[PATCH v5 08/21] KVM: selftests: Add helpers to write proc IRQ affinity for IRQ test

[Josh Hilke <jrhilke@google.com>]

Introduce utility functions to open and write IRQ affinity settings
via the proc filesystem.

Specifically, add:
- open_proc_irq_smp_affinity_list() to open
  /proc/irq/<irq>/smp_affinity_list for writing.
- write_proc_irq_smp_affinity_list() to write a target CPU to the list.

These will be used a subsequent patch to set IRQ affinity in the KVM IRQ
test.

Signed-off-by: Josh Hilke <jrhilke@google.com>
---
 .../testing/selftests/kvm/include/proc_util.h |  2 ++
 tools/testing/selftests/kvm/lib/proc_util.c   | 20 +++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/tools/testing/selftests/kvm/include/proc_util.h b/tools/testing/selftests/kvm/include/proc_util.h
index 704839b6d7af..e381c7818275 100644
--- a/tools/testing/selftests/kvm/include/proc_util.h
+++ b/tools/testing/selftests/kvm/include/proc_util.h
@@ -6,4 +6,6 @@
 
 unsigned int vfio_msix_to_host_irq(const char *vfio_device_bdf, int msix);
 
+FILE *open_proc_irq_smp_affinity_list(unsigned int irq);
+void write_proc_irq_smp_affinity_list(FILE *fp, unsigned int irq, int irq_cpu);
 #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
index 84d30f055a0a..938c90d94f4d 100644
--- a/tools/testing/selftests/kvm/lib/proc_util.c
+++ b/tools/testing/selftests/kvm/lib/proc_util.c
@@ -38,3 +38,23 @@ unsigned int vfio_msix_to_host_irq(const char *device_bdf, int msix)
 	return (unsigned int)irq;
 }
 
+FILE *open_proc_irq_smp_affinity_list(unsigned int irq)
+{
+	char path[PATH_MAX];
+	FILE *fp;
+
+	snprintf(path, sizeof(path), "/proc/irq/%u/smp_affinity_list", irq);
+	fp = fopen(path, "w");
+	TEST_ASSERT(fp, "fopen(%s) failed", path);
+
+	return fp;
+}
+
+void write_proc_irq_smp_affinity_list(FILE *fp, unsigned int irq, int irq_cpu)
+{
+	int ret;
+
+	ret = fprintf(fp, "%d\n", irq_cpu);
+	TEST_ASSERT(ret > 0, "Failed to affinitize IRQ-%u to CPU %d", irq, irq_cpu);
+	fflush(fp);
+}
-- 
2.54.0.1032.g2f8565e1d1-goog