🚀 go-pugleaf

While reading article <1992Apr03.091904.19206@Logix.DE>, I noticed that
jpm@Logix.DE (Jan-Piet Mens) said the following:
 >The subject actually says it all. I need to simulate the BSD
 >calls ftruncate() and fchmod() in SYS5. I'm all out of ideas.
 >Can someone help ?

As far as ftruncate() goes, one from the vaults:

If you have the F_FREESP fcntl on your system (most releases of SVR3.2 do),
you can use the undocumented (in SVR3) F_FREESP command to write a version
of ftruncate():

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#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>

int
ftruncate(fd, length)
int     fd;     /* file descriptor */
off_t   length; /* length to set file to */
{
        extern  long    lseek();

        struct  flock   fl;
        struct  stat    filebuf;

        if (fstat(fd, &filebuf) < 0)
                return(-1);

        if (filebuf.st_size < length) {
                /* extend file length */

                if ((lseek(fd, (length - 1), SEEK_SET)) < 0)
                        return(-1);

                /* write a "0" byte */

                if ((write(fd, "", 1)) != 1)
                        return(-1);
        } else {
                /* truncate length */

                fl.l_whence = 0;
                fl.l_len = 0;
                fl.l_start = length;
                fl.l_type = F_WRLCK;    /* write lock on file space */

                /*
                 * This relies on the UNDOCUMENTED F_FREESP argument to
                 * fcntl(2), which truncates the file so that it ends at the
                 * position indicated by fl.l_start.
                 *
                 * Will minor miracles never cease?
                 */

		if (fcntl(fd, F_FREESP, &fl) < 0)
			return(-1);

        }

        return(0);
}
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