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    SubjectRe: [PATCH v14 08/56] media: videobuf2: Use vb2_get_num_buffers() helper
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    Le 08/11/2023 à 10:42, Tomasz Figa a écrit :
    > On Tue, Oct 31, 2023 at 05:30:16PM +0100, Benjamin Gaignard wrote:
    >> Stop using queue num_buffers field directly, instead use
    >> vb2_get_num_buffers().
    >> This prepares for the future 'delete buffers' feature where there are
    >> holes in the buffer indices.
    >>
    >> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
    >> ---
    >> .../media/common/videobuf2/videobuf2-core.c | 92 +++++++++++--------
    >> .../media/common/videobuf2/videobuf2-v4l2.c | 4 +-
    >> 2 files changed, 54 insertions(+), 42 deletions(-)
    >>
    >> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
    >> index b406a30a9b35..c5c5ae4d213d 100644
    >> --- a/drivers/media/common/videobuf2/videobuf2-core.c
    >> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
    >> @@ -444,13 +444,14 @@ static int __vb2_queue_alloc(struct vb2_queue *q, enum vb2_memory memory,
    >> unsigned int num_buffers, unsigned int num_planes,
    >> const unsigned plane_sizes[VB2_MAX_PLANES])
    >> {
    >> + unsigned int q_num_buffers = vb2_get_num_buffers(q);
    >> unsigned int buffer, plane;
    >> struct vb2_buffer *vb;
    >> int ret;
    >>
    >> /* Ensure that q->num_buffers+num_buffers is below VB2_MAX_FRAME */
    >> num_buffers = min_t(unsigned int, num_buffers,
    >> - VB2_MAX_FRAME - q->num_buffers);
    >> + VB2_MAX_FRAME - q_num_buffers);
    > I guess it's safe in this specific situation, but was there any reason
    > behind not just calling vb2_get_num_buffers() directly here?
    >
    >>
    >> for (buffer = 0; buffer < num_buffers; ++buffer) {
    >> /* Allocate vb2 buffer structures */
    >> @@ -470,7 +471,7 @@ static int __vb2_queue_alloc(struct vb2_queue *q, enum vb2_memory memory,
    >> vb->planes[plane].min_length = plane_sizes[plane];
    >> }
    >>
    >> - vb2_queue_add_buffer(q, vb, q->num_buffers + buffer);
    >> + vb2_queue_add_buffer(q, vb, q_num_buffers + buffer);
    > In this case it should also be fine, but actually now this is a loop and if
    > somone doesn't know what the other code in the loop does, one could be
    > concerned that the num buffers actually could have changed, but we still
    > use the cached one that we got at the beginning of the function.
    >
    > (Ideally I'd imagine vb2_queue_add_buffer() to append the buffer
    > at the end of the queue and increment the num_buffers internally, but it
    > doesn't have to happen now, as this series is already quite complex...)

    That will be the case later in the series when I replace num_buffers field
    by a bitmap. Until that I prefer to limit the changes in this loop.

    >
    >> call_void_bufop(q, init_buffer, vb);
    >>
    >> /* Allocate video buffer memory for the MMAP type */
    > [snip]
    >> @@ -2513,7 +2519,8 @@ void vb2_core_queue_release(struct vb2_queue *q)
    >> __vb2_cleanup_fileio(q);
    >> __vb2_queue_cancel(q);
    >> mutex_lock(&q->mmap_lock);
    >> - __vb2_queue_free(q, q->num_buffers);
    >> + __vb2_queue_free(q, vb2_get_num_buffers(q));
    >> + q->num_buffers = 0;
    > Unrelated change?

    No because I found a case where q->num_buffers wasn't correctly reset while testing.

    >
    >> mutex_unlock(&q->mmap_lock);
    >> }
    >> EXPORT_SYMBOL_GPL(vb2_core_queue_release);
    >> @@ -2542,7 +2549,7 @@ __poll_t vb2_core_poll(struct vb2_queue *q, struct file *file,
    >> /*
    >> * Start file I/O emulator only if streaming API has not been used yet.
    >> */
    >> - if (q->num_buffers == 0 && !vb2_fileio_is_active(q)) {
    >> + if (vb2_get_num_buffers(q) == 0 && !vb2_fileio_is_active(q)) {
    >> if (!q->is_output && (q->io_modes & VB2_READ) &&
    >> (req_events & (EPOLLIN | EPOLLRDNORM))) {
    >> if (__vb2_init_fileio(q, 1))
    >> @@ -2580,7 +2587,7 @@ __poll_t vb2_core_poll(struct vb2_queue *q, struct file *file,
    >> * For output streams you can call write() as long as there are fewer
    >> * buffers queued than there are buffers available.
    >> */
    >> - if (q->is_output && q->fileio && q->queued_count < q->num_buffers)
    >> + if (q->is_output && q->fileio && q->queued_count < vb2_get_num_buffers(q))
    >> return EPOLLOUT | EPOLLWRNORM;
    >>
    >> if (list_empty(&q->done_list)) {
    >> @@ -2629,8 +2636,8 @@ struct vb2_fileio_buf {
    >> * struct vb2_fileio_data - queue context used by file io emulator
    >> *
    >> * @cur_index: the index of the buffer currently being read from or
    >> - * written to. If equal to q->num_buffers then a new buffer
    >> - * must be dequeued.
    >> + * written to. If equal to number of already queued buffers
    >> + * then a new buffer must be dequeued.
    > Hmm, that's a significant meaning change compared to the original text. Is
    > it indended?

