Re: [Qemu-devel] HEAD is failing virt-test on migration tests

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Alexander Graf (agraf@suse.de) wrote:

<snip>

> Can you please test whether the patch below makes things work for you again?

The patch below fixes RDMA migration (same host); however, see comments.

> Alex
> 
> From ef6fde21007e62529799264f57a65c6bb3d0d414 Mon Sep 17 00:00:00 2001
> From: Alexander Graf <agraf@suse.de>
> Date: Sat, 14 Feb 2015 00:21:01 +0100
> Subject: [PATCH] migration: Read JSON VM description on incoming migration
> 
> 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>
> 
> diff --git a/savevm.c b/savevm.c
> index 8040766..ff4bead 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 +1035,22 @@ 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) {

You could use qemu_peek_byte for that?

> +        uint32_t size = qemu_get_be32(f);
> +        uint8_t *buf = g_malloc(size);
> +
> +        if (buf) {
> +            qemu_get_buffer(f, buf, size);
> +            g_free(buf);
> +        }

This is slightly dangerous; a malformed file could send you a huge
value and get you to allocate lots of memory for no good reason.

You could do some clever; but personally I'd just loop around a
nice small buffer until it's gone.

As mentioned on IRC; I'm still worried though that this is only
a fix for loading on newer versions; migration to an older QEMU
with the same machine type would fail.
(Yes I know mythically that no one cares about this; but I do).

Dave

> +    }
> +
>      cpu_synchronize_all_post_init();
> 
>      ret = 0;
> @@ -1045,7 +1062,8 @@ 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;
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK