linux-kernel - Fwd: Bug#826328: util-linux: losetup -d disfunctional for cloop and similar loop-compatible block devices

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Message-ID: <20160608075040.GH14586@knopper.net>
Date:	Wed, 8 Jun 2016 09:50:40 +0200
From:	"Prof. Dipl.-Ing. Klaus Knopper" <knopper@...pper.net>
To:	linux-kernel@...r.kernel.org
Subject: Fwd: Bug#826328: util-linux: losetup -d disfunctional for cloop and
 similar loop-compatible block devices

Hello,

As recommended by the Debian package maintainer, I'm forwarding this as
upstream bug report to the kernel list.

Package: util-linux
Version: 2.28-5
Severity: normal
Tags: upstream

Losetup was able to setup compressed loopback (cloop) devices, which
have a similar ioctl API, until recently the code in sys-utils/losetup.c
and lib/loopdev.c was changed to only accept devices with loopbacks
major device id.

While attaching a file to a cloop device still works (no check here),
detaching with -d fails with error message:

losetup: /dev/cloop7: failed to use device: Success

The reason for this is:

---

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.

Using busybox losetup for now.

Suggestion: Remove the check for

		major(st.st_rdev) == LOOPDEV_MAJOR);

in is_loopdev() in lib/loopdev.c.

Regards
-Klaus Knopper