lavd/v4l2: copy frames into normally allocated packets whenever there is just one buffer left available

This will avoid the possibility that we dequeue more buffers than we
have obtained from the v4l2 driver.

Fixes ticket #1570

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavdevice/v4l2.c

@@ -111,6 +111,7 @@ struct video_data {
     int buffers;
     void **buf_start;
     unsigned int *buf_len;
+    int *buf_dequeued;
     char *standard;
     v4l2_std_id std_id;
     int channel;
@@ -123,6 +124,7 @@ struct video_data {
 struct buff_data {
     int index;
     int fd;
+    int *buf_dequeued;
 };
 
 struct fmt_map {
@@ -436,6 +438,11 @@ static int mmap_init(AVFormatContext *ctx)
         av_free(s->buf_start);
         return AVERROR(ENOMEM);
     }
+    s->buf_dequeued = av_mallocz(sizeof(int) * s->buffers);
+    if (s->buf_dequeued == NULL) {
+        av_log(ctx, AV_LOG_ERROR, "Cannot allocate buffer array\n");
+        return AVERROR(ENOMEM);
+    }
 
     for (i = 0; i < req.count; i++) {
         struct v4l2_buffer buf = {
@@ -470,25 +477,37 @@ static int mmap_init(AVFormatContext *ctx)
     return 0;
 }
 
+static int enqueue_buffer(int fd, int index)
+{
+    int res;
+    struct v4l2_buffer buf = { 0 };
+
+    buf.type   = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+    buf.memory = V4L2_MEMORY_MMAP;
+    buf.index  = index;
+
+    if (v4l2_ioctl(fd, VIDIOC_QBUF, &buf) < 0) {
+        res = AVERROR(errno);
+        av_log(NULL, AV_LOG_ERROR, "ioctl(VIDIOC_QBUF): %s\n", av_err2str(res));
+        return res;
+    }
+    return 0;
+}
+
 static void mmap_release_buffer(AVPacket *pkt)
 {
-    struct v4l2_buffer buf = { 0 };
-    int res, fd;
     struct buff_data *buf_descriptor = pkt->priv;
 
     if (pkt->data == NULL)
         return;
 
-    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
-    buf.memory = V4L2_MEMORY_MMAP;
-    buf.index = buf_descriptor->index;
-    fd = buf_descriptor->fd;
-    av_free(buf_descriptor);
-
-    if (v4l2_ioctl(fd, VIDIOC_QBUF, &buf) < 0) {
-        res = AVERROR(errno);
-        av_log(NULL, AV_LOG_ERROR, "ioctl(VIDIOC_QBUF): %s\n", av_err2str(res));
+    if (buf_descriptor->index == -1) {
+        av_free(pkt->data);
+    } else {
+        if (!enqueue_buffer(buf_descriptor->fd, buf_descriptor->index))
+            buf_descriptor->buf_dequeued[buf_descriptor->index] = 0;
     }
+    av_free(buf_descriptor);
 
     pkt->data = NULL;
     pkt->size = 0;
@@ -562,15 +581,13 @@ static int mmap_read_frame(AVFormatContext *ctx, AVPacket *pkt)
         .memory = V4L2_MEMORY_MMAP
     };
     struct buff_data *buf_descriptor;
-    int res;
+    int res, i, free_buffers;
 
     /* FIXME: Some special treatment might be needed in case of loss of signal... */
     while ((res = v4l2_ioctl(s->fd, VIDIOC_DQBUF, &buf)) < 0 && (errno == EINTR));
     if (res < 0) {
-        if (errno == EAGAIN) {
-            pkt->size = 0;
+        if (errno == EAGAIN)
             return AVERROR(EAGAIN);
-        }
         res = AVERROR(errno);
         av_log(ctx, AV_LOG_ERROR, "ioctl(VIDIOC_DQBUF): %s\n", av_err2str(res));
         return res;
@@ -591,17 +608,10 @@ static int mmap_read_frame(AVFormatContext *ctx, AVPacket *pkt)
         av_log(ctx, AV_LOG_ERROR,
                "The v4l2 frame is %d bytes, but %d bytes are expected\n",
                buf.bytesused, s->frame_size);
+        enqueue_buffer(s->fd, buf.index);
         return AVERROR_INVALIDDATA;
     }
 
-    /* Image is at s->buff_start[buf.index] */
-    pkt->data= s->buf_start[buf.index];
-    pkt->size = buf.bytesused;
-    pkt->pts = buf.timestamp.tv_sec * INT64_C(1000000) + buf.timestamp.tv_usec;
-    res = convert_timestamp(ctx, &pkt->pts);
-    if (res < 0)
-        return res;
-    pkt->destruct = mmap_release_buffer;
     buf_descriptor = av_malloc(sizeof(struct buff_data));
     if (buf_descriptor == NULL) {
         /* Something went wrong... Since av_malloc() failed, we cannot even
@@ -612,8 +622,36 @@ static int mmap_read_frame(AVFormatContext *ctx, AVPacket *pkt)
         return AVERROR(ENOMEM);
     }
     buf_descriptor->fd = s->fd;
-    buf_descriptor->index = buf.index;
+    buf_descriptor->buf_dequeued = s->buf_dequeued;
+
+    free_buffers = -1; /* start from -1 because we just dequeued a buffer */
+    for (i = 0; i < s->buffers; i++)
+        if (s->buf_dequeued[i] == 0)
+            free_buffers++;
+
+    if (free_buffers == 0) {
+        if ((res = av_new_packet(pkt, buf.bytesused)) < 0) {
+            enqueue_buffer(s->fd, buf.index);
+            return res;
+        }
+        memcpy(pkt->data, s->buf_start[buf.index], buf.bytesused);
+        enqueue_buffer(s->fd, buf.index);
+        buf_descriptor->index = -1;
+    } else {
+        /* Image is at s->buff_start[buf.index] */
+        pkt->data = s->buf_start[buf.index];
+        buf_descriptor->index = buf.index;
+        buf_descriptor->buf_dequeued[buf.index] = 1;
+    }
+    pkt->size = buf.bytesused;
     pkt->priv = buf_descriptor;
+    pkt->destruct = mmap_release_buffer;
+    pkt->pts = buf.timestamp.tv_sec * INT64_C(1000000) + buf.timestamp.tv_usec;
+    res = convert_timestamp(ctx, &pkt->pts);
+    if (res < 0) {
+        mmap_release_buffer(pkt);
+        return res;
+    }
 
     return s->buf_len[buf.index];
 }
@@ -663,6 +701,7 @@ static void mmap_close(struct video_data *s)
     }
     av_free(s->buf_start);
     av_free(s->buf_len);
+    av_free(s->buf_dequeued);
 }
 
 static int v4l2_set_parameters(AVFormatContext *s1)
@@ -963,6 +1002,8 @@ static int v4l2_read_packet(AVFormatContext *s1, AVPacket *pkt)
     int res;
 
     av_init_packet(pkt);
+    pkt->data = NULL;
+    pkt->size = 0;
     if ((res = mmap_read_frame(s1, pkt)) < 0) {
         return res;
     }