[PATCH v2 3/5] vfio: selftests: Print the known IOMMU modes on an unrecognized mode

[David Matlack <dmatlack@google.com>]

Print the names of all known IOMMU modes when iommu_init() is passed an
unrecognized IOMMU mode, and expose the list of names via
iommu_mode_names() so that tests can also print it, e.g. in their help
output.

Users can specify the IOMMU mode for some tests on the command line (e.g.
irq_test -t), and so a typo or unsupported mode should tell the user what
the valid options are rather than leaving them to go read the library.

Suggested-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/kvm/auit0kVkAaWcNUvk@google.com/
Signed-off-by: David Matlack <dmatlack@google.com>
---
 .../vfio/lib/include/libvfio/iommu.h          |  3 +++
 tools/testing/selftests/vfio/lib/iommu.c      | 20 ++++++++++++++++++-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/vfio/lib/include/libvfio/iommu.h b/tools/testing/selftests/vfio/lib/include/libvfio/iommu.h
index f204c71494fe..42d1de742c0c 100644
--- a/tools/testing/selftests/vfio/lib/include/libvfio/iommu.h
+++ b/tools/testing/selftests/vfio/lib/include/libvfio/iommu.h
@@ -51,6 +51,9 @@ bool iommu_mode_is_available(const char *iommu_mode);
  */
 const char *iommu_mode_unavailable_msg(const char *iommu_mode);
 
+/* Returns a comma-separated list of the names of all IOMMU modes. */
+const char *iommu_mode_names(void);
+
 int __iommu_map(struct iommu *iommu, struct dma_region *region);
 
 static inline void iommu_map(struct iommu *iommu, struct dma_region *region)
diff --git a/tools/testing/selftests/vfio/lib/iommu.c b/tools/testing/selftests/vfio/lib/iommu.c
index 526bb21f2766..64614325c49b 100644
--- a/tools/testing/selftests/vfio/lib/iommu.c
+++ b/tools/testing/selftests/vfio/lib/iommu.c
@@ -90,6 +90,23 @@ static const struct iommu_mode *iommu_mode_detect(void)
 	return NULL;
 }
 
+const char *iommu_mode_names(void)
+{
+	static char names[256];
+	int i, len = 0;
+
+	if (names[0])
+		return names;
+
+	for (i = 0; i < ARRAY_SIZE(iommu_modes); i++) {
+		len += snprintf(names + len, sizeof(names) - len, "%s%s",
+				i ? ", " : "", iommu_modes[i].name);
+		VFIO_ASSERT_LT(len, (int)sizeof(names));
+	}
+
+	return names;
+}
+
 /*
  * Returns the IOMMU mode with the given name, or if iommu_mode is NULL, the
  * most preferred IOMMU mode that is available (or NULL if none).
@@ -108,7 +125,8 @@ static const struct iommu_mode *iommu_mode_lookup(const char *iommu_mode)
 		return &iommu_modes[i];
 	}
 
-	VFIO_FAIL("Unrecognized IOMMU mode: %s\n", iommu_mode);
+	VFIO_FAIL("Unrecognized IOMMU mode: %s (known modes: %s)\n",
+		  iommu_mode, iommu_mode_names());
 }
 
 bool iommu_mode_is_available(const char *iommu_mode)
-- 
2.56.0.385.gac671c819a-goog