Re: [Qemu-devel] [PATCH] tap: close fd conditionally when error occured

[Jason Wang <jasowang@redhat.com>]

On 2018年01月12日 15:30, Jay Zhou wrote:
> If netdev_add tap,id=net0,vhost=on failed in net_init_tap_one(),
> the followed up device_add virtio-net-pci,netdev=net0 will fail
> too, prints:
>
>    TUNSETOFFLOAD ioctl() failed: Bad file descriptor TUNSETOFFLOAD
>    ioctl() failed: Bad file descriptor
>
> The reason is that the fd of tap is closed when error occured after
> calling net_init_tap_one().
>
> I think the fd should be closed in these two case:
>    1.tap_set_sndbuf() failed
>    2.tap_set_sndbuf() succeeded but vhost failed to initialize with
>      vhostforce flag on
> Meanwhile, the fd should not be closed just because vhost failed to
> initialize but without vhostforce flag. So the followed up device_add
> can fall back to userspace virtio successfully.
>
> Suggested-by: Michael S. Tsirkin <mst@redhat.com>
> Suggested-by: Igor Mammedov <imammedo@redhat.com>
> Suggested-by: Jason Wang <jasowang@redhat.com>
> Signed-off-by: Jay Zhou <jianjay.zhou@huawei.com>
> ---
>   net/tap.c | 18 +++++++++++++-----
>   1 file changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/net/tap.c b/net/tap.c
> index 979e622..3ed72eb 100644
> --- a/net/tap.c
> +++ b/net/tap.c
> @@ -651,6 +651,9 @@ static void net_init_tap_one(const NetdevTapOptions *tap, NetClientState *peer,
>       tap_set_sndbuf(s->fd, tap, &err);
>       if (err) {
>           error_propagate(errp, err);
> +        if (!tap->has_fd && !tap->has_fds) {
> +            close(fd);
> +        }
>           return;
>       }
>   
> @@ -687,14 +690,14 @@ static void net_init_tap_one(const NetdevTapOptions *tap, NetClientState *peer,
>               vhostfd = monitor_fd_param(cur_mon, vhostfdname, &err);
>               if (vhostfd == -1) {
>                   error_propagate(errp, err);
> -                return;
> +                goto cleanup;
>               }
>           } else {
>               vhostfd = open("/dev/vhost-net", O_RDWR);
>               if (vhostfd < 0) {
>                   error_setg_errno(errp, errno,
>                                    "tap: open vhost char device failed");
> -                return;
> +                goto cleanup;
>               }
>               fcntl(vhostfd, F_SETFL, O_NONBLOCK);
>           }
> @@ -704,11 +707,18 @@ static void net_init_tap_one(const NetdevTapOptions *tap, NetClientState *peer,
>           if (!s->vhost_net) {
>               error_setg(errp,
>                          "vhost-net requested but could not be initialized");

So error_setg() is not appropriate here consider it was not trated as an 
error. We probably just need some warning.

> -            return;
> +            goto cleanup;
>           }
>       } else if (vhostfdname) {
>           error_setg(errp, "vhostfd(s)= is not valid without vhost");
>       }
> +
> +cleanup:
> +    if (!tap->has_fd && !tap->has_fds && tap->has_vhostforce &&
> +        tap->vhostforce) {
> +        close(fd);

I would still let caller to decide whether or not to close the fd.

Thanks

> +    }
> +    return;
>   }
>   
>   static int get_fds(char *str, char *fds[], int max)
> @@ -877,7 +887,6 @@ free_fail:
>                            vnet_hdr, fd, &err);
>           if (err) {
>               error_propagate(errp, err);
> -            close(fd);
>               return -1;
>           }
>       } else {
> @@ -916,7 +925,6 @@ free_fail:
>                                vhostfdname, vnet_hdr, fd, &err);
>               if (err) {
>                   error_propagate(errp, err);
> -                close(fd);
>                   return -1;
>               }
>           }