umount: allow unmounting loopdev specified by associated file

Make it possible to unmount a filesystem on a loop device if it is
specified by associated backing file. It does not attempt to unmount
anything if there are more than one loop device associated with the
given file.

Umount looks for associated loopdevice(s) only if umount is called
with the regular file as an argument.

Before:
	mount -o loop -t ext2 img mnt
	umount -v img
	> Could not find /home/puzel/upstream/util-linux/img in mtab
	> umount: img: not mounted

After:
	mount -o loop -t ext2 img mnt
	umount -v img
	> img is associated with /dev/loop0, trying to unmount it
	> /dev/loop0 has been unmounted

[kzak@redhat.com: - fix memory leak in lomount.c]

Addresses: https://bugzilla.novell.com/show_bug.cgi?id=666161
Signed-off-by: Petr Uzel <petr.uzel@suse.cz>
Signed-off-by: Karel Zak <kzak@redhat.com>

3 files changed, 76 insertions, 0 deletions

diff --git a/mount/lomount.c b/mount/lomount.c
index ceb321751..0bbcbc19d 100644
--- a/mount/lomount.c
+++ b/mount/lomount.c
@@ -403,6 +403,51 @@ done:
 	return -1;
 }
 
+/* Find loop device associated with given @filename. Used for unmounting loop
+ * device specified by associated backing file.
+ *
+ * returns: 1 no such device/error
+ *          2 more than one loop device associated with @filename
+ *          0 exactly one loop device associated with @filename
+ *            (@loopdev points to string containing full device name)
+ */
+int
+find_loopdev_by_backing_file(const char *filename, char **loopdev)
+{
+	struct looplist ll;
+	struct stat filestat;
+	int fd;
+	int devs_n = 0;		/* number of loop devices found */
+	char* devname = NULL;
+
+	if (stat(filename, &filestat) == -1) {
+		perror(filename);
+		return 1;
+	}
+
+	if (looplist_open(&ll, LLFLG_USEDONLY) == -1) {
+		error(_("%s: /dev directory does not exist."), progname);
+		return 1;
+	}
+
+	while((devs_n < 2) && (fd = looplist_next(&ll)) != -1) {
+		if (is_associated(fd, &filestat, 0, 0) == 1) {
+			if (!devname)
+				devname = xstrdup(ll.name);
+			devs_n++;
+		}
+		close(fd);
+	}
+	looplist_close(&ll);
+
+	if (devs_n == 1) {
+		*loopdev = devname;
+		return 0;		/* exactly one loopdev */
+	}
+	free(devname);
+	return devs_n ? 2 : 1;		/* more loopdevs or error */
+}
+
 #ifdef MAIN
 
 static int
@@ -565,6 +610,7 @@ show_associated_loop_devices(char *filename, unsigned long long offset, int isof
 	return 0;
 }
 
+
 #endif /* MAIN */
 
 /* check if the loopfile is already associated with the same given
@@ -946,6 +992,13 @@ find_unused_loop_device (void) {
 	return 0;
 }
 
+int
+find_loopdev_by_backing_file(const char *filename, char **loopdev)
+{
+	mutter();
+	return 1;
+}
+
 #endif /* !LOOP_SET_FD */
 
 #ifdef MAIN
diff --git a/mount/lomount.h b/mount/lomount.h
index de8b76bf4..4acc37185 100644
--- a/mount/lomount.h
+++ b/mount/lomount.h
@@ -11,6 +11,7 @@ extern char * find_unused_loop_device(void);
 extern int loopfile_used_with(char *devname, const char *filename, unsigned long long offset);
 extern char *loopfile_used (const char *filename, unsigned long long offset);
 extern char *loopdev_get_loopfile(const char *device);
+extern int find_loopdev_by_backing_file(const char *filename, char **loopdev);
 
 
 #define SETLOOP_RDONLY     (1<<0)  /* Open loop read-only */
diff --git a/mount/umount.c b/mount/umount.c
index 468fb6013..8ef342a52 100644
--- a/mount/umount.c
+++ b/mount/umount.c
@@ -502,6 +502,7 @@ umount_file (char *arg) {
 	const char *file, *options;
 	int fstab_has_user, fstab_has_users, fstab_has_owner, fstab_has_group;
 	int ok;
+	struct stat statbuf;
 
 	if (!*arg) {		/* "" would be expanded to `pwd` */
 		die(2, _("Cannot unmount \"\"\n"));
@@ -509,6 +510,27 @@ umount_file (char *arg) {
 	}
 
 	file = canonicalize(arg); /* mtab paths are canonicalized */
+
+	/* if file is a regular file, check if it is associated
+	 * with some loop device
+	 */
+	if (!stat(file, &statbuf) && S_ISREG(statbuf.st_mode)) {
+		char *loopdev = NULL;
+		switch (find_loopdev_by_backing_file(file, &loopdev)) {
+		case 0:
+			if (verbose)
+				printf(_("%s is associated with %s, trying to unmount it\n"),
+				       arg, loopdev);
+			file = loopdev;
+			break;
+		case 2:
+			if (verbose)
+				printf(_("%s is associated with more than one loop device: not unmounting\n"),
+				       arg);
+			break;
+		}
+	}
+
 	if (verbose > 1)
 		printf(_("Trying to unmount %s\n"), file);