From e6aae1d0368a152924c38775e517f4e83c1d898b Mon Sep 17 00:00:00 2001
From: Eric Blake <eblake@redhat.com>
Date: Wed, 11 May 2022 19:49:23 -0500
Subject: [PATCH 1/2] qemu-nbd: Pass max connections to blockdev layer
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RH-Author: Eric Blake <eblake@redhat.com>
RH-MergeRequest: 90: Advertise MULTI_CONN on writeable NBD servers
RH-Commit: [1/2] b0e33fd125bf3523b8b9a4dead3c8bb2342bfd4e (ebblake/centos-qemu-kvm)
RH-Bugzilla: 1708300
RH-Acked-by: Nir Soffer <None>
RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
RH-Acked-by: Daniel P. Berrangé <berrange@redhat.com>

The next patch wants to adjust whether the NBD server code advertises
MULTI_CONN based on whether it is known if the server limits to
exactly one client.  For a server started by QMP, this information is
obtained through nbd_server_start (which can support more than one
export); but for qemu-nbd (which supports exactly one export), it is
controlled only by the command-line option -e/--shared.  Since we
already have a hook function used by qemu-nbd, it's easiest to just
alter its signature to fit our needs.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20220512004924.417153-2-eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit a5fced40212ed73c715ca298a2929dd4d99c9999)
Signed-off-by: Eric Blake <eblake@redhat.com>
---
 blockdev-nbd.c      | 8 ++++----
 include/block/nbd.h | 2 +-
 qemu-nbd.c          | 2 +-
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/blockdev-nbd.c b/blockdev-nbd.c
index 9840d25a82..add41a23af 100644
--- a/blockdev-nbd.c
+++ b/blockdev-nbd.c
@@ -30,18 +30,18 @@ typedef struct NBDServerData {
 } NBDServerData;
 
 static NBDServerData *nbd_server;
-static bool is_qemu_nbd;
+static int qemu_nbd_connections = -1; /* Non-negative if this is qemu-nbd */
 
 static void nbd_update_server_watch(NBDServerData *s);
 
-void nbd_server_is_qemu_nbd(bool value)
+void nbd_server_is_qemu_nbd(int max_connections)
 {
-    is_qemu_nbd = value;
+    qemu_nbd_connections = max_connections;
 }
 
 bool nbd_server_is_running(void)
 {
-    return nbd_server || is_qemu_nbd;
+    return nbd_server || qemu_nbd_connections >= 0;
 }
 
 static void nbd_blockdev_client_closed(NBDClient *client, bool ignored)
diff --git a/include/block/nbd.h b/include/block/nbd.h
index a98eb665da..c5a29ce1c6 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -344,7 +344,7 @@ void nbd_client_new(QIOChannelSocket *sioc,
 void nbd_client_get(NBDClient *client);
 void nbd_client_put(NBDClient *client);
 
-void nbd_server_is_qemu_nbd(bool value);
+void nbd_server_is_qemu_nbd(int max_connections);
 bool nbd_server_is_running(void);
 void nbd_server_start(SocketAddress *addr, const char *tls_creds,
                       const char *tls_authz, uint32_t max_connections,
diff --git a/qemu-nbd.c b/qemu-nbd.c
index 713e7557a9..8c25ae93df 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -1087,7 +1087,7 @@ int main(int argc, char **argv)
 
     bs->detect_zeroes = detect_zeroes;
 
-    nbd_server_is_qemu_nbd(true);
+    nbd_server_is_qemu_nbd(shared);
 
     export_opts = g_new(BlockExportOptions, 1);
     *export_opts = (BlockExportOptions) {
-- 
2.31.1