slirp: Enable multiple instances

Once again this was a long journey to reach the destination: Allow to
instantiate slirp multiple times. But as in the past, the journey was
worthwhile, cleaning up, fixing and enhancing various parts of the user
space network stack along the way.

What is this particular change good for? Multiple slirps instances
allow separated user space networks for guests with multiple NICs. This
is already possible, but without any slirp support for the second
network, ie. without a chance to talk to that network from the host via
IP. We have a legacy guest system here that benefits from this slirp
enhancement, allowing us to run both of its NICs purely over
unprivileged user space IP stacks.

Another benefit of this patch is that it simply removes an artificial
restriction of the configuration space qemu is providing, avoiding
another source of surprises that users may face when playing with
possible setups.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 19 insertions, 18 deletions

diff --git a/net.c b/net.c
index 389be4a6adb..f180b33c718 100644
--- a/net.c
+++ b/net.c
@@ -678,6 +678,7 @@ struct slirp_config_str {
 };
 
 typedef struct SlirpState {
+    TAILQ_ENTRY(SlirpState) entry;
     VLANClientState *vc;
     Slirp *slirp;
 } SlirpState;
@@ -685,7 +686,8 @@ typedef struct SlirpState {
 static struct slirp_config_str *slirp_configs;
 const char *legacy_tftp_prefix;
 const char *legacy_bootp_filename;
-static SlirpState *slirp_state;
+static TAILQ_HEAD(slirp_stacks, SlirpState) slirp_stacks =
+    TAILQ_HEAD_INITIALIZER(slirp_stacks);
 
 static void slirp_hostfwd(SlirpState *s, Monitor *mon, const char *redir_str,
                           int legacy_format);
@@ -734,7 +736,7 @@ static void net_slirp_cleanup(VLANClientState *vc)
     SlirpState *s = vc->opaque;
 
     slirp_cleanup(s->slirp);
-    slirp_state = NULL;
+    TAILQ_REMOVE(&slirp_stacks, s, entry);
     qemu_free(s);
 }
 
@@ -842,7 +844,7 @@ static int net_slirp_init(Monitor *mon, VLANState *vlan, const char *model,
     s = qemu_mallocz(sizeof(SlirpState));
     s->slirp = slirp_init(restricted, net, mask, host, vhostname,
                           tftp_export, bootfile, dhcp, dns, s);
-    slirp_state = s;
+    TAILQ_INSERT_TAIL(&slirp_stacks, s, entry);
 
     while (slirp_configs) {
         struct slirp_config_str *config = slirp_configs;
@@ -881,7 +883,7 @@ void net_slirp_hostfwd_remove(Monitor *mon, const char *src_str)
     int is_udp = 0;
     int err;
 
-    if (!slirp_state) {
+    if (TAILQ_EMPTY(&slirp_stacks)) {
         monitor_printf(mon, "user mode network stack not in use\n");
         return;
     }
@@ -908,7 +910,7 @@ void net_slirp_hostfwd_remove(Monitor *mon, const char *src_str)
 
     host_port = atoi(p);
 
-    err = slirp_remove_hostfwd(slirp_state->slirp, is_udp,
+    err = slirp_remove_hostfwd(TAILQ_FIRST(&slirp_stacks)->slirp, is_udp,
                                host_addr, host_port);
 
     monitor_printf(mon, "host forwarding rule for %s %s\n", src_str,
@@ -984,19 +986,19 @@ static void slirp_hostfwd(SlirpState *s, Monitor *mon, const char *redir_str,
 
 void net_slirp_hostfwd_add(Monitor *mon, const char *redir_str)
 {
-    if (!slirp_state) {
+    if (TAILQ_EMPTY(&slirp_stacks)) {
         monitor_printf(mon, "user mode network stack not in use\n");
         return;
     }
 
-    slirp_hostfwd(slirp_state, mon, redir_str, 0);
+    slirp_hostfwd(TAILQ_FIRST(&slirp_stacks), mon, redir_str, 0);
 }
 
 void net_slirp_redir(const char *redir_str)
 {
     struct slirp_config_str *config;
 
-    if (!slirp_state) {
+    if (TAILQ_EMPTY(&slirp_stacks)) {
         config = qemu_malloc(sizeof(*config));
         pstrcpy(config->str, sizeof(config->str), redir_str);
         config->flags = SLIRP_CFG_HOSTFWD | SLIRP_CFG_LEGACY;
@@ -1005,7 +1007,7 @@ void net_slirp_redir(const char *redir_str)
         return;
     }
 
-    slirp_hostfwd(slirp_state, NULL, redir_str, 1);
+    slirp_hostfwd(TAILQ_FIRST(&slirp_stacks), NULL, redir_str, 1);
 }
 
 #ifndef _WIN32
@@ -1106,8 +1108,8 @@ void net_slirp_smb(const char *exported_dir)
         exit(1);
     }
     legacy_smb_export = exported_dir;
-    if (slirp_state) {
-        slirp_smb(slirp_state, exported_dir, vserver_addr);
+    if (!TAILQ_EMPTY(&slirp_stacks)) {
+        slirp_smb(TAILQ_FIRST(&slirp_stacks), exported_dir, vserver_addr);
     }
 }
 
@@ -1198,13 +1200,12 @@ static void slirp_guestfwd(SlirpState *s, Monitor *mon, const char *config_str,
 
 void do_info_usernet(Monitor *mon)
 {
-    SlirpState *s = slirp_state;
+    SlirpState *s;
 
-    if (!s) {
-        return;
+    TAILQ_FOREACH(s, &slirp_stacks, entry) {
+        monitor_printf(mon, "VLAN %d (%s):\n", s->vc->vlan->id, s->vc->name);
+        slirp_connection_info(s->slirp, mon);
     }
-    monitor_printf(mon, "VLAN %d (%s):\n", s->vc->vlan->id, s->vc->name);
-    slirp_connection_info(s->slirp, mon);
 }
 
 #endif /* CONFIG_SLIRP */
@@ -2515,7 +2516,7 @@ int net_client_init(Monitor *mon, const char *device, const char *p)
         qemu_free(smb_export);
         qemu_free(vsmbsrv);
     } else if (!strcmp(device, "channel")) {
-        if (!slirp_state) {
+        if (TAILQ_EMPTY(&slirp_stacks)) {
             struct slirp_config_str *config;
 
             config = qemu_malloc(sizeof(*config));
@@ -2524,7 +2525,7 @@ int net_client_init(Monitor *mon, const char *device, const char *p)
             config->next = slirp_configs;
             slirp_configs = config;
         } else {
-            slirp_guestfwd(slirp_state, mon, p, 1);
+            slirp_guestfwd(TAILQ_FIRST(&slirp_stacks), mon, p, 1);
         }
         ret = 0;
     } else