V4L/DVB (9133): v4l: disconnect kernel number from minor

The v4l core creates four different video devices (video, vbi, radio, vtx)
and each has its own range of minor numbers. However, modern devices keep
increasing the number of devices that they need so a maximum of 64 video
devices will not be enough in the future. In addition this scheme makes
it very hard to add new device types.

This patch disconnects the kernel number allocation (e.g. video0, video1,
etc.) from the actual minor number (just pick the first free minor).

This allows for much more flexibility in the future. However, it does
require the use of udev. For those who cannot use udev a new CONFIG option
was created that changes the allocation scheme back to the old behavior.

Thanks to Greg KH for suggesting this approach during the 2008 LPC.

In addition, several bugs were fixed in the ivtv and cx18 drivers: these
drivers try to allocate specific kernel numbers but that scheme contained
a bug which caused what should have been e.g. video17 to appear as e.g.
video2.

Signed-off-by: Hans Verkuil <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/video/Kconfig

···
 	  V4L devices.
 	  In doubt, say N.
 
+config VIDEO_FIXED_MINOR_RANGES
+	bool "Enable old-style fixed minor ranges for video devices"
+	default n
+	---help---
+	  Say Y here to enable the old-style fixed-range minor assignments.
+	  Only useful if you rely on the old behavior and use mknod instead of udev.
+
+	  When in doubt, say N.
+
 config VIDEO_HELPER_CHIPS_AUTO
 	bool "Autoselect pertinent encoders/decoders and other helper chips"
 	default y

drivers/media/video/cx18/cx18-driver.c

···
 		 "Encoder PCM buffers (in MB)\n"
 		 "\t\t\tDefault: " __stringify(CX18_DEFAULT_ENC_PCM_BUFFERS));
 
-MODULE_PARM_DESC(cx18_first_minor, "Set minor assigned to first card");
+MODULE_PARM_DESC(cx18_first_minor, "Set kernel number assigned to first card");
 
 MODULE_AUTHOR("Hans Verkuil");
 MODULE_DESCRIPTION("CX23418 driver");
···
 
 	/* Validate parameters */
 	if (cx18_first_minor < 0 || cx18_first_minor >= CX18_MAX_CARDS) {
-		printk(KERN_ERR "cx18:  Exiting, ivtv_first_minor must be between 0 and %d\n",
+		printk(KERN_ERR "cx18:  Exiting, cx18_first_minor must be between 0 and %d\n",
 		     CX18_MAX_CARDS - 1);
 		return -1;
 	}

drivers/media/video/cx18/cx18-streams.c

···
 static struct {
 	const char *name;
 	int vfl_type;
-	int minor_offset;
+	int num_offset;
 	int dma;
 	enum v4l2_buf_type buf_type;
 	struct file_operations *fops;
···
 {
 	struct cx18_stream *s = &cx->streams[type];
 	u32 cap = cx->v4l2_cap;
-	int minor_offset = cx18_stream_info[type].minor_offset;
-	int minor;
+	int num_offset = cx18_stream_info[type].num_offset;
+	int num = cx->num + cx18_first_minor + num_offset;
 
 	/* These four fields are always initialized. If v4l2dev == NULL, then
 	   this stream is not in use. In that case no other fields but these
···
 	    !(cap & (V4L2_CAP_VBI_CAPTURE | V4L2_CAP_SLICED_VBI_CAPTURE)))
 		return 0;
 
-	/* card number + user defined offset + device offset */
-	minor = cx->num + cx18_first_minor + minor_offset;
-
 	/* User explicitly selected 0 buffers for these streams, so don't
 	   create them. */
 	if (cx18_stream_info[type].dma != PCI_DMA_NONE &&
···
 
 	cx18_stream_init(cx, type);
 
-	if (minor_offset == -1)
+	if (num_offset == -1)
 		return 0;
 
 	/* allocate and initialize the v4l2 video device structure */
···
 	snprintf(s->v4l2dev->name, sizeof(s->v4l2dev->name), "cx18-%d",
 			cx->num);
 
