*
         * Truncate count to end at max lock offset.
         */

        if (offset + count < 0 || offset + count > max_positive_lock_offset)
                count = max_positive_lock_offset - offset;

        /*
         * If we ate all the count, ignore this lock.
         */

        if (count == 0) {
                DEBUG(10,("posix_lock_in_range: Count = 0. Ignoring lock u_offset = %.0f, u_count = %.0f\n",
                                (double)u_offset, (double)u_count ));
                return False;
        }

        /*
         * The mapping was successful.
         */

        DEBUG(10,("posix_lock_in_range: offset_out = %.0f, count_out = %.0f\n",
                        (double)offset, (double)count ));

        *offset_out = offset;
        *count_out = count;
        
        return True;
}

/****************************************************************************
 Pathetically try and map a 64 bit lock offset into 31 bits. I hate Windows :-).
****************************************************************************/

uint32 map_lock_offset(uint32 high, uint32 low)
{
        unsigned int i;
        uint32 mask = 0;
        uint32 highcopy = high;

        /*
         * Try and find out how many significant bits there are in high.
         */

        for(i = 0; highcopy; i++)
                highcopy >>= 1;

        /*
         * We use 31 bits not 32 here as POSIX
         * lock offsets may not be negative.
         */

        mask = (~0) << (31 - i);

        if(low & mask)
                return 0; /* Fail. */

        high <<= (31 - i);

        return (high|low);
}

/****************************************************************************
 Actual function that does POSIX locks. Copes with 64 -> 32 bit cruft and
 broken NFS implementations.
****************************************************************************/

static BOOL posix_fcntl_lock(files_struct *fsp, int op, SMB_OFF_T offset, SMB_OFF_T count, int type)
{
        int ret;
        struct connection_struct *conn = fsp->conn;

#if defined(LARGE_SMB_OFF_T)
        /*
         * In the 64 bit locking case we store the original
         * values in case we have to map to a 32 bit lock on
         * a filesystem that doesn't support 64 bit locks.
         */
        SMB_OFF_T orig_offset = offset;
        SMB_OFF_T orig_count = count;
#endif /* LARGE_SMB_OFF_T */

        DEBUG(8,("posix_fcntl_lock %d %d %.0f %.0f %d\n",fsp->fd,op,(double)offset,(double)count,type));

        ret = conn->vfs_ops.lock(fsp,fsp->fd,op,offset,count,type);

        if (!ret && (errno == EFBIG)) {
                if( DEBUGLVL( 0 )) {
                        dbgtext("posix_fcntl_lock: WARNING: lock request at offset %.0f, length %.0f returned\n", (double)offset,(double)count);
                        dbgtext("a 'file too large' error. This can happen when using 64 bit lock offsets\n");
                        dbgtext("on 32 bit NFS mounted file systems. Retrying with 32 bit truncated length.\n");
                }
                /* 32 bit NFS file system, retry with smaller offset */
                errno = 0;
                count &= 0x7fffffff;
                ret = conn->vfs_ops.lock(fsp,fsp->fd,op,offset,count,type);
        }

        /* A lock query - just return. */
        if (op == SMB_F_GETLK)
                return ret;

        /* A lock set or unset. */
        if (!ret) {
                DEBUG(3,("posix_fcntl_lock: lock failed at offset %.0f count %.0f op %d type %d (%s)\n",
                                (double)offset,(double)count,op,type,strerror(errno)));

                /* Perhaps it doesn't support this sort of locking ? */
                if (errno == EINVAL) {
#if defined(LARGE_SMB_OFF_T)
                        {
                                /*
                                 * Ok - if we get here then we have a 64 bit lock request
                                 * that has returned EINVAL. Try and map to 31 bits for offset
                                 * and length and try again. This may happen if a filesystem
                                 * doesn't support 64 bit offsets (efs/ufs) although the underlying
                                 * OS does.
                                 */
                                uint32 off_low = (orig_offset & 0xFFFFFFFF);
                                uint32 off_high = ((orig_offset >> 32) & 0xFFFFFFFF);

