Re: [PATCH] net: improve error message for missing netdev backend

[Jason Wang]

On Thu, Oct 27, 2022 at 6:52 PM Daniel P. Berrangé <berrange@redhat.com> wrote:
>
> ping: Jason, are you willing to queue this since it has two
> positive reviews.
>

Yes, I've queued this.

Thanks

> On Mon, Oct 03, 2022 at 11:06:12AM +0100, Daniel P. Berrangé wrote:
> > The current message when using '-net user...' with SLIRP disabled at
> > compile time is:
> >
> >   qemu-system-x86_64: -net user: Parameter 'type' expects a net backend 
> > type (maybe it is not compiled into this binary)
> >
> > An observation is that we're using the 'netdev->type' field here which
> > is an enum value, produced after QAPI has converted from its string
> > form.
> >
> > IOW, at this point in the code, we know that the user's specified
> > type name was a valid network backend. The only possible scenario that
> > can make the backend init function be NULL, is if support for that
> > backend was disabled at build time. Given this, we don't need to caveat
> > our error message with a 'maybe' hint, we can be totally explicit.
> >
> > The use of QERR_INVALID_PARAMETER_VALUE doesn't really lend itself to
> > user friendly error message text. Since this is not used to set a
> > specific QAPI error class, we can simply stop using this pre-formatted
> > error text and provide something better.
> >
> > Thus the new message is:
> >
> >   qemu-system-x86_64: -net user: network backend 'user' is not compiled 
> > into this binary
> >
> > The case of passing 'hubport' for -net is also given a message reminding
> > people they should have used -netdev/-nic instead, as this backend type
> > is only valid for the modern syntax.
> >
> > Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> > ---
> >
> > NB, this does not make any difference to people who were relying on the
> > QEMU built-in default hub that was created if you don't list any -net /
> > -netdev / -nic argument, only those using explicit args.
> >
> >  net/net.c | 18 +++++++++++-------
> >  1 file changed, 11 insertions(+), 7 deletions(-)
> >
> > diff --git a/net/net.c b/net/net.c
> > index 2db160e063..8ddafacf13 100644
> > --- a/net/net.c
> > +++ b/net/net.c
> > @@ -1036,19 +1036,23 @@ static int net_client_init1(const Netdev *netdev, 
> > bool is_netdev, Error **errp)
> >      if (is_netdev) {
> >          if (netdev->type == NET_CLIENT_DRIVER_NIC ||
> >              !net_client_init_fun[netdev->type]) {
> > -            error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "type",
> > -                       "a netdev backend type");
> > +            error_setg(errp, "network backend '%s' is not compiled into 
> > this binary",
> > +                       NetClientDriver_str(netdev->type));
> >              return -1;
> >          }
> >      } else {
> >          if (netdev->type == NET_CLIENT_DRIVER_NONE) {
> >              return 0; /* nothing to do */
> >          }
> > -        if (netdev->type == NET_CLIENT_DRIVER_HUBPORT ||
> > -            !net_client_init_fun[netdev->type]) {
> > -            error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "type",
> > -                       "a net backend type (maybe it is not compiled "
> > -                       "into this binary)");
> > +        if (netdev->type == NET_CLIENT_DRIVER_HUBPORT) {
> > +            error_setg(errp, "network backend '%s' is only supported with 
> > -netdev/-nic",
> > +                       NetClientDriver_str(netdev->type));
> > +            return -1;
> > +        }
> > +
> > +        if (!net_client_init_fun[netdev->type]) {
> > +            error_setg(errp, "network backend '%s' is not compiled into 
> > this binary",
> > +                       NetClientDriver_str(netdev->type));
> >              return -1;
> >          }
> >
> > --
> > 2.37.3
> >
>
> With regards,
> Daniel
> --
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