-	s->v4l2dev->minor = minor;
+	s->v4l2dev->num = num;
 	s->v4l2dev->parent = &cx->dev->dev;
 	s->v4l2dev->fops = cx18_stream_info[type].fops;
 	s->v4l2dev->release = video_device_release;
···
 {
 	struct cx18_stream *s = &cx->streams[type];
 	int vfl_type = cx18_stream_info[type].vfl_type;
-	int minor;
+	int num;
 
 	/* TODO: Shouldn't this be a VFL_TYPE_TRANSPORT or something?
 	 * We need a VFL_TYPE_TS defined.
···
 	if (s->v4l2dev == NULL)
 		return 0;
 
-	minor = s->v4l2dev->minor;
+	num = s->v4l2dev->num;
+	/* card number + user defined offset + device offset */
+	if (type != CX18_ENC_STREAM_TYPE_MPG) {
+		struct cx18_stream *s_mpg = &cx->streams[CX18_ENC_STREAM_TYPE_MPG];
+
+		if (s_mpg->v4l2dev)
+			num = s_mpg->v4l2dev->num + cx18_stream_info[type].num_offset;
+	}
 
 	/* Register device. First try the desired minor, then any free one. */
-	if (video_register_device(s->v4l2dev, vfl_type, minor) &&
-			video_register_device(s->v4l2dev, vfl_type, -1)) {
-		CX18_ERR("Couldn't register v4l2 device for %s minor %d\n",
-			s->name, minor);
+	if (video_register_device(s->v4l2dev, vfl_type, num)) {
+		CX18_ERR("Couldn't register v4l2 device for %s kernel number %d\n",
+			s->name, num);
 		video_device_release(s->v4l2dev);
 		s->v4l2dev = NULL;
 		return -ENOMEM;
 	}
-	minor = s->v4l2dev->minor;
+	num = s->v4l2dev->num;
 
 	switch (vfl_type) {
 	case VFL_TYPE_GRABBER:
 		CX18_INFO("Registered device video%d for %s (%d MB)\n",
-			minor, s->name, cx->options.megabytes[type]);
+			num, s->name, cx->options.megabytes[type]);
 		break;
 
 	case VFL_TYPE_RADIO:
 		CX18_INFO("Registered device radio%d for %s\n",
-			minor - MINOR_VFL_TYPE_RADIO_MIN, s->name);
+			num, s->name);
 		break;
 
 	case VFL_TYPE_VBI:
 		if (cx->options.megabytes[type])
 			CX18_INFO("Registered device vbi%d for %s (%d MB)\n",
-				minor - MINOR_VFL_TYPE_VBI_MIN,
+				num,
 				s->name, cx->options.megabytes[type]);
 		else
 			CX18_INFO("Registered device vbi%d for %s\n",
-				minor - MINOR_VFL_TYPE_VBI_MIN, s->name);
+				num, s->name);
 		break;
 	}
 

drivers/media/video/em28xx/em28xx-video.c

···
 	/*FIXME: I2C IR should be disconnected */
 
 	em28xx_info("V4L2 devices /dev/video%d and /dev/vbi%d deregistered\n",
-				dev->vdev->minor-MINOR_VFL_TYPE_GRABBER_MIN,
-				dev->vbi_dev->minor-MINOR_VFL_TYPE_VBI_MIN);
+				dev->vdev->num, dev->vbi_dev->num);
 	list_del(&dev->devlist);
 	if (dev->sbutton_input_dev)
 		em28xx_deregister_snapshot_button(dev);
···
 	video_mux(dev, 0);
 
 	em28xx_info("V4L2 device registered as /dev/video%d and /dev/vbi%d\n",
-				dev->vdev->minor-MINOR_VFL_TYPE_GRABBER_MIN,
-				dev->vbi_dev->minor-MINOR_VFL_TYPE_VBI_MIN);
+				dev->vdev->num, dev->vbi_dev->num);
 
 	mutex_lock(&em28xx_extension_devlist_lock);
 	if (!list_empty(&em28xx_extension_devlist)) {
···
 		em28xx_warn
 		    ("device /dev/video%d is open! Deregistration and memory "
 		     "deallocation are deferred on close.\n",
-				dev->vdev->minor-MINOR_VFL_TYPE_GRABBER_MIN);
+				dev->vdev->num);
 
 		dev->state |= DEV_MISCONFIGURED;
 		em28xx_uninit_isoc(dev);

drivers/media/video/ivtv/ivtv-driver.c

···
 #include "tuner-xc2028.h"
 
