[PATCH rc v2 4/4] iommufd/selftest: Fix build warnings due to uninitialized mfd

[Nicolin Chen <nicolinc@nvidia.com>]

Commit 869c788909b9 ("selftests: harness: Stop using setjmp()/longjmp()")
changed the harness structure. For some unknown reason, two build warnings
occur to the iommufd selftest:

iommufd.c: In function ‘wrapper_iommufd_mock_domain_all_aligns’:
iommufd.c:1807:17: warning: ‘mfd’ may be used uninitialized in this function
 1807 |                 close(mfd);
      |                 ^~~~~~~~~~
iommufd.c:1767:13: note: ‘mfd’ was declared here
 1767 |         int mfd;
      |             ^~~
iommufd.c: In function ‘wrapper_iommufd_mock_domain_all_aligns_copy’:
iommufd.c:1870:17: warning: ‘mfd’ may be used uninitialized in this function
 1870 |                 close(mfd);
      |                 ^~~~~~~~~~
iommufd.c:1819:13: note: ‘mfd’ was declared here
 1819 |         int mfd;
      |             ^~~

All the mfd have been used in the variant->file path only, so it's likely
a false alarm.

FWIW, the commit mentioned above does not cause this, yet it might affect
gcc in a certain way that resulted in the warnings. It is also found that
ading a dummy setjmp (which doesn't make sense) could mute the warnings:
https://lore.kernel.org/all/aEi8DV+ReF3v3Rlf@nvidia.com/

The job of this selftest is to catch kernel bug, while such warnings will
unlikely disrupt its role. Mute the warning by force initializing the mfd
and add an ASSERT_GT().

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
 tools/testing/selftests/iommu/iommufd.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/iommu/iommufd.c b/tools/testing/selftests/iommu/iommufd.c
index e61218c0537f..1926ef6b40ab 100644
--- a/tools/testing/selftests/iommu/iommufd.c
+++ b/tools/testing/selftests/iommu/iommufd.c
@@ -1748,13 +1748,15 @@ TEST_F(iommufd_mock_domain, all_aligns)
 	unsigned int end;
 	uint8_t *buf;
 	int prot = PROT_READ | PROT_WRITE;
-	int mfd;
+	int mfd = -1;
 
 	if (variant->file)
 		buf = memfd_mmap(buf_size, prot, MAP_SHARED, &mfd);
 	else
 		buf = mmap(0, buf_size, prot, self->mmap_flags, -1, 0);
 	ASSERT_NE(MAP_FAILED, buf);
+	if (variant->file)
+		ASSERT_GT(mfd, 0);
 	check_refs(buf, buf_size, 0);
 
 	/*
@@ -1800,13 +1802,15 @@ TEST_F(iommufd_mock_domain, all_aligns_copy)
 	unsigned int end;
 	uint8_t *buf;
 	int prot = PROT_READ | PROT_WRITE;
-	int mfd;
+	int mfd = -1;
 
 	if (variant->file)
 		buf = memfd_mmap(buf_size, prot, MAP_SHARED, &mfd);
 	else
 		buf = mmap(0, buf_size, prot, self->mmap_flags, -1, 0);
 	ASSERT_NE(MAP_FAILED, buf);
+	if (variant->file)
+		ASSERT_GT(mfd, 0);
 	check_refs(buf, buf_size, 0);
 
 	/*
-- 
2.43.0