From 8e51bdb10db34d2ad6da49d57c0671f40fb22b40 Mon Sep 17 00:00:00 2001
From: Tianon Gravi <admwiggin@gmail.com>
Date: Fri, 19 Mar 2021 08:57:33 -0700
Subject: [PATCH] Try writing zero bytes to "/dev/kvm" as a more robust test
 for access

Looking at https://lwn.net/Articles/658511/, this seems like it should be reasonably harmless as a simple test of whether we can expect `/dev/kvm` to work.

Fixes #4
---
 4.2/start-qemu | 3 ++-
 5.0/start-qemu | 3 ++-
 5.1/start-qemu | 3 ++-
 5.2/start-qemu | 3 ++-
 start-qemu     | 3 ++-
 5 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/4.2/start-qemu b/4.2/start-qemu
index 897fac2..908443c 100755
--- a/4.2/start-qemu
+++ b/4.2/start-qemu
@@ -25,7 +25,8 @@ if [ -z "${QEMU_NO_SSH:-}" ]; then
 fi
 qemuPorts+=( ${QEMU_PORTS:-} )
 
-if [ -e /dev/kvm ]; then
+if [ -e /dev/kvm ] && sh -c 'echo -n > /dev/kvm' &> /dev/null; then
+	# https://github.com/tianon/docker-qemu/issues/4
 	qemuArgs+=( -enable-kvm )
 elif [ "$hostArch" = "$qemuArch" ]; then
 	echo >&2
diff --git a/5.0/start-qemu b/5.0/start-qemu
index 897fac2..908443c 100755
--- a/5.0/start-qemu
+++ b/5.0/start-qemu
@@ -25,7 +25,8 @@ if [ -z "${QEMU_NO_SSH:-}" ]; then
 fi
 qemuPorts+=( ${QEMU_PORTS:-} )
 
-if [ -e /dev/kvm ]; then
+if [ -e /dev/kvm ] && sh -c 'echo -n > /dev/kvm' &> /dev/null; then
+	# https://github.com/tianon/docker-qemu/issues/4
 	qemuArgs+=( -enable-kvm )
 elif [ "$hostArch" = "$qemuArch" ]; then
 	echo >&2
diff --git a/5.1/start-qemu b/5.1/start-qemu
index 897fac2..908443c 100755
--- a/5.1/start-qemu
+++ b/5.1/start-qemu
@@ -25,7 +25,8 @@ if [ -z "${QEMU_NO_SSH:-}" ]; then
 fi
 qemuPorts+=( ${QEMU_PORTS:-} )
 
-if [ -e /dev/kvm ]; then
+if [ -e /dev/kvm ] && sh -c 'echo -n > /dev/kvm' &> /dev/null; then
+	# https://github.com/tianon/docker-qemu/issues/4
 	qemuArgs+=( -enable-kvm )
 elif [ "$hostArch" = "$qemuArch" ]; then
 	echo >&2
diff --git a/5.2/start-qemu b/5.2/start-qemu
index 897fac2..908443c 100755
--- a/5.2/start-qemu
+++ b/5.2/start-qemu
@@ -25,7 +25,8 @@ if [ -z "${QEMU_NO_SSH:-}" ]; then
 fi
 qemuPorts+=( ${QEMU_PORTS:-} )
 
-if [ -e /dev/kvm ]; then
+if [ -e /dev/kvm ] && sh -c 'echo -n > /dev/kvm' &> /dev/null; then
+	# https://github.com/tianon/docker-qemu/issues/4
 	qemuArgs+=( -enable-kvm )
 elif [ "$hostArch" = "$qemuArch" ]; then
 	echo >&2
diff --git a/start-qemu b/start-qemu
index 897fac2..908443c 100755
--- a/start-qemu
+++ b/start-qemu
@@ -25,7 +25,8 @@ if [ -z "${QEMU_NO_SSH:-}" ]; then
 fi
 qemuPorts+=( ${QEMU_PORTS:-} )
 
-if [ -e /dev/kvm ]; then
+if [ -e /dev/kvm ] && sh -c 'echo -n > /dev/kvm' &> /dev/null; then
+	# https://github.com/tianon/docker-qemu/issues/4
 	qemuArgs+=( -enable-kvm )
 elif [ "$hostArch" = "$qemuArch" ]; then
 	echo >&2