Hello all,
This is my first time inside of the qemu code, so your help is greatly
appreciated!
I have been experimenting with stop/start of VMs to/from a migration
stream that excludes RAM pages and let the RAM pages come from memory file
provided by the memory-backend-file called '/dev/shm/mem'.
To disable writing of memory pages to the migration stream, I've disabled
calls to ram_find_and_save_block in ram_save_iterate() and
ram_save_complete() (see patch below). Thus, the migration stream has the
"ram" SaveStateEntry section start/ends, but no pages:
qemu-system-x86_64 \
-object
memory-backend-file,prealloc=no,mem-path=/dev/shm/mem,id=ram-node0,host-nodes=0,policy=bind,size=64m,share=on
\
-numa node,nodeid=0,cpus=0,memdev=ram-node0\
-m 64 -vnc 0:0
Once the VM is running, I press ctrl-B to get the IPXE prompt and then
run 'kernel http://192.168.0.1/foo' to start a network request and watch
it in tcpdump.
Once the download starts, I save the migration file:
migrate "exec:cat > /dev/shm/t"
# ls -lh /dev/shm/t
-rw-r--r-- 1 root root 321K Apr 26 16:06 /dev/shm/t
Now I can kill qemu and boot it again with -incoming:
qemu-system-x86_64 \
-object
memory-backend-file,prealloc=no,mem-path=/dev/shm/mem,id=ram-node0,host-nodes=0,policy=bind,size=64m,share=on
\
-numa node,nodeid=0,cpus=0,memdev=ram-node0\
-m 64 -vnc 0:0 \
-incoming 'exec:cat /dev/shm/t'
It seems to work. That is, network traffic continues (http from IPXE)
which I can see from tcpdump. I can type into the console and it moves
the cursor around---but there is nothing on the screen except the blinking
text-mode cursor! I can even blindly start a new transfer in ipxe: kernel
http://192.168.0.222/foo2 and see it in tcpdump.
So what am I missing here? Is the video memory not saved to /dev/shm/mem?
Or perhaps it is saved, but VGA isn't initialized to use what is
already in /dev/shm/mem? I've tried the cirrus, std, and vmware drivers
to see if they behave differently, but the do not seem to.
Thanks for your help!
--
Eric Wheeler
diff --git a/migration/ram.c b/migration/ram.c
index 021d583..9f4bfff 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -2267,9 +2267,9 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
t0 = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
i = 0;
while ((ret = qemu_file_rate_limit(f)) == 0) {
- int pages;
+ int pages = 0;
- pages = ram_find_and_save_block(rs, false);
+ if (0) pages = ram_find_and_save_block(rs, false);
/* no more pages to sent */
if (pages == 0) {
done = 1;
@@ -2338,9 +2338,9 @@ static int ram_save_complete(QEMUFile *f, void *opaque)
/* flush all remaining blocks regardless of rate limiting */
while (true) {
- int pages;
+ int pages = 0;
- pages = ram_find_and_save_block(rs, !migration_in_colo_state());
+ if (0) pages = ram_find_and_save_block(rs, !migration_in_colo_state());
/* no more blocks to sent */
if (pages == 0) {
break;
