Re: [PATCH v5 13/17] iio: buffer: add ioctl() to support opening extra buffers for IIO device

[Alexandru Ardelean]

On Sun, Feb 14, 2021 at 4:38 PM Jonathan Cameron <jic23@xxxxxxxxxx> wrote:
>
> On Thu, 11 Feb 2021 14:24:48 +0200
> Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx> wrote:
>
> > With this change, an ioctl() call is added to open a character device for a
> > buffer. The ioctl() number is 'i' 0x91, which follows the
> > IIO_GET_EVENT_FD_IOCTL ioctl.
> >
> > The ioctl() will return an FD for the requested buffer index. The indexes
> > are the same from the /sys/iio/devices/iio:deviceX/bufferY (i.e. the Y
> > variable).
> >
> > Since there doesn't seem to be a sane way to return the FD for buffer0 to
> > be the same FD for the /dev/iio:deviceX, this ioctl() will return another
> > FD for buffer0 (or the first buffer). This duplicate FD will be able to
> > access the same buffer object (for buffer0) as accessing directly the
> > /dev/iio:deviceX chardev.
> >
> > Also, there is no IIO_BUFFER_GET_BUFFER_COUNT ioctl() implemented, as the
> > index for each buffer (and the count) can be deduced from the
> > '/sys/bus/iio/devices/iio:deviceX/bufferY' folders (i.e the number of
> > bufferY folders).
> >
> > Used following C code to test this:
> > -------------------------------------------------------------------
> >
> >  #include <stdio.h>
> >  #include <stdlib.h>
> >  #include <unistd.h>
> >  #include <sys/ioctl.h>
> >  #include <fcntl.h"
> >  #include <errno.h>
> >
> >  #define IIO_BUFFER_GET_FD_IOCTL      _IOWR('i', 0x91, int)
> >
> > int main(int argc, char *argv[])
> > {
> >         int fd;
> >         int fd1;
> >         int ret;
> >
> >         if ((fd = open("/dev/iio:device0", O_RDWR))<0) {
> >                 fprintf(stderr, "Error open() %d errno %d\n",fd, errno);
> >                 return -1;
> >         }
> >
> >         fprintf(stderr, "Using FD %d\n", fd);
> >
> >         fd1 = atoi(argv[1]);
> >
> >         ret = ioctl(fd, IIO_BUFFER_GET_FD_IOCTL, &fd1);
> >         if (ret < 0) {
> >                 fprintf(stderr, "Error for buffer %d ioctl() %d errno %d\n", fd1, ret, errno);
> >                 close(fd);
> >                 return -1;
> >         }
> >
> >         fprintf(stderr, "Got FD %d\n", fd1);
> >
> >         close(fd1);
> >         close(fd);
> >
> >         return 0;
> > }
> > -------------------------------------------------------------------
> >
> > Results are:
> > -------------------------------------------------------------------
> >  # ./test 0
> >  Using FD 3
> >  Got FD 4
> >
> >  # ./test 1
> >  Using FD 3
> >  Got FD 4
> >
> >  # ./test 2
> >  Using FD 3
> >  Got FD 4
> >
> >  # ./test 3
> >  Using FD 3
> >  Got FD 4
> >
> >  # ls /sys/bus/iio/devices/iio\:device0
> >  buffer  buffer0  buffer1  buffer2  buffer3  dev
> >  in_voltage_sampling_frequency  in_voltage_scale
> >  in_voltage_scale_available
> >  name  of_node  power  scan_elements  subsystem  uevent
> > -------------------------------------------------------------------
> >
> > iio:device0 has some fake kfifo buffers attached to an IIO device.
> >
> > Signed-off-by: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>
>
> There are a few corners of this that I'm not quite confident enough to just
> 'fix up' whilst applying.
