[libvirt] [PATCH] qemu_conf: Check for namespaces availability more wisely

[Michal Privoznik]

On 02/15/2017 10:43 AM, Daniel P. Berrange wrote:
> On Wed, Feb 15, 2017 at 10:20:27AM +0100, Michal Privoznik wrote:
>> The bare fact that mnt namespace is available is not enough for
>> us to allow/enable qemu namespaces feature. There are other
>> requirements: we must copy all the ACL & SELinux labels otherwise
>> we might grant access that is administratively forbidden or vice
>> versa.
>> At the same time, the check for namespace prerequisites is moved
>> from domain startup time to qemu.conf parser as it doesn't make
>> much sense to allow users to start misconfigured libvirt just to
>> find out they can't start a single domain.
>>
>> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
>> ---
>>  src/qemu/qemu_conf.c   | 20 ++++++++++++++++----
>>  src/qemu/qemu_conf.h   |  3 ++-
>>  src/qemu/qemu_domain.c | 43 ++++++++++++++++++++++++++++---------------
>>  src/qemu/qemu_domain.h |  2 ++
>>  src/qemu/qemu_driver.c |  2 +-
>>  5 files changed, 49 insertions(+), 21 deletions(-)
>>


>> +bool
>> +qemuDomainNamespaceAvailable(qemuDomainNamespace ns)
>> +{
>> +
>> +    switch (ns) {
>> +    case QEMU_DOMAIN_NS_MOUNT:
>> +#if !defined(__linux__)
>> +        /* Namespaces are Linux specific. */
>> +        return false;
>> +#endif
>> +#if !defined(HAVE_SYS_ACL_H) || !defined(WITH_SELINUX)
>> +        /* We can't create the exact copy of paths if either of
>> +         * these is not available. */
>> +        return false;
>> +#endif
> 
> Pretty sure this will cause the compiler to complain about
> unreachable code paths because you'll get
> 
>     return false;
>     return false;
>     if (virProcessNamespaceAvailable(....)

Ah. Obviously. What about this?

+bool
+qemuDomainNamespaceAvailable(qemuDomainNamespace ns ATTRIBUTE_UNUSED)
+{
+#if !defined(__linux__)
+    /* Namespaces are Linux specific. */
+    return false;
+
+#else /* defined(__linux__) */
+
+    switch (ns) {
+    case QEMU_DOMAIN_NS_MOUNT:
+# if !defined(HAVE_SYS_ACL_H) || !defined(WITH_SELINUX)
+        /* We can't create the exact copy of paths if either of
+         * these is not available. */
+        return false;
+# else
+        if (virProcessNamespaceAvailable(VIR_PROCESS_NAMESPACE_MNT) < 0)
+            return false;
+# endif
+        break;
+    case QEMU_DOMAIN_NS_LAST:
+        break;
+    }
+
+    return true;
+#endif /* defined(__linux__) */
+}
+
+

Michal