On 10/25/17 7:41 PM, Hangbin Liu wrote:
> +static int rtnl_recvmsg(int fd, struct msghdr *msg, char **answer)
> +{
> + struct iovec *iov = msg->msg_iov;
> + char *buf;
> + int len;
> +
> + iov->iov_base = NULL;
> + iov->iov_len = 0;
> +
> + len = __rtnl_recvmsg(fd, msg, MSG_PEEK | MSG_TRUNC);
> + if (len < 0)
> + return len;
> +
> + buf = malloc(len);
> + if (!buf) {
> + fprintf(stderr, "malloc error: not enough buffer\n");
> + return -ENOMEM;
> + }
> +
> + iov->iov_base = buf;
> + iov->iov_len = len;
> +
> + len = __rtnl_recvmsg(fd, msg, 0);
> + if (len < 0) {
> + free(buf);
> + return len;
> + }
The kernel needs a flag that says "give me the message of the buffer is
large enough; if not just PEEK and tell me the length." That would avoid
the double call in most cases.
