Re: [Qemu-devel] [PATCH v2 3/4] net/socket: Convert error report message to Error

[Markus Armbruster]

"Daniel P. Berrange" <address@hidden> writes:

> On Thu, Apr 27, 2017 at 06:24:17PM +0200, Markus Armbruster wrote:
>> No review, just an observation.
>> 
>> Mao Zhongyi <address@hidden> writes:
>> 
>> > Currently, net_socket_mcast_create(), net_socket_fd_init_dgram() and
>> > net_socket_fd_init() use the function such as fprintf(), perror() to
>> > report an error message.
>> >
>> > Now, convert these functions to Error.
>> >
>> > CC: address@hidden, address@hidden
>> > Signed-off-by: Mao Zhongyi <address@hidden>
>> > ---
>> >  net/socket.c | 66 
>> > +++++++++++++++++++++++++++++++++++++-----------------------
>> >  1 file changed, 41 insertions(+), 25 deletions(-)
>> >
>> > diff --git a/net/socket.c b/net/socket.c
>> > index b0decbe..559e09a 100644
>> > --- a/net/socket.c
>> > +++ b/net/socket.c
>> [...]
>> > @@ -433,25 +437,27 @@ static NetSocketState 
>> > *net_socket_fd_init_stream(NetClientState *peer,
>> >  
>> >  static NetSocketState *net_socket_fd_init(NetClientState *peer,
>> >                                            const char *model, const char 
>> > *name,
>> > -                                          int fd, int is_connected)
>> > +                                          int fd, int is_connected,
>> > +                                          Error **errp)
>> >  {
>> >      int so_type = -1, optlen=sizeof(so_type);
>> >  
>> >      if(getsockopt(fd, SOL_SOCKET, SO_TYPE, (char *)&so_type,
>> >          (socklen_t *)&optlen)< 0) {
>> > -        fprintf(stderr, "qemu: error: getsockopt(SO_TYPE) for fd=%d 
>> > failed\n",
>> > +        error_setg(errp, "qemu: error: getsockopt(SO_TYPE) for fd=%d 
>> > failed",
>> >                  fd);
>> >          closesocket(fd);
>> >          return NULL;
>> >      }
>> >      switch(so_type) {
>> >      case SOCK_DGRAM:
>> > -        return net_socket_fd_init_dgram(peer, model, name, fd, 
>> > is_connected);
>> > +        return net_socket_fd_init_dgram(peer, model, name, fd, 
>> > is_connected, errp);
>> >      case SOCK_STREAM:
>> >          return net_socket_fd_init_stream(peer, model, name, fd, 
>> > is_connected);
>> >      default:
>> >          /* who knows ... this could be a eg. a pty, do warn and continue 
>> > as stream */
>> > -        fprintf(stderr, "qemu: warning: socket type=%d for fd=%d is not 
>> > SOCK_DGRAM or SOCK_STREAM\n", so_type, fd);
>> > +        error_setg(errp, "qemu: warning: socket type=%d for fd=%d is not 
>> > SOCK_DGRAM"
>> > +                   " or SOCK_STREAM", so_type, fd);
>> 
>> Not this patches problem: this case is odd, and the comment is bogus.
>> If @fd really was a pty, getsockopt() would fail with ENOTSOCK, wouldn't
>> it?  If @fd is a socket, but neither SOCK_DGRAM nor SOCK_STREAM (say
>> SOCK_RAW), why is it safe to continue as if it was SOCK_STREAM?  Jason?
>
> IMHO it is a problem with this patch. Previously we merely printed
> a warning & carried on, which is conceptually ok in general, though
> dubious here for the reason you say.
>
> Now we are filling an Error **errp object, and carrying on - this is
> conceptually broken anywhere. If an Error ** is filled, we must return.
> If we want to carry on, we shouldn't fill Error **.

You're right.

>> >          return net_socket_fd_init_stream(peer, model, name, fd, 
>> > is_connected);
>
> IMHO, we just kill this and put return NULL here. If there is a genuine
> reason to support something like SOCK_RAW, it should be explicitly
> handled, because this default: case will certainly break SOCK_SEQPACKET
> and SOCK_RDM which can't be treated as streams.

It's either magic or misguided defensive programming.  Probably the
latter, but I'd like to hear Jason's opinion.

If it's *necessary* magic, we can't use error_setg().  Else, we should
drop the default, and insert a closesocket(fd) before the final return
NULL.

>> >      }
>> >      return NULL;
>> 
>> Not reachable.  Ugly, but not your patch's concern.
>
>
> Regards,
> Daniel