migration: discard RAMBlocks of type ram_device

Commit Message

Cédric Le Goater April 12, 2018, 3:16 p.m. UTC

On 04/12/2018 04:11 PM, Paolo Bonzini wrote:
> On 12/04/2018 15:51, Peter Maydell wrote:
>> Paolo may have an opinion what the API here should be, but
>> at the MemoryRegion level we already have a mix of functions
>> memory_region_init_foo_nomigrate() and memory_region_init_foo(),
>> which at the moment just control whether we call
>> vmstate_register_ram() or not. Is it possible to hook into that,
>> so that we default to marking RAMBlocks as not-migrated, and
>> when vmstate_register_ram() is called we set the flag to
>> "migrated"?
> 
> Yes, that sounds pretty.

I have added the MIGRATABLE flag un/setting under qemu_ram_un/set_idstr() 
which are the only routines called by vmstate_un/register_ram().   
Tell me if that's fine or if you'd rather have helpers to
set MIGRATABLE from savem ? below is some code extract.

Thanks,

C.

>> NB: this probably requires careful thought to make sure we
>> don't accidentally break migration compat, but it seems like
>> the cleaner approach. At the moment we do weird things if you
>> migrate a RAM block that hasn't had its ID string set, IIRC,
>> so just not migrating those RAM blocks seems like a better
>> plan than mishandling them. It would also mean that the
>> vmstate_register/unregister_ram() functions did what they
>> claim to do based on the function name, I think.

Patch

--- qemu-xive.git.orig/exec.c
+++ qemu-xive.git/exec.c
@@ -104,6 +104,9 @@  static MemoryRegion io_mem_unassigned;
  * (Set during postcopy)
  */
 #define RAM_UF_ZEROPAGE (1 << 3)
+
+/* RAM can be migrated */
+#define RAM_MIGRATABLE (1 << 4)
 #endif
 
 #ifdef TARGET_PAGE_BITS_VARY
@@ -1807,6 +1810,11 @@  void qemu_ram_set_uf_zeroable(RAMBlock *
     rb->flags |= RAM_UF_ZEROPAGE;
 }
 
+bool qemu_ram_is_migratable(RAMBlock *rb)
+{
+    return rb->flags & RAM_MIGRATABLE;
+}
+
 /* Called with iothread lock held.  */
 void qemu_ram_set_idstr(RAMBlock *new_block, const char *name, DeviceState *dev)
 {
@@ -1823,6 +1831,7 @@  void qemu_ram_set_idstr(RAMBlock *new_bl
         }
     }
     pstrcat(new_block->idstr, sizeof(new_block->idstr), name);
+    new_block->flags |= RAM_MIGRATABLE;
 
     rcu_read_lock();
     RAMBLOCK_FOREACH(block) {
@@ -1845,6 +1854,7 @@  void qemu_ram_unset_idstr(RAMBlock *bloc
      */
     if (block) {
         memset(block->idstr, 0, sizeof(block->idstr));
+        block->flags &= ~RAM_MIGRATABLE;
     }
 }