 /* var to keep track of the number of array elements in use */
-int ivtv_cards_active = 0;
+int ivtv_cards_active;
 
 /* If you have already X v4l cards, then set this to X. This way
    the device numbers stay matched. Example: you have a WinTV card
    without radio and a PVR-350 with. Normally this would give a
    video1 device together with a radio0 device for the PVR. By
    setting this to 1 you ensure that radio0 is now also radio1. */
-int ivtv_first_minor = 0;
+int ivtv_first_minor;
 
 /* Master variable for all ivtv info */
 struct ivtv *ivtv_cards[IVTV_MAX_CARDS];
···
 		 "\t\t\t-1 is autodetect, 0 is off, 1 is on\n"
 		 "\t\t\tDefault is autodetect");
 
-MODULE_PARM_DESC(ivtv_first_minor, "Set minor assigned to first card");
+MODULE_PARM_DESC(ivtv_first_minor, "Set kernel number assigned to first card");
 
 MODULE_AUTHOR("Kevin Thayer, Chris Kennedy, Hans Verkuil");
 MODULE_DESCRIPTION("CX23415/CX23416 driver");

drivers/media/video/ivtv/ivtv-streams.c

···
 static struct {
 	const char *name;
 	int vfl_type;
-	int minor_offset;
+	int num_offset;
 	int dma, pio;
 	enum v4l2_buf_type buf_type;
 	const struct file_operations *fops;
···
 static int ivtv_prep_dev(struct ivtv *itv, int type)
 {
 	struct ivtv_stream *s = &itv->streams[type];
-	int minor_offset = ivtv_stream_info[type].minor_offset;
-	int minor;
+	int num_offset = ivtv_stream_info[type].num_offset;
+	int num = itv->num + ivtv_first_minor + num_offset;
 
 	/* These four fields are always initialized. If v4l2dev == NULL, then
 	   this stream is not in use. In that case no other fields but these
···
 		return 0;
 	if (type >= IVTV_DEC_STREAM_TYPE_MPG && !(itv->v4l2_cap & V4L2_CAP_VIDEO_OUTPUT))
 		return 0;
-
-	/* card number + user defined offset + device offset */
-	minor = itv->num + ivtv_first_minor + minor_offset;
 
 	/* User explicitly selected 0 buffers for these streams, so don't
 	   create them. */
···
 	snprintf(s->v4l2dev->name, sizeof(s->v4l2dev->name), "ivtv%d %s",
 			itv->num, s->name);
 
-	s->v4l2dev->minor = minor;
+	s->v4l2dev->num = num;
 	s->v4l2dev->parent = &itv->dev->dev;
 	s->v4l2dev->fops = ivtv_stream_info[type].fops;
 	s->v4l2dev->release = video_device_release;
···
 {
 	struct ivtv_stream *s = &itv->streams[type];
 	int vfl_type = ivtv_stream_info[type].vfl_type;
-	int minor;
+	int num;
 
 	if (s->v4l2dev == NULL)
 		return 0;
 
-	minor = s->v4l2dev->minor;
+	num = s->v4l2dev->num;
+	/* card number + user defined offset + device offset */
+	if (type != IVTV_ENC_STREAM_TYPE_MPG) {
+		struct ivtv_stream *s_mpg = &itv->streams[IVTV_ENC_STREAM_TYPE_MPG];
+
+		if (s_mpg->v4l2dev)
+			num = s_mpg->v4l2dev->num + ivtv_stream_info[type].num_offset;
+	}
+
 	/* Register device. First try the desired minor, then any free one. */
-	if (video_register_device(s->v4l2dev, vfl_type, minor) &&
-			video_register_device(s->v4l2dev, vfl_type, -1)) {
-		IVTV_ERR("Couldn't register v4l2 device for %s minor %d\n",
-				s->name, minor);
+	if (video_register_device(s->v4l2dev, vfl_type, num)) {
+		IVTV_ERR("Couldn't register v4l2 device for %s kernel number %d\n",
+				s->name, num);
 		video_device_release(s->v4l2dev);
 		s->v4l2dev = NULL;
 		return -ENOMEM;
 	}
+	num = s->v4l2dev->num;
 
