Hans Verkuil <hverkuil@xxxxxxxxx> wrote:
>Hi Andy,
>
>This seems more complex than is necessary. See my comments below...
>
>On 11/21/13 02:05, Andy Walls wrote:
>> (This patch is RFC, because it was compiled and tested against kernel
>> v3.5)
>>
>> videobuf2 file I/O emulation assumed that buffers dequeued from the
>> driver would return in the order they were enqueued in the driver.
>>
>> Improve the file I/O emulator's book-keeping to remove this
>assumption.
>>
>> Also remove the, AFAICT, assumption that only read() calls would need
>to
>> dequeue a buffer from the driver.
>>
>> Also set the buf->size properly, if a write() dequeues a buffer.
>>
>>
>> Signed-off-by: Andy Walls <awalls@xxxxxxxxxxxxxxxx>
>> Cc: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
>> Cc: PawelOsciak<pawel@xxxxxxxxxx>
>> Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
>>
>>
>> diff --git a/drivers/media/video/videobuf2-core.c
>b/drivers/media/video/videobuf2-core.c
>> index 9d4e9ed..f330aa4 100644
>> --- a/drivers/media/video/videobuf2-core.c
>> +++ b/drivers/media/video/videobuf2-core.c
>> @@ -1796,6 +1796,7 @@ struct vb2_fileio_data {
>> unsigned int dq_count;
>> unsigned int flags;
>> };
>> +#define FILEIO_INDEX_NOT_SET ((unsigned int) INT_MAX)
>>
>> /**
>> * __vb2_init_fileio() - initialize file io emulator
>> @@ -1889,6 +1890,7 @@ static int __vb2_init_fileio(struct vb2_queue
>*q, int read)
>> goto err_reqbufs;
>> fileio->bufs[i].queued = 1;
>> }
>> + fileio->index = FILEIO_INDEX_NOT_SET;
>>
>> /*
>> * Start streaming.
>> @@ -1975,15 +1977,11 @@ static size_t __vb2_perform_fileio(struct
>vb2_queue *q, char __user *data, size_
>> */
>> q->fileio = NULL;
>>
>> - index = fileio->index;
>> - buf = &fileio->bufs[index];
>> -
>> /*
>> * Check if we need to dequeue the buffer.
>> */
>> - if (buf->queued) {
>> - struct vb2_buffer *vb;
>> -
>> + index = fileio->index;
>> + if (index == FILEIO_INDEX_NOT_SET) {
>> /*
>> * Call vb2_dqbuf to get buffer back.
>> */
>> @@ -1997,12 +1995,19 @@ static size_t __vb2_perform_fileio(struct
>vb2_queue *q, char __user *data, size_
>> goto end;
>> fileio->dq_count += 1;
>>
>> + fileio->index = fileio->b.index;
>> + index = fileio->index;
>> + buf = &fileio->bufs[index];
>> +
>> /*
>> * Get number of bytes filled by the driver
>> */
>> - vb = q->bufs[index];
>> - buf->size = vb2_get_plane_payload(vb, 0);
>> + buf->pos = 0;
>> buf->queued = 0;
>> + buf->size = read ? vb2_get_plane_payload(q->bufs[index], 0)
>> + : vb2_plane_size(q->bufs[index], 0);
>> + } else {
>> + buf = &fileio->bufs[index];
>> }
>>
>> /*
>> @@ -2070,13 +2075,28 @@ static size_t __vb2_perform_fileio(struct
>vb2_queue *q, char __user *data, size_
>> */
>> buf->pos = 0;
>> buf->queued = 1;
>> - buf->size = q->bufs[0]->v4l2_planes[0].length;
>> + buf->size = vb2_plane_size(q->bufs[index], 0);
>> fileio->q_count += 1;
>>
>> /*
>> - * Switch to the next buffer
>> + * Decide on the next buffer
>> */
>> - fileio->index = (index + 1) % q->num_buffers;
>> + if (read || (q->num_buffers == 1)) {
>> + /* Use the next buffer the driver provides back */
>> + fileio->index = FILEIO_INDEX_NOT_SET;
>> + } else {
>> + /* Prefer a buffer that is not quequed in the driver */
>> + int initial_index = fileio->index;
>> + fileio->index = FILEIO_INDEX_NOT_SET;
>> + do {
>> + if (++index == q->num_buffers)
>> + index = 0;
>> + if (!fileio->bufs[index].queued) {
>> + fileio->index = index;
>> + break;
>> + }
>> + } while (index != initial_index);
>
>Why bother finding an unused index? There are really just two
>situations:
>either all the buffers have been queued, and after that you just
>dequeue
>and queue them (and you get the index from the dequeued buffer), or you
>are still only queuing buffers (in the write case, for the read case
>that
>already happened) and you can use a simple counter as the index.
