[Qemu-devel] [PATCH v4 3/4] Fix address handling in inet_nonblocking_connect

[Orit Wasserman]

getaddrinfo can give us a list of addresses, but we only try to
connect to the first one. If that fails we never proceed to
the next one.  This is common on desktop setups that often have ipv6
configured but not actually working.

To fix this make inet_connect_nonblocking retry connection with a different
address.
callers on inet_nonblocking_connect register a callback function that will
be called when connect opertion completes, in case of failure the fd will have
a negative value

Signed-off-by: Orit Wasserman <address@hidden>
Signed-off-by: Michael S. Tsirkin <address@hidden>
---
 migration-tcp.c |   37 +++++--------------
 qemu-char.c     |    2 +-
 qemu-sockets.c  |  108 ++++++++++++++++++++++++++++++++++++++++++++++---------
 qemu_socket.h   |   33 ++++++++++++-----
 4 files changed, 125 insertions(+), 55 deletions(-)

diff --git a/migration-tcp.c b/migration-tcp.c
index 7f6ad98..a15c2b8 100644
--- a/migration-tcp.c
+++ b/migration-tcp.c
@@ -53,54 +53,35 @@ static int tcp_close(MigrationState *s)
     return r;
 }
 
-static void tcp_wait_for_connect(void *opaque)
+static void tcp_wait_for_connect(int fd, void *opaque)
 {
     MigrationState *s = opaque;
-    int val, ret;
-    socklen_t valsize = sizeof(val);
 
-    DPRINTF("connect completed\n");
-    do {
-        ret = getsockopt(s->fd, SOL_SOCKET, SO_ERROR, (void *) &val, &valsize);
-    } while (ret == -1 && (socket_error()) == EINTR);
-
-    if (ret < 0) {
+    if (fd < 0) {
+        DPRINTF("migrate connect error\n");
+        s->fd = -1;
         migrate_fd_error(s);
-        return;
-    }
-
-    qemu_set_fd_handler2(s->fd, NULL, NULL, NULL, NULL);
-
-    if (val == 0)
+    } else {
+        DPRINTF("migrate connect success\n");
+        s->fd = fd;
         migrate_fd_connect(s);
-    else {
-        DPRINTF("error connecting %d\n", val);
-        migrate_fd_error(s);
     }
 }
 
 int tcp_start_outgoing_migration(MigrationState *s, const char *host_port,
                                  Error **errp)
 {
-    bool in_progress;
-
     s->get_error = socket_errno;
     s->write = socket_write;
     s->close = tcp_close;
 
-    s->fd = inet_nonblocking_connect(host_port, &in_progress, errp);
+    s->fd = inet_nonblocking_connect(host_port, tcp_wait_for_connect, s,
+                                     errp);
     if (error_is_set(errp)) {
         migrate_fd_error(s);
         return -1;
     }
 
-    if (in_progress) {
-        DPRINTF("connect in progress\n");
-        qemu_set_fd_handler2(s->fd, NULL, NULL, tcp_wait_for_connect, s);
-    } else {
-        migrate_fd_connect(s);
-    }
-
     return 0;
 }
 
diff --git a/qemu-char.c b/qemu-char.c
index 13b87b5..b082bae 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -2456,7 +2456,7 @@ static CharDriverState *qemu_chr_open_socket(QemuOpts 
*opts)
         if (is_listen) {
             fd = inet_listen_opts(opts, 0, NULL);
         } else {
-            fd = inet_connect_opts(opts, true, NULL, NULL);
+            fd = inet_connect_opts(opts, NULL, NULL, NULL);
         }
     }
     if (fd < 0) {
diff --git a/qemu-sockets.c b/qemu-sockets.c
index 99a1500..9a4be15 100644
--- a/qemu-sockets.c
+++ b/qemu-sockets.c
@@ -24,6 +24,7 @@
 
 #include "qemu_socket.h"
 #include "qemu-common.h" /* for qemu_isdigit */
+#include "main-loop.h"
 
 #ifndef AI_ADDRCONFIG
 # define AI_ADDRCONFIG 0
@@ -214,8 +215,64 @@ listen:
     ((rc) == -EINPROGRESS)
 #endif
 
