common/bsd/ftruncate.c

#ifndef LINT
static const char rcsid[] = "$Id: ftruncate.c,v 1.3 2005/04/27 18:16:45 sra Exp $";
#endif

/*! \file
 * \brief
 * ftruncate - set file size, BSD Style
 *
 * shortens or enlarges the file as neeeded
 * uses some undocumented locking call. It is known to work on SCO unix,
 * other vendors should try.
 * The #error directive prevents unsupported OSes
 */

#include "port_before.h"

#if defined(M_UNIX)
#define OWN_FTRUNCATE
#include <stdio.h>
#ifdef _XOPEN_SOURCE
#undef _XOPEN_SOURCE
#endif
#ifdef _POSIX_SOURCE
#undef _POSIX_SOURCE
#endif

#include <fcntl.h>

#include "port_after.h"

int
__ftruncate(int fd, long wantsize) {
    long cursize;

    /* determine current file size */
    if ((cursize = lseek(fd, 0L, 2)) == -1)
        return (-1);

    /* maybe lengthen... */
    if (cursize < wantsize) {
        if (lseek(fd, wantsize - 1, 0) == -1 ||
            write(fd, "", 1) == -1) {
            return (-1);
        }
        return (0);
    }

    /* maybe shorten... */
    if (wantsize < cursize) {
        struct flock fl;

        fl.l_whence = 0;
        fl.l_len = 0;
        fl.l_start = wantsize;
        fl.l_type = F_WRLCK;
        return (fcntl(fd, F_FREESP, &fl));
    }
    return (0);
}
#endif

#ifndef OWN_FTRUNCATE
int __bindcompat_ftruncate;
#endif