[Qemu-devel] [PATCH v2 1/3] migration: Read JSON VM description on incoming migration

[Alexander Graf <agraf@suse.de>]

One of the really nice things about the VM description format is that it goes
over the wire when live migration is happening. Unfortunately QEMU today closes
any socket once it sees VM_EOF coming, so we never give the VMDESC the chance to
actually land on the wire.

This patch makes QEMU read the description as well. This way we ensure that
anything wire tapping us in between will get the chance to also interpret the
stream.

Along the way we also fix virt tests that assume that number_bytes_sent on the
sender side is equal to number_bytes_read which was true before the VMDESC
patches and is true again with this patch.

Signed-off-by: Alexander Graf <agraf@suse.de>

---

v1 -> v2:

  - read in small chunks
---
 savevm.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/savevm.c b/savevm.c
index 8040766..1b78654 100644
--- a/savevm.c
+++ b/savevm.c
@@ -929,6 +929,7 @@ int qemu_loadvm_state(QEMUFile *f)
     uint8_t section_type;
     unsigned int v;
     int ret;
+    int file_error_after_eof = -1;
 
     if (qemu_savevm_state_blocked(&local_err)) {
         error_report("%s", error_get_pretty(local_err));
@@ -1034,6 +1035,24 @@ int qemu_loadvm_state(QEMUFile *f)
         }
     }
 
+    file_error_after_eof = qemu_file_get_error(f);
+
+    /*
+     * Try to read in the VMDESC section as well, so that dumping tools that
+     * intercept our migration stream have the chance to see it.
+     */
+    if (qemu_get_byte(f) == QEMU_VM_VMDESCRIPTION) {
+        uint32_t size = qemu_get_be32(f);
+        uint8_t *buf = g_malloc(0x1000);
+
+        while (size > 0) {
+            uint32_t read_chunk = MIN(size, 0x1000);
+            qemu_get_buffer(f, buf, read_chunk);
+            size -= read_chunk;
+        }
+        g_free(buf);
+    }
+
     cpu_synchronize_all_post_init();
 
     ret = 0;
@@ -1045,7 +1064,8 @@ out:
     }
 
     if (ret == 0) {
-        ret = qemu_file_get_error(f);
+        /* We may not have a VMDESC section, so ignore relative errors */
+        ret = file_error_after_eof;
     }
 
     return ret;
-- 
1.7.12.4