-static int inet_connect_addr(struct addrinfo *addr, bool block,
-                             bool *in_progress)
+/* Struct to store connect state for non blocking connect */
+typedef struct ConnectState ConnectState;
+
+struct ConnectState {
+    int fd;
+    struct addrinfo *addr_list;
+    struct addrinfo *current_addr;
+    ConnectHandler *callback;
+    void *opaque;
+};
+
+static int inet_connect_addr(struct addrinfo *addr, bool *in_progress,
+                             ConnectState *connect_state);
+
+static void wait_for_connect(void *opaque)
+{
+    ConnectState *s = opaque;
+    int val = 0, rc = 0;
+    socklen_t valsize = sizeof(val);
+    bool in_progress = false;
+
+    qemu_set_fd_handler2(s->fd, NULL, NULL, NULL, NULL);
+
+    do {
+        rc = getsockopt(s->fd, SOL_SOCKET, SO_ERROR, (void *) &val, &valsize);
+    } while (rc == -1 && socket_error() == EINTR);
+
+    /* update rc to contain error */
+    if (!rc && val) {
+        rc = -1;
+    }
+
+    /* connect error */
+    if (rc < 0) {
+        closesocket(s->fd);
+        s->fd = rc;
+    }
+
+    /* try to connect to the next address on the list */
+    while (s->current_addr->ai_next != NULL && s->fd < 0) {
+        s->current_addr = s->current_addr->ai_next;
+        s->fd = inet_connect_addr(s->current_addr, &in_progress, s);
+        /* connect in progress */
+        if (in_progress) {
+            return;
+        }
+    }
+
+    freeaddrinfo(s->addr_list);
+    if (s->callback) {
+        s->callback(s->fd, s->opaque);
+    }
+    g_free(s);
+    return;
+}
+
+static int inet_connect_addr(struct addrinfo *addr, bool *in_progress,
+                             ConnectState *connect_state)
 {
     int sock, rc;
 
@@ -230,7 +287,7 @@ static int inet_connect_addr(struct addrinfo *addr, bool 
block,
         return -1;
     }
     setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));
-    if (!block) {
+    if (connect_state != NULL) {
         socket_set_nonblock(sock);
     }
     /* connect to peer */
@@ -241,7 +298,10 @@ static int inet_connect_addr(struct addrinfo *addr, bool 
block,
         }
     } while (rc == -EINTR);
 
-    if (!block && QEMU_SOCKET_RC_INPROGRESS(rc)) {
+    if (connect_state != NULL && QEMU_SOCKET_RC_INPROGRESS(rc)) {
+        connect_state->fd = sock;
+        qemu_set_fd_handler2(sock, NULL, NULL, wait_for_connect,
+                             connect_state);
         if (in_progress) {
             *in_progress = true;
         }
@@ -260,6 +320,7 @@ static struct addrinfo *inet_parse_connect_opts(QemuOpts 
*opts, Error **errp)
     const char *port;
 
     memset(&ai, 0, sizeof(ai));
+
     ai.ai_flags = AI_CANONNAME | AI_ADDRCONFIG;
     ai.ai_family = PF_UNSPEC;
     ai.ai_socktype = SOCK_STREAM;
@@ -291,30 +352,42 @@ static struct addrinfo *inet_parse_connect_opts(QemuOpts 
*opts, Error **errp)
     return res;
 }
 
-int inet_connect_opts(QemuOpts *opts, bool block, bool *in_progress,
-                      Error **errp)
+int inet_connect_opts(QemuOpts *opts, Error **errp, ConnectHandler *callback,
+                      void *opaque)
 {
     struct addrinfo *res, *e;
     int sock = -1;
+    bool in_progress = false;
+    ConnectState *connect_state = NULL;
 
     res = inet_parse_connect_opts(opts, errp);
     if (!res) {
         return -1;
     }
 
