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[Qemu-devel] [PATCH v4 20/21] nbd/client: Work around 3.0 bug for listin
From: |
Eric Blake |
Subject: |
[Qemu-devel] [PATCH v4 20/21] nbd/client: Work around 3.0 bug for listing meta contexts |
Date: |
Thu, 17 Jan 2019 13:36:57 -0600 |
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 <address@hidden>
Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>
---
v4: minor rebase
---
nbd/client.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/nbd/client.c b/nbd/client.c
index 798b82f205a..8a083c2f42c 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;
}
--
2.20.1
- [Qemu-devel] [PATCH v4 05/21] nbd/server: Hoist length check to qmp_nbd_server_add, (continued)
- [Qemu-devel] [PATCH v4 05/21] nbd/server: Hoist length check to qmp_nbd_server_add, Eric Blake, 2019/01/17
- [Qemu-devel] [PATCH v4 06/21] nbd/server: Favor [u]int64_t over off_t, Eric Blake, 2019/01/17
- [Qemu-devel] [PATCH v4 07/21] qemu-nbd: Avoid strtol open-coding, Eric Blake, 2019/01/17
- [Qemu-devel] [PATCH v4 08/21] nbd/client: Refactor nbd_receive_list(), Eric Blake, 2019/01/17
- [Qemu-devel] [PATCH v4 09/21] nbd/client: Move export name into NBDExportInfo, Eric Blake, 2019/01/17
- [Qemu-devel] [PATCH v4 15/21] nbd/client: Pull out oldstyle size determination, Eric Blake, 2019/01/17
- [Qemu-devel] [PATCH v4 11/21] nbd/client: Split out nbd_send_meta_query(), Eric Blake, 2019/01/17
- [Qemu-devel] [PATCH v4 20/21] nbd/client: Work around 3.0 bug for listing meta contexts,
Eric Blake <=
- [Qemu-devel] [PATCH v4 10/21] nbd/client: Change signature of nbd_negotiate_simple_meta_context(), Eric Blake, 2019/01/17
- [Qemu-devel] [PATCH v4 16/21] nbd/client: Refactor nbd_opt_go() to support NBD_OPT_INFO, Eric Blake, 2019/01/17
- [Qemu-devel] [PATCH v4 17/21] nbd/client: Add nbd_receive_export_list(), Eric Blake, 2019/01/17
- [Qemu-devel] [PATCH v4 18/21] nbd/client: Add meta contexts to nbd_receive_export_list(), Eric Blake, 2019/01/17
- [Qemu-devel] [PATCH v4 14/21] nbd/client: Split handshake into two functions, Eric Blake, 2019/01/17
- [Qemu-devel] [PATCH v4 19/21] qemu-nbd: Add --list option, Eric Blake, 2019/01/17
- [Qemu-devel] [PATCH v4 12/21] nbd/client: Split out nbd_receive_one_meta_context(), Eric Blake, 2019/01/17