On Wed, Jun 25, 2008 at 12:59:32PM +0200, Matthias Koenig wrote:
> The new loop auto-destruct feature detaches automatically loop devices
> when no longer used. This means they are detached with the umount()
> call. But when we call umount with -d, del_loop is called and fails
> because the ioctl() returns ENXIO.

 ah, good catch. Thanks!

> We probably should ignore this error here.

 I think we could be smarter. We can try to detect autoclear
 loop devices. See the patch below.

 [I'm going to create a stable/v2.14 branch.]

    Karel


>From e84feaecfdf44a33ef9eccc5a56c8a6999466140 Mon Sep 17 00:00:00 2001
From: Karel Zak <kzak@redhat.com>
Date: Wed, 2 Jul 2008 14:26:51 +0200
Subject: [PATCH] umount: improve "-d" option for autoclear loops

The new loop auto-destruct feature detaches automatically loop devices
when no longer used. This means they are detached with the umount()
call. But when we call umount with -d, del_loop() is called and fails
because the ioctl() returns ENXIO. We have to check for autoclear
loop devices rather than blindly call del_loop().

Reported-by: Matthias Koenig <mkoenig@suse.de>
Signed-off-by: Karel Zak <kzak@redhat.com>
---
 mount/lomount.c |   23 +++++++++++++++++++++++
 mount/lomount.h |    1 +
 mount/umount.c  |   12 ++++++++++--
 3 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/mount/lomount.c b/mount/lomount.c
index c3ac68a..7937052 100644
--- a/mount/lomount.c
+++ b/mount/lomount.c
@@ -102,6 +102,29 @@ is_loop_used(int fd)
 	return ioctl (fd, LOOP_GET_STATUS, &li) == 0;
 }
 
+int
+is_loop_autoclear(const char *device)
+{
+	struct loop_info lo;
+	struct loop_info64 lo64;
+	int fd, rc = 0;
+
+	if ((fd = open(device, O_RDONLY)) < 0)
+		return 0;
+
+	if (ioctl(fd, LOOP_GET_STATUS64, &lo64) == 0) {
+		if (lo64.lo_flags & LO_FLAGS_AUTOCLEAR)
+			rc = 1;
+
+	} else if (ioctl(fd, LOOP_GET_STATUS, &lo) == 0) {
+		if (lo.lo_flags & LO_FLAGS_AUTOCLEAR)
+			rc = 1;
+	}
+
+	close(fd);
+	return rc;
+}
+
 static char *
 looplist_mk_devname(struct looplist *ll, int num)
 {
diff --git a/mount/lomount.h b/mount/lomount.h
index f332a70..59108d4 100644
--- a/mount/lomount.h
+++ b/mount/lomount.h
@@ -2,6 +2,7 @@ extern int set_loop(const char *, const char *, unsigned long long, unsigned lon
 		    const char *, int, int *);
 extern int del_loop(const char *);
 extern int is_loop_device(const char *);
+extern int is_loop_autoclear(const char *device);
 extern char * find_unused_loop_device(void);
 
 extern int loopfile_used_with(char *devname, const char *filename, unsigned long long offset);
diff --git a/mount/umount.c b/mount/umount.c
index 65c8622..b2bbdae 100644
--- a/mount/umount.c
+++ b/mount/umount.c
@@ -190,6 +190,7 @@ umount_one (const char *spec, const char *node, const char *type,
 	int res;
 	int status;
 	const char *loopdev;
+	int myloop = 0;
 
 	/* Special case for root.  As of 0.99pl10 we can (almost) unmount root;
 	   the kernel will remount it readonly so that we can carry on running
@@ -201,7 +202,7 @@ umount_one (const char *spec, const char *node, const char *type,
 		  || streq (node, "rootfs"));
 	if (isroot)
 		nomtab++;
-	
+
 	/*
 	 * Call umount.TYPE for types that require a separate umount program.
 	 * All such special things must occur isolated in the types string.
@@ -209,6 +210,13 @@ umount_one (const char *spec, const char *node, const char *type,
 	if (check_special_umountprog(spec, node, type, &status))
 		return status;
 
+	/*
+	 * Ignore the option "-d" for non-loop devices and loop devices with
+	 * LO_FLAGS_AUTOCLEAR flag.
+	 */
+	if (delloop && is_loop_device(spec) && !is_loop_autoclear(spec))
+		myloop = 1;
+
 	umnt_err = umnt_err2 = 0;
 	if (lazy) {
 		res = umount2 (node, MNT_DETACH);
@@ -310,7 +318,7 @@ umount_one (const char *spec, const char *node, const char *type,
 		}
 
 		/* Also free loop devices when -d flag is given */
-		if (delloop && is_loop_device(spec))
+		if (myloop)
 			loopdev = spec;
 	}
  gotloop: