os_truncate.c

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 2004-2005
 *      Sleepycat Software.  All rights reserved.
 *
 * $Id: os_truncate.c,v 12.4 2005/10/12 17:57:33 bostic Exp $
 */

#include "db_config.h"

#include "db_int.h"

/*
 * __os_truncate --
 *      Truncate the file.
 */
int
__os_truncate(dbenv, fhp, pgno, pgsize)
        DB_ENV *dbenv;
        DB_FH *fhp;
        db_pgno_t pgno;
        u_int32_t pgsize;
{
        /* Yes, this really is how Microsoft have designed their API */
        union {
                __int64 bigint;
                struct {
                        unsigned long low;
                        long high;
                };
        } off;
        off_t offset;
        HANDLE dup_handle;
        int ret;

        ret = 0;
        offset = (off_t)pgsize * pgno;

        if (DB_GLOBAL(j_ftruncate) != NULL) {
                ret = DB_GLOBAL(j_ftruncate)(fhp->fd, offset);
                goto done;
        }

#ifdef HAVE_FILESYSTEM_NOTZERO
        /*
         * If the filesystem doesn't zero fill, it isn't safe to extend the
         * file, or we end up with junk blocks.  Just return in that case.
         */
        if (__os_fs_notzero()) {
                off_t stat_offset;
                u_int32_t mbytes, bytes;

                /* Stat the file. */
                if ((ret =
                    __os_ioinfo(dbenv, NULL, fhp, &mbytes, &bytes, NULL)) != 0)
                        return (ret);
                stat_offset = (off_t)mbytes * MEGABYTE + bytes;

                if (offset > stat_offset)
                        return (0);
        }
#endif

        /*
         * Windows doesn't provide truncate directly.  Instead, it has
         * SetEndOfFile, which truncates to the current position.  To
         * deal with that, we first duplicate the file handle, then
         * seek and set the end of file.  This is necessary to avoid
         * races with {Read,Write}File in other threads.
         */
        if (!DuplicateHandle(GetCurrentProcess(), fhp->handle,
            GetCurrentProcess(), &dup_handle, 0, FALSE,
            DUPLICATE_SAME_ACCESS)) {
                ret = __os_get_errno();
                goto done;
        }

        off.bigint = (__int64)pgsize * pgno;
        RETRY_CHK((SetFilePointer(dup_handle,
            off.low, &off.high, FILE_BEGIN) == INVALID_SET_FILE_POINTER &&
            GetLastError() != NO_ERROR) ||
            !SetEndOfFile(dup_handle), ret);

        if (!CloseHandle(dup_handle) && ret == 0)
                ret = __os_get_errno();

done:   if (ret != 0)
                __db_err(dbenv,
                    "ftruncate: %lu: %s", pgno * pgsize, strerror(ret));

        return (ret);
}

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