From d4423cce9b9001c9de7ebc6f64f6cc2bb854944c Mon Sep 17 00:00:00 2001
From: Karel Zak <kzak@redhat.com>
Date: Tue, 20 Apr 2021 13:20:12 +0200
Subject: [PATCH] lib/loopdev: fix is_loopdev() to be usable with partitions

The current implementation of the function does not care if the device
is whole-disk device or partition, all is loopdev. This is regression
as the original is_loopdev() version was based on whole-disk devices
major numbers only.

Fixes: https://github.com/karelzak/util-linux/issues/1202
Signed-off-by: Karel Zak <kzak@redhat.com>
---
 lib/Makemodule.am |  9 ++++++++-
 lib/loopdev.c     | 21 ++++++++++++++++++++-
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/lib/Makemodule.am b/lib/Makemodule.am
index 0f18c9489..d112736da 100644
--- a/lib/Makemodule.am
+++ b/lib/Makemodule.am
@@ -101,7 +101,8 @@ endif
 check_PROGRAMS += \
 	test_sysfs \
 	test_pager \
-	test_caputils
+	test_caputils \
+	test_loopdev
 endif
 
 if HAVE_OPENAT
@@ -164,6 +165,7 @@ test_pty_LDADD = $(LDADD) libcommon.la $(MATH_LIBS) $(REALTIME_LIBS) -lutil
 endif
 
 if LINUX
+
 test_cpuset_SOURCES = lib/cpuset.c
 test_cpuset_CFLAGS = $(AM_CFLAGS) -DTEST_PROGRAM_CPUSET
 
@@ -199,3 +201,8 @@ test_remove_env_CFLAGS = $(AM_CFLAGS) -DTEST_PROGRAM
 
 test_buffer_SOURCES = lib/buffer.c
 test_buffer_CFLAGS = $(AM_CFLAGS) -DTEST_PROGRAM_BUFFER
+
+test_loopdev_SOURCES = lib/loopdev.c \
+		       $(test_sysfs_SOURCES) \
+		       $(test_canonicalize_SOURCES)
+test_loopdev_CFLAGS = $(AM_CFLAGS) -DTEST_PROGRAM_LOOPDEV
diff --git a/lib/loopdev.c b/lib/loopdev.c
index b946acf31..1eef15d89 100644
--- a/lib/loopdev.c
+++ b/lib/loopdev.c
@@ -641,7 +641,7 @@ int is_loopdev(const char *device)
 		rc = 0;
 	else if (major(st.st_rdev) == LOOPDEV_MAJOR)
 		rc = 1;
-	else {
+	else if (sysfs_devno_is_wholedisk(st.st_rdev)) {
 		/* It's possible that kernel creates a device with a different
 		 * major number ... check by /sys it's really loop device.
 		 */
@@ -1881,3 +1881,22 @@ int loopdev_count_by_backing_file(const char *filename, char **loopdev)
 	return count;
 }
 
+#ifdef TEST_PROGRAM_LOOPDEV
+int main(int argc, char *argv[])
+{
+	if (argc < 2)
+		goto usage;
+
+	if (strcmp(argv[1], "--is-loopdev") == 0 && argc == 3)
+		printf("%s: %s\n", argv[2], is_loopdev(argv[2]) ? "OK" : "FAIL");
+	else
+		goto usage;
+
+	return EXIT_SUCCESS;
+usage:
+	fprintf(stderr, "usage: %1$s --is-loopdev <dev>\n",
+			program_invocation_short_name);
+	return EXIT_FAILURE;
+}
+#endif
+