[PATCH RFCv1 6/8] kvm: Add helper kvm_dirty_ring_init()

[Gavin Shan]

Due to multiple capabilities associated with the dirty ring for different
architectures: KVM_CAP_DIRTY_{LOG_RING, LOG_RING_ACQ_REL} for x86 and
arm64 separately. There will be more to be done in order to support the
dirty ring for arm64.

Lets add helper kvm_dirty_ring_init() to enable the dirty ring. With this,
the code looks a bit clean.

No functional change intended.

Signed-off-by: Gavin Shan <gshan@redhat.com>
---
 accel/kvm/kvm-all.c | 73 ++++++++++++++++++++++++++++-----------------
 1 file changed, 46 insertions(+), 27 deletions(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 9ec117c441..399ef0f7e6 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -1476,6 +1476,49 @@ static int kvm_dirty_ring_reaper_init(KVMState *s)
     return 0;
 }
 
+static int kvm_dirty_ring_init(KVMState *s)
+{
+    uint64_t ring_bytes;
+    int ret;
+
+    /*
+     * Read the max supported pages. Fall back to dirty logging mode
+     * if the dirty ring isn't supported.
+     */
+    ret = kvm_vm_check_extension(s, KVM_CAP_DIRTY_LOG_RING);
+    if (ret <= 0) {
+        warn_report("KVM dirty ring not available, using bitmap method");
+        s->kvm_dirty_ring_size = 0;
+        return 0;
+    }
+
+    ring_bytes = s->kvm_dirty_ring_size * sizeof(struct kvm_dirty_gfn);
+    if (ring_bytes > ret) {
+        error_report("KVM dirty ring size %" PRIu32 " too big "
+                     "(maximum is %ld).  Please use a smaller value.",
+                     s->kvm_dirty_ring_size,
+                     (long)ret / sizeof(struct kvm_dirty_gfn));
+        ret = -EINVAL;
+        goto out;
+    }
+
+    ret = kvm_vm_enable_cap(s, KVM_CAP_DIRTY_LOG_RING, 0, ring_bytes);
+    if (ret) {
+        error_report("Enabling of KVM dirty ring failed: %s. "
+                     "Suggested minimum value is 1024.", strerror(-ret));
+        ret = -EIO;
+    }
+
+out:
+    if (ret) {
+        s->kvm_dirty_ring_size = 0;
+    } else {
+        s->kvm_dirty_ring_bytes = ring_bytes;
+    }
+
+    return ret;
+}
+
 static void kvm_region_add(MemoryListener *listener,
                            MemoryRegionSection *section)
 {
@@ -2545,33 +2588,9 @@ static int kvm_init(MachineState *ms)
      * dirty logging mode
      */
     if (s->kvm_dirty_ring_size > 0) {
-        uint64_t ring_bytes;
-
-        ring_bytes = s->kvm_dirty_ring_size * sizeof(struct kvm_dirty_gfn);
-
-        /* Read the max supported pages */
-        ret = kvm_vm_check_extension(s, KVM_CAP_DIRTY_LOG_RING);
-        if (ret > 0) {
-            if (ring_bytes > ret) {
-                error_report("KVM dirty ring size %" PRIu32 " too big "
-                             "(maximum is %ld).  Please use a smaller value.",
-                             s->kvm_dirty_ring_size,
-                             (long)ret / sizeof(struct kvm_dirty_gfn));
-                ret = -EINVAL;
-                goto err;
-            }
-
-            ret = kvm_vm_enable_cap(s, KVM_CAP_DIRTY_LOG_RING, 0, ring_bytes);
-            if (ret) {
-                error_report("Enabling of KVM dirty ring failed: %s. "
-                             "Suggested minimum value is 1024.", 
strerror(-ret));
-                goto err;
-            }
-
-            s->kvm_dirty_ring_bytes = ring_bytes;
-         } else {
-             warn_report("KVM dirty ring not available, using bitmap method");
-             s->kvm_dirty_ring_size = 0;
+        ret = kvm_dirty_ring_init(s);
+        if (ret < 0) {
+            goto err;
         }
     }
 
-- 
2.23.0