netlink-socket: Let the kernel choose Netlink pids for us.

The Netlink code in the Linux kernel has been willing to choose unique
Netlink pids for userspace sockets since at least 2.4.36 and probably
earlier.  There's no value in choosing them ourselves.

This simplifies the code and eliminates the possibility of exhausting our
supply of Netlink PIDs.

diff --git a/lib/netlink-socket.c b/lib/netlink-socket.c
index 7f49626..bc46235 100644 (file)
--- a/lib/netlink-socket.c
+++ b/lib/netlink-socket.c
@@ -78,8 +78,6 @@ struct nl_sock
  * Initialized by nl_sock_create(). */
 static int max_iovs;
 
-static int alloc_pid(uint32_t *);
-static void free_pid(uint32_t);
 static int nl_sock_cow__(struct nl_sock *);
 
 /* Creates a new netlink socket for the given netlink 'protocol'
@@ -90,6 +88,7 @@ nl_sock_create(int protocol, struct nl_sock **sockp)
 {
     struct nl_sock *sock;
     struct sockaddr_nl local, remote;
+    socklen_t local_size;
     int retval = 0;
 
     if (!max_iovs) {
@@ -130,34 +129,31 @@ nl_sock_create(int protocol, struct nl_sock **sockp)
     }
     sock->rcvbuf = retval;
 
-    retval = alloc_pid(&sock->pid);
-    if (retval) {
-        goto error;
-    }
-
-    /* Bind local address as our selected pid. */
-    memset(&local, 0, sizeof local);
-    local.nl_family = AF_NETLINK;
-    local.nl_pid = sock->pid;
-    if (bind(sock->fd, (struct sockaddr *) &local, sizeof local) < 0) {
-        VLOG_ERR("bind(%"PRIu32"): %s", sock->pid, strerror(errno));
-        goto error_free_pid;
-    }
-
-    /* Bind remote address as the kernel (pid 0). */
+    /* Connect to kernel (pid 0) as remote address. */
     memset(&remote, 0, sizeof remote);
     remote.nl_family = AF_NETLINK;
     remote.nl_pid = 0;
     if (connect(sock->fd, (struct sockaddr *) &remote, sizeof remote) < 0) {
         VLOG_ERR("connect(0): %s", strerror(errno));
-        goto error_free_pid;
+        goto error;
+    }
+
+    /* Obtain pid assigned by kernel. */
+    local_size = sizeof local;
+    if (getsockname(sock->fd, (struct sockaddr *) &local, &local_size) < 0) {
+        VLOG_ERR("getsockname: %s", strerror(errno));
+        goto error;
+    }
+    if (local_size < sizeof local || local.nl_family != AF_NETLINK) {
+        VLOG_ERR("getsockname returned bad Netlink name");
+        retval = EINVAL;
+        goto error;
     }
+    sock->pid = local.nl_pid;
 
     *sockp = sock;
     return 0;
 
-error_free_pid:
-    free_pid(sock->pid);
 error:
     if (retval == 0) {
         retval = errno;
@@ -190,7 +186,6 @@ nl_sock_destroy(struct nl_sock *sock)
             sock->dump = NULL;
         } else {
             close(sock->fd);
-            free_pid(sock->pid);
             free(sock);
         }
     }
@@ -1055,54 +1050,6 @@ nl_lookup_genl_family(const char *name, int *number)
     return *number > 0 ? 0 : -*number;
 }
 \f
-/* Netlink PID.
- *
- * Every Netlink socket must be bound to a unique 32-bit PID.  By convention,
- * programs that have a single Netlink socket use their Unix process ID as PID,
- * and programs with multiple Netlink sockets add a unique per-socket
- * identifier in the bits above the Unix process ID.
- *
- * The kernel has Netlink PID 0.
- */
-
-/* Parameters for how many bits in the PID should come from the Unix process ID
- * and how many unique per-socket. */
-#define SOCKET_BITS 10
-#define MAX_SOCKETS (1u << SOCKET_BITS)
-
-#define PROCESS_BITS (32 - SOCKET_BITS)
-#define MAX_PROCESSES (1u << PROCESS_BITS)
-#define PROCESS_MASK ((uint32_t) (MAX_PROCESSES - 1))
-
-/* Bit vector of unused socket identifiers. */
-static uint32_t avail_sockets[ROUND_UP(MAX_SOCKETS, 32)];
-
-/* Allocates and returns a new Netlink PID. */
-static int
-alloc_pid(uint32_t *pid)
-{
-    int i;
-
-    for (i = 0; i < MAX_SOCKETS; i++) {
-        if ((avail_sockets[i / 32] & (1u << (i % 32))) == 0) {
-            avail_sockets[i / 32] |= 1u << (i % 32);
-            *pid = (getpid() & PROCESS_MASK) | (i << PROCESS_BITS);
-            return 0;
-        }
-    }
-    VLOG_ERR("netlink pid space exhausted");
-    return ENOBUFS;
-}
-
-/* Makes the specified 'pid' available for reuse. */
-static void
-free_pid(uint32_t pid)
-{
-    int sock = pid >> PROCESS_BITS;
-    assert(avail_sockets[sock / 32] & (1u << (sock % 32)));
-    avail_sockets[sock / 32] &= ~(1u << (sock % 32));
-}
-\f
 static void
 nlmsghdr_to_string(const struct nlmsghdr *h, int protocol, struct ds *ds)
 {
@@ -1151,10 +1098,8 @@ nlmsghdr_to_string(const struct nlmsghdr *h, int protocol, struct ds *ds)
     if (flags_left) {
         ds_put_format(ds, "[OTHER:%"PRIx16"]", flags_left);
     }
-    ds_put_format(ds, ", seq=%"PRIx32", pid=%"PRIu32"(%d:%d))",
-                  h->nlmsg_seq, h->nlmsg_pid,
-                  (int) (h->nlmsg_pid & PROCESS_MASK),
-                  (int) (h->nlmsg_pid >> PROCESS_BITS));
+    ds_put_format(ds, ", seq=%"PRIx32", pid=%"PRIu32,
+                  h->nlmsg_seq, h->nlmsg_pid);
 }
 
 static char *