>
>
> > ---
> >  drivers/iio/iio_core.h            |  12 +--
> >  drivers/iio/industrialio-buffer.c | 138 ++++++++++++++++++++++++++++--
> >  drivers/iio/industrialio-core.c   |   1 +
> >  include/linux/iio/buffer_impl.h   |   5 ++
> >  include/linux/iio/iio-opaque.h    |   2 +
> >  include/uapi/linux/iio/buffer.h   |  10 +++
> >  6 files changed, 157 insertions(+), 11 deletions(-)
> >  create mode 100644 include/uapi/linux/iio/buffer.h
> >
> > diff --git a/drivers/iio/iio_core.h b/drivers/iio/iio_core.h
> > index 4690c3240a5d..88db1feb5857 100644
> > --- a/drivers/iio/iio_core.h
> > +++ b/drivers/iio/iio_core.h
> > @@ -64,16 +64,16 @@ ssize_t iio_format_value(char *buf, unsigned int type, int size, int *vals);
> >  #ifdef CONFIG_IIO_BUFFER
> >  struct poll_table_struct;
> >
> > -__poll_t iio_buffer_poll(struct file *filp,
> > -                          struct poll_table_struct *wait);
> > -ssize_t iio_buffer_read_outer(struct file *filp, char __user *buf,
> > -                           size_t n, loff_t *f_ps);
> > +__poll_t iio_buffer_poll_wrapper(struct file *filp,
> > +                              struct poll_table_struct *wait);
> > +ssize_t iio_buffer_read_wrapper(struct file *filp, char __user *buf,
> > +                             size_t n, loff_t *f_ps);
> >
> >  int iio_buffer_alloc_sysfs_and_mask(struct iio_dev *indio_dev);
> >  void iio_buffer_free_sysfs_and_mask(struct iio_dev *indio_dev);
> >
> > -#define iio_buffer_poll_addr (&iio_buffer_poll)
> > -#define iio_buffer_read_outer_addr (&iio_buffer_read_outer)
> > +#define iio_buffer_poll_addr (&iio_buffer_poll_wrapper)
> > +#define iio_buffer_read_outer_addr (&iio_buffer_read_wrapper)
> >
> >  void iio_disable_all_buffers(struct iio_dev *indio_dev);
> >  void iio_buffer_wakeup_poll(struct iio_dev *indio_dev);
> > diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
> > index 1e8e4c2ff00e..3aa6702a5811 100644
> > --- a/drivers/iio/industrialio-buffer.c
> > +++ b/drivers/iio/industrialio-buffer.c
> > @@ -9,6 +9,7 @@
> >   * - Better memory allocation techniques?
> >   * - Alternative access techniques?
> >   */
> > +#include <linux/anon_inodes.h>
> >  #include <linux/kernel.h>
> >  #include <linux/export.h>
> >  #include <linux/device.h>
> > @@ -89,7 +90,7 @@ static bool iio_buffer_ready(struct iio_dev *indio_dev, struct iio_buffer *buf,
> >  }
> >
> >  /**
> > - * iio_buffer_read_outer() - chrdev read for buffer access
> > + * iio_buffer_read() - chrdev read for buffer access
> >   * @filp:    File structure pointer for the char device
> >   * @buf:     Destination buffer for iio buffer read
> >   * @n:               First n bytes to read
> > @@ -101,8 +102,8 @@ static bool iio_buffer_ready(struct iio_dev *indio_dev, struct iio_buffer *buf,
> >   * Return: negative values corresponding to error codes or ret != 0
> >   *      for ending the reading activity
> >   **/
> > -ssize_t iio_buffer_read_outer(struct file *filp, char __user *buf,
> > -                           size_t n, loff_t *f_ps)
> > +static ssize_t iio_buffer_read(struct file *filp, char __user *buf,
> > +                            size_t n, loff_t *f_ps)
> >  {
> >       struct iio_dev_buffer_pair *ib = filp->private_data;
> >       struct iio_buffer *rb = ib->buffer;
> > @@ -168,8 +169,8 @@ ssize_t iio_buffer_read_outer(struct file *filp, char __user *buf,
> >   * Return: (EPOLLIN | EPOLLRDNORM) if data is available for reading
> >   *      or 0 for other cases
> >   */
> > -__poll_t iio_buffer_poll(struct file *filp,
> > -                          struct poll_table_struct *wait)