                                count = (orig_count & 0x7FFFFFFF);
                                offset = (SMB_OFF_T)map_lock_offset(off_high, off_low);
                                ret = conn->vfs_ops.lock(fsp,fsp->fd,op,offset,count,type);
                                if (!ret) {
                                        if (errno == EINVAL) {
                                                DEBUG(3,("posix_fcntl_lock: locking not supported? returning True\n"));
                                                return(True);
                                        }
                                        return False;
                                }
                                DEBUG(3,("posix_fcntl_lock: 64 -> 32 bit modified lock call successful\n"));
                                return True;
                        }
#else /* LARGE_SMB_OFF_T */
                        DEBUG(3,("locking not supported? returning True\n"));
                        return(True);
#endif /* LARGE_SMB_OFF_T */
                }

                return(False);
        }

        DEBUG(8,("posix_fcntl_lock: Lock call successful\n"));

        return(True);
}

/****************************************************************************
 POSIX function to see if a file region is locked. Returns True if the
 region is locked, False otherwise.
****************************************************************************/

BOOL is_posix_locked(files_struct *fsp, SMB_BIG_UINT u_offset, SMB_BIG_UINT u_count, enum brl_type lock_type)
{
        SMB_OFF_T offset;
        SMB_OFF_T count;
        int posix_lock_type = map_posix_lock_type(fsp,lock_type);

        DEBUG(10,("is_posix_locked: File %s, offset = %.0f, count = %.0f, type = %s\n",
                        fsp->fsp_name, (double)u_offset, (double)u_count, posix_lock_type_name(lock_type) ));

        /*
         * If the requested lock won't fit in the POSIX range, we will
         * never set it, so presume it is not locked.
         */

        if(!posix_lock_in_range(&offset, &count, u_offset, u_count))
                return False;

        /*
         * Note that most UNIX's can *test* for a write lock on
         * a read-only fd, just not *set* a write lock on a read-only
         * fd. So we don't need to use map_lock_type here.
         */ 

        return posix_fcntl_lock(fsp,SMB_F_GETLK,offset,count,posix_lock_type);
}

/*
 * Structure used when splitting a lock range
 * into a POSIX lock range. Doubly linked list.
 */

struct lock_list {
    struct lock_list *next;
    struct lock_list *prev;
    SMB_OFF_T start;
    SMB_OFF_T size;
};

/****************************************************************************
 Create a list of lock ranges that don't overlap a given range. Used in calculating
 POSIX locks and unlocks. This is a difficult function that requires ASCII art to
 understand it :-).
****************************************************************************/

static struct lock_list *posix_lock_list(TALLOC_CTX *ctx, struct lock_list *lhead, files_struct *fsp)
{
        TDB_DATA kbuf = locking_key_fsp(fsp);
        TDB_DATA dbuf;
        struct posix_lock *locks;
        size_t num_locks, i;

        dbuf.dptr = NULL;

        dbuf = tdb_fetch(posix_lock_tdb, kbuf);

        if (!dbuf.dptr)
                return lhead;
        
        locks = (struct posix_lock *)dbuf.dptr;
        num_locks = (size_t)(dbuf.dsize / sizeof(*locks));

        /*
         * Check the current lock list on this dev/inode pair.
         * Quit if the list is deleted.
         */

        DEBUG(10,("posix_lock_list: curr: start=%.0f,size=%.0f\n",
                (double)lhead->start, (double)lhead->size ));

        for (i=0; i<num_locks && lhead; i++) {

                struct posix_lock *lock = &locks[i];
                struct lock_list *l_curr;

                /*
                 * Walk the lock list, checking for overlaps. Note that
                 * the lock list can expand within this loop if the current
                 * range being examined needs to be split.
                 */

                for (l_curr = lhead; l_curr;) {

                        DEBUG(10,("posix_lock_list: lock: fd=%d: start=%.0f,size=%.0f:type=%s", lock->fd,
                                (double)lock->start, (double)lock->size, posix_lock_type_name(lock->lock_type) ));

                        if ( (l_curr->start >= (lock->start + lock->size)) ||
                                 (lock->start >= (l_curr->start + l_curr->size))) {

                                /* No overlap with this lock - leave this range alone. */
/*********************************************
                                             +---------+
                                             | l_curr  |
                                             +---------+
                                +-------+
                                | lock  |
                                +-------+
OR....
             +---------+
             |  l_curr |
             +---------+
**********************************************/

                                DEBUG(10,("no overlap case.\n" ));

                                l_curr = l_curr->next;

                        } else if ( (l_curr->start >= lock->start) &&
                                                (l_curr->start + l_curr->size <= lock->start + lock->size) ) {

