From bf6a3825b5c4feb198881fbc3413a1e34ea298a4 Mon Sep 17 00:00:00 2001
From: "Daniel P. Berrange" <berrange@redhat.com>
Date: Wed, 2 Feb 2011 12:35:31 +0000
Subject: [PATCH] Add check for binary existing in machine type probe

When probing machine types if the QEMU binary does not exist
we get a hard to diagnose error, due to the execve() in the
child failing

error: internal error Child process exited with status 1.

Add an explicit check so that we get

error: Cannot find QEMU binary /usr/libexec/qem3u-kvm: No such file or directory

* src/qemu/qemu_capabilities.c: Check for QEMU binary
---
 src/qemu/qemu_capabilities.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
index 0e1f79cd20..4504b7e9f1 100644
--- a/src/qemu/qemu_capabilities.c
+++ b/src/qemu/qemu_capabilities.c
@@ -172,6 +172,15 @@ qemuCapsProbeMachineTypes(const char *binary,
     int ret = -1;
     virCommandPtr cmd;
 
+    /* Make sure the binary we are about to try exec'ing exists.
+     * Technically we could catch the exec() failure, but that's
+     * in a sub-process so it's hard to feed back a useful error.
+     */
+    if (access(binary, X_OK) < 0) {
+        virReportSystemError(errno, _("Cannot find QEMU binary %s"), binary);
+        return -1;
+    }
+
     cmd = virCommandNewArgList(binary, "-M", "?", NULL);
     virCommandAddEnvPassCommon(cmd);
     virCommandSetOutputBuffer(cmd, &output);