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Re: [Qemu-devel] [PATCH v3 18/19] nbd/client: Work around 3.0 bug for li
From: |
Vladimir Sementsov-Ogievskiy |
Subject: |
Re: [Qemu-devel] [PATCH v3 18/19] nbd/client: Work around 3.0 bug for listing meta contexts |
Date: |
Wed, 16 Jan 2019 15:43:38 +0000 |
12.01.2019 20:58, Eric Blake wrote:
> 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>
> Message-Id: <address@hidden>
Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> ---
> nbd/client.c | 19 +++++++++++++++++++
> 1 file changed, 19 insertions(+)
>
> diff --git a/nbd/client.c b/nbd/client.c
> index 2001e6e8160..64f3e45edd4 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_one_meta_context(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
if we are saying about 3.0, it is base:allocation for sure, isn't it?
> + * 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;
> }
>
--
Best regards,
Vladimir
- Re: [Qemu-devel] [PATCH v3 15/19] nbd/client: Add nbd_receive_export_list(), (continued)
[Qemu-devel] [PATCH v3 04/19] nbd/server: Hoist length check to qemp_nbd_server_add, Eric Blake, 2019/01/12
Re: [Qemu-devel] [PATCH v3 04/19] nbd/server: Hoist length check to qemp_nbd_server_add, Eric Blake, 2019/01/16