    Does "If equal to number of buffers in the vb2_queue then a new buffer must be dequeued."
    sound better for you ?

    >
    >> * @initial_index: in the read() case all buffers are queued up immediately
    >> * in __vb2_init_fileio() and __vb2_perform_fileio() just cycles
    >> * buffers. However, in the write() case no buffers are initially
    >> @@ -2640,7 +2647,7 @@ struct vb2_fileio_buf {
    >> * buffers. This means that initially __vb2_perform_fileio()
    >> * needs to know what buffer index to use when it is queuing up
    >> * the buffers for the first time. That initial index is stored
    >> - * in this field. Once it is equal to q->num_buffers all
    >> + * in this field. Once it is equal to num_buffers all
    > It's not clear what num_buffers means here. Would it make sense to instead
    > say "number of buffers in the vb2_queue"?

    Yes I will change that

    >
    >> * available buffers have been queued and __vb2_perform_fileio()
    >> * should start the normal dequeue/queue cycle.
    >> *
    >> @@ -2690,7 +2697,7 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read)
    >> /*
    >> * Check if streaming api has not been already activated.
    >> */
    >> - if (q->streaming || q->num_buffers > 0)
    >> + if (q->streaming || vb2_get_num_buffers(q) > 0)
    >> return -EBUSY;
    >>
    >> /*
    >> @@ -2740,7 +2747,7 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read)
    >> /*
    >> * Get kernel address of each buffer.
    >> */
    >> - for (i = 0; i < q->num_buffers; i++) {
    >> + for (i = 0; i < vb2_get_num_buffers(q); i++) {
    >> /* vb can never be NULL when using fileio. */
    >> vb = vb2_get_buffer(q, i);
    >>
    >> @@ -2759,18 +2766,23 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read)
    >> /*
    >> * Queue all buffers.
    >> */
    >> - for (i = 0; i < q->num_buffers; i++) {
    >> - ret = vb2_core_qbuf(q, q->bufs[i], NULL, NULL);
    >> + for (i = 0; i < vb2_get_num_buffers(q); i++) {
    >> + struct vb2_buffer *vb2 = vb2_get_buffer(q, i);
    >> +
    >> + if (!vb2)
    >> + continue;
    >> +
    >> + ret = vb2_core_qbuf(q, vb2, NULL, NULL);
    >> if (ret)
    >> goto err_reqbufs;
    >> fileio->bufs[i].queued = 1;
    >> }
    > Doesn't this part belong to the previous patch that changes q->bufs[x] to
    > vb2_get_buffer()?

    Yes I will change that too.

    >
    >> /*
    >> * All buffers have been queued, so mark that by setting
    >> - * initial_index to q->num_buffers
    >> + * initial_index to num_buffers
    > What num_buffers?

    I will use your wording: "the number of buffers in the vb2_queue"

    >
    >> */
    >> - fileio->initial_index = q->num_buffers;
    >> - fileio->cur_index = q->num_buffers;
    >> + fileio->initial_index = vb2_get_num_buffers(q);
    >> + fileio->cur_index = fileio->initial_index;
    >> }
    >>
    >> /*
    >> @@ -2964,12 +2976,12 @@ static size_t __vb2_perform_fileio(struct vb2_queue *q, char __user *data, size_
    >> * If we are queuing up buffers for the first time, then
    >> * increase initial_index by one.
    >> */
    >> - if (fileio->initial_index < q->num_buffers)
    >> + if (fileio->initial_index < vb2_get_num_buffers(q))
    >> fileio->initial_index++;
    >> /*
    >> * The next buffer to use is either a buffer that's going to be
    >> - * queued for the first time (initial_index < q->num_buffers)
    >> - * or it is equal to q->num_buffers, meaning that the next
    >> + * queued for the first time (initial_index < num_buffers)
    >> + * or it is equal to num_buffers, meaning that the next
    > What num_buffers?

    Same here

    >
    > Best regards,
    > Tomasz
    > _______________________________________________
    > Kernel mailing list -- kernel@mailman.collabora.com
    > To unsubscribe send an email to kernel-leave@mailman.collabora.com

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