network/tuntap: save tun or tap file descriptor in fd store

src/network/netdev/netdev.c

@@ -237,6 +237,9 @@ void netdev_drop(NetDev *netdev) {
                 return;
         }
 
+        if (NETDEV_VTABLE(netdev) && NETDEV_VTABLE(netdev)->drop)
+                NETDEV_VTABLE(netdev)->drop(netdev);
+
         netdev->state = NETDEV_STATE_LINGER;
 
         log_netdev_debug(netdev, "netdev removed");

src/network/netdev/netdev.h

@@ -142,6 +142,9 @@ typedef struct NetDevVTable {
          * to be set != 0. */
         void (*init)(NetDev *n);
 
+        /* This is called when the interface is removed. */
+        void (*drop)(NetDev *n);
+
         /* This should free all kind-specific variables. It should be
          * idempotent. */
         void (*done)(NetDev *n);

src/network/netdev/tuntap.c

@@ -10,7 +10,11 @@
 #include <linux/if_tun.h>
 
 #include "alloc-util.h"
+#include "daemon-util.h"
 #include "fd-util.h"
+#include "networkd-link.h"
+#include "networkd-manager.h"
+#include "socket-util.h"
 #include "tuntap.h"
 #include "user-util.h"
 
@@ -29,6 +33,73 @@ static TunTap* TUNTAP(NetDev *netdev) {
         }
 }
 
+static void *close_fd_ptr(void *p) {
+        safe_close(PTR_TO_FD(p));
+        return NULL;
+}
+
+DEFINE_PRIVATE_HASH_OPS_FULL(named_fd_hash_ops, char, string_hash_func, string_compare_func, free, void, close_fd_ptr);
+
+int manager_add_tuntap_fd(Manager *m, int fd, const char *name) {
+        _cleanup_free_ char *tuntap_name = NULL;
+        const char *p;
+        int r;
+
+        assert(m);
+        assert(fd >= 0);
+        assert(name);
+
+        p = startswith(name, "tuntap-");
+        if (!p)
+                return log_debug_errno(SYNTHETIC_ERRNO(EINVAL), "Received unknown fd (%s).", name);
+
+        if (!ifname_valid(p))
+                return log_debug_errno(SYNTHETIC_ERRNO(EINVAL), "Received tuntap fd with invalid name (%s).", p);
+
+        tuntap_name = strdup(p);
+        if (!tuntap_name)
+                return log_oom_debug();
+
+        r = hashmap_ensure_put(&m->tuntap_fds_by_name, &named_fd_hash_ops, tuntap_name, FD_TO_PTR(fd));
+        if (r < 0)
+                return log_debug_errno(r, "Failed to store tuntap fd: %m");
+
+        TAKE_PTR(tuntap_name);
+        return 0;
+}
+
+void manager_clear_unmanaged_tuntap_fds(Manager *m) {
+        char *name;
+        void *p;
+
+        assert(m);
+
+        while ((p = hashmap_steal_first_key_and_value(m->tuntap_fds_by_name, (void**) &name))) {
+                close_and_notify_warn(PTR_TO_FD(p), name);
+                name = mfree(name);
+        }
+}
+
+static int tuntap_take_fd(NetDev *netdev) {
+        _cleanup_free_ char *name = NULL;
+        void *p;
+        int r;
+
+        assert(netdev);
+        assert(netdev->manager);
+
+        r = link_get_by_name(netdev->manager, netdev->ifname, NULL);
+        if (r < 0)
+                return r;
+
+        p = hashmap_remove2(netdev->manager->tuntap_fds_by_name, netdev->ifname, (void**) &name);
+        if (!p)
+                return -ENOENT;
+
+        log_netdev_debug(netdev, "Found file descriptor in fd store.");
+        return PTR_TO_FD(p);
+}
+
 static int netdev_create_tuntap(NetDev *netdev) {
         _cleanup_close_ int fd = -1;
         struct ifreq ifr = {};
@@ -39,7 +110,11 @@ static int netdev_create_tuntap(NetDev *netdev) {
         t = TUNTAP(netdev);
         assert(t);
 
-        fd = open(TUN_DEV, O_RDWR|O_CLOEXEC);
+        fd = TAKE_FD(t->fd);
+        if (fd < 0)
+                fd = tuntap_take_fd(netdev);
+        if (fd < 0)
+                fd = open(TUN_DEV, O_RDWR|O_CLOEXEC);
         if (fd < 0)
                 return log_netdev_error_errno(netdev, errno,  "Failed to open " TUN_DEV ": %m");
 
@@ -90,8 +165,10 @@ static int netdev_create_tuntap(NetDev *netdev) {
         if (ioctl(fd, TUNSETPERSIST, 1) < 0)
                 return log_netdev_error_errno(netdev, errno, "TUNSETPERSIST failed: %m");
 
-        if (t->keep_fd)
+        if (t->keep_fd) {
                 t->fd = TAKE_FD(fd);
+                (void) notify_push_fdf(t->fd, "tuntap-%s", netdev->ifname);
+        }
 
         return 0;
 }
@@ -106,6 +183,16 @@ static void tuntap_init(NetDev *netdev) {
         t->fd = -1;
 }
 
+static void tuntap_drop(NetDev *netdev) {
+        TunTap *t;
+
+        assert(netdev);
+        t = TUNTAP(netdev);
+        assert(t);
+
+        t->fd = close_and_notify_warn(t->fd, netdev->ifname);
+}
+
 static void tuntap_done(NetDev *netdev) {
         TunTap *t;
 
@@ -141,6 +228,7 @@ const NetDevVTable tun_vtable = {
         .sections = NETDEV_COMMON_SECTIONS "Tun\0",
         .config_verify = tuntap_verify,
         .init = tuntap_init,
+        .drop = tuntap_drop,
         .done = tuntap_done,
         .create = netdev_create_tuntap,
         .create_type = NETDEV_CREATE_INDEPENDENT,
@@ -152,6 +240,7 @@ const NetDevVTable tap_vtable = {
         .sections = NETDEV_COMMON_SECTIONS "Tap\0",
         .config_verify = tuntap_verify,
         .init = tuntap_init,
+        .drop = tuntap_drop,
         .done = tuntap_done,
         .create = netdev_create_tuntap,
         .create_type = NETDEV_CREATE_INDEPENDENT,

src/network/netdev/tuntap.h

@@ -21,3 +21,6 @@ DEFINE_NETDEV_CAST(TUN, TunTap);
 DEFINE_NETDEV_CAST(TAP, TunTap);
 extern const NetDevVTable tun_vtable;
 extern const NetDevVTable tap_vtable;
+
+int manager_add_tuntap_fd(Manager *m, int fd, const char *name);
+void manager_clear_unmanaged_tuntap_fds(Manager *m);