Reconnect will be implemented in the following commit, so for now,
in semantics below, disconnect itself is a "serious error".

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 qapi/block-core.json | 12 +++++++++++-
 block/nbd-client.h   |  1 +
 block/nbd-client.c   |  1 +
 block/nbd.c          | 16 +++++++++++++++-
 4 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/qapi/block-core.json b/qapi/block-core.json
index 7ccbfff9d0..815258bd89 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -3798,13 +3798,23 @@
 #                  traditional "base:allocation" block status (see
 #                  NBD_OPT_LIST_META_CONTEXT in the NBD protocol) (since 3.0)
 #
+# @reconnect-delay: Reconnect delay. On unexpected disconnect, nbd client tries
+#                   to connect again, until success or serious error. During
+#                   first @reconnect-delay seconds of reconnecting loop all
+#                   requests are paused and have a chance to rerun, if
+#                   successful connect occurs during this time. After
+#                   @reconnect-delay seconds all delayed requests are failed
+#                   and all following requests will be failed too (until
+#                   successful reconnect). Default 0 (Since 4.1)
+#
 # Since: 2.9
 ##
 { 'struct': 'BlockdevOptionsNbd',
   'data': { 'server': 'SocketAddress',
             '*export': 'str',
             '*tls-creds': 'str',
-            '*x-dirty-bitmap': 'str' } }
+            '*x-dirty-bitmap': 'str',
+            '*reconnect-delay': 'uint32' } }
 
 ##
 # @BlockdevOptionsRaw:
diff --git a/block/nbd-client.h b/block/nbd-client.h
index e45b7b0a14..91a6b32bdd 100644
--- a/block/nbd-client.h
+++ b/block/nbd-client.h
@@ -52,6 +52,7 @@ int nbd_client_init(BlockDriverState *bs,
                     QCryptoTLSCreds *tlscreds,
                     const char *hostname,
                     const char *x_dirty_bitmap,
+                    uint32_t reconnect_delay,
                     Error **errp);
 void nbd_client_close(BlockDriverState *bs);
 
diff --git a/block/nbd-client.c b/block/nbd-client.c
index 9f5c86eaa3..1359aff162 100644
--- a/block/nbd-client.c
+++ b/block/nbd-client.c
@@ -1218,6 +1218,7 @@ int nbd_client_init(BlockDriverState *bs,
                     QCryptoTLSCreds *tlscreds,
                     const char *hostname,
                     const char *x_dirty_bitmap,
+                    uint32_t reconnect_delay,
                     Error **errp)
 {
     int ret;
diff --git a/block/nbd.c b/block/nbd.c
index 208be59602..cffb2aee89 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -360,6 +360,18 @@ static QemuOptsList nbd_runtime_opts = {
             .help = "experimental: expose named dirty bitmap in place of "
                     "block status",
         },
+        {
+            .name = "reconnect-delay",
+            .type = QEMU_OPT_NUMBER,
+            .help = "Reconnect delay. On unexpected disconnect, nbd client "
+                    "tries to connect again, until success or serious error. "
+                    "During first @reconnect-delay seconds of reconnecting "
+                    "loop all requests are paused and have a chance to rerun, "
+                    "if successful connect occurs during this time. After"
+                    "@reconnect-delay seconds all delayed requests are failed"
+                    "and all following requests will be failed too (until"
+                    "successful reconnect). Default 0",
+        },
         { /* end of list */ }
     },
 };
@@ -411,7 +423,9 @@ static int nbd_open(BlockDriverState *bs, QDict *options, int flags,
 
     /* NBD handshake */
     ret = nbd_client_init(bs, s->saddr, s->export, tlscreds, hostname,
-                          qemu_opt_get(opts, "x-dirty-bitmap"), errp);
+                          qemu_opt_get(opts, "x-dirty-bitmap"),
+                          qemu_opt_get_number(opts, "reconnect-delay", 0),
+                          errp);
 
  error:
     if (tlscreds) {
-- 
2.18.0

On 4/11/19 12:27 PM, Vladimir Sementsov-Ogievskiy wrote:
> Reconnect will be implemented in the following commit, so for now,
> in semantics below, disconnect itself is a "serious error".
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  qapi/block-core.json | 12 +++++++++++-
>  block/nbd-client.h   |  1 +
>  block/nbd-client.c   |  1 +
>  block/nbd.c          | 16 +++++++++++++++-
>  4 files changed, 28 insertions(+), 2 deletions(-)
> 
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index 7ccbfff9d0..815258bd89 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -3798,13 +3798,23 @@
>  #                  traditional "base:allocation" block status (see
>  #                  NBD_OPT_LIST_META_CONTEXT in the NBD protocol) (since 3.0)
>  #
> +# @reconnect-delay: Reconnect delay. On unexpected disconnect, nbd client tries
> +#                   to connect again, until success or serious error. During
> +#                   first @reconnect-delay seconds of reconnecting loop all
> +#                   requests are paused and have a chance to rerun, if
> +#                   successful connect occurs during this time. After
> +#                   @reconnect-delay seconds all delayed requests are failed
> +#                   and all following requests will be failed too (until
> +#                   successful reconnect). Default 0 (Since 4.1)

Maybe:

On an unexpected disconnect, the nbd client tries to connect again until
succeeding or encountering a serious error.  During the first
@reconnect-delay seconds, all requests are paused and will be rerun on a
successful reconnect. After that time, any delayed requests and all
future requests before a successful reconnect will immediately fail.


> +++ b/block/nbd.c
> @@ -360,6 +360,18 @@ static QemuOptsList nbd_runtime_opts = {
>              .help = "experimental: expose named dirty bitmap in place of "
>                      "block status",
>          },
> +        {
> +            .name = "reconnect-delay",
> +            .type = QEMU_OPT_NUMBER,
> +            .help = "Reconnect delay. On unexpected disconnect, nbd client "
> +                    "tries to connect again, until success or serious error. "
> +                    "During first @reconnect-delay seconds of reconnecting "
> +                    "loop all requests are paused and have a chance to rerun, "
> +                    "if successful connect occurs during this time. After"
> +                    "@reconnect-delay seconds all delayed requests are failed"
> +                    "and all following requests will be failed too (until"
> +                    "successful reconnect). Default 0",

And of course copy any changes to the QMP text to here.

I can touch up grammar, so if there's no other reason to respin,

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org