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[Qemu-devel] [PATCH for-2.8] migration: Fix return code of ram_save_iter

From: Thomas Huth
Subject: [Qemu-devel] [PATCH for-2.8] migration: Fix return code of ram_save_iterate()
Date: Fri, 4 Nov 2016 14:10:17 +0100

qemu_savevm_state_iterate() expects the iterators to return 1
when they are done, and 0 if there is still something left to do.
However, ram_save_iterate() does not obey this rule and returns
the number of saved pages instead. This causes a fatal hang with
ppc64 guests when you run QEMU like this (also works with TCG):

 qemu-img create -f qcow2  /tmp/test.qcow2 1M
 qemu-system-ppc64 -nographic -nodefaults -m 256 \
                   -hda /tmp/test.qcow2 -serial mon:stdio

... then switch to the monitor by pressing CTRL-a c and try to
save a snapshot with "savevm test1" for example.

After the first iteration, ram_save_iterate() always returns 0 here,
so that qemu_savevm_state_iterate() hangs in an endless loop and you
can only "kill -9" the QEMU process.
Fix it by using proper return values in ram_save_iterate().

Signed-off-by: Thomas Huth <address@hidden>
 migration/ram.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/migration/ram.c b/migration/ram.c
index fb9252d..a1c8089 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1987,7 +1987,7 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
     int ret;
     int i;
     int64_t t0;
-    int pages_sent = 0;
+    int done = 0;
     if (ram_list.version != last_version) {
@@ -2007,9 +2007,9 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
         pages = ram_find_and_save_block(f, false, &bytes_transferred);
         /* no more pages to sent */
         if (pages == 0) {
+            done = 1;
-        pages_sent += pages;
         /* we want to check in the 1st loop, just in case it was the 1st time
@@ -2044,7 +2044,7 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
         return ret;
-    return pages_sent;
+    return done;
 /* Called with iothread lock */

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