util: extract the request sending code from virNetlinkCommand()

Allow to reuse as much as possible from virNetlinkCommand(). This
comment prepares for the introduction of virNetlinkDumpCommand()
only differing by how it handles the responses.

src/util/virnetlink.c

@@ -209,61 +209,38 @@ virNetlinkCreateSocket(int protocol)
     goto cleanup;
 }
 
-
-/**
- * virNetlinkCommand:
- * @nlmsg: pointer to netlink message
- * @respbuf: pointer to pointer where response buffer will be allocated
- * @respbuflen: pointer to integer holding the size of the response buffer
- *      on return of the function.
- * @src_pid: the pid of the process to send a message
- * @dst_pid: the pid of the process to talk to, i.e., pid = 0 for kernel
- * @protocol: netlink protocol
- * @groups: the group identifier
- *
- * Send the given message to the netlink layer and receive response.
- * Returns 0 on success, -1 on error. In case of error, no response
- * buffer will be returned.
- */
-int virNetlinkCommand(struct nl_msg *nl_msg,
-                      struct nlmsghdr **resp, unsigned int *respbuflen,
-                      uint32_t src_pid, uint32_t dst_pid,
+static virNetlinkHandle *
+virNetlinkSendRequest(struct nl_msg *nl_msg, uint32_t src_pid,
+                      struct sockaddr_nl nladdr,
                       unsigned int protocol, unsigned int groups)
 {
-    int ret = -1;
-    struct sockaddr_nl nladdr = {
-            .nl_family = AF_NETLINK,
-            .nl_pid    = dst_pid,
-            .nl_groups = 0,
-    };
     ssize_t nbytes;
-    struct pollfd fds[1];
     int fd;
     int n;
-    struct nlmsghdr *nlmsg = nlmsg_hdr(nl_msg);
     virNetlinkHandle *nlhandle = NULL;
-    int len = 0;
+    struct pollfd fds[1];
+    struct nlmsghdr *nlmsg = nlmsg_hdr(nl_msg);
 
     if (protocol >= MAX_LINKS) {
         virReportSystemError(EINVAL,
                              _("invalid protocol argument: %d"), protocol);
-        goto cleanup;
+        goto error;
     }
 
     if (!(nlhandle = virNetlinkCreateSocket(protocol)))
-        goto cleanup;
+        goto error;
 
     fd = nl_socket_get_fd(nlhandle);
     if (fd < 0) {
         virReportSystemError(errno,
                              "%s", _("cannot get netlink socket fd"));
-        goto cleanup;
+        goto error;
     }
 
     if (groups && nl_socket_add_membership(nlhandle, groups) < 0) {
         virReportSystemError(errno,
                              "%s", _("cannot add netlink membership"));
-        goto cleanup;
+        goto error;
     }
 
     nlmsg_set_dst(nl_msg, &nladdr);
@@ -274,10 +251,11 @@ int virNetlinkCommand(struct nl_msg *nl_msg,
     if (nbytes < 0) {
         virReportSystemError(errno,
                              "%s", _("cannot send to netlink socket"));
-        goto cleanup;
+        goto error;
     }
 
     memset(fds, 0, sizeof(fds));
+
     fds[0].fd = fd;
     fds[0].events = POLLIN;
 
@@ -289,9 +267,51 @@ int virNetlinkCommand(struct nl_msg *nl_msg,
         if (n == 0)
             virReportSystemError(ETIMEDOUT, "%s",
                                  _("no valid netlink response was received"));
-        goto cleanup;
     }
 
+    return nlhandle;
+
+ error:
+    virNetlinkFree(nlhandle);
+    return NULL;
+}
+
+/**
+ * virNetlinkCommand:
+ * @nlmsg: pointer to netlink message
+ * @respbuf: pointer to pointer where response buffer will be allocated
+ * @respbuflen: pointer to integer holding the size of the response buffer
+ *      on return of the function.
+ * @src_pid: the pid of the process to send a message
+ * @dst_pid: the pid of the process to talk to, i.e., pid = 0 for kernel
+ * @protocol: netlink protocol
+ * @groups: the group identifier
+ *
+ * Send the given message to the netlink layer and receive response.
+ * Returns 0 on success, -1 on error. In case of error, no response
+ * buffer will be returned.
+ */
+int virNetlinkCommand(struct nl_msg *nl_msg,
+                      struct nlmsghdr **resp, unsigned int *respbuflen,
+                      uint32_t src_pid, uint32_t dst_pid,
+                      unsigned int protocol, unsigned int groups)
+{
+    int ret = -1;
+    struct sockaddr_nl nladdr = {
+            .nl_family = AF_NETLINK,
+            .nl_pid    = dst_pid,
+            .nl_groups = 0,
+    };
+    struct pollfd fds[1];
+    virNetlinkHandle *nlhandle = NULL;
+    int len = 0;
+
+    memset(fds, 0, sizeof(fds));
+
+    if (!(nlhandle = virNetlinkSendRequest(nl_msg, src_pid, nladdr,
+                                           protocol, groups)))
+        goto cleanup;
+
     len = nl_recv(nlhandle, &nladdr, (unsigned char **)resp, NULL);
     if (len == 0) {
         virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
@@ -315,7 +335,6 @@ int virNetlinkCommand(struct nl_msg *nl_msg,
     return ret;
 }
 
-
 /**
  * virNetlinkDumpLink:
  *