On Fri, Feb 5, 2021 at 8:57 PM Eric Blake <ebl...@redhat.com> wrote:
>
> Our default of a backlog of 1 connection is rather puny, particularly
> for scenarios where we expect multiple listeners to connect (such as
> qemu-nbd -e X). This is especially important for Unix sockets, as a
> definite benefit to clients: at least on Linux, a client trying to
> connect to a Unix socket with a backlog gets an EAGAIN failure with no
> way to poll() for when the backlog is no longer present short of
> sleeping an arbitrary amount of time before retrying.
>
> See https://bugzilla.redhat.com/1925045 for a demonstration of where
> our low backlog prevents libnbd from connecting as many parallel
> clients as it wants.
>
> Reported-by: Richard W.M. Jones <rjo...@redhat.com>
> Signed-off-by: Eric Blake <ebl...@redhat.com>
> ---
>
> v2: target the correct API used by qemu-nbd, rather than an unrelated
> legacy wrapper [Dan]
>
> qemu-nbd.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/qemu-nbd.c b/qemu-nbd.c
> index 608c63e82a25..cd20ee73be19 100644
> --- a/qemu-nbd.c
> +++ b/qemu-nbd.c
> @@ -965,7 +965,8 @@ int main(int argc, char **argv)
> server = qio_net_listener_new();
> if (socket_activation == 0) {
> saddr = nbd_build_socket_address(sockpath, bindto, port);
> - if (qio_net_listener_open_sync(server, saddr, 1, &local_err) < 0) {
> + if (qio_net_listener_open_sync(server, saddr, SOMAXCONN,
Shouldn't we use value based on --shared=N?
Using maximum value makes sense for generic server expecting to handle many
connections from different clients. qemu-nbd is typically used by one
client, and we
need to make it possible to connect a known number of connections quickly.
> + &local_err) < 0) {
> object_unref(OBJECT(server));
> error_report_err(local_err);
> exit(EXIT_FAILURE);
> --
> 2.30.0
>
>
