Re: [PATCH v3 2/2] drm/uapi: add explicit virtgpu context debug name

[Dmitry Osipenko <dmitry.osipenko@collabora.com>]

On 10/18/23 21:17, Gurchetan Singh wrote:
> There are two problems with the current method of determining the
> virtio-gpu debug name.
> 
> 1) TASK_COMM_LEN is defined to be 16 bytes only, and this is a
>    Linux kernel idiom (see PR_SET_NAME + PR_GET_NAME). Though,
>    Android/FreeBSD get around this via setprogname(..)/getprogname(..)
>    in libc.
> 
>    On Android, names longer than 16 bytes are common.  For example,
>    one often encounters a program like "com.android.systemui".
> 
>    The virtio-gpu spec allows the debug name to be up to 64 bytes, so
>    ideally userspace should be able to set debug names up to 64 bytes.
> 
> 2) The current implementation determines the debug name using whatever
>    task initiated virtgpu.  This is could be a "RenderThread" of a
>    larger program, when we actually want to propagate the debug name
>    of the program.
> 
> To fix these issues, add a new CONTEXT_INIT param that allows userspace
> to set the debug name when creating a context.
> 
> It takes a null-terminated C-string as the param value. The length of the
> string (excluding the terminator) **should** be <= 64 bytes.  Otherwise,
> the debug_name will be truncated to 64 bytes.
> 
> Link to open-source userspace:
> https://android-review.googlesource.com/c/platform/hardware/google/gfxstream/+/2787176
> 
> Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>
> Reviewed-by: Josh Simonot <josh.simonot@gmail.com>
> ---
> Fixes suggested by Dmitry Osipenko
> v2:
>     - Squash implementation and UAPI change into one commit
>     - Avoid unnecessary casts
>     - Use bool when necessary
> v3:
>     - Use DEBUG_NAME_MAX_LEN - 1 when copying string
> 
>  drivers/gpu/drm/virtio/virtgpu_drv.h   |  5 ++++
>  drivers/gpu/drm/virtio/virtgpu_ioctl.c | 39 ++++++++++++++++++++++----
>  include/uapi/drm/virtgpu_drm.h         |  2 ++
>  3 files changed, 40 insertions(+), 6 deletions(-)
...
> +			ret = strncpy_from_user(vfpriv->debug_name,
> +						u64_to_user_ptr(value),
> +						DEBUG_NAME_MAX_LEN - 1);
> +
> +			if (ret < 0) {
> +				ret = -EFAULT;
> +				goto out_unlock;
> +			}

The strncpy_from_user() itself returns -EFAULT. I changed code to return
the "ret" directly and applied to misc-next.

Gerd, let us know if have any objections to this patch.

-- 
Best regards,
Dmitry