[Qemu-devel] [RFC PATCH v3 10/19] fix live-migration when "populated=on" is missing

[Vasilis Liaskovitis <vasilis.liaskovitis@profitbricks.com>]

Live migration works after memory hot-add events, as long as the
qemu command line "-dimm" arguments are changed on the destination host
to specify "populated=on" for the dimms that have been hot-added.

If a command-line change has not occured, the destination host does not yet
have the corresponding ramblock in its ram_list. Activate the dimm on the
destination during ram_load.

Perhaps several fields of the DimmDevice should be part of a
VMStateDescription to handle migration in a cleaner way. But the problem
is that ramblocks are checked before qdev vmstates.

Signed-off-by: Vasilis Liaskovitis <vasilis.liaskovitis@profitbricks.com>
---
 arch_init.c |   24 +++++++++++++++++++++---
 1 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/arch_init.c b/arch_init.c
index 5a1173e..b63caa7 100644
--- a/arch_init.c
+++ b/arch_init.c
@@ -45,6 +45,7 @@
 #include "hw/pcspk.h"
 #include "qemu/page_cache.h"
 #include "qmp-commands.h"
+#include "hw/dimm.h"
 
 #ifdef DEBUG_ARCH_INIT
 #define DPRINTF(fmt, ...) \
@@ -740,10 +741,27 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
                     }
 
                     if (!block) {
-                        fprintf(stderr, "Unknown ramblock \"%s\", cannot "
+                        /* this can happen if a dimm was hot-added at source host */
+                        bool ramblock_found = false;
+                        if (dimm_add(id)) {
+                            fprintf(stderr, "Cannot add unknown ramblock \"%s\", "
+                                    "cannot accept migration\n", id);
+                            ret = -EINVAL;
+                            goto done;
+                        }
+                        /* rescan ram_list, verify ramblock is there now */
+                        QLIST_FOREACH(block, &ram_list.blocks, next) {
+                            if (!strncmp(id, block->idstr, sizeof(id))) {
+                                ramblock_found = true;
+                                break;
+                            }
+                        }
+                        if (!ramblock_found) {
+                            fprintf(stderr, "Unknown ramblock \"%s\", cannot "
                                 "accept migration\n", id);
-                        ret = -EINVAL;
-                        goto done;
+                            ret = -EINVAL;
+                            goto done;
+                        }
                     }
 
                     total_ram_bytes -= length;
-- 
1.7.9