[LTP] [PATCH] tst_virt: Add fallback KVM detection via virtio block devices

[Darren Chang]

Currently, is_kvm() relies on reading /proc/cpuinfo to find the
"QEMU Virtual CPU" string.

This patch introduces a fallback mechanism to detect KVM environments
by checking for the existence of standard virtio block devices when the
CPU info check fails. Specifically, it probes for:
- /sys/block/vda (Reliable sysfs kernel interface)
- /dev/vda       (Standard Linux device node)
- /dev/block/vda (Android's ueventd device node)

Including "/dev/block/vda" ensures that the detection works seamlessly
within Android emulator environments (such as Cuttlefish),
which use ueventd and place block devices under /dev/block/ instead of
the standard Linux /dev/.

Signed-off-by: Darren Chang <chihsheng@google.com>
---
 lib/tst_virt.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/lib/tst_virt.c b/lib/tst_virt.c
index 109d7a853..ac0aef665 100644
--- a/lib/tst_virt.c
+++ b/lib/tst_virt.c
@@ -44,6 +44,19 @@ static int is_kvm(void)
 	}
 
 	SAFE_FCLOSE(NULL, cpuinfo);
+
+	/* * Fallback check for KVM:
+	 * Android's ueventd creates block devices in /dev/block/
+	 * instead of the standard Linux /dev/, so we check both.
+	 */
+	if (!found) {
+		if (access("/dev/vda", F_OK) == 0 ||
+			access("/sys/block/vda", F_OK) == 0 ||
+			access("/dev/block/vda", F_OK) == 0) {
+			found = 1;
+		}
+	}
+
 	return found;
 }
 
-- 
2.54.0.545.g6539524ca2-goog