sockets: Make abstract UnixSocketAddress depend on CONFIG_LINUX

The abstract socket namespace is a non-portable Linux extension.  An
attempt to use it elsewhere should fail with ENOENT (the abstract
address looks like a "" pathname, which does not resolve).  We report
this failure like

    Failed to connect socket abc: No such file or directory

Tolerable, although ENOTSUP would be better.

However, introspection lies: it has @abstract regardless of host
support.  Easy enough to fix: since Linux provides them since 2.2,
'if': 'defined(CONFIG_LINUX)' should do.

The above failure becomes

    Parameter 'backend.data.addr.data.abstract' is unexpected

I consider this an improvement.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

chardev/char-socket.c

@@ -447,12 +447,14 @@ static char *qemu_chr_socket_address(SocketChardev *s, const char *prefix)
         const char *tight = "", *abstract = "";
         UnixSocketAddress *sa = &s->addr->u.q_unix;
 
+#ifdef CONFIG_LINUX
         if (sa->has_abstract && sa->abstract) {
             abstract = ",abstract";
             if (sa->has_tight && sa->tight) {
                 tight = ",tight";
             }
         }
+#endif
 
         return g_strdup_printf("%sunix:%s%s%s%s", prefix, sa->path,
                                abstract, tight,
@@ -1398,8 +1400,10 @@ 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");
+#ifdef CONFIG_LINUX
     bool tight = qemu_opt_get_bool(opts, "tight", true);
     bool abstract = qemu_opt_get_bool(opts, "abstract", false);
+#endif
     SocketAddressLegacy *addr;
     ChardevSocket *sock;
 
@@ -1451,10 +1455,12 @@ 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);
+#ifdef CONFIG_LINUX
         q_unix->has_tight = true;
         q_unix->tight = tight;
         q_unix->has_abstract = true;
         q_unix->abstract = abstract;
+#endif
     } else if (host) {
         addr->type = SOCKET_ADDRESS_LEGACY_KIND_INET;
         addr->u.inet.data = g_new(InetSocketAddress, 1);

chardev/char.c

@@ -928,6 +928,7 @@ QemuOptsList qemu_chardev_opts = {
         },{
             .name = "logappend",
             .type = QEMU_OPT_BOOL,
+#ifdef CONFIG_LINUX
         },{
             .name = "tight",
             .type = QEMU_OPT_BOOL,
@@ -935,6 +936,7 @@ QemuOptsList qemu_chardev_opts = {
         },{
             .name = "abstract",
             .type = QEMU_OPT_BOOL,
+#endif
         },
         { /* end of list */ }
     },

qapi/sockets.json

@@ -74,18 +74,20 @@
 # 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: if true, this is a Linux abstract socket address.  @path
-#         abstract string, rather than the full sockaddr_un record length
+#            will be prefixed by a null byte, and optionally padded
-#         (only matters for abstract sockets, default true). (Since 5.1)
+#            with null bytes.  Defaults to false.  (Since 5.1)
-# @abstract: whether this is an abstract address, default false. (Since 5.1)
+# @tight: if false, pad an abstract socket address with enough null
+#         bytes to make it fill struct sockaddr_un member sun_path.
+#         Defaults to true.  (Since 5.1)
 #
 # Since: 1.3
 ##
 { 'struct': 'UnixSocketAddress',
   'data': {
     'path': 'str',
-    '*tight': 'bool',
+    '*abstract': { 'type': 'bool', 'if': 'defined(CONFIG_LINUX)' },
-    '*abstract': 'bool' } }
+    '*tight': { 'type': 'bool', 'if': 'defined(CONFIG_LINUX)' } } }
 
 ##
 # @VsockSocketAddress:

tests/test-util-sockets.c

@@ -229,7 +229,7 @@ static void test_socket_fd_pass_num_nocli(void)
 }
 #endif
 
-#ifdef __linux__
+#ifdef CONFIG_LINUX
 
 #define ABSTRACT_SOCKET_VARIANTS 3
 
@@ -326,7 +326,8 @@ static void test_socket_unix_abstract(void)
 
     g_free(addr.u.q_unix.path);
 }
-#endif
+
+#endif  /* CONFIG_LINUX */
 
 int main(int argc, char **argv)
 {
@@ -368,7 +369,7 @@ int main(int argc, char **argv)
 #endif
     }
 
