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SubjectRe: [patch] 2.5 videodev redesign -- #3
Date
Gerd Knorr wrote:
> > > Comments? Bugs? I plan to feed this to Linus soon ...
> >
> > Hi,
> >
> > it seems to me that you are not holding the BKL during
> > the open method of the individual driver. This will
> > cause races with unplugging on some USB cameras.
>
> What race exactly?

Ok, I've found one: videodev_unregister() must be locked against
video_open(). New version of the patch below.

Gerd

==============================[ cut here ]==============================
This patch is a redesign for videodev.[ch]. Changes:

- drop the function pointers (read/write/mmap/poll/...) from struct
video_device, use struct file_operations directly instead.
Dispatching to different drivers by minor number is done the same way
soundcore.o handles this: swap file->f_fops at open() time.

- also drop the now obsolete video_red/write/mmap/poll/... functions
from videodev.c

- Stop using the BKL, use a mutex to protect open,register+unregister
calls against races.

- provide a video_generic_ioctl() function which can (and should) be
used by v4l drivers to handle copying from and to userspace.

- provide video_exclusive_open/release functions which can be used by
v4l drivers to make sure only one process at a time opens the
device. They can be hooked directly into struct file_operations if
some driver has nothing to initialize at open time (which is true
for many drivers in drivers/media/radio/).

--- linux-2.5.6-pre2/drivers/media/video/videodev.c Mon Mar 4 13:30:22 2002
+++ linux/drivers/media/video/videodev.c Mon Mar 4 13:33:25 2002
@@ -25,15 +25,13 @@
#include <linux/mm.h>
#include <linux/string.h>
#include <linux/errno.h>
-#include <linux/videodev.h>
#include <linux/init.h>
-
+#include <linux/kmod.h>
#include <asm/uaccess.h>
#include <asm/system.h>
#include <asm/semaphore.h>

-#include <linux/kmod.h>
-
+#include <linux/videodev.h>

#define VIDEO_NUM_DEVICES 256

@@ -42,6 +40,7 @@
*/

static struct video_device *video_device[VIDEO_NUM_DEVICES];
+static DECLARE_MUTEX(videodev_lock);


#if defined(CONFIG_PROC_FS) && defined(CONFIG_VIDEO_PROC_FS)
@@ -62,155 +61,138 @@

#endif /* CONFIG_PROC_FS && CONFIG_VIDEO_PROC_FS */

-
-/*
- * Read will do some smarts later on. Buffer pin etc.
- */
-
-static ssize_t video_read(struct file *file,
- char *buf, size_t count, loff_t *ppos)
+struct video_device* video_devdata(struct file *file)
{
- struct video_device *vfl=video_device[minor(file->f_dentry->d_inode->i_rdev)];
- if(vfl->read)
- return vfl->read(vfl, buf, count, file->f_flags&O_NONBLOCK);
- else
- return -EINVAL;
+ return video_device[minor(file->f_dentry->d_inode->i_rdev)];
}

-
-/*
- * Write for now does nothing. No reason it shouldnt do overlay setting
- * for some boards I guess..
- */
-
-static ssize_t video_write(struct file *file, const char *buf,
- size_t count, loff_t *ppos)
-{
- struct video_device *vfl=video_device[minor(file->f_dentry->d_inode->i_rdev)];
- if(vfl->write)
- return vfl->write(vfl, buf, count, file->f_flags&O_NONBLOCK);
- else
- return 0;
-}
-
-/*
- * Poll to see if we're readable, can probably be used for timing on incoming
- * frames, etc..
- */
-
-static unsigned int video_poll(struct file *file, poll_table * wait)
-{
- struct video_device *vfl=video_device[minor(file->f_dentry->d_inode->i_rdev)];
- if(vfl->poll)
- return vfl->poll(vfl, file, wait);
- else
- return 0;
-}
-
-
/*
* Open a video device.
*/
-
static int video_open(struct inode *inode, struct file *file)
{
unsigned int minor = minor(inode->i_rdev);
- int err, retval = 0;
+ int err = 0;
struct video_device *vfl;
+ struct file_operations *old_fops;

if(minor>=VIDEO_NUM_DEVICES)
return -ENODEV;
- lock_kernel();
+ down(&videodev_lock);
vfl=video_device[minor];
if(vfl==NULL) {
char modname[20];

