Re: [PATCH v3 18/33] nbd/client-connection: shutdown connection on release

[Roman Kagan]

On Fri, Apr 16, 2021 at 11:08:56AM +0300, Vladimir Sementsov-Ogievskiy wrote:
> Now, when thread can do negotiation and retry, it may run relatively
> long. We need a mechanism to stop it, when user is not interested in
> result anymore. So, on nbd_client_connection_release() let's shutdown
> the socked, and do not retry connection if thread is detached.

This kinda answers my question to the previous patch about reconnect
cancellation.

> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  nbd/client-connection.c | 36 ++++++++++++++++++++++++++----------
>  1 file changed, 26 insertions(+), 10 deletions(-)
> 
> diff --git a/nbd/client-connection.c b/nbd/client-connection.c
> index 002bd91f42..54f73c6c24 100644
> --- a/nbd/client-connection.c
> +++ b/nbd/client-connection.c
> @@ -158,9 +158,13 @@ static void *connect_thread_func(void *opaque)
>      uint64_t timeout = 1;
>      uint64_t max_timeout = 16;
>  
> -    while (true) {
> +    qemu_mutex_lock(&conn->mutex);
> +    while (!conn->detached) {
> +        assert(!conn->sioc);
>          conn->sioc = qio_channel_socket_new();
>  
> +        qemu_mutex_unlock(&conn->mutex);
> +
>          error_free(conn->err);
>          conn->err = NULL;
>          conn->updated_info = conn->initial_info;
> @@ -171,14 +175,20 @@ static void *connect_thread_func(void *opaque)
>          conn->updated_info.x_dirty_bitmap = NULL;
>          conn->updated_info.name = NULL;
>  
> +        qemu_mutex_lock(&conn->mutex);
> +
>          if (ret < 0) {
>              object_unref(OBJECT(conn->sioc));
>              conn->sioc = NULL;
> -            if (conn->do_retry) {
> +            if (conn->do_retry && !conn->detached) {
> +                qemu_mutex_unlock(&conn->mutex);
> +
>                  sleep(timeout);
>                  if (timeout < max_timeout) {
>                      timeout *= 2;
>                  }
> +
> +                qemu_mutex_lock(&conn->mutex);
>                  continue;
>              }
>          }
> @@ -186,15 +196,17 @@ static void *connect_thread_func(void *opaque)
>          break;
>      }
>  
> -    WITH_QEMU_LOCK_GUARD(&conn->mutex) {
> -        assert(conn->running);
> -        conn->running = false;
> -        if (conn->wait_co) {
> -            aio_co_schedule(NULL, conn->wait_co);
> -            conn->wait_co = NULL;
> -        }
> -        do_free = conn->detached;
> +    /* mutex is locked */
> +
> +    assert(conn->running);
> +    conn->running = false;
> +    if (conn->wait_co) {
> +        aio_co_schedule(NULL, conn->wait_co);
> +        conn->wait_co = NULL;
>      }
> +    do_free = conn->detached;
> +
> +    qemu_mutex_unlock(&conn->mutex);

This basically reverts some hunks from patch 15 "nbd/client-connection:
use QEMU_LOCK_GUARD".  How about dropping them there (they weren't an
obvious improvement even then).

Roman.

>  
>      if (do_free) {
>          nbd_client_connection_do_free(conn);
> @@ -215,6 +227,10 @@ void nbd_client_connection_release(NBDClientConnection 
> *conn)
>      if (conn->running) {
>          conn->detached = true;
>      }
> +    if (conn->sioc) {
> +        qio_channel_shutdown(QIO_CHANNEL(conn->sioc),
> +                             QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
> +    }
>      do_free = !conn->running && !conn->detached;
>      qemu_mutex_unlock(&conn->mutex);
>  
> -- 
> 2.29.2
>