[PATCH v4 1/7] nbd: allow reconnect on open, with corresponding new options

[Vladimir Sementsov-Ogievskiy]

It is useful when start of vm and start of nbd server are not
simple to sync.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
 qapi/block-core.json |  9 ++++++++-
 block/nbd.c          | 45 +++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/qapi/block-core.json b/qapi/block-core.json
index 1d3dd9cb48..8cf82417a6 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -4096,6 +4096,12 @@
 #                   future requests before a successful reconnect will
 #                   immediately fail. Default 0 (Since 4.2)
 #
+# @open-timeout: In seconds. If zero, the nbd driver tries the connection
+#                only once, and fails to open if the connection fails.
+#                If non-zero, the nbd driver will repeat connection attempts
+#                until successful or until @open-timeout seconds have elapsed.
+#                Default 0 (Since 6.2)
+#
 # Features:
 # @unstable: Member @x-dirty-bitmap is experimental.
 #
@@ -4106,7 +4112,8 @@
             '*export': 'str',
             '*tls-creds': 'str',
             '*x-dirty-bitmap': { 'type': 'str', 'features': [ 'unstable' ] },
-            '*reconnect-delay': 'uint32' } }
+            '*reconnect-delay': 'uint32',
+            '*open-timeout': 'uint32' } }
 
 ##
 # @BlockdevOptionsRaw:
diff --git a/block/nbd.c b/block/nbd.c
index 5ef462db1b..63dbfa807d 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -80,6 +80,7 @@ typedef struct BDRVNBDState {
     NBDClientState state;
 
     QEMUTimer *reconnect_delay_timer;
+    QEMUTimer *open_timer;
 
     NBDClientRequest requests[MAX_NBD_REQUESTS];
     NBDReply reply;
@@ -87,6 +88,7 @@ typedef struct BDRVNBDState {
 
     /* Connection parameters */
     uint32_t reconnect_delay;
+    uint32_t open_timeout;
     SocketAddress *saddr;
     char *export, *tlscredsid;
     QCryptoTLSCreds *tlscreds;
@@ -218,6 +220,32 @@ static void nbd_teardown_connection(BlockDriverState *bs)
     s->state = NBD_CLIENT_QUIT;
 }
 
+static void open_timer_del(BDRVNBDState *s)
+{
+    if (s->open_timer) {
+        timer_free(s->open_timer);
+        s->open_timer = NULL;
+    }
+}
+
+static void open_timer_cb(void *opaque)
+{
+    BDRVNBDState *s = opaque;
+
+    nbd_co_establish_connection_cancel(s->conn);
+    open_timer_del(s);
+}
+
+static void open_timer_init(BDRVNBDState *s, uint64_t expire_time_ns)
+{
+    assert(!s->open_timer);
+    s->open_timer = aio_timer_new(bdrv_get_aio_context(s->bs),
+                                  QEMU_CLOCK_REALTIME,
+                                  SCALE_NS,
+                                  open_timer_cb, s);
+    timer_mod(s->open_timer, expire_time_ns);
+}
+
 static bool nbd_client_connecting(BDRVNBDState *s)
 {
     NBDClientState state = qatomic_load_acquire(&s->state);
@@ -1742,6 +1770,15 @@ static QemuOptsList nbd_runtime_opts = {
                     "future requests before a successful reconnect will "
                     "immediately fail. Default 0",
         },
+        {
+            .name = "open-timeout",
+            .type = QEMU_OPT_NUMBER,
+            .help = "In seconds. If zero, the nbd driver tries the connection "
+                    "only once, and fails to open if the connection fails. "
+                    "If non-zero, the nbd driver will repeat connection "
+                    "attempts until successful or until @open-timeout seconds "
+                    "have elapsed. Default 0",
+        },
         { /* end of list */ }
     },
 };
@@ -1797,6 +1834,7 @@ static int nbd_process_options(BlockDriverState *bs, 
QDict *options,
     }
 
     s->reconnect_delay = qemu_opt_get_number(opts, "reconnect-delay", 0);
+    s->open_timeout = qemu_opt_get_number(opts, "open-timeout", 0);
 
     ret = 0;
 
@@ -1828,7 +1866,12 @@ static int nbd_open(BlockDriverState *bs, QDict 
*options, int flags,
     s->conn = nbd_client_connection_new(s->saddr, true, s->export,
                                         s->x_dirty_bitmap, s->tlscreds);
 
-    /* TODO: Configurable retry-until-timeout behaviour. */
+    if (s->open_timeout) {
+        nbd_client_connection_enable_retry(s->conn);
+        open_timer_init(s, qemu_clock_get_ns(QEMU_CLOCK_REALTIME) +
+                        s->open_timeout * NANOSECONDS_PER_SECOND);
+    }
+
     s->state = NBD_CLIENT_CONNECTING_WAIT;
     ret = nbd_do_establish_connection(bs, errp);
     if (ret < 0) {
-- 
2.31.1