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SubjectRe: [PATCH] drm/drm_vblank: Change EINVAL by the correct errno
Date
Quoting Rodrigo Siqueira (2018-10-08 15:52:20)
> 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 ENOTTY
> (Inappropriate ioctl for device). Additionally, some operations are
> unsupported by this function, and returns EINVAL; this patch changes the
> return value to EOPNOTSUPP (Operation not supported). 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.
>
> Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
> ---
> drivers/gpu/drm/drm_vblank.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> index 98e091175921..88ec6fb49afb 100644
> --- a/drivers/gpu/drm/drm_vblank.c
> +++ b/drivers/gpu/drm/drm_vblank.c
> @@ -1533,10 +1533,10 @@ int drm_wait_vblank_ioctl(struct drm_device *dev, void *data,
> unsigned int flags, pipe, high_pipe;
>
> if (!dev->irq_enabled)
> - return -EINVAL;
> + return -ENOTTY;

Arguable.

>
> if (vblwait->request.type & _DRM_VBLANK_SIGNAL)
> - return -EINVAL;

User error -> einval.

> + return -EOPNOTSUPP;
>
> if (vblwait->request.type &
> ~(_DRM_VBLANK_TYPES_MASK | _DRM_VBLANK_FLAGS_MASK |
> @@ -1545,7 +1545,7 @@ int drm_wait_vblank_ioctl(struct drm_device *dev, void *data,
> vblwait->request.type,
> (_DRM_VBLANK_TYPES_MASK | _DRM_VBLANK_FLAGS_MASK |
> _DRM_VBLANK_HIGH_CRTC_MASK));
> - return -EINVAL;
> + return -EOPNOTSUPP;

User error -> einval.
-Chris

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