On Sun, Feb 28, 2021 at 9:58 AM Lars-Peter Clausen <lars@xxxxxxxxxx> wrote:
>
> On 2/15/21 11:40 AM, Alexandru Ardelean wrote:
> > [...]
> > /**
> > * iio_buffer_wakeup_poll - Wakes up the buffer waitqueue
> > * @indio_dev: The IIO device
> > @@ -1343,6 +1371,96 @@ static void iio_buffer_unregister_legacy_sysfs_groups(struct iio_dev *indio_dev)
> > kfree(iio_dev_opaque->legacy_scan_el_group.attrs);
> > }
> >
> > [...]
> > +static long iio_device_buffer_getfd(struct iio_dev *indio_dev, unsigned long arg)
> > +{
> > + struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
> > + int __user *ival = (int __user *)arg;
> > + struct iio_dev_buffer_pair *ib;
> > + struct iio_buffer *buffer;
> > + int fd, idx, ret;
> > +
> > + if (copy_from_user(&idx, ival, sizeof(idx)))
> > + return -EFAULT;
>
> If we only want to pass an int, we can pass that directly, no need to
> pass it as a pointer.
>
> int fd = arg;
I guess I can simplify this a bit.
>
> > +
> > + if (idx >= iio_dev_opaque->attached_buffers_cnt)
> > + return -ENODEV;
> > +
> > + iio_device_get(indio_dev);
> > +
> > + buffer = iio_dev_opaque->attached_buffers[idx];
> > +
> > + if (test_and_set_bit(IIO_BUSY_BIT_POS, &buffer->flags)) {
> > + ret = -EBUSY;
> > + goto error_iio_dev_put;
> > + }
> > +
> > + ib = kzalloc(sizeof(*ib), GFP_KERNEL);
> > + if (!ib) {
> > + ret = -ENOMEM;
> > + goto error_clear_busy_bit;
> > + }
> > +
> > + ib->indio_dev = indio_dev;
> > + ib->buffer = buffer;
> > +
> > + fd = anon_inode_getfd("iio:buffer", &iio_buffer_chrdev_fileops,
> > + ib, O_RDWR | O_CLOEXEC);
>
> I wonder if we need to allow to pass flags, like e.g. O_NONBLOCK.
>
> Something like
> https://elixir.bootlin.com/linux/latest/source/fs/signalfd.c#L288
Umm, no idea.
I guess we could.
Would a syscall make more sense than an ioctl() here?
I guess for the ioctl() case we would need to change the type (of the
data) to some sort of
struct iio_buffer_get_fd {
unsigned int buffer_idx;
unsigned int fd_flags;
};
Or do we just let userspace use fcntl() to change flags to O_NONBLOCK ?
>
> > + if (fd < 0) {
> > + ret = fd;
> > + goto error_free_ib;
> > + }
> > +
> > + if (copy_to_user(ival, &fd, sizeof(fd))) {
> > + put_unused_fd(fd);
> > + ret = -EFAULT;
> > + goto error_free_ib;
> > + }
>
> Here we copy back the fd, but also return it. Just return is probably
> enough.
Hmm.
Yes, it is a bit duplicate.
But it is a good point. Maybe we should return 0 to userspace.
>
> > +
> > + return fd;
> > +
> > +error_free_ib:
> > + kfree(ib);
> > +error_clear_busy_bit:
> > + clear_bit(IIO_BUSY_BIT_POS, &buffer->flags);
> > +error_iio_dev_put:
> > + iio_device_put(indio_dev);
> > + return ret;
> > +}
> > [...]
> > diff --git a/include/linux/iio/iio-opaque.h b/include/linux/iio/iio-opaque.h
> > index b6ebc04af3e7..32addd5e790e 100644
> > --- a/include/linux/iio/iio-opaque.h
> > +++ b/include/linux/iio/iio-opaque.h
> > @@ -9,6 +9,7 @@
> > * @event_interface: event chrdevs associated with interrupt lines
> > * @attached_buffers: array of buffers statically attached by the driver
> > * @attached_buffers_cnt: number of buffers in the array of statically attached buffers
> > + * @buffer_ioctl_handler: ioctl() handler for this IIO device's buffer interface
> > * @buffer_list: list of all buffers currently attached
> > * @channel_attr_list: keep track of automatically created channel
> > * attributes
> > @@ -28,6 +29,7 @@ struct iio_dev_opaque {
> > struct iio_event_interface *event_interface;
> > struct iio_buffer **attached_buffers;
> > unsigned int attached_buffers_cnt;
> > + struct iio_ioctl_handler *buffer_ioctl_handler;
>
> Can we just embedded this struct so we do not have to
> allocate/deallocate it?
Unfortunately we can't.
The type of ' struct iio_ioctl_handler ' is stored in iio_core.h.
So, we don't know the size here. So we need to keep it as a pointer
and allocate it.
It is a bit of an unfortunate consequence of the design of this
generic ioctl() registering.
>
> > struct list_head buffer_list;
> > struct list_head channel_attr_list;
> > struct attribute_group chan_attr_group;
>
>
