[PATCH v7 10/20] KVM: selftests: Add a helper to set proc IRQ affinity for IRQ test

[Sean Christopherson <seanjc@google.com>]

From: Josh Hilke <jrhilke@google.com>

Add a utility, proc_irq_set_smp_affinity(), to set the CPU affinity of a
Linux host IRQ via the proc filesystem.  Use smp_affinity_list instead of
smp_affinity to avoid having to convert the single CPU to a bitmask.

The helper will be used by the eventfd IRQ test to verify delivery of IRQs
when the affinity is randomized/modified.

Signed-off-by: Josh Hilke <jrhilke@google.com>
[sean: make the utility self-contained, drop "list", massage changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 tools/testing/selftests/kvm/include/proc_util.h |  2 ++
 tools/testing/selftests/kvm/lib/proc_util.c     | 14 ++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/tools/testing/selftests/kvm/include/proc_util.h b/tools/testing/selftests/kvm/include/proc_util.h
index 704839b6d7af..d1ddc967d11d 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);
 
+void proc_irq_set_smp_affinity(unsigned int irq, int 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..3960b3841d63 100644
--- a/tools/testing/selftests/kvm/lib/proc_util.c
+++ b/tools/testing/selftests/kvm/lib/proc_util.c
@@ -38,3 +38,17 @@ unsigned int vfio_msix_to_host_irq(const char *device_bdf, int msix)
 	return (unsigned int)irq;
 }
 
+void proc_irq_set_smp_affinity(unsigned int irq, int cpu)
+{
+	char path[PATH_MAX];
+	int r, fd;
+
+	snprintf(path, sizeof(path), "/proc/irq/%u/smp_affinity_list", irq);
+	fd = open(path, O_RDWR);
+	TEST_ASSERT(fd >= 0, "Failed to open %s", path);
+
+	r = dprintf(fd, "%d\n", cpu);
+	TEST_ASSERT(r > 0, "Failed to affinitize IRQ-%u to CPU %d", irq, cpu);
+
+	kvm_close(fd);
+}
-- 
2.54.0.1136.gdb2ca164c4-goog