+ up(&videodev_lock);
sprintf (modname, "char-major-%d-%d", VIDEO_MAJOR, minor);
request_module(modname);
+ down(&videodev_lock);
vfl=video_device[minor];
if (vfl==NULL) {
- retval = -ENODEV;
- goto error_out;
- }
- }
- if(vfl->busy) {
- retval = -EBUSY;
- goto error_out;
- }
- vfl->busy=1; /* In case vfl->open sleeps */
-
- if(vfl->owner)
- __MOD_INC_USE_COUNT(vfl->owner);
-
- if(vfl->open)
- {
- err=vfl->open(vfl,0); /* Tell the device it is open */
- if(err)
- {
- vfl->busy=0;
- if(vfl->owner)
- __MOD_DEC_USE_COUNT(vfl->owner);
-
- unlock_kernel();
- return err;
+ up(&videodev_lock);
+ return -ENODEV;
}
}
- unlock_kernel();
- return 0;
-error_out:
- unlock_kernel();
- return retval;
+ old_fops = file->f_op;
+ file->f_op = fops_get(vfl->fops);
+ if(file->f_op->open)
+ err = file->f_op->open(inode,file);
+ if (err) {
+ fops_put(file->f_op);
+ file->f_op = fops_get(old_fops);
+ }
+ fops_put(old_fops);
+ up(&videodev_lock);
+ return err;
}

/*
- * Last close of a video for Linux device
+ * ioctl helper function -- handles userspace copying
*/
+int
+video_generic_ioctl(struct inode *inode, struct file *file,
+ unsigned int cmd, unsigned long arg)
+{
+ struct video_device *vfl = video_devdata(file);
+ char sbuf[128];
+ void *mbuf = NULL;
+ void *parg = NULL;
+ int err = -EINVAL;

-static int video_release(struct inode *inode, struct file *file)
-{
- struct video_device *vfl;
- lock_kernel();
- vfl=video_device[minor(inode->i_rdev)];
- if(vfl->close)
- vfl->close(vfl);
- vfl->busy=0;
- if(vfl->owner)
- __MOD_DEC_USE_COUNT(vfl->owner);
- unlock_kernel();
- return 0;
-}
+ if (vfl->kernel_ioctl == NULL)
+ return -EINVAL;

-static int video_ioctl(struct inode *inode, struct file *file,
- unsigned int cmd, unsigned long arg)
-{
- struct video_device *vfl=video_device[minor(inode->i_rdev)];
- int err=vfl->ioctl(vfl, cmd, (void *)arg);
+ /* Copy arguments into temp kernel buffer */
+ switch (_IOC_DIR(cmd)) {
+ case _IOC_NONE:
+ parg = (void *)arg;
+ break;
+ case _IOC_READ: /* some v4l ioctls are marked wrong ... */
+ case _IOC_WRITE:
+ case (_IOC_WRITE | _IOC_READ):
+ if (_IOC_SIZE(cmd) <= sizeof(sbuf)) {
+ parg = sbuf;
+ } else {
+ /* too big to allocate from stack */
+ mbuf = kmalloc(_IOC_SIZE(cmd),GFP_KERNEL);
+ if (NULL == mbuf)
+ return -ENOMEM;
+ parg = mbuf;
+ }
+
+ err = -EFAULT;
+ if (copy_from_user(parg, (void *)arg, _IOC_SIZE(cmd)))
+ goto out;
+ break;
+ }

- if(err!=-ENOIOCTLCMD)
- return err;
-
- switch(cmd)
+ /* call driver */
+ err = vfl->kernel_ioctl(inode, file, cmd, parg);
+ if (err == -ENOIOCTLCMD)
+ err = -EINVAL;
+ if (err < 0)
+ goto out;
+
+ /* Copy results into user buffer */
+ switch (_IOC_DIR(cmd))
{
- default:
- return -EINVAL;
+ case _IOC_READ:
+ case (_IOC_WRITE | _IOC_READ):
+ if (copy_to_user((void *)arg, parg, _IOC_SIZE(cmd)))
+ err = -EFAULT;
+ break;
}
+
+out:
+ if (mbuf)
+ kfree(mbuf);
+ return err;
}

