[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH 12/14] nbd/client: Work around 3.0 bug for listi
From: |
Vladimir Sementsov-Ogievskiy |
Subject: |
Re: [Qemu-devel] [PATCH 12/14] nbd/client: Work around 3.0 bug for listing meta contexts |
Date: |
Fri, 7 Dec 2018 11:21:17 +0000 |
01.12.2018 1:03, 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 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).
related thing:
should we document these bugs with corresponding version numbers in
docs/interop/nbd.txt?
>
> Signed-off-by: Eric Blake <address@hidden>
>
> ---
> Done as a separate patch to make it easier to revert when we no
> longer care about 3.0 servers
> ---
> nbd/client.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/nbd/client.c b/nbd/client.c
> index 6292de560ee..928ecabd420 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 */
>
> @@ -736,12 +737,13 @@ static int nbd_negotiate_simple_meta_context(QIOChannel
> *ioc,
> return -1;
> }
> g_free(name);
> + received = true;
> } else {
> info->contexts = g_renew(char *, info->contexts,
> ++info->n_contexts);
> info->contexts[info->n_contexts - 1] = name;
> + received |= strstart(name, "qemu:", NULL);
so, for _LIST_, it is actually received_qemu var. It has taken some time for me
to understand that it's ok (turns out, that this variable actually isn't used
for
_LIST_ case).. Personally I don't like it, for me it's too tricky, but anyway,
you
said, you'll refactor this function somehow.
> }
> - received = true;
>
> /* receive NBD_REP_ACK */
> if (nbd_receive_option_reply(ioc, opt, &reply, errp) < 0) {
> @@ -771,6 +773,13 @@ static int nbd_negotiate_simple_meta_context(QIOChannel
> *ioc,
> info->meta_base_allocation_id = received_id;
> }
>
> + /* Recurse to work around qemu 3.0 bug - the server forgot to send
> + * "qemu:" replies to 0 queries. */
> + if (!context && !received) {
> + return nbd_negotiate_simple_meta_context(ioc, opt, "qemu:", info,
> + errp);
> + }
> +
> return received || opt == NBD_OPT_LIST_META_CONTEXT;
> }
>
--
Best regards,
Vladimir
- Re: [Qemu-devel] [PATCH 12/14] nbd/client: Work around 3.0 bug for listing meta contexts,
Vladimir Sementsov-Ogievskiy <=