[Libva] using libva video compression on system with no monitor

[Xiang, Haihao]

On Fri, 2012-08-17 at 06:10 +0200, Gwenole Beauchesne wrote: 
> 2012/8/16 Xiang, Haihao <haihao.xiang at intel.com>:
> > On Thu, 2012-08-16 at 10:25 +0200, Gwenole Beauchesne wrote:
> >> Hi,
> >>
> >> 2012/8/16 Xiang, Haihao <haihao.xiang at intel.com>:
> >>
> >> >> I see a comment in /va/drm/va_drm_auth.c
> >> >>
> >> >>  /* Default: root + master privs are needed for the following call */
> >> >
> >> > Master is enough.
> >>
> >> Master requires "root" privileges.
> >
> > It works for me with just my user name.
> 
> You only need to be authenticated to submit drm commands, you don't
> necessarily need master privs for that. Master privs requires root.

It is drmSetMaster()/drmDropMaster() requires root, not master itself. 
It is possible that a fd opened by a normal user is the master fd too . 

See drm_open_helper() in drm_fops.c

static int drm_open_helper(struct inode *inode, struct file *filp,                                                                                                     
                           struct drm_device * dev)
{
 ...
        if (!priv->minor->master) {
                /* create a new master */
                priv->minor->master = drm_master_create(priv->minor);
                if (!priv->minor->master) {
                        mutex_unlock(&dev->struct_mutex);
                        ret = -ENOMEM;
                        goto out_free;
                }

                priv->is_master = 1;   <==== It doesn't require root.
           ...
         }
...
}


> > xhh at xhh-snb32:~/graphics/ex/vaapi/libva/test/vainfo$ ./vainfo
> > error: can't connect to X server!    <------ Without X server
> > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 
> This is what I am saying. If you don't have an X server running, then
> a simple user can get authenticated, should he have the correct access
> rights to the device. In this case, you are authenticated and you
> don't call into drmAuthMagic(), unlike what you suggested.

Yes. My previous email also mentioned drmAuthMagic() isn't called in
this case. 

However according to the ioctl table in drm_drv.c

...
DRM_IOCTL_DEF(DRM_IOCTL_AUTH_MAGIC, drm_authmagic, DRM_AUTH|DRM_MASTER),
...

root isn't needed for DRM_IOCTL_AUTH_MAGIC, so calling into
drmAuthMagic() doesn't require root. Actually if we change 

    if (!va_drm_is_authenticated(drm_state->fd)) {
        if (!va_drm_authenticate(drm_state->fd, magic))
            return VA_STATUS_ERROR_OPERATION_FAILED;
        if (!va_drm_is_authenticated(drm_state->fd))
            return VA_STATUS_ERROR_OPERATION_FAILED;
    }  

to 

    if (1) {
        if (!va_drm_authenticate(drm_state->fd, magic))
            return VA_STATUS_ERROR_OPERATION_FAILED;
        if (!va_drm_is_authenticated(drm_state->fd))
            return VA_STATUS_ERROR_OPERATION_FAILED;
    }  

A normal user can also run vainfo on DRM too if drm_state->fd is the
master fd. 

Thanks
Haihao