[PATCH 2/2] tools/virtio: Add hints when module is not installed

Michael S. Tsirkin
Mon, 09 Oct 2023 10:52:32 -0000

On Mon, Oct 09, 2023 at 02:44:55AM +0000, Liming Wu
wrote:
>
>
> > -----Original Message-----
> > From: Jason Wang <jasowang at redhat.com>
> > Sent: Sunday, October 8, 2023 12:36 PM
> > To: Liming Wu <liming.wu at jaguarmicro.com>
> > Cc: Michael S . Tsirkin <mst at redhat.com>; kvm at
vger.kernel.org;
> > virtualization at lists.linux-foundation.org; netdev at
vger.kernel.org; linux-
> > kernel at vger.kernel.org; 398776277 at qq.com
> > Subject: Re: [PATCH 2/2] tools/virtio: Add hints when module is not
installed
> >
> > On Tue, Sep 26, 2023 at 1:00?PM <liming.wu at jaguarmicro.com>
wrote:
> > >
> > > From: Liming Wu <liming.wu at jaguarmicro.com>
> > >
> > > Need to insmod vhost_test.ko before run virtio_test.
> > > Give some hints to users.
> > >
> > > Signed-off-by: Liming Wu <liming.wu at jaguarmicro.com>
> > > ---
> > >  tools/virtio/virtio_test.c | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > >
> > > diff --git a/tools/virtio/virtio_test.c
b/tools/virtio/virtio_test.c
> > > index 028f54e6854a..ce2c4d93d735 100644
> > > --- a/tools/virtio/virtio_test.c
> > > +++ b/tools/virtio/virtio_test.c
> > > @@ -135,6 +135,10 @@ static void vdev_info_init(struct vdev_info*
dev,
> > unsigned long long features)
> > >         dev->buf = malloc(dev->buf_size);
> > >         assert(dev->buf);
> > >         dev->control = open("/dev/vhost-test",
O_RDWR);
> > > +
> > > +       if (dev->control < 0)
> > > +               fprintf(stderr, "Install vhost_test
module" \
> > > +               "(./vhost_test/vhost_test.ko)
firstly\n");
> >
> > There should be many other reasons to fail for open().
> >
> > Let's use strerror()?
> Yes,  Thanks for the review.
> Please rechecked the code as follow:
> --- a/tools/virtio/virtio_test.c
> +++ b/tools/virtio/virtio_test.c
> @@ -135,6 +135,11 @@ static void vdev_info_init(struct vdev_info* dev,
unsigned long long features)
>         dev->buf = malloc(dev->buf_size);
>         assert(dev->buf);
>         dev->control = open("/dev/vhost-test", O_RDWR);
> +
> +       if (dev->control == NULL)


???
Why are you comparing a file descriptor to NULL?

> +               fprintf(stderr,
> +                       "%s: Check whether vhost_test.ko is
installed.\n",
> +                       strerror(errno));


No, do not suggest checking unconditionally this is just wasting user's
time.  You would have to check the exact errno value. You will either
get ENOENT or ENODEV if module is not loaded. Other errors indicate
other problems.  And what matters is whether it's loaded, not installed
- vhost_test.ko will not get auto-loaded even if installed.


>         assert(dev->control >= 0);
>         r = ioctl(dev->control, VHOST_SET_OWNER, NULL);
>         assert(r >= 0);
>
> Thanks
>

In short, I am not applying this patch. If you really want to make
things a bit easier in case of errors, replace all assert r >= 0 with
a macro that prints out strerror(errno), that should be enough.
Maybe print file/line number too while we are at it.

--
MST