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 --- 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); } - 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; } -- 2.17.2