Date: Sun, 20 Nov 2011 17:51:00 +0000 From: Alexander Best <arundel@freebsd.org> To: Dieter BSD <dieterbsd@engineer.com> Cc: freebsd-hackers@freebsd.org Subject: Re: easy way to determine if a stream or fd is seekable Message-ID: <20111120175100.GA10240@freebsd.org> In-Reply-To: <20111120174025.233420@gmx.com> References: <20111120174025.233420@gmx.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Sun Nov 20 11, Dieter BSD wrote:
> > something like the following inside lseek() would take care of tape drives:
> >
> > if (S_ISCHR(sb.st_mode) || S_ISBLK(sb.st_mode)) {
> > if (ioctl(io->fd, FIODTYPE, &type) == -1)
> > err(1, "%s", io->name);
> >
> > if (type & D_TAPE)
> > return(EBADF)
> > }
>
> I'd suggest ENODEV ("Operation not supported by device") rather than
> EBADF ("Bad file descriptor").
>
> To do this correctly, we'd need some standard way to ask the
> device driver if the device can perform the seek or not.
this might be a bit of a problem, since those devices and drivers that don't
support seeking are mostly legacy tape drives. i don't think these drivers
are actively being maintained atm.
another issue are removable media. running the patched version of hexdump
(i posted a patch earlier today) shows that running fseeko() against /dev/cd0,
where no media is present, succeeds. with a media inserted however, /dev/cd0 is
very well capable of seeking.
cheers.
alex
>
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20111120175100.GA10240>