os_seek.c

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1997-2005
 *      Sleepycat Software.  All rights reserved.
 *
 * $Id: os_seek.c,v 12.1 2005/06/16 20:23:30 bostic Exp $
 */

#include "db_config.h"

#include "db_int.h"

/*
 * __os_seek --
 *      Seek to a page/byte offset in the file.
 */
int
__os_seek(dbenv, fhp, pgsize, pageno, relative, isrewind, db_whence)
        DB_ENV *dbenv;
        DB_FH *fhp;
        u_int32_t pgsize;
        db_pgno_t pageno;
        u_int32_t relative;
        int isrewind;
        DB_OS_SEEK db_whence;
{
        /* Yes, this really is how Microsoft have designed their API */
        union {
                __int64 bigint;
                struct {
                        unsigned long low;
                        long high;
                };
        } offbytes;
        off_t offset;
        int ret, whence;
        DWORD from;

        offset = (off_t)pgsize * pageno + relative;
        if (isrewind)
                offset = -offset;

        if (DB_GLOBAL(j_seek) != NULL) {
                switch (db_whence) {
                case DB_OS_SEEK_CUR:
                        whence = SEEK_CUR;
                        break;
                case DB_OS_SEEK_END:
                        whence = SEEK_END;
                        break;
                case DB_OS_SEEK_SET:
                        whence = SEEK_SET;
                        break;
                default:
                        return (EINVAL);
                }

                ret = DB_GLOBAL(j_seek)(fhp->fd, offset, whence);
        } else {
                switch (db_whence) {
                case DB_OS_SEEK_CUR:
                        from = FILE_CURRENT;
                        break;
                case DB_OS_SEEK_END:
                        from = FILE_END;
                        break;
                case DB_OS_SEEK_SET:
                        from = FILE_BEGIN;
                        break;
                default:
                        return (EINVAL);
                }

                offbytes.bigint = offset;
                ret = (SetFilePointer(fhp->handle,
                    offbytes.low, &offbytes.high, from) == (DWORD) - 1) ?
                    __os_get_errno() : 0;
        }

        if (ret == 0) {
                fhp->pgsize = pgsize;
                fhp->pgno = pageno;
                fhp->offset = relative;
        } else {
                __db_err(dbenv, "seek: %lu %d %d: %s",
                    (u_long)pgsize * pageno + relative,
                    isrewind, db_whence, strerror(ret));
        }

        return (ret);
}

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