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Re: [Qemu-devel] [PATCH v3] tap: close fd conditionally when error occur


From: Zhoujian (jay)
Subject: Re: [Qemu-devel] [PATCH v3] tap: close fd conditionally when error occured
Date: Tue, 6 Feb 2018 11:26:04 +0000

Hi Jason,

> -----Original Message-----
> From: Jason Wang [mailto:address@hidden
> Sent: Tuesday, February 06, 2018 5:29 PM
> To: Zhoujian (jay) <address@hidden>; address@hidden
> Cc: address@hidden; address@hidden; Huangweidong (C)
> <address@hidden>; wangxin (U) <address@hidden>; Gonglei
> (Arei) <address@hidden>
> Subject: Re: [PATCH v3] tap: close fd conditionally when error occured
> 
> 
> 
> On 2018年02月02日 17:50, 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().
> >
> > The fd should be closed when calling net_init_tap_one failed:
> >     - if tap_set_sndbuf() failed
> >     - if tap_set_sndbuf() succeeded but vhost failed to open or
> >       initialize with vhostforce flag on The fd should not be closed
> > just because vhost failed to open or initialize but without vhostforce
> > flag. So the followed up device_add can fall back to userspace virtio
> > successfully.
> >
> > Suggested-by: Michael S. Tsirkin <address@hidden>
> > Suggested-by: Igor Mammedov <address@hidden>
> > Suggested-by: Jason Wang <address@hidden>
> > Signed-off-by: Jay Zhou <address@hidden>
> > ---
> >   net/tap.c | 44 ++++++++++++++++++++++++++++++++------------
> >   1 file changed, 32 insertions(+), 12 deletions(-)
> >
> > diff --git a/net/tap.c b/net/tap.c
> > index 979e622..c46ab14 100644
> > --- a/net/tap.c
> > +++ b/net/tap.c
> > @@ -651,7 +651,7 @@ static void net_init_tap_one(const NetdevTapOptions
> *tap, NetClientState *peer,
> >       tap_set_sndbuf(s->fd, tap, &err);
> >       if (err) {
> >           error_propagate(errp, err);
> > -        return;
> > +        goto error;
> >       }
> >
> >       if (tap->has_fd || tap->has_fds) { @@ -686,15 +686,26 @@ static
> > void net_init_tap_one(const NetdevTapOptions *tap, NetClientState *peer,
> >           if (vhostfdname) {
> >               vhostfd = monitor_fd_param(cur_mon, vhostfdname, &err);
> >               if (vhostfd == -1) {
> > -                error_propagate(errp, err);
> > -                return;
> > +                if (tap->has_vhostforce && tap->vhostforce) {
> > +                    error_propagate(errp, err);
> > +                    goto error;
> > +                } else {
> > +                    warn_report_err(err);
> > +                    return;
> > +                }
> >               }
> >           } else {
> >               vhostfd = open("/dev/vhost-net", O_RDWR);
> >               if (vhostfd < 0) {
> > -                error_setg_errno(errp, errno,
> > -                                 "tap: open vhost char device failed");
> > -                return;
> > +                if (tap->has_vhostforce && tap->vhostforce) {
> > +                    error_setg_errno(errp, errno,
> > +                                     "tap: open vhost char device failed");
> > +                    goto error;
> > +                } else {
> > +                    warn_report("tap: open vhost char device failed: %s",
> > +                                strerror(errno));
> > +                    return;
> > +                }
> >               }
> >               fcntl(vhostfd, F_SETFL, O_NONBLOCK);
> >           }
> > @@ -702,12 +713,23 @@ static void net_init_tap_one(const
> > NetdevTapOptions *tap, NetClientState *peer,
> >
> >           s->vhost_net = vhost_net_init(&options);
> >           if (!s->vhost_net) {
> > -            error_setg(errp,
> > -                       "vhost-net requested but could not be initialized");
> > -            return;
> > +            if (tap->has_vhostforce && tap->vhostforce) {
> > +                error_setg(errp,
> > +                           "vhost-net requested but could not be
> initialized");
> > +                goto error;
> > +            } else {
> > +                warn_report("vhost-net requested but could not be
> initialized");
> > +                return;
> > +            }
> 
> Can we reduce the duplication by doing such in a common error label?
> 

Yeah, I plan to define it like this in vhost_net.h

#define VHOST_NET_INIT_FAILED \
    "vhost-net requested but could not be initialized"

> >           }
> >       } else if (vhostfdname) {
> > -        error_setg(errp, "vhostfd(s)= is not valid without vhost");
> > +        warn_report("vhostfd(s)= is not valid without vhost");
> > +        return;
> > +    }
> > +
> > +error:
> > +    if (!tap->has_fd && !tap->has_fds) {
> > +        close(fd);
> 
> I believe you can do this in the caller by setting errp appropriately (e.g
> don't set it when we only need a warn).

You're right, thanks! :)

Regards,
Jay

> 
> Thanks
> 
> >       }
> >   }
> >
> > @@ -877,7 +899,6 @@ free_fail:
> >                            vnet_hdr, fd, &err);
> >           if (err) {
> >               error_propagate(errp, err);
> > -            close(fd);
> >               return -1;
> >           }
> >       } else {
> > @@ -916,7 +937,6 @@ free_fail:
> >                                vhostfdname, vnet_hdr, fd, &err);
> >               if (err) {
> >                   error_propagate(errp, err);
> > -                close(fd);
> >                   return -1;
> >               }
> >           }


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