[Qemu-devel] [PATCH] RFC: use logging count for individual regions

[Glauber Costa <glommer@redhat.com>]

qemu-kvm use this scheme of logging count of individual regions,
which is, IMHO, more flexible which the one we have right now.
I'm proposing we use it.

Anthony, please don't apply this patch yet, as I would want it
to receive proper testing, and FYI, current migration broken ;(
- and I don't really have time to go debug it now.

Jan: Please let me know what you think of it.

Thanks!

Signed-off-by: Glauber Costa <glommer@redhat.com>
CC: Jan Kiszka <jan.kiszka@siemens.com>
---
 kvm-all.c |   21 ++++++++++++---------
 1 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/kvm-all.c b/kvm-all.c
index 8567ac9..7d942c8 100644
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -46,6 +46,7 @@ typedef struct KVMSlot
     ram_addr_t phys_offset;
     int slot;
     int flags;
+    uint32_t logging_count;
 } KVMSlot;
 
 typedef struct kvm_dirty_log KVMDirtyLog;
@@ -59,7 +60,6 @@ struct KVMState
     int vmfd;
     int coalesced_mmio;
     int broken_set_mem_region;
-    int migration_log;
 #ifdef KVM_CAP_SET_GUEST_DEBUG
     struct kvm_sw_breakpoint_head kvm_sw_breakpoints;
 #endif
@@ -137,9 +137,7 @@ static int kvm_set_user_memory_region(KVMState *s, KVMSlot *slot)
     mem.memory_size = slot->memory_size;
     mem.userspace_addr = (unsigned long)qemu_get_ram_ptr(slot->phys_offset);
     mem.flags = slot->flags;
-    if (s->migration_log) {
-        mem.flags |= KVM_MEM_LOG_DIRTY_PAGES;
-    }
+
     return kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem);
 }
 
@@ -230,15 +228,22 @@ static int kvm_dirty_pages_log_change(target_phys_addr_t phys_addr,
             return -EINVAL;
     }
 
+    if (flags & KVM_MEM_LOG_DIRTY_PAGES) {
+        if (mem->logging_count++) {
+            return 0;
+        }
+    } else {
+        if (--mem->logging_count) {
+            return 0;
+        }
+    }
+
     old_flags = mem->flags;
 
     flags = (mem->flags & ~mask) | flags;
     mem->flags = flags;
 
     /* If nothing changed effectively, no need to issue ioctl */
-    if (s->migration_log) {
-        flags |= KVM_MEM_LOG_DIRTY_PAGES;
-    }
     if (flags == old_flags) {
             return 0;
     }
@@ -266,8 +271,6 @@ int kvm_set_migration_log(int enable)
     KVMSlot *mem;
     int i, err;
 
-    s->migration_log = enable;
-
     for (i = 0; i < ARRAY_SIZE(s->slots); i++) {
         mem = &s->slots[i];
 
-- 
1.6.2.2