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: Daniel P. Berrange <berrange@redhat.com>

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,
+                                const char *dev_name,
-                          virHostValidateLevel level,
+                                virHostValidateLevel level,
-                          const char *hint)
+                                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

@@ -42,10 +42,15 @@ 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,
+                                       const char *dev_name,
-                                 virHostValidateLevel level,
+                                       virHostValidateLevel level,
-                                 const char *hint);
+                                       const char *hint);
+
+extern int virHostValidateDeviceAccessible(const char *hvname,
+                                           const char *dev_name,
+                                           virHostValidateLevel level,
+                                           const char *hint);
 
 extern bool virHostValidateHasCPUFlag(const char *name);
 

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"
 
@@ -32,25 +31,30 @@ int virHostValidateQEMU(void)
     if (virHostValidateHasCPUFlag("svm") ||
         virHostValidateHasCPUFlag("vmx")) {
         virHostMsgPass();
-        if (virHostValidateDevice("QEMU", "/dev/kvm",
+        if (virHostValidateDeviceExists("QEMU", "/dev/kvm",
-                                  VIR_HOST_VALIDATE_FAIL,
+                                        VIR_HOST_VALIDATE_FAIL,
-                                  _("Check that the 'kvm-intel' or 'kvm-amd' modules are "
+                                        _("Check that the 'kvm-intel' or 'kvm-amd' modules are "
-                                    "loaded & the BIOS has enabled virtualization")) < 0)
+                                          "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,
+                                    VIR_HOST_VALIDATE_WARN,
-                              _("Load the 'vhost_net' module to improve performance "
+                                    _("Load the 'vhost_net' module to improve performance "
-                                "of virtio networking")) < 0)
+                                      "of virtio networking")) < 0)
         ret = -1;
 
-    if (virHostValidateDevice("QEMU", "/dev/net/tun",
+    if (virHostValidateDeviceExists("QEMU", "/dev/net/tun",
-                              VIR_HOST_VALIDATE_FAIL,
+                                    VIR_HOST_VALIDATE_FAIL,
-                              _("Load the 'tun' module to enable networking for QEMU guests")) < 0)
+                                    _("Load the 'tun' module to enable networking for QEMU guests")) < 0)
         ret = -1;
 
     return ret;