                                /*
                                 * This unlock is completely overlapped by this existing lock range
                                 * and thus should have no effect (not be unlocked). Delete it from the list.
                                 */
/*********************************************
                +---------+
                |  l_curr |
                +---------+
        +---------------------------+
        |       lock                |
        +---------------------------+
**********************************************/
                                /* Save the next pointer */
                                struct lock_list *ul_next = l_curr->next;

                                DEBUG(10,("delete case.\n" ));

                                DLIST_REMOVE(lhead, l_curr);
                                if(lhead == NULL)
                                        break; /* No more list... */

                                l_curr = ul_next;
                                
                        } else if ( (l_curr->start >= lock->start) &&
                                                (l_curr->start < lock->start + lock->size) &&
                                                (l_curr->start + l_curr->size > lock->start + lock->size) ) {

                                /*
                                 * This unlock overlaps the existing lock range at the high end.
                                 * Truncate by moving start to existing range end and reducing size.
                                 */
/*********************************************
                +---------------+
                |  l_curr       |
                +---------------+
        +---------------+
        |    lock       |
        +---------------+
BECOMES....
                        +-------+
                        | l_curr|
                        +-------+
**********************************************/

                                l_curr->size = (l_curr->start + l_curr->size) - (lock->start + lock->size);
                                l_curr->start = lock->start + lock->size;

                                DEBUG(10,("truncate high case: start=%.0f,size=%.0f\n",
                                                                (double)l_curr->start, (double)l_curr->size ));

                                l_curr = l_curr->next;

                        } else if ( (l_curr->start < lock->start) &&
                                                (l_curr->start + l_curr->size > lock->start) &&
                                                (l_curr->start + l_curr->size <= lock->start + lock->size) ) {

                                /*
                                 * This unlock overlaps the existing lock range at the low end.
                                 * Truncate by reducing size.
                                 */
/*********************************************
   +---------------+
   |  l_curr       |
   +---------------+
           +---------------+
           |    lock       |
           +---------------+
BECOMES....
   +-------+
   | l_curr|
   +-------+
**********************************************/

                                l_curr->size = lock->start - l_curr->start;

                                DEBUG(10,("truncate low case: start=%.0f,size=%.0f\n",
                                                                (double)l_curr->start, (double)l_curr->size ));

                                l_curr = l_curr->next;
                
                        } else if ( (l_curr->start < lock->start) &&
                                                (l_curr->start + l_curr->size > lock->start + lock->size) ) {
                                /*
                                 * Worst case scenario. Unlock request completely overlaps an existing
                                 * lock range. Split the request into two, push the new (upper) request
                                 * into the dlink list, and continue with the entry after ul_new (as we
                                 * know that ul_new will not overlap with this lock).
                                 */
/*********************************************
        +---------------------------+
        |        l_curr             |
        +---------------------------+
                +---------+
                | lock    |
                +---------+
BECOMES.....
        +-------+         +---------+
        | l_curr|         | l_new   |
        +-------+         +---------+
**********************************************/
                                struct lock_list *l_new = (struct lock_list *)talloc(ctx,
                                                                                                        sizeof(struct lock_list));

                                if(l_new == NULL) {
                                        DEBUG(0,("posix_lock_list: talloc fail.\n"));
                                        return NULL; /* The talloc_destroy takes care of cleanup. */
                                }

                                ZERO_STRUCTP(l_new);
                                l_new->start = lock->start + lock->size;
                                l_new->size = l_curr->start + l_curr->size - l_new->start;

                                /* Truncate the l_curr. */
                                l_curr->size = lock->start - l_curr->start;

                                DEBUG(10,("split case: curr: start=%.0f,size=%.0f \
new: start=%.0f,size=%.0f\n", (double)l_curr->start, (double)l_curr->size,
                                                                (double)l_new->start, (double)l_new->size ));

                                /*
                                 * Add into the dlink list after the l_curr point - NOT at lhead. 
                                 * Note we can't use DLINK_ADD here as this inserts at the head of the given list.
                                 */

                                l_new->prev = l_curr;
                                l_new->next = l_curr->next;
                                l_curr->next = l_new;

                                /* And move after the link we added. */
                                l_curr = l_new->next;

