Is it possible to increase TCP listen backlog for smbd?

Environment

• Red Hat Enterprise Linux 7, 8, 9
• samba

Issue

• Is it possible to increase TCP listen backlog for smbd?

Resolution

• No, the backlog argument of listen() is a hardcoded value with a macro definition, SMBD_LISTEN_BACKLOG.

samba-4.15.5-108.el9_0.src.rpm(RHEL9)
source3/include/local.h:

/* size of listen() backlog in smbd */
#define SMBD_LISTEN_BACKLOG 50

source3/smbd/server.c:

static bool smbd_open_one_socket(struct smbd_parent_context *parent,
                                 struct tevent_context *ev_ctx,
                                 const struct sockaddr_storage *ifss,
                                 uint16_t port)
{
...

        if (listen(s->fd, SMBD_LISTEN_BACKLOG) == -1) {
                DEBUG(0,("smbd_open_one_socket: listen: "
                        "%s\n", strerror(errno)));
                        close(s->fd);
                TALLOC_FREE(s);
                return false;
        }

Diagnostic Steps

• Refer to How do I view the listen backlog of a TCP socket?.

$ ss -npl src :445
Netid          State           Recv-Q          Send-Q                   Local Address:Port                    Peer Address:Port          Process          
tcp            LISTEN          0               50                             0.0.0.0:445                          0.0.0.0:*                              
tcp            LISTEN          0               50                                [::]:445                             [::]:*                              
$ ss -npl src :139
Netid          State           Recv-Q          Send-Q                   Local Address:Port                    Peer Address:Port          Process          
tcp            LISTEN          0               50                             0.0.0.0:139                          0.0.0.0:*                              
tcp            LISTEN          0               50                                [::]:139                             [::]:*                              
$ sysctl net.core.somaxconn
net.core.somaxconn = 4096

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