Commit 3d068aff forgot to advertise available qemu: contexts
when the client requests a list with 0 queries. Furthermore,
3.0 shipped with a qemu-img hack of x-dirty-bitmap (commit
216ee365) that _silently_ acts as though the entire image is
clean if a requested bitmap is not present. Both bugs have
been recently fixed to give full output from the start, and
to refuse a connection if a requested x-dirty-bitmap was not
found.
Still, it is likely that there will be users that have to
work with a mix of old and new qemu versions, depending on
which features get backported where, at which point being
able to rely on 'qemu-img --list' output to know for sure
whether a given NBD export has the desired dirty bitmap is
much nicer than blindly connecting and risking that the
entire image may appear clean. We can make our --list code
smart enough to work around buggy servers by tracking
whether we've seen any qemu: replies in the original 0-query
list; if not, recurse to a single query on "qemu:" (which
may still have no replies, but then we know for sure we
didn't trip up on the server bug).
Signed-off-by: Eric Blake <ebl...@redhat.com>
---
Done as a separate patch to make it easier to revert when we no
longer care about 3.0 servers
v2: rebase on top of earlier patch splits
---
nbd/client.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/nbd/client.c b/nbd/client.c
index d392b5e8bee..48fa6e10b92 100644
--- a/nbd/client.c
+++ b/nbd/client.c
@@ -21,6 +21,7 @@
#include "qapi/error.h"
#include "trace.h"
#include "nbd-internal.h"
+#include "qemu/cutils.h"
/* Definitions for opaque data types */
@@ -819,6 +820,8 @@ static int nbd_list_meta_contexts(QIOChannel *ioc,
Error **errp)
{
int ret;
+ int seen_any = false;
+ int seen_qemu = false;
if (nbd_send_one_meta_context(ioc, NBD_OPT_LIST_META_CONTEXT,
info->name, NULL, errp) < 0) {
@@ -830,9 +833,25 @@ static int nbd_list_meta_contexts(QIOChannel *ioc,
ret = nbd_receive_one_meta_context(ioc, NBD_OPT_LIST_META_CONTEXT,
&context, NULL, errp);
+ if (ret == 0 && seen_any && !seen_qemu) {
+ /*
+ * Work around qemu 3.0 bug: the server forgot to send
+ * "qemu:" replies to 0 queries. If we saw at least one
+ * reply (probably base:allocation), but none of them were
+ * qemu:, then run a more specific query to make sure.
+ */
+ seen_qemu = true;
+ if (nbd_send_one_meta_context(ioc, NBD_OPT_LIST_META_CONTEXT,
+ info->name, "qemu:", errp) < 0) {
+ return -1;
+ }
+ continue;
+ }
if (ret <= 0) {
return ret;
}
+ seen_any = true;
+ seen_qemu |= strstart(context, "qemu:", NULL);
info->contexts = g_renew(char *, info->contexts, ++info->n_contexts);
info->contexts[info->n_contexts - 1] = context;
}
--
2.17.2