                        } else {

                                /*
                                 * This logic case should never happen. Ensure this is the
                                 * case by forcing an abort.... Remove in production.
                                 */
                                pstring msg;

                                slprintf(msg, sizeof(msg)-1, "logic flaw in cases: l_curr: start = %.0f, size = %.0f : \
lock: start = %.0f, size = %.0f\n", (double)l_curr->start, (double)l_curr->size, (double)lock->start, (double)lock->size );

                                smb_panic(msg);
                        }
                } /* end for ( l_curr = lhead; l_curr;) */
        } /* end for (i=0; i<num_locks && ul_head; i++) */

        if (dbuf.dptr)
                free(dbuf.dptr);
        
        return lhead;
}

/****************************************************************************
 POSIX function to acquire a lock. Returns True if the
 lock could be granted, False if not.
****************************************************************************/

BOOL set_posix_lock(files_struct *fsp, SMB_BIG_UINT u_offset, SMB_BIG_UINT u_count, enum brl_type lock_type)
{
        SMB_OFF_T offset;
        SMB_OFF_T count;
        BOOL ret = True;
        size_t entry_num = 0;
        size_t lock_count;
        TALLOC_CTX *l_ctx = NULL;
        struct lock_list *llist = NULL;
        struct lock_list *ll = NULL;
        int posix_lock_type = map_posix_lock_type(fsp,lock_type);

        DEBUG(5,("set_posix_lock: File %s, offset = %.0f, count = %.0f, type = %s\n",
                        fsp->fsp_name, (double)u_offset, (double)u_count, posix_lock_type_name(lock_type) ));

        /*
         * If the requested lock won't fit in the POSIX range, we will
         * pretend it was successful.
         */

        if(!posix_lock_in_range(&offset, &count, u_offset, u_count))
                return True;

        /*
         * Windows is very strange. It allows read locks to be overlayed
         * (even over a write lock), but leaves the write lock in force until the first
         * unlock. It also reference counts the locks. This means the following sequence :
         *
         * process1                                      process2
         * ------------------------------------------------------------------------
         * WRITE LOCK : start = 2, len = 10
         *                                            READ LOCK: start =0, len = 10 - FAIL
         * READ LOCK : start = 0, len = 14 
         *                                            READ LOCK: start =0, len = 10 - FAIL
         * UNLOCK : start = 2, len = 10
         *                                            READ LOCK: start =0, len = 10 - OK
         *
         * Under POSIX, the same sequence in steps 1 and 2 would not be reference counted, but
         * would leave a single read lock over the 0-14 region. In order to
         * re-create Windows semantics mapped to POSIX locks, we create multiple TDB
         * entries, one for each overlayed lock request. We are guarenteed by the brlock
         * semantics that if a write lock is added, then it will be first in the array.
         */
        
        if ((l_ctx = talloc_init()) == NULL) {
                DEBUG(0,("set_posix_lock: unable to init talloc context.\n"));
                return True; /* Not a fatal error. */
        }

        if ((ll = (struct lock_list *)talloc(l_ctx, sizeof(struct lock_list))) == NULL) {
                DEBUG(0,("set_posix_lock: unable to talloc unlock list.\n"));
                talloc_destroy(l_ctx);
                return True; /* Not a fatal error. */
        }

        /*
         * Create the initial list entry containing the
         * lock we want to add.
         */

        ZERO_STRUCTP(ll);
        ll->start = offset;
        ll->size = count;

        DLIST_ADD(llist, ll);

        /*
         * The following call calculates if there are any
         * overlapping locks held by this process on
         * fd's open on the same file and splits this list
         * into a list of lock ranges that do not overlap with existing
         * POSIX locks.
         */

        llist = posix_lock_list(l_ctx, llist, fsp);

        /*
         * Now we have the list of ranges to lock it is safe to add the
         * entry into the POSIX lock tdb. We take note of the entry we
         * added here in case we have to remove it on POSIX lock fail.
         */

        if (!add_posix_lock_entry(fsp,offset,count,posix_lock_type,&entry_num)) {
                DEBUG(0,("set_posix_lock: Unable to create posix lock entry !\n"));
                talloc_destroy(l_ctx);
                return False;
        }

        /*
         * Add the POSIX locks on the list of ranges returned.
         * As the lock is supposed to be added atomically, we need to
         * back out all the locks if any one of these calls fail.
         */

        for (lock_count = 0, ll = llist; ll; ll = ll->next, lock_count++) {
                offset = ll->start;
                count = ll->size;

                DEBUG(5,("set_posix_lock: Real lock: Type = %s: offset = %.0f, count = %.0f\n",
                        posix_lock_type_name(posix_lock_type), (double)offset, (double)count ));

                if (!posix_fcntl_lock(fsp,SMB_F_SETLK,offset,count,posix_lock_type)) {
                        DEBUG(5,("set_posix_lock: Lock fail !: Type = %s: offset = %.0f, count = %.0f. Errno = %s\n",
                                posix_lock_type_name(posix_lock_type), (double)offset, (double)count, strerror(errno) ));
                        ret = False;
                        break;
                }
        }

        if (!ret) {

                /*
                 * Back out all the POSIX locks we have on fail.
                 */

                for (ll = llist; lock_count; ll = ll->next, lock_count--) {
                        offset = ll->start;
                        count = ll->size;

                        DEBUG(5,("set_posix_lock: Backing out locks: Type = %s: offset = %.0f, count = %.0f\n",
                                posix_lock_type_name(posix_lock_type), (double)offset, (double)count ));

                        posix_fcntl_lock(fsp,SMB_F_SETLK,offset,count,F_UNLCK);
                }

                /*
                 * Remove the tdb entry for this lock.
                 */

                delete_posix_lock_entry_by_index(fsp,entry_num);
        }

        talloc_destroy(l_ctx);
        return ret;
}

/****************************************************************************
 POSIX function to release a lock. Returns True if the
 lock could be released, False if not.
****************************************************************************/

BOOL release_posix_lock(files_struct *fsp, SMB_BIG_UINT u_offset, SMB_BIG_UINT u_count)
{
        SMB_OFF_T offset;
        SMB_OFF_T count;
        BOOL ret = True;
        TALLOC_CTX *ul_ctx = NULL;
        struct lock_list *ulist = NULL;
        struct lock_list *ul = NULL;
        struct posix_lock deleted_lock;
        int num_overlapped_entries;

        DEBUG(5,("release_posix_lock: File %s, offset = %.0f, count = %.0f\n",
                fsp->fsp_name, (double)u_offset, (double)u_count ));

        /*
         * If the requested lock won't fit in the POSIX range, we will
         * pretend it was successful.
         */

        if(!posix_lock_in_range(&offset, &count, u_offset, u_count))
                return True;

        /*
         * We treat this as one unlock request for POSIX accounting purposes even
         * if it may later be split into multiple smaller POSIX unlock ranges.
         * num_overlapped_entries is the number of existing locks that have any
         * overlap with this unlock request.
         */ 

        num_overlapped_entries = delete_posix_lock_entry(fsp, offset, count, &deleted_lock);

        if (num_overlapped_entries == -1) {
        smb_panic("release_posix_lock: unable find entry to delete !\n");
        }

        /*
         * If num_overlapped_entries is > 0, and the lock_type we just deleted from the tdb was
         * a POSIX write lock, then before doing the unlock we need to downgrade
         * the POSIX lock to a read lock. This allows any overlapping read locks
         * to be atomically maintained.
         */

        if (num_overlapped_entries > 0 && deleted_lock.lock_type == F_WRLCK) {
                if (!posix_fcntl_lock(fsp,SMB_F_SETLK,offset,count,F_RDLCK)) {
                        DEBUG(0,("release_posix_lock: downgrade of lock failed with error %s !\n", strerror(errno) ));
                        return False;
                }
        }

        if ((ul_ctx = talloc_init()) == NULL) {
                DEBUG(0,("release_posix_lock: unable to init talloc context.\n"));
                return True; /* Not a fatal error. */
        }

        if ((ul = (struct lock_list *)talloc(ul_ctx, sizeof(struct lock_list))) == NULL) {
                DEBUG(0,("release_posix_lock: unable to talloc unlock list.\n"));
                talloc_destroy(ul_ctx);
                return True; /* Not a fatal error. */
        }

        /*
         * Create the initial list entry containing the
         * lock we want to remove.
         */

        ZERO_STRUCTP(ul);
        ul->start = offset;
        ul->size = count;

        DLIST_ADD(ulist, ul);