/*
- * We need to do MMAP support
+ * open/release helper functions -- handle exclusive opens
*/
-
-int video_mmap(struct file *file, struct vm_area_struct *vma)
+extern int video_exclusive_open(struct inode *inode, struct file *file)
{
- int ret = -EINVAL;
- struct video_device *vfl=video_device[minor(file->f_dentry->d_inode->i_rdev)];
- if(vfl->mmap) {
- lock_kernel();
- ret = vfl->mmap(vma, vfl, (char *)vma->vm_start,
- (unsigned long)(vma->vm_end-vma->vm_start));
- unlock_kernel();
+ struct video_device *vfl = video_devdata(file);
+ int retval = 0;
+
+ down(&vfl->lock);
+ if (vfl->users) {
+ retval = -EBUSY;
+ } else {
+ vfl->users++;
}
- return ret;
+ up(&vfl->lock);
+ return retval;
+}
+
+extern int video_exclusive_release(struct inode *inode, struct file *file)
+{
+ struct video_device *vfl = video_devdata(file);
+
+ vfl->users--;
+ return 0;
}

/*
@@ -392,13 +374,10 @@
* %VFL_TYPE_RADIO - A radio card
*/

-static DECLARE_MUTEX(videodev_register_lock);
-
int video_register_device(struct video_device *vfd, int type, int nr)
{
int i=0;
int base;
- int err;
int end;
char *name_base;
char name[16];
@@ -430,50 +409,36 @@
}

/* pick a minor number */
- down(&videodev_register_lock);
+ down(&videodev_lock);
if (-1 == nr) {
/* use first free */
for(i=base;i<end;i++)
if (NULL == video_device[i])
break;
if (i == end) {
- up(&videodev_register_lock);
+ up(&videodev_lock);
return -ENFILE;
}
} else {
/* use the one the driver asked for */
i = base+nr;
if (NULL != video_device[i]) {
- up(&videodev_register_lock);
+ up(&videodev_lock);
return -ENFILE;
}
}
video_device[i]=vfd;
vfd->minor=i;
- up(&videodev_register_lock);
+ up(&videodev_lock);

- /* The init call may sleep so we book the slot out
- then call */
- MOD_INC_USE_COUNT;
- if(vfd->initialize) {
- err=vfd->initialize(vfd);
- if(err<0) {
- video_device[i]=NULL;
- MOD_DEC_USE_COUNT;
- return err;
- }
- }
sprintf (name, "v4l/%s%d", name_base, i - base);
- /*
- * Start the device root only. Anything else
- * has serious privacy issues.
- */
vfd->devfs_handle =
devfs_register (NULL, name, DEVFS_FL_DEFAULT,
VIDEO_MAJOR, vfd->minor,
S_IFCHR | S_IRUSR | S_IWUSR,
&video_fops,
NULL);
+ init_MUTEX(&vfd->lock);

#if defined(CONFIG_PROC_FS) && defined(CONFIG_VIDEO_PROC_FS)
sprintf (name, "%s%d", name_base, i - base);
@@ -492,8 +457,9 @@

void video_unregister_device(struct video_device *vfd)
{
+ down(&videodev_lock);
if(video_device[vfd->minor]!=vfd)
- panic("vfd: bad unregister");
+ panic("videodev: bad unregister");

#if defined(CONFIG_PROC_FS) && defined(CONFIG_VIDEO_PROC_FS)
videodev_proc_destroy_dev (vfd);
@@ -501,7 +467,7 @@

devfs_unregister (vfd->devfs_handle);
video_device[vfd->minor]=NULL;
- MOD_DEC_USE_COUNT;
+ up(&videodev_lock);
}


@@ -509,13 +475,7 @@
{
owner: THIS_MODULE,
llseek: no_llseek,
- read: video_read,
- write: video_write,
- ioctl: video_ioctl,
- mmap: video_mmap,
open: video_open,
- release: video_release,
- poll: video_poll,
};

/*
@@ -540,12 +500,9 @@

static void __exit videodev_exit(void)
{
-#ifdef MODULE
#if defined(CONFIG_PROC_FS) && defined(CONFIG_VIDEO_PROC_FS)
videodev_proc_destroy ();
#endif
-#endif
-
devfs_unregister_chrdev(VIDEO_MAJOR, "video_capture");
}