>
>> + }
>>
>> /*
>> * Start streaming if required.
>>
>>
>
>See my version of this patch below (it might not cleanly apply as this
>sits
>on top of a bunch of other vb2 patches that I will post soon):
>
>diff --git a/drivers/media/v4l2-core/videobuf2-core.c
>b/drivers/media/v4l2-core/videobuf2-core.c
>index 66cd81d..257b4ca 100644
>--- a/drivers/media/v4l2-core/videobuf2-core.c
>+++ b/drivers/media/v4l2-core/videobuf2-core.c
>@@ -2309,6 +2309,7 @@ static int __vb2_init_fileio(struct vb2_queue *q,
>int read)
> goto err_reqbufs;
> fileio->bufs[i].queued = 1;
> }
>+ fileio->index = q->num_buffers;
> }
>
> /*
>@@ -2384,15 +2385,11 @@ static size_t __vb2_perform_fileio(struct
>vb2_queue *q, char __user *data, size_
> }
> fileio = q->fileio;
>
>- index = fileio->index;
>- buf = &fileio->bufs[index];
>-
> /*
> * Check if we need to dequeue the buffer.
> */
>- if (buf->queued) {
>- struct vb2_buffer *vb;
>-
>+ index = fileio->index;
>+ if (index >= q->num_buffers) {
> /*
> * Call vb2_dqbuf to get buffer back.
> */
>@@ -2405,12 +2402,18 @@ static size_t __vb2_perform_fileio(struct
>vb2_queue *q, char __user *data, size_
> return ret;
> fileio->dq_count += 1;
>
>+ index = fileio->b.index;
>+ buf = &fileio->bufs[index];
>+
> /*
> * Get number of bytes filled by the driver
> */
>- vb = q->bufs[index];
>- buf->size = vb2_get_plane_payload(vb, 0);
>+ buf->pos = 0;
> buf->queued = 0;
>+ buf->size = read ? vb2_get_plane_payload(q->bufs[index], 0)
>+ : vb2_plane_size(q->bufs[index], 0);
>+ } else {
>+ buf = &fileio->bufs[index];
> }
>
> /*
>@@ -2473,13 +2476,10 @@ static size_t __vb2_perform_fileio(struct
>vb2_queue *q, char __user *data, size_
> */
> buf->pos = 0;
> buf->queued = 1;
>- buf->size = q->bufs[0]->v4l2_planes[0].length;
>+ buf->size = vb2_plane_size(q->bufs[index], 0);
> fileio->q_count += 1;
>-
>- /*
>- * Switch to the next buffer
>- */
>- fileio->index = (index + 1) % q->num_buffers;
>+ if (fileio->index < q->num_buffers)
>+ fileio->index++;
> }
>
> /*
>
>
>Regards,
>
> Hans
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Hi Hans,
You are correct. The initial queuing for write() can just use a simple, incrementing index.
(I developed the patch at work under some deadline pressure. Overly complex still worked to get the job done at the time.)
I will review your patch later this evening.
Regards,
Andy
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