        /*
         * The following call calculates if there are any
         * overlapping locks held by this process on
         * fd's open on the same file and creates a
         * list of unlock ranges that will allow
         * POSIX lock ranges to remain on the file whilst the
         * unlocks are performed.
         */

        ulist = posix_lock_list(ul_ctx, ulist, fsp);

        /*
         * Release the POSIX locks on the list of ranges returned.
         */

        for(; ulist; ulist = ulist->next) {
                offset = ulist->start;
                count = ulist->size;

                DEBUG(5,("release_posix_lock: Real unlock: offset = %.0f, count = %.0f\n",
                        (double)offset, (double)count ));

                if (!posix_fcntl_lock(fsp,SMB_F_SETLK,offset,count,F_UNLCK))
                        ret = False;
        }

        talloc_destroy(ul_ctx);

        return ret;
}

/****************************************************************************
 Remove all lock entries for a specific dev/inode pair from the tdb.
****************************************************************************/

static void delete_posix_lock_entries(files_struct *fsp)
{
        TDB_DATA kbuf = locking_key_fsp(fsp);

        if (tdb_delete(posix_lock_tdb, kbuf) == -1)
                DEBUG(0,("delete_close_entries: tdb_delete fail !\n"));
}

/****************************************************************************
 Debug function.
****************************************************************************/

static void dump_entry(struct posix_lock *pl)
{
        DEBUG(10,("entry: start=%.0f, size=%.0f, type=%d, fd=%i\n",
                (double)pl->start, (double)pl->size, (int)pl->lock_type, pl->fd ));
}

/****************************************************************************
 Remove any locks on this fd. Called from file_close().
****************************************************************************/

void posix_locking_close_file(files_struct *fsp)
{
        struct posix_lock *entries = NULL;
        size_t count, i;

        /*
         * Optimization for the common case where we are the only
         * opener of a file. If all fd entries are our own, we don't
         * need to explicitly release all the locks via the POSIX functions,
         * we can just remove all the entries in the tdb and allow the
         * close to remove the real locks.
         */

        count = get_posix_lock_entries(fsp, &entries);

        if (count == 0) {
                DEBUG(10,("posix_locking_close_file: file %s has no outstanding locks.\n", fsp->fsp_name ));
                return;
        }

        for (i = 0; i < count; i++) {
                if (entries[i].fd != fsp->fd )
                        break;

                dump_entry(&entries[i]);
        }

        if (i == count) {
                /* All locks are ours. */
                DEBUG(10,("posix_locking_close_file: file %s has %u outstanding locks, but all on one fd.\n", 
                        fsp->fsp_name, (unsigned int)count ));
                free((char *)entries);
                delete_posix_lock_entries(fsp);
                return;
        }

        /*
         * Difficult case. We need to delete all our locks, whilst leaving
         * all other POSIX locks in place.
         */

        for (i = 0; i < count; i++) {
                struct posix_lock *pl = &entries[i];
                if (pl->fd == fsp->fd)
                        release_posix_lock(fsp, (SMB_BIG_UINT)pl->start, (SMB_BIG_UINT)pl->size );
        }
        free((char *)entries);
}

/*******************************************************************
 Create the in-memory POSIX lock databases.
********************************************************************/

BOOL posix_locking_init(int read_only)
{
        if (posix_lock_tdb && posix_pending_close_tdb)
                return True;
        
        if (!posix_lock_tdb)
                posix_lock_tdb = tdb_open_log(NULL, 0, TDB_INTERNAL,
                                          read_only?O_RDONLY:(O_RDWR|O_CREAT), 0644);
        if (!posix_lock_tdb) {
                DEBUG(0,("Failed to open POSIX byte range locking database.\n"));
                return False;
        }
        if (!posix_pending_close_tdb)
                posix_pending_close_tdb = tdb_open_log(NULL, 0, TDB_INTERNAL,
                                                   read_only?O_RDONLY:(O_RDWR|O_CREAT), 0644);
        if (!posix_pending_close_tdb) {
                DEBUG(0,("Failed to open POSIX pending close database.\n"));
                return False;
        }

        return True;
}

/*******************************************************************
 Delete the in-memory POSIX lock databases.
********************************************************************/

BOOL posix_locking_end(void)
{
    if (posix_lock_tdb && tdb_close(posix_lock_tdb) != 0)
                return False;
    if (posix_pending_close_tdb && tdb_close(posix_pending_close_tdb) != 0)
                return False;
        return True;
}