virt-host-validate: distinguish exists vs accessible for devices

Currently we just check that various devices are accessible.
This leads to inaccurate errors reported for /dev/kvm and
/dev/vhost-net if they exist but an unprivileged user lacks
access. Switch existing checks to look for file existance,
and add a separate check for accessibility of /dev/kvm
since some distros don't grant users access by default.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>
(cherry picked from commit fd6d506c)

tools/virt-host-validate-common.c

@@ -115,12 +115,29 @@ void virHostMsgFail(virHostValidateLevel level,
 }
 
 
-int virHostValidateDevice(const char *hvname,
+int virHostValidateDeviceExists(const char *hvname,
                                 const char *dev_name,
                                 virHostValidateLevel level,
                                 const char *hint)
 {
-    virHostMsgCheck(hvname, "for device %s", dev_name);
+    virHostMsgCheck(hvname, "if device %s exists", dev_name);
+
+    if (access(dev_name, F_OK) < 0) {
+        virHostMsgFail(level, hint);
+        return -1;
+    }
+
+    virHostMsgPass();
+    return 0;
+}
+
+
+int virHostValidateDeviceAccessible(const char *hvname,
+                                    const char *dev_name,
+                                    virHostValidateLevel level,
+                                    const char *hint)
+{
+    virHostMsgCheck(hvname, "if device %s is accessible", dev_name);
 
     if (access(dev_name, R_OK|W_OK) < 0) {
         virHostMsgFail(level, hint);

tools/virt-host-validate-common.h

@@ -42,7 +42,12 @@ extern void virHostMsgPass(void);
 extern void virHostMsgFail(virHostValidateLevel level,
                            const char *hint);
 
-extern int virHostValidateDevice(const char *hvname,
+extern int virHostValidateDeviceExists(const char *hvname,
+                                       const char *dev_name,
+                                       virHostValidateLevel level,
+                                       const char *hint);
+
+extern int virHostValidateDeviceAccessible(const char *hvname,
                                            const char *dev_name,
                                            virHostValidateLevel level,
                                            const char *hint);

tools/virt-host-validate-qemu.c

@@ -20,7 +20,6 @@
  */
 
 #include <config.h>
-
 #include "virt-host-validate-qemu.h"
 #include "virt-host-validate-common.h"
 
@@ -32,23 +31,28 @@ int virHostValidateQEMU(void)
     if (virHostValidateHasCPUFlag("svm") ||
         virHostValidateHasCPUFlag("vmx")) {
         virHostMsgPass();
-        if (virHostValidateDevice("QEMU", "/dev/kvm",
+        if (virHostValidateDeviceExists("QEMU", "/dev/kvm",
                                         VIR_HOST_VALIDATE_FAIL,
                                         _("Check that the 'kvm-intel' or 'kvm-amd' modules are "
                                           "loaded & the BIOS has enabled virtualization")) < 0)
             ret = -1;
+        else if (virHostValidateDeviceAccessible("QEMU", "/dev/kvm",
+                                                 VIR_HOST_VALIDATE_FAIL,
+                                                 _("Check /dev/kvm is world writable or you are in "
+                                                   "a group that is allowed to access it")) < 0)
+            ret = -1;
     } else {
         virHostMsgFail(VIR_HOST_VALIDATE_WARN,
                        _("Only emulated CPUs are available, performance will be significantly limited"));
     }
 
-    if (virHostValidateDevice("QEMU", "/dev/vhost-net",
+    if (virHostValidateDeviceExists("QEMU", "/dev/vhost-net",
                                     VIR_HOST_VALIDATE_WARN,
                                     _("Load the 'vhost_net' module to improve performance "
                                       "of virtio networking")) < 0)
         ret = -1;
 
-    if (virHostValidateDevice("QEMU", "/dev/net/tun",
+    if (virHostValidateDeviceExists("QEMU", "/dev/net/tun",
                                     VIR_HOST_VALIDATE_FAIL,
                                     _("Load the 'tun' module to enable networking for QEMU guests")) < 0)
         ret = -1;