crypto/luks: Support creating LUKS image on Darwin

When the user creates a LUKS-encrypted qcow2 image using the qemu-img
program, the passphrase is hashed using PBKDF2 with a dynamic
number of iterations. The number of iterations is determined by
measuring thread cpu time usage, such that it takes approximately
2 seconds to compute the hash.

Because Darwin doesn't implement getrusage(RUSAGE_THREAD), we get an
error message:
> qemu-img: test.qcow2: Unable to calculate thread CPU usage on this platform
for this command:
> qemu-img create --object secret,id=key,data=1234 -f qcow2 -o 'encrypt.format=luks,encrypt.key-secret=key' test.qcow2 100M

This patch implements qcrypto_pbkdf2_get_thread_cpu() for Darwin so that
the above command works.

Signed-off-by: Jungmin Park <pjm0616@gmail.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

crypto/pbkdf.c

@@ -24,6 +24,11 @@
 #ifndef _WIN32
 #include <sys/resource.h>
 #endif
+#ifdef CONFIG_DARWIN
+#include <mach/mach_init.h>
+#include <mach/thread_act.h>
+#include <mach/mach_port.h>
+#endif
 
 
 static int qcrypto_pbkdf2_get_thread_cpu(unsigned long long *val_ms,
@@ -45,6 +50,24 @@ static int qcrypto_pbkdf2_get_thread_cpu(unsigned long long *val_ms,
     /* QuadPart is units of 100ns and we want ms as unit */
     *val_ms = thread_time.QuadPart / 10000ll;
     return 0;
+#elif defined(CONFIG_DARWIN)
+    mach_port_t thread;
+    kern_return_t kr;
+    mach_msg_type_number_t count;
+    thread_basic_info_data_t info;
+
+    thread = mach_thread_self();
+    count = THREAD_BASIC_INFO_COUNT;
+    kr = thread_info(thread, THREAD_BASIC_INFO, (thread_info_t)&info, &count);
+    mach_port_deallocate(mach_task_self(), thread);
+    if (kr != KERN_SUCCESS || (info.flags & TH_FLAGS_IDLE) != 0) {
+        error_setg_errno(errp, errno, "Unable to get thread CPU usage");
+        return -1;
+    }
+
+    *val_ms = ((info.user_time.seconds * 1000ll) +
+               (info.user_time.microseconds / 1000));
+    return 0;
 #elif defined(RUSAGE_THREAD)
     struct rusage ru;
     if (getrusage(RUSAGE_THREAD, &ru) < 0) {