[libcamera-devel] [PATCH v2] libcamera: v4l2_device: openat(2) with O_CLOEXEC to cleanup after exec(3)

[Elias Naur]

On Mon, 20 Mar 2023 at 17:56, Laurent Pinchart
<laurent.pinchart at ideasonboard.com> wrote:

> On Sun, Mar 12, 2023 at 03:22:05PM -0600, Elias Naur via libcamera-devel wrote:
> > It's generally a good idea to openat(2) with O_CLOEXEC, but this patch
> > also fixes a real (corner-)case: I have an excutable that (1) uses
> > v4l2-compat to drive a RPi camera, (2) self-updates through exec(3).
> > Without O_CLOEXEC of the kernel devices, an update while the
> > camera is opened will result in -EBUSY errors when the update tries to
> > open the camera.
>
> I agree about the change, but I wonder what returns -EBUSY, as V4L2
> allows opening device nodes multiple times. Do you get a -EBUSY error
> from V4L2Device::open() after exec(), or from a different location ? If
> the error comes from V4L2Device::open(), what device does it come from ?
>

Efter exec'ing an update while the camera device is open, the next
open results in

[91]  INFO RPI raspberrypi.cpp:1487 Registered camera
/base/soc/i2c0mux/i2c at 1/ov5647 at 36 to Unicam device /dev/media3 and ISP
device /dev/media1
[89]  INFO Camera camera.cpp:1028 configuring streams: (0) 960x960-YUV420
[91] ERROR V4L2 v4l2_videodevice.cpp:1047 /dev/video0[149:cap]: Unable
to set format: Resource busy

Let me know if you need more.

Elias