Re: [Qemu-devel] [PATCH v3 3/9] net: introduce tcp_client_start()

[Michael Roth <mdroth@linux.vnet.ibm.com>]

On Wed, Mar 07, 2012 at 06:48:03AM +0800, Amos Kong wrote:
> Introduce tcp_client_start() by moving original code in
> tcp_start_outgoing_migration().
> 
> Signed-off-by: Amos Kong <akong@redhat.com>
> ---
>  net.c         |   41 +++++++++++++++++++++++++++++++++++++++++
>  qemu_socket.h |    1 +
>  2 files changed, 42 insertions(+), 0 deletions(-)
> 
> diff --git a/net.c b/net.c
> index e90ff23..9afb0d1 100644
> --- a/net.c
> +++ b/net.c
> @@ -127,6 +127,47 @@ int tcp_server_start(const char *str, int *fd)
>      return ret;
>  }
> 
> +int tcp_client_start(const char *str, int *fd)
> +{
> +    struct sockaddr_in saddr;
> +    int ret;
> +
> +    *fd = -1;
> +    if (parse_host_port(&saddr, str) < 0) {
> +        error_report("invalid host/port combination: %s", str);
> +        return -EINVAL;
> +    }
> +
> +    *fd = qemu_socket(PF_INET, SOCK_STREAM, 0);
> +    if (fd < 0) {
> +        perror("socket");
> +        return -1;
> +    }
> +    socket_set_nonblock(*fd);
> +
> +    for (;;) {
> +        ret = connect(*fd, (struct sockaddr *)&saddr, sizeof(saddr));
> +        if (ret < 0) {
> +            ret = -socket_error();
> +            if (ret == -EINPROGRESS) {
> +                break;

The previous implementation and your next patch seem to be expecting a break on
-EWOULDBLOCK/-EAGAIN as well. Was the behavior changed on purpose?  I'm not
sure what the proper handling is for -EAGAIN: whether a non-blocking connect()
can eventually succeed or not. I suspect that it's not, but that previously we
treated it synonymously with -EINPROGRESS, then eventually got an error via
getsockopt() before failing the migration. If so, we're now changing the
behavior to retry until successful, but given the man page entry I don't
think that's a good idea since you might block indefinitely:

 EAGAIN No  more  free local ports or insufficient
              entries in the routing cache.  For AF_INET
              see        the        description       of
              /proc/sys/net/ipv4/ip_local_port_range
              ip(7)  for  information on how to increase
              the number of local ports.

> +#ifdef _WIN32
> +            } else if (ret == -WSAEALREADY || ret == -WSAEINVAL) {
> +                break;
> +#endif
> +            } else if (ret != -EINTR && ret != -EWOULDBLOCK) {
> +                perror("connect");
> +                closesocket(*fd);
> +                return ret;
> +            }
> +        } else {
> +            break;
> +        }
> +    }
> +
> +    return ret;
> +}
> +
>  int parse_host_port(struct sockaddr_in *saddr, const char *str)
>  {
>      char buf[512];
> diff --git a/qemu_socket.h b/qemu_socket.h
> index d612793..9246578 100644
> --- a/qemu_socket.h
> +++ b/qemu_socket.h
> @@ -55,6 +55,7 @@ int unix_connect_opts(QemuOpts *opts);
>  int unix_connect(const char *path);
> 
>  int tcp_server_start(const char *str, int *fd);
> +int tcp_client_start(const char *str, int *fd);
> 
>  /* Old, ipv4 only bits.  Don't use for new code. */
>  int parse_host_port(struct sockaddr_in *saddr, const char *str);
> 
>