-#ifdef __linux__
+#ifdef CONFIG_LINUX
     g_test_add_func("/util/socket/unix-abstract",
                     test_socket_unix_abstract);
 #endif

util/qemu-sockets.c

@@ -860,10 +860,29 @@ static int vsock_parse(VsockSocketAddress *addr, const char *str,
 
 #ifndef _WIN32
 
+static bool saddr_is_abstract(UnixSocketAddress *saddr)
+{
+#ifdef CONFIG_LINUX
+    return saddr->abstract;
+#else
+    return false;
+#endif
+}
+
+static bool saddr_is_tight(UnixSocketAddress *saddr)
+{
+#ifdef CONFIG_LINUX
+    return !saddr->has_tight || saddr->tight;
+#else
+    return false;
+#endif
+}
+
 static int unix_listen_saddr(UnixSocketAddress *saddr,
                              int num,
                              Error **errp)
 {
+    bool abstract = saddr_is_abstract(saddr);
     struct sockaddr_un un;
     int sock, fd;
     char *pathbuf = NULL;
@@ -877,7 +896,7 @@ static int unix_listen_saddr(UnixSocketAddress *saddr,
         return -1;
     }
 
-    if (saddr->path[0] || saddr->abstract) {
+    if (saddr->path[0] || abstract) {
         path = saddr->path;
     } else {
         const char *tmpdir = getenv("TMPDIR");
@@ -887,10 +906,10 @@ static int unix_listen_saddr(UnixSocketAddress *saddr,
 
     pathlen = strlen(path);
     if (pathlen > sizeof(un.sun_path) ||
-        (saddr->abstract && pathlen > (sizeof(un.sun_path) - 1))) {
+        (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 :
+                          abstract ? sizeof(un.sun_path) - 1 :
                           sizeof(un.sun_path));
         goto err;
     }
@@ -912,7 +931,7 @@ static int unix_listen_saddr(UnixSocketAddress *saddr,
         close(fd);
     }
 
-    if (!saddr->abstract && unlink(path) < 0 && errno != ENOENT) {
+    if (!abstract && unlink(path) < 0 && errno != ENOENT) {
         error_setg_errno(errp, errno,
                          "Failed to unlink socket %s", path);
         goto err;
@@ -922,10 +941,10 @@ static int unix_listen_saddr(UnixSocketAddress *saddr,
     un.sun_family = AF_UNIX;
     addrlen = sizeof(un);
 
-    if (saddr->abstract) {
+    if (abstract) {
         un.sun_path[0] = '\0';
         memcpy(&un.sun_path[1], path, pathlen);
-        if (!saddr->has_tight || saddr->tight) {
+        if (saddr_is_tight(saddr)) {
             addrlen = offsetof(struct sockaddr_un, sun_path) + 1 + pathlen;
         }
     } else {
@@ -952,6 +971,7 @@ err:
 
 static int unix_connect_saddr(UnixSocketAddress *saddr, Error **errp)
 {
+    bool abstract = saddr_is_abstract(saddr);
     struct sockaddr_un un;
     int sock, rc;
     size_t pathlen;
@@ -970,10 +990,10 @@ static int unix_connect_saddr(UnixSocketAddress *saddr, Error **errp)
 
     pathlen = strlen(saddr->path);
     if (pathlen > sizeof(un.sun_path) ||
-        (saddr->abstract && pathlen > (sizeof(un.sun_path) - 1))) {
+        (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 :
+                          abstract ? sizeof(un.sun_path) - 1 :
                           sizeof(un.sun_path));
         goto err;
     }
@@ -982,10 +1002,10 @@ static int unix_connect_saddr(UnixSocketAddress *saddr, Error **errp)
     un.sun_family = AF_UNIX;
     addrlen = sizeof(un);
 
-    if (saddr->abstract) {
+    if (abstract) {
         un.sun_path[0] = '\0';
         memcpy(&un.sun_path[1], saddr->path, pathlen);
-        if (!saddr->has_tight || saddr->tight) {
+        if (saddr_is_tight(saddr)) {
             addrlen = offsetof(struct sockaddr_un, sun_path) + 1 + pathlen;
         }
     } else {