linux-kernel - Re: [PATCH V4] drm/drm_vblank: Change EINVAL by the correct errno

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Date:   Tue, 25 Jun 2019 23:00:05 -0300
From:   Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>
To:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org, intel-gfx@...ts.freedesktop.org
Subject: Re: [PATCH V4] drm/drm_vblank: Change EINVAL by the correct errno

On 06/19, Daniel Vetter wrote:
> On Wed, Jun 19, 2019 at 09:48:56AM +0200, Daniel Vetter wrote:
> > On Tue, Jun 18, 2019 at 11:07:50PM -0300, Rodrigo Siqueira wrote:
> > > For historical reason, the function drm_wait_vblank_ioctl always return
> > > -EINVAL if something gets wrong. This scenario limits the flexibility
> > > for the userspace make detailed verification of the problem and take
> > > some action. In particular, the validation of “if (!dev->irq_enabled)”
> > > in the drm_wait_vblank_ioctl is responsible for checking if the driver
> > > support vblank or not. If the driver does not support VBlank, the
> > > function drm_wait_vblank_ioctl returns EINVAL which does not represent
> > > the real issue; this patch changes this behavior by return EOPNOTSUPP.
> > > Additionally, some operations are unsupported by this function, and
> > > returns EINVAL; this patch also changes the return value to EOPNOTSUPP
> > > in this case. Lastly, the function drm_wait_vblank_ioctl is invoked by
> > > libdrm, which is used by many compositors; because of this, it is
> > > important to check if this change breaks any compositor. In this sense,
> > > the following projects were examined:
> > > 
> > > * Drm-hwcomposer
> > > * Kwin
> > > * Sway
> > > * Wlroots
> > > * Wayland-core
> > > * Weston
> > > * Xorg (67 different drivers)
> > > 
> > > For each repository the verification happened in three steps:
> > > 
> > > * Update the main branch
> > > * Look for any occurrence "drmWaitVBlank" with the command:
> > >   git grep -n "drmWaitVBlank"
> > > * Look in the git history of the project with the command:
> > >   git log -SdrmWaitVBlank
> > > 
> > > Finally, none of the above projects validate the use of EINVAL which
> > > make safe, at least for these projects, to change the return values.
> > > 
> > > Change since V3:
> > >  - Return EINVAL for _DRM_VBLANK_SIGNAL (Daniel)
> > > 
> > > Change since V2:
> > >  Daniel Vetter and Chris Wilson
> > >  - Replace ENOTTY by EOPNOTSUPP
> > >  - Return EINVAL if the parameters are wrong
> > > 
> > 
> > Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
> > 
> > Apologies for the confusion on the last time around. btw if someone tells
> > you "r-b (or a-b) with these changes", then just apply the r-b/a-b tag
> > next time around. Otherwise people will re-review the same thing over and
> > over again.
> 
> btw when resending patches it's good practice to add anyone who commented
> on it (or who commented on the igt test for the same patch and other way
> round) onto the explicit Cc: list of the patch. That way it's easier for
> them to follow the patch evolution and do a quick r-b once they're happy.

Thanks for these valuable tips.
Do you think that is a good idea to resend this patch CC's everybody? Or
is it ok if I just apply it?
 
> If you don't do that then much bigger chances your patch gets ignored.
> -Daniel
> > 
> > > Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>
> > > ---
> > >  drivers/gpu/drm/drm_vblank.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> > > index 603ab105125d..bed233361614 100644
> > > --- a/drivers/gpu/drm/drm_vblank.c
> > > +++ b/drivers/gpu/drm/drm_vblank.c
> > > @@ -1582,7 +1582,7 @@ int drm_wait_vblank_ioctl(struct drm_device *dev, void *data,
> > >  	unsigned int flags, pipe, high_pipe;
> > >  
> > >  	if (!dev->irq_enabled)
> > > -		return -EINVAL;
> > > +		return -EOPNOTSUPP;
> > >  
> > >  	if (vblwait->request.type & _DRM_VBLANK_SIGNAL)
> > >  		return -EINVAL;
> > > -- 
> > > 2.21.0
> > 
> > -- 
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > http://blog.ffwll.ch
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

-- 
Rodrigo Siqueira
https://siqueira.tech

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