From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [213.167.242.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 89A1D3F4854; Mon, 10 Aug 2026 16:29:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.167.242.64 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786379344; cv=none; b=ue1L3iGWIHC14hL/hRKliwmvHnNrFyW2HYljPrl2HcCMLn0DHifM7LzjQ8+g6QhRVhjqk/af3uVxWGTGjyoyUwxdmKqp/VJTY74zmMTec8QJ7iW1Bc38dMpWCcVdSZI28+b7VV5KyQ5r+TkvxvrcykhnqeODSHOV6/9zKi1K/xE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786379344; c=relaxed/simple; bh=jJNjLStpPeNYF9zCNXMZJpQw2Z3R2h7Km5P/3NNSPV0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=slHCBjaL7SYPuADxd4U8vqkxBFCbTY9lj4UP8qLynG4DN4A9SrAiPjB6g2fSjAy7oWeC3RUPECvTQwsQc357/m+JjqEBC46z6Epdq1loTb79j59wGhbKZIi+o+BqT0p+ubfbPvqpwgsWqFNwILDqdSGZmAIHF+Vw9v70SrAVuMk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=ideasonboard.com; spf=pass smtp.mailfrom=ideasonboard.com; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b=u3WQ+rqt; arc=none smtp.client-ip=213.167.242.64 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="u3WQ+rqt" Received: from killaraus.ideasonboard.com (2001-14ba-70f3-e800--a06.rev.dnainternet.fi [IPv6:2001:14ba:70f3:e800::a06]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 17EAF12F; Mon, 10 Aug 2026 18:27:46 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1786379266; bh=jJNjLStpPeNYF9zCNXMZJpQw2Z3R2h7Km5P/3NNSPV0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=u3WQ+rqtErN9Zyb11fbroqvBkXDHWR9YCJbBgCLBxXzFMUfX6VYaCgB5ePxaXxbIZ 5BsIs7Czssv13soTMIbcFXN51Y3r8LZe0EuVx6NmKQ55PB5hYqc97SIwUPE40x5iMl 9NoNG55yPrlfxfT3cYErSTwkbuMoTUeH3zJnIKiY= Date: Mon, 10 Aug 2026 19:28:58 +0300 From: Laurent Pinchart To: Ali Nasrollahi Cc: linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, mchehab@kernel.org, Frank.Li@nxp.com, hverkuil+cisco@kernel.org, guoniu.zhou@oss.nxp.com Subject: Re: [PATCH] media: v4l2-core: make number of video devices configurable Message-ID: <20260810162858.GA3012183@killaraus.ideasonboard.com> References: <20260810162406.118981-2-A.Nasrolahi01@gmail.com> Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260810162406.118981-2-A.Nasrolahi01@gmail.com> On Mon, Aug 10, 2026 at 07:54:07PM +0330, Ali Nasrollahi wrote: > The V4L2 core currently limits the number of registered video devices to > 256. This can become a restriction for workloads that create a large > number of virtual video devices, such as v4l2loopback instances. We don't support v4l2loopback upstream though. > Make the maximum number of video devices configurable through a module > parameter. The default and minimum remain at the existing limit of 256, > while the maximum is capped at 4096. > > The parameter is only available when CONFIG_VIDEO_FIXED_MINOR_RANGES is > disabled, as the fixed minor allocation scheme relies on the existing > minor ranges. > > The device array is allocated according to the configured limit, while > the allocation bitmaps remain statically sized to the maximum supported > limit of 4096. > > Signed-off-by: Ali Nasrollahi > --- > drivers/media/v4l2-core/v4l2-dev.c | 70 +++++++++++++++++++++++------- > 1 file changed, 55 insertions(+), 15 deletions(-) > > diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c > index fd267fb74905..5a526b577970 100644 > --- a/drivers/media/v4l2-core/v4l2-dev.c > +++ b/drivers/media/v4l2-core/v4l2-dev.c > @@ -31,7 +31,8 @@ > #include > #include > > -#define VIDEO_NUM_DEVICES 256 > +#define VIDEO_MIN_NUM_DEVICES 256 > +#define VIDEO_MAX_NUM_DEVICES 4096 > #define VIDEO_NAME "video4linux" > > #define dprintk(fmt, arg...) do { \ > @@ -39,6 +40,27 @@ > __func__, ##arg); \ > } while (0) > > +static unsigned int video_nr_devices = VIDEO_MIN_NUM_DEVICES; > + > +#ifndef CONFIG_VIDEO_FIXED_MINOR_RANGES > +static int param_set_video_nr_devices(const char *val, > + const struct kernel_param *kp) > +{ > + return param_set_uint_minmax(val, kp, VIDEO_MIN_NUM_DEVICES, > + VIDEO_MAX_NUM_DEVICES); > +} > + > +static const struct kernel_param_ops param_ops_video_nr_devices = { > + .set = param_set_video_nr_devices, > + .get = param_get_uint, > +}; > + > +module_param_cb(video_nr_devices, ¶m_ops_video_nr_devices, > + &video_nr_devices, 0444); > + > +MODULE_PARM_DESC(video_nr_devices, "Maximum number of V4L2 devices (256-4096)"); > +#endif > + > /* > * sysfs stuff > */ > @@ -98,9 +120,14 @@ static struct dentry *v4l2_debugfs_root_dir; > /* > * Active devices > */ > -static struct video_device *video_devices[VIDEO_NUM_DEVICES]; > +#ifdef CONFIG_VIDEO_FIXED_MINOR_RANGES > +static struct video_device *video_devices[VIDEO_MIN_NUM_DEVICES]; > +static DECLARE_BITMAP(devnode_nums[VFL_TYPE_MAX], VIDEO_MIN_NUM_DEVICES); > +#else > +static struct video_device **video_devices; > +static DECLARE_BITMAP(devnode_nums[VFL_TYPE_MAX], VIDEO_MAX_NUM_DEVICES); > +#endif > static DEFINE_MUTEX(videodev_lock); > -static DECLARE_BITMAP(devnode_nums[VFL_TYPE_MAX], VIDEO_NUM_DEVICES); > > /* Device node utility functions */ > > @@ -504,7 +531,7 @@ static const struct file_operations v4l2_fops = { > * in the video_device array, but it was able to obtain a minor number. > * > * This means that we can always obtain a free stream index number since > - * the worst case scenario is that there are VIDEO_NUM_DEVICES - 1 slots in > + * the worst case scenario is that there are video_nr_devices - 1 slots in > * use of the video_device array. > * > * Returns a free index number. > @@ -513,19 +540,19 @@ static int get_index(struct video_device *vdev) > { > /* This can be static since this function is called with the global > videodev_lock held. */ > - static DECLARE_BITMAP(used, VIDEO_NUM_DEVICES); > + static DECLARE_BITMAP(used, VIDEO_MAX_NUM_DEVICES); > int i; > > - bitmap_zero(used, VIDEO_NUM_DEVICES); > + bitmap_zero(used, VIDEO_MAX_NUM_DEVICES); > > - for (i = 0; i < VIDEO_NUM_DEVICES; i++) { > + for (i = 0; i < video_nr_devices; i++) { > if (video_devices[i] != NULL && > video_devices[i]->v4l2_dev == vdev->v4l2_dev) { > __set_bit(video_devices[i]->index, used); > } > } > > - return find_first_zero_bit(used, VIDEO_NUM_DEVICES); > + return find_first_zero_bit(used, video_nr_devices); > } > > #define SET_VALID_IOCTL(ops, cmd, op) \ > @@ -915,7 +942,7 @@ int __video_register_device(struct video_device *vdev, > int i = 0; > int ret; > int minor_offset = 0; > - int minor_cnt = VIDEO_NUM_DEVICES; > + int minor_cnt = video_nr_devices; > const char *name_base; > > /* A minor value of -1 marks this video device as never > @@ -1020,10 +1047,10 @@ int __video_register_device(struct video_device *vdev, > #else > /* The device node number and minor numbers are independent, so > we just find the first free minor number. */ > - for (i = 0; i < VIDEO_NUM_DEVICES; i++) > + for (i = 0; i < video_nr_devices; i++) > if (video_devices[i] == NULL) > break; > - if (i == VIDEO_NUM_DEVICES) { > + if (i == video_nr_devices) { > mutex_unlock(&videodev_lock); > pr_err("could not get a free minor\n"); > return -ENFILE; > @@ -1032,7 +1059,7 @@ int __video_register_device(struct video_device *vdev, > vdev->minor = i + minor_offset; > vdev->num = nr; > > - if (WARN_ON(vdev->minor >= VIDEO_NUM_DEVICES)) { > + if (WARN_ON(vdev->minor >= video_nr_devices)) { > mutex_unlock(&videodev_lock); > return -EINVAL; > } > @@ -1241,7 +1268,7 @@ static int __init videodev_init(void) > int ret; > > pr_info("Linux video capture interface: v2.00\n"); > - ret = register_chrdev_region(dev, VIDEO_NUM_DEVICES, VIDEO_NAME); > + ret = register_chrdev_region(dev, video_nr_devices, VIDEO_NAME); > if (ret < 0) { > pr_warn("videodev: unable to get major %d\n", > VIDEO_MAJOR); > @@ -1250,11 +1277,21 @@ static int __init videodev_init(void) > > ret = class_register(&video_class); > if (ret < 0) { > - unregister_chrdev_region(dev, VIDEO_NUM_DEVICES); > + unregister_chrdev_region(dev, video_nr_devices); > pr_warn("video_dev: class_register failed\n"); > return -EIO; > } > > +#ifndef CONFIG_VIDEO_FIXED_MINOR_RANGES > + video_devices = kzalloc_objs(*video_devices, video_nr_devices); > + if (!video_devices) { > + class_unregister(&video_class); > + unregister_chrdev_region(dev, video_nr_devices); > + pr_warn("video_dev: failed to allocate video_devices\n"); > + return -ENOMEM; > + } > +#endif > + > return 0; > } > > @@ -1262,8 +1299,11 @@ static void __exit videodev_exit(void) > { > dev_t dev = MKDEV(VIDEO_MAJOR, 0); > > +#ifndef CONFIG_VIDEO_FIXED_MINOR_RANGES > + kvfree(video_devices); > +#endif > class_unregister(&video_class); > - unregister_chrdev_region(dev, VIDEO_NUM_DEVICES); > + unregister_chrdev_region(dev, video_nr_devices); > debugfs_remove_recursive(v4l2_debugfs_root_dir); > v4l2_debugfs_root_dir = NULL; > } -- Regards, Laurent Pinchart