[PULL,1/3] qemu-sockets: add abstract UNIX domain socket support

diff --git a/chardev/char-socket.c b/chardev/char-socket.c
index 232e0a8604..e77699db48 100644
--- a/chardev/char-socket.c
+++ b/chardev/char-socket.c
@@ -1380,6 +1380,8 @@  static void qemu_chr_parse_socket(QemuOpts *opts, ChardevBackend *backend,
     const char *host = qemu_opt_get(opts, "host");
     const char *port = qemu_opt_get(opts, "port");
     const char *fd = qemu_opt_get(opts, "fd");
+    bool tight = qemu_opt_get_bool(opts, "tight", true);
+    bool abstract = qemu_opt_get_bool(opts, "abstract", false);
     SocketAddressLegacy *addr;
     ChardevSocket *sock;
 
@@ -1431,6 +1433,8 @@  static void qemu_chr_parse_socket(QemuOpts *opts, ChardevBackend *backend,
         addr->type = SOCKET_ADDRESS_LEGACY_KIND_UNIX;
         q_unix = addr->u.q_unix.data = g_new0(UnixSocketAddress, 1);
         q_unix->path = g_strdup(path);
+        q_unix->tight = tight;
+        q_unix->abstract = abstract;
     } else if (host) {
         addr->type = SOCKET_ADDRESS_LEGACY_KIND_INET;
         addr->u.inet.data = g_new(InetSocketAddress, 1);
diff --git a/chardev/char.c b/chardev/char.c
index 0196e2887b..ea06c5ff4d 100644
--- a/chardev/char.c
+++ b/chardev/char.c
@@ -939,6 +939,13 @@  QemuOptsList qemu_chardev_opts = {
         },{
             .name = "logappend",
             .type = QEMU_OPT_BOOL,
+        },{
+            .name = "tight",
+            .type = QEMU_OPT_BOOL,
+            .def_value_str = "on",
+        },{
+            .name = "abstract",
+            .type = QEMU_OPT_BOOL,
         },
         { /* end of list */ }
     },
diff --git a/qapi/sockets.json b/qapi/sockets.json
index ea933ed4b2..cbd6ef35d0 100644
--- a/qapi/sockets.json
+++ b/qapi/sockets.json
@@ -73,12 +73,18 @@ 
 # Captures a socket address in the local ("Unix socket") namespace.
 #
 # @path: filesystem path to use
+# @tight: pass a socket address length confined to the minimum length of the
+#         abstract string, rather than the full sockaddr_un record length
+#         (only matters for abstract sockets, default true). (Since 5.1)
+# @abstract: whether this is an abstract address, default false. (Since 5.1)
 #
 # Since: 1.3
 ##
 { 'struct': 'UnixSocketAddress',
   'data': {
-    'path': 'str' } }
+    'path': 'str',
+    '*tight': 'bool',
+    '*abstract': 'bool' } }
 
 ##
 # @VsockSocketAddress:
diff --git a/util/qemu-sockets.c b/util/qemu-sockets.c
index 86c48b9fa5..b37d288866 100644
--- a/util/qemu-sockets.c
+++ b/util/qemu-sockets.c
@@ -863,6 +863,7 @@  static int unix_listen_saddr(UnixSocketAddress *saddr,
     char *pathbuf = NULL;
     const char *path;
     size_t pathlen;
+    size_t addrlen;
 
     sock = qemu_socket(PF_UNIX, SOCK_STREAM, 0);
     if (sock < 0) {
@@ -879,9 +880,11 @@  static int unix_listen_saddr(UnixSocketAddress *saddr,
     }
 
     pathlen = strlen(path);
-    if (pathlen > sizeof(un.sun_path)) {
+    if (pathlen > sizeof(un.sun_path) ||
+        (saddr->abstract && pathlen > (sizeof(un.sun_path) - 1))) {
         error_setg(errp, "UNIX socket path '%s' is too long", path);
         error_append_hint(errp, "Path must be less than %zu bytes\n",
+                          saddr->abstract ? sizeof(un.sun_path) - 1 :
                           sizeof(un.sun_path));
         goto err;
     }
@@ -903,7 +906,7 @@  static int unix_listen_saddr(UnixSocketAddress *saddr,
         close(fd);
     }
 
-    if (unlink(path) < 0 && errno != ENOENT) {
+    if (!saddr->abstract && unlink(path) < 0 && errno != ENOENT) {
         error_setg_errno(errp, errno,
                          "Failed to unlink socket %s", path);
         goto err;
@@ -911,9 +914,19 @@  static int unix_listen_saddr(UnixSocketAddress *saddr,
 
     memset(&un, 0, sizeof(un));
     un.sun_family = AF_UNIX;
-    memcpy(un.sun_path, path, pathlen);
+    addrlen = sizeof(un);
 
-    if (bind(sock, (struct sockaddr*) &un, sizeof(un)) < 0) {
+    if (saddr->abstract) {
+        un.sun_path[0] = '\0';
+        memcpy(&un.sun_path[1], path, pathlen);
+        if (saddr->tight) {
+            addrlen = offsetof(struct sockaddr_un, sun_path) + 1 + pathlen;
+        }
+    } else {
+        memcpy(un.sun_path, path, pathlen);
+    }
+
+    if (bind(sock, (struct sockaddr *) &un, addrlen) < 0) {
         error_setg_errno(errp, errno, "Failed to bind socket to %s", path);
         goto err;
     }
@@ -936,6 +949,7 @@  static int unix_connect_saddr(UnixSocketAddress *saddr, Error **errp)
     struct sockaddr_un un;
     int sock, rc;
     size_t pathlen;
+    size_t addrlen;
 
     if (saddr->path == NULL) {
         error_setg(errp, "unix connect: no path specified");
@@ -949,21 +963,32 @@  static int unix_connect_saddr(UnixSocketAddress *saddr, Error **errp)
     }
 
     pathlen = strlen(saddr->path);
-    if (pathlen > sizeof(un.sun_path)) {
+    if (pathlen > sizeof(un.sun_path) ||
+        (saddr->abstract && pathlen > (sizeof(un.sun_path) - 1))) {
         error_setg(errp, "UNIX socket path '%s' is too long", saddr->path);
         error_append_hint(errp, "Path must be less than %zu bytes\n",
+                          saddr->abstract ? sizeof(un.sun_path) - 1 :
                           sizeof(un.sun_path));
         goto err;
     }
 
     memset(&un, 0, sizeof(un));
     un.sun_family = AF_UNIX;
-    memcpy(un.sun_path, saddr->path, pathlen);
+    addrlen = sizeof(un);
 
+    if (saddr->abstract) {
+        un.sun_path[0] = '\0';
+        memcpy(&un.sun_path[1], saddr->path, pathlen);
+        if (saddr->tight) {
+            addrlen = offsetof(struct sockaddr_un, sun_path) + 1 + pathlen;
+        }
+    } else {
+        memcpy(un.sun_path, saddr->path, pathlen);
+    }
     /* connect to peer */
     do {
         rc = 0;
-        if (connect(sock, (struct sockaddr *) &un, sizeof(un)) < 0) {
+        if (connect(sock, (struct sockaddr *) &un, addrlen) < 0) {
             rc = -errno;
         }
     } while (rc == -EINTR);