Re: losetup from 7.6.1 can't detach a cloop device

[Klaus Knopper <debian-knoppix@knopper.net>]

Hi,

Worse... Apparently, losetup has been deliberately changed by its
developer(s) to only execute the -d option for devices having the
loopback major block device id.

---

sys-utils/losetup.c:

case 'd':
	act = A_DELETE;
		if (!is_loopdev(optarg) ||
		    loopcxt_set_device(&lc, optarg))
			err(EXIT_FAILURE, _("%s: failed to use device"),
			optarg);
	break;

---

lib/loopdev.c:

int is_loopdev(const char *device)
{
	struct stat st;

	if (!device)
		return 0;

	return (stat(device, &st) == 0 &&
		S_ISBLK(st.st_mode) &&
		major(st.st_rdev) == LOOPDEV_MAJOR);
}

---

Because of this, losetup from util-linux no longer works for cloop
devices. I just filed a bug report, hoping the very strict checking can
be reconsidered for removal.

Use busybox losetup for now.

Regards
-Klaus

>    On 4 June 2016 at 15:53, Klaus Knopper <[1]debian-knoppix@knopper.net>
>    wrote:
> 
>      Hello hb,
>      On Sat, Jun 04, 2016 at 01:42:19PM +0200, hb wrote:
>      > In this example cx.iso was created with genisoimage and
>      create_compressed_fs
>      >
>      > # ls -l cx.iso
>      > -rw-r--r-- 1 root root 122052675 Jun  4 00:39 cx.iso
>      > #
>      > # losetup -V
>      > losetup from util-linux 2.27.1
>      > #
>      > # losetup -r /dev/cloop7 cx.iso
>      > losetup: cx.iso: Warning: file does not fit into a 512-byte sector;
>      the
>      > end of the file will be ignored.
>      > # losetup -d /dev/cloop7
>      > losetup: /dev/cloop7: failed to use device: Success
>      > #
>      >
>      > ... and cloop7 is still attached.
>      [...]
> 
>      I've seen this, and have been wondering about it, too. The new losetup
>      error message does not make much sense to me, it's probably supposed to
>      mean "file size is not aligned to sector size". I still don't see why
>      this should be a problem now, it has always worked in the past. And,
>      losetup failing to detach the file that it attached happily before, is
>      definitiely a bug, from my point of view.
> 
>      I'd recommend using busybox internal losetup command for now for
>      attaching and detaching cloop files manually.
> 
>      Detach:
>      sudo busybox losetup -d /dev/cloop7
> 
>      Attach:
>      sudo busybox losetup -r /dev/cloop7 cx.iso[.cloop]
> 
>      Knoppix only uses the busybox-internal losetup during startup and
>      shutdown, anyways.
> 
>      Regards
>      -Klaus