 	switch (vfl_type) {
 	case VFL_TYPE_GRABBER:
 		IVTV_INFO("Registered device video%d for %s (%d kB)\n",
-			s->v4l2dev->minor, s->name, itv->options.kilobytes[type]);
+			num, s->name, itv->options.kilobytes[type]);
 		break;
 	case VFL_TYPE_RADIO:
 		IVTV_INFO("Registered device radio%d for %s\n",
-			s->v4l2dev->minor - MINOR_VFL_TYPE_RADIO_MIN, s->name);
+			num, s->name);
 		break;
 	case VFL_TYPE_VBI:
 		if (itv->options.kilobytes[type])
 			IVTV_INFO("Registered device vbi%d for %s (%d kB)\n",
-				s->v4l2dev->minor - MINOR_VFL_TYPE_VBI_MIN,
-				s->name, itv->options.kilobytes[type]);
+				num, s->name, itv->options.kilobytes[type]);
 		else
 			IVTV_INFO("Registered device vbi%d for %s\n",
-				s->v4l2dev->minor - MINOR_VFL_TYPE_VBI_MIN, s->name);
+				num, s->name);
 		break;
 	}
 	return 0;

drivers/media/video/v4l2-dev.c

···
  */
 static struct video_device *video_device[VIDEO_NUM_DEVICES];
 static DEFINE_MUTEX(videodev_lock);
+static DECLARE_BITMAP(video_nums[VFL_TYPE_MAX], VIDEO_NUM_DEVICES);
 
 struct video_device *video_device_alloc(void)
 {
···
 
 	/* Free up this device for reuse */
 	video_device[vfd->minor] = NULL;
+	clear_bit(vfd->num, video_nums[vfd->vfl_type]);
 	mutex_unlock(&videodev_lock);
 
 	/* Release the character device */
···
 					int index)
 {
 	int i = 0;
-	int base;
-	int end;
 	int ret;
-	char *name_base;
+	int minor_offset = 0;
+	int minor_cnt = VIDEO_NUM_DEVICES;
+	const char *name_base;
 	void *priv = video_get_drvdata(vfd);
 
 	/* the release callback MUST be present */
···
 
 	switch (type) {
 	case VFL_TYPE_GRABBER:
-		base = MINOR_VFL_TYPE_GRABBER_MIN;
-		end = MINOR_VFL_TYPE_GRABBER_MAX+1;
 		name_base = "video";
 		break;
 	case VFL_TYPE_VTX:
-		base = MINOR_VFL_TYPE_VTX_MIN;
-		end = MINOR_VFL_TYPE_VTX_MAX+1;
 		name_base = "vtx";
 		break;
 	case VFL_TYPE_VBI:
-		base = MINOR_VFL_TYPE_VBI_MIN;
-		end = MINOR_VFL_TYPE_VBI_MAX+1;
 		name_base = "vbi";
 		break;
 	case VFL_TYPE_RADIO:
-		base = MINOR_VFL_TYPE_RADIO_MIN;
-		end = MINOR_VFL_TYPE_RADIO_MAX+1;
 		name_base = "radio";
 		break;
 	default:
···
 		return -EINVAL;
 	}
 
