[PATCH v5 06/21] KVM: selftests: Add helper to get host IRQ from device MSIX for IRQ bypass test

[Josh Hilke <jrhilke@google.com>]

From: David Matlack <dmatlack@google.com>

Introduce proc_util.c and proc_util.h to house utility functions for
interacting with the proc filesystem.

Add vfio_msix_to_host_irq(), which parses
/proc/interrupts to map a VFIO device BDF and MSI-X vector to its
corresponding host IRQ number.

This helper will be used in a subsequent patch for debugging when
implementing support for IRQ bypass in the KVM IRQ test.

Suggested-by: Sean Christopherson <seanjc@google.com>
Co-developed-by: Josh Hilke <jrhilke@google.com>
Signed-off-by: Josh Hilke <jrhilke@google.com>
Signed-off-by: David Matlack <dmatlack@google.com>
---
 tools/testing/selftests/kvm/Makefile.kvm      |  1 +
 .../testing/selftests/kvm/include/proc_util.h |  9 +++++
 tools/testing/selftests/kvm/lib/proc_util.c   | 40 +++++++++++++++++++
 3 files changed, 50 insertions(+)
 create mode 100644 tools/testing/selftests/kvm/include/proc_util.h
 create mode 100644 tools/testing/selftests/kvm/lib/proc_util.c

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index b859098121c7..63355b56c42f 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/tools/testing/selftests/kvm/Makefile.kvm
@@ -11,6 +11,7 @@ LIBKVM += lib/kvm_util.c
 LIBKVM += lib/lru_gen_util.c
 LIBKVM += lib/memstress.c
 LIBKVM += lib/guest_sprintf.c
+LIBKVM += lib/proc_util.c
 LIBKVM += lib/rbtree.c
 LIBKVM += lib/sparsebit.c
 LIBKVM += lib/test_util.c
diff --git a/tools/testing/selftests/kvm/include/proc_util.h b/tools/testing/selftests/kvm/include/proc_util.h
new file mode 100644
index 000000000000..704839b6d7af
--- /dev/null
+++ b/tools/testing/selftests/kvm/include/proc_util.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef SELFTEST_KVM_PROC_UTIL_H
+#define SELFTEST_KVM_PROC_UTIL_H
+
+#include <stdint.h>
+
+unsigned int vfio_msix_to_host_irq(const char *vfio_device_bdf, int msix);
+
+#endif /* SELFTEST_KVM_PROC_UTIL_H */
diff --git a/tools/testing/selftests/kvm/lib/proc_util.c b/tools/testing/selftests/kvm/lib/proc_util.c
new file mode 100644
index 000000000000..84d30f055a0a
--- /dev/null
+++ b/tools/testing/selftests/kvm/lib/proc_util.c
@@ -0,0 +1,40 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "kvm_util.h"
+#include "test_util.h"
+#include "proc_util.h"
+
+static FILE *open_proc_interrupts(void)
+{
+	FILE *fp;
+
+	fp = fopen("/proc/interrupts", "r");
+	TEST_ASSERT(fp, "fopen(/proc/interrupts) failed");
+
+	return fp;
+}
+
+unsigned int vfio_msix_to_host_irq(const char *device_bdf, int msix)
+{
+	char search_string[64];
+	char line[4096];
+	int irq = -1;
+	FILE *fp;
+
+	fp = open_proc_interrupts();
+
+	snprintf(search_string, sizeof(search_string), "vfio-msix[%d]", msix);
+
+	while (fgets(line, sizeof(line), fp)) {
+		if (strstr(line, device_bdf) && strstr(line, search_string)) {
+			TEST_ASSERT_EQ(1, sscanf(line, "%d:", &irq));
+			break;
+		}
+	}
+
+	fclose(fp);
+
+	TEST_ASSERT(irq != -1, "Failed to locate IRQ for %s %s", device_bdf,
+		    search_string);
+	return (unsigned int)irq;
+}
+
-- 
2.54.0.1032.g2f8565e1d1-goog