@@ -554,6 +511,10 @@

EXPORT_SYMBOL(video_register_device);
EXPORT_SYMBOL(video_unregister_device);
+EXPORT_SYMBOL(video_devdata);
+EXPORT_SYMBOL(video_generic_ioctl);
+EXPORT_SYMBOL(video_exclusive_open);
+EXPORT_SYMBOL(video_exclusive_release);

MODULE_AUTHOR("Alan Cox");
MODULE_DESCRIPTION("Device registrar for Video4Linux drivers");
--- linux-2.5.6-pre2/include/linux/videodev.h Mon Mar 4 13:30:27 2002
+++ linux/include/linux/videodev.h Mon Mar 4 13:32:51 2002
@@ -4,6 +4,18 @@
#include <linux/types.h>
#include <linux/version.h>

+#if 0
+/*
+ * v4l2 is still work-in-progress, integration planed for 2.5.x
+ * v4l2 project homepage: http://www.thedirks.org/v4l2/
+ * patches available from: http://bytesex.org/patches/
+ */
+# define HAVE_V4L2 1
+# include <linux/videodev2.h>
+#else
+# undef HAVE_V4L2
+#endif
+
#ifdef __KERNEL__

#include <linux/poll.h>
@@ -13,24 +25,25 @@
struct video_device
{
struct module *owner;
- char name[32];
- int type;
+ char name[32];
+ int type; /* v4l1 */
+ int type2; /* v4l2 */
int hardware;
+ int minor;

- int (*open)(struct video_device *, int mode);
- void (*close)(struct video_device *);
- long (*read)(struct video_device *, char *, unsigned long, int noblock);
- /* Do we need a write method ? */
- long (*write)(struct video_device *, const char *, unsigned long, int noblock);
-#if LINUX_VERSION_CODE >= 0x020100
- unsigned int (*poll)(struct video_device *, struct file *, poll_table *);
-#endif
- int (*ioctl)(struct video_device *, unsigned int , void *);
- int (*mmap)(struct vm_area_struct *vma, struct video_device *, const char *, unsigned long);
- int (*initialize)(struct video_device *);
+ /* new interface -- we will use file_operations directly
+ * like soundcore does.
+ * kernel_ioctl() will be called by video_generic_ioctl.
+ * video_generic_ioctl() does the userspace copying of the
+ * ioctl arguments */
+ struct file_operations *fops;
+ int (*kernel_ioctl)(struct inode *inode, struct file *file,
+ unsigned int cmd, void *arg);
void *priv; /* Used to be 'private' but that upsets C++ */
- int busy;
- int minor;
+
+ /* for videodev.c intenal usage -- don't touch */
+ int users;
+ struct semaphore lock;
devfs_handle_t devfs_handle;
};

@@ -43,8 +56,13 @@
#define VFL_TYPE_VTX 3

extern void video_unregister_device(struct video_device *);
-#endif
+extern struct video_device* video_devdata(struct file*);

+extern int video_exclusive_open(struct inode *inode, struct file *file);
+extern int video_exclusive_release(struct inode *inode, struct file *file);
+extern int video_generic_ioctl(struct inode *inode, struct file *file,
+ unsigned int cmd, unsigned long arg);
+#endif /* __KERNEL__ */

#define VID_TYPE_CAPTURE 1 /* Can capture */
#define VID_TYPE_TUNER 2 /* Can tune */
@@ -150,6 +168,7 @@
#define VIDEO_AUDIO_VOLUME 4
#define VIDEO_AUDIO_BASS 8
#define VIDEO_AUDIO_TREBLE 16
+#define VIDEO_AUDIO_BALANCE 32
char name[16];
#define VIDEO_SOUND_MONO 1
#define VIDEO_SOUND_STEREO 2
@@ -379,4 +398,10 @@
#define VID_HARDWARE_MEYE 32 /* Sony Vaio MotionEye cameras */
#define VID_HARDWARE_CPIA2 33

-#endif
+#endif /* __LINUX_VIDEODEV_H */
+
+/*
+ * Local variables:
+ * c-basic-offset: 8
+ * End:
+ */
-
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