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authorEric Blake <eblake@redhat.com>2019-01-17 13:36:57 -0600
committerEric Blake <eblake@redhat.com>2019-01-21 15:49:52 -0600
commit7c6f5ddca62905e67025aa0657e8a011cbdffa11 (patch)
tree3265f47024862755978ed6054486d78e95878794 /nbd
parent68b96f15838d309ef791cb83b5eec1bd7da271c2 (diff)
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nbd/client: Work around 3.0 bug for listing meta contexts
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, so that a modern qemu server gives full context output right away, and the client refuses 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, repeat with 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 <eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20190117193658.16413-21-eblake@redhat.com>
Diffstat (limited to 'nbd')
-rw-r--r--nbd/client.c19
1 files changed, 19 insertions, 0 deletions
diff --git a/nbd/client.c b/nbd/client.c
index 798b82f..8a083c2 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 */
@@ -828,6 +829,8 @@ static int nbd_list_meta_contexts(QIOChannel *ioc,
Error **errp)
{
int ret;
+ int seen_any = false;
+ int seen_qemu = false;
if (nbd_send_meta_query(ioc, NBD_OPT_LIST_META_CONTEXT,
info->name, NULL, errp) < 0) {
@@ -839,9 +842,25 @@ 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_meta_query(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;
}