+	vfd->vfl_type = type;
+
+#ifdef CONFIG_VIDEO_FIXED_MINOR_RANGES
+	/* Keep the ranges for the first four types for historical
+	 * reasons.
+	 * Newer devices (not yet in place) should use the range
+	 * of 128-191 and just pick the first free minor there
+	 * (new style). */
+	switch (type) {
+	case VFL_TYPE_GRABBER:
+		minor_offset = 0;
+		minor_cnt = 64;
+		break;
+	case VFL_TYPE_RADIO:
+		minor_offset = 64;
+		minor_cnt = 64;
+		break;
+	case VFL_TYPE_VTX:
+		minor_offset = 192;
+		minor_cnt = 32;
+		break;
+	case VFL_TYPE_VBI:
+		minor_offset = 224;
+		minor_cnt = 32;
+		break;
+	default:
+		minor_offset = 128;
+		minor_cnt = 64;
+		break;
+	}
+#endif
+
 	/* Initialize the character device */
 	cdev_init(&vfd->cdev, vfd->fops);
 	vfd->cdev.owner = vfd->fops->owner;
 	/* pick a minor number */
 	mutex_lock(&videodev_lock);
-	if (nr >= 0 && nr < end-base) {
-		/* use the one the driver asked for */
-		i = base + nr;
-		if (NULL != video_device[i]) {
-			mutex_unlock(&videodev_lock);
-			return -ENFILE;
-		}
-	} else {
-		/* use first free */
-		for (i = base; i < end; i++)
-			if (NULL == video_device[i])
-				break;
-		if (i == end) {
-			mutex_unlock(&videodev_lock);
-			return -ENFILE;
-		}
+	nr = find_next_zero_bit(video_nums[type], minor_cnt, nr == -1 ? 0 : nr);
+	if (nr == minor_cnt)
+		nr = find_first_zero_bit(video_nums[type], minor_cnt);
+	if (nr == minor_cnt) {
+		printk(KERN_ERR "could not get a free kernel number\n");
+		mutex_unlock(&videodev_lock);
+		return -ENFILE;
 	}
-	video_device[i] = vfd;
-	vfd->vfl_type = type;
-	vfd->minor = i;
+#ifdef CONFIG_VIDEO_FIXED_MINOR_RANGES
+	/* 1-on-1 mapping of kernel number to minor number */
+	i = nr;
+#else
+	/* The kernel number and minor numbers are independent */
+	for (i = 0; i < VIDEO_NUM_DEVICES; i++)
+		if (video_device[i] == NULL)
+			break;
+	if (i == VIDEO_NUM_DEVICES) {
+		mutex_unlock(&videodev_lock);
+		printk(KERN_ERR "could not get a free minor\n");
+		return -ENFILE;
+	}
+#endif
+	vfd->minor = i + minor_offset;
+	vfd->num = nr;
+	set_bit(nr, video_nums[type]);
+	BUG_ON(video_device[vfd->minor]);
+	video_device[vfd->minor] = vfd;
 
 	ret = get_index(vfd, index);
 	vfd->index = ret;
···
 	vfd->dev.devt = MKDEV(VIDEO_MAJOR, vfd->minor);
 	if (vfd->parent)
 		vfd->dev.parent = vfd->parent;
-	sprintf(vfd->dev.bus_id, "%s%d", name_base, i - base);
+	sprintf(vfd->dev.bus_id, "%s%d", name_base, nr);
 	ret = device_register(&vfd->dev);
 	if (ret < 0) {
 		printk(KERN_ERR "%s: device_register failed\n", __func__);
···
 fail_minor:
 	mutex_lock(&videodev_lock);
 	video_device[vfd->minor] = NULL;
+	clear_bit(vfd->num, video_nums[type]);
 	mutex_unlock(&videodev_lock);
 	vfd->minor = -1;
 	return ret;

include/media/v4l2-dev.h

···
 
 #define VIDEO_MAJOR	81
 
-/* Minor device allocation */
-#define MINOR_VFL_TYPE_GRABBER_MIN   0
-#define MINOR_VFL_TYPE_GRABBER_MAX  63
-#define MINOR_VFL_TYPE_RADIO_MIN    64
-#define MINOR_VFL_TYPE_RADIO_MAX   127
-#define MINOR_VFL_TYPE_VTX_MIN     192
-#define MINOR_VFL_TYPE_VTX_MAX     223
-#define MINOR_VFL_TYPE_VBI_MIN     224
-#define MINOR_VFL_TYPE_VBI_MAX     255
-
 #define VFL_TYPE_GRABBER	0
 #define VFL_TYPE_VBI		1
 #define VFL_TYPE_RADIO		2
 #define VFL_TYPE_VTX		3
+#define VFL_TYPE_MAX		4
 
 struct v4l2_ioctl_callbacks;
 
···
 	char name[32];
 	int vfl_type;
 	int minor;
+	u16 num;
 	/* attribute to differentiate multiple indices on one physical device */
 	int index;