V4L/DVB (6584): Fix read() method

Backport read() fixes from Markus Rechberger.

Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

1 files changed, 22 insertions, 8 deletions

diff --git a/drivers/media/video/em28xx/em28xx-video.c b/drivers/media/video/em28xx/em28xx-video.c
index f0191779a8e2..8a4d221a4fe4 100644
--- a/drivers/media/video/em28xx/em28xx-video.c
+++ b/drivers/media/video/em28xx/em28xx-video.c
@@ -416,6 +416,9 @@ em28xx_v4l2_read(struct file *filp, char __user * buf, size_t count,
         struct em28xx_fh *fh = filp->private_data;
         struct em28xx *dev = fh->dev;
 
+        /* FIXME: read() is not prepared to allow changing the video
+           resolution while streaming. Seems a bug at em28xx_set_fmt
+         */
 
         if (unlikely(res_get(fh) < 0))
                 return -EBUSY;
@@ -498,25 +501,36 @@ em28xx_v4l2_read(struct file *filp, char __user * buf, size_t count,
                         mutex_unlock(&dev->lock);
                         return -ENODEV;
                 }
+                dev->video_bytesread = 0;
         }
 
         f = list_entry(dev->outqueue.prev, struct em28xx_frame_t, frame);
 
-        spin_lock_irqsave(&dev->queue_lock, lock_flags);
-        list_for_each_entry(i, &dev->outqueue, frame)
-            i->state = F_UNUSED;
-        INIT_LIST_HEAD(&dev->outqueue);
-        spin_unlock_irqrestore(&dev->queue_lock, lock_flags);
-
         em28xx_queue_unusedframes(dev);
 
         if (count > f->buf.length)
                 count = f->buf.length;
 
-        if (copy_to_user(buf, f->bufmem, count)) {
-                mutex_unlock(&dev->lock);
+        if ((dev->video_bytesread + count) > dev->frame_size)
+                count = dev->frame_size - dev->video_bytesread;
+
+        if (copy_to_user(buf, f->bufmem+dev->video_bytesread, count)) {
+                em28xx_err("Error while copying to user\n");
                 return -EFAULT;
         }
+        dev->video_bytesread += count;
+
+        if (dev->video_bytesread == dev->frame_size) {
+                spin_lock_irqsave(&dev->queue_lock, lock_flags);
+                list_for_each_entry(i, &dev->outqueue, frame)
+                                    i->state = F_UNUSED;
+                INIT_LIST_HEAD(&dev->outqueue);
+                spin_unlock_irqrestore(&dev->queue_lock, lock_flags);
+
+                em28xx_queue_unusedframes(dev);
+                dev->video_bytesread = 0;
+        }
+
         *f_pos += count;
 
         mutex_unlock(&dev->lock);