-    if (in_progress) {
-        *in_progress = false;
-    }
-
     for (e = res; e != NULL; e = e->ai_next) {
-        sock = inet_connect_addr(e, block, in_progress);
-        if (sock >= 0) {
+        if (callback != NULL) {
+            connect_state = g_malloc0(sizeof(*connect_state));
+            connect_state->addr_list = res;
+            connect_state->current_addr = e;
+            connect_state->callback = callback;
+            connect_state->opaque = opaque;
+        }
+        sock = inet_connect_addr(e, &in_progress, connect_state);
+        if (in_progress) {
+            return sock;
+        } else if (sock >= 0) {
+            /* non blocking socket immediate success, call callback */
+            if (callback != NULL) {
+                callback(sock, opaque);
+            }
             break;
         }
     }
     if (sock < 0) {
         error_set(errp, QERR_SOCKET_CONNECT_FAILED);
     }
+    g_free(connect_state);
     freeaddrinfo(res);
     return sock;
 }
@@ -519,7 +592,7 @@ int inet_connect(const char *str, Error **errp)
 
     opts = qemu_opts_create(&dummy_opts, NULL, 0, NULL);
     if (inet_parse(opts, str) == 0) {
-        sock = inet_connect_opts(opts, true, NULL, errp);
+        sock = inet_connect_opts(opts, errp, NULL, NULL);
     } else {
         error_set(errp, QERR_SOCKET_CREATE_FAILED);
     }
@@ -527,16 +600,17 @@ int inet_connect(const char *str, Error **errp)
     return sock;
 }
 
-
-int inet_nonblocking_connect(const char *str, bool *in_progress,
-                             Error **errp)
+int inet_nonblocking_connect(const char *str, ConnectHandler *callback,
+                             void *opaque, Error **errp)
 {
     QemuOpts *opts;
     int sock = -1;
 
+    g_assert(callback != NULL);
+
     opts = qemu_opts_create(&dummy_opts, NULL, 0, NULL);
     if (inet_parse(opts, str) == 0) {
-        sock = inet_connect_opts(opts, false, in_progress, errp);
+        sock = inet_connect_opts(opts, errp, callback, opaque);
     } else {
         error_set(errp, QERR_SOCKET_CREATE_FAILED);
     }
diff --git a/qemu_socket.h b/qemu_socket.h
index 3247fb7..da93509 100644
--- a/qemu_socket.h
+++ b/qemu_socket.h
@@ -38,20 +38,31 @@ void socket_set_block(int fd);
 void socket_set_nonblock(int fd);
 int send_all(int fd, const void *buf, int len1);
 
+/* callback function for nonblocking connect
+ * vaild fd on success, negative error code on failure
+ */
+typedef void ConnectHandler(int fd, void *opaque);
+
 /* New, ipv6-ready socket helper functions, see qemu-sockets.c */
 int inet_listen_opts(QemuOpts *opts, int port_offset, Error **errp);
 int inet_listen(const char *str, char *ostr, int olen,
                 int socktype, int port_offset, Error **errp);
 /**
  * Connect function
+ * Use callback for nonblocking connect.
+ *
  * Returns -1 in case of error, fd in case of success
+ * For non-blocking connect calls the callback function
+ * with fd in case of success or -1 in case of error.
  * @opts: QEMU options
- * @block: set true for blocking socket
- * @in_progress: set to true in case of on going connect
+ * @callback: callback function that is called when connect completes,
+ *            not NULL for nonblocking.
+ * @opaque: opaque for callback function
  * @errp: set in case of an error
  **/
-int inet_connect_opts(QemuOpts *opts, bool block, bool *in_progress,
-                      Error **errp);
+int inet_connect_opts(QemuOpts *opts, Error **errp, ConnectHandler *callback,
+                      void *opaque);
+
 /**
  * Blocking connect
  * Returns -1 in case of error, fd in case of success
@@ -61,14 +72,18 @@ int inet_connect_opts(QemuOpts *opts, bool block, bool 
*in_progress,
 int inet_connect(const char *str, Error **errp);
 
 /**
- * Nonblocking connect
- * Returns -1 in case of error, fd in case of success
+ * Non-blocking connect
+ * Returns -1 in case of immediate error.
+ * Calls the callback function with fd in case of success or -1 in case of
+ * error.
  * @str: address string
- * @in_progress: set to true in case of on going connect
+ * @callback: callback function that is called when connect completes,
+ *            cannot be NULL.
+ * @opaque: opaque for callback function
  * @errp: set in case of an error
  **/
-int inet_nonblocking_connect(const char *str, bool *in_progress,
-                             Error **errp);
+int inet_nonblocking_connect(const char *str, ConnectHandler *callback,
+                             void *opaque, Error **errp);
 
 int inet_dgram_opts(QemuOpts *opts);
 const char *inet_strfamily(int family);
-- 
1.7.7.6