> > +static __poll_t iio_buffer_poll(struct file *filp,
> > +                             struct poll_table_struct *wait)
> >  {
> >       struct iio_dev_buffer_pair *ib = filp->private_data;
> >       struct iio_buffer *rb = ib->buffer;
> > @@ -184,6 +185,32 @@ __poll_t iio_buffer_poll(struct file *filp,
> >       return 0;
> >  }
> >
> > +ssize_t iio_buffer_read_wrapper(struct file *filp, char __user *buf,
> > +                             size_t n, loff_t *f_ps)
> > +{
> > +     struct iio_dev_buffer_pair *ib = filp->private_data;
> > +     struct iio_buffer *rb = ib->buffer;
> > +
> > +     /* check if buffer was opened through new API */
> > +     if (test_bit(IIO_BUSY_BIT_POS, &rb->flags))
> > +             return -EBUSY;
> > +
> > +     return iio_buffer_read(filp, buf, n, f_ps);
> > +}
> > +
> > +__poll_t iio_buffer_poll_wrapper(struct file *filp,
> > +                              struct poll_table_struct *wait)
> > +{
> > +     struct iio_dev_buffer_pair *ib = filp->private_data;
> > +     struct iio_buffer *rb = ib->buffer;
> > +
> > +     /* check if buffer was opened through new API */
> > +     if (test_bit(IIO_BUSY_BIT_POS, &rb->flags))
> > +             return 0;
> > +
> > +     return iio_buffer_poll(filp, wait);
> > +}
> > +
> >  /**
> >   * iio_buffer_wakeup_poll - Wakes up the buffer waitqueue
> >   * @indio_dev: The IIO device
> > @@ -1343,6 +1370,91 @@ static void iio_buffer_unregister_legacy_sysfs_groups(struct iio_dev *indio_dev)
> >       kfree(iio_dev_opaque->legacy_scan_el_group.attrs);
> >  }
> >
> > +static int iio_buffer_chrdev_release(struct inode *inode, struct file *filep)
> > +{
> > +     struct iio_dev_buffer_pair *ib = filep->private_data;
> > +     struct iio_dev *indio_dev = ib->indio_dev;
> > +     struct iio_buffer *buffer = ib->buffer;
> > +
> > +     wake_up(&buffer->pollq);
> > +     clear_bit(IIO_BUSY_BIT_POS, &buffer->flags);
> > +     iio_device_put(indio_dev);
>
> Ordering here isn't quite the reverse of that done in _getfd()
> below.  Good to tidy that up, probably by swapping the test_and_set_bit()
> and iio_device_get below (with additional goto needed I think).
>
> > +     kfree(ib);
> > +
> > +     return 0;
> > +}
> > +
> > +static const struct file_operations iio_buffer_chrdev_fileops = {
> > +     .owner = THIS_MODULE,
> > +     .llseek = noop_llseek,
> > +     .read = iio_buffer_read,
> > +     .poll = iio_buffer_poll,
> > +     .compat_ioctl = compat_ptr_ioctl,
> > +     .release = iio_buffer_chrdev_release,
> > +};
> > +
> > +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;
> > +     char buf_name[sizeof("iio:buffer:xxx")];
>
> I'm missing where this is assigned.  Also not immediately sure, but I think
> this can just be a string used directly in anon_inode_getfd().
> I don't think we need to be unique for the different buffers as it's
> a 'class name' rather than needing to be specific.
>
> > +     struct iio_dev_buffer_pair *ib;
> > +     struct iio_buffer *buffer;
> > +     int fd, idx;
> > +
> > +     if (copy_from_user(&idx, ival, sizeof(idx)))
> > +             return -EFAULT;
> > +
> > +     if (idx >= iio_dev_opaque->attached_buffers_cnt)
> > +             return -ENODEV;
> > +
> > +     buffer = iio_dev_opaque->attached_buffers[idx];
> > +
> > +     if (test_and_set_bit(IIO_BUSY_BIT_POS, &buffer->flags))
> > +             return -EBUSY;
> > +
> > +     iio_device_get(indio_dev);
> > +
> > +     ib = kzalloc(sizeof(*ib), GFP_KERNEL);
> > +     if (!ib) {
> > +             fd = -ENOMEM;
> > +             goto error_iio_dev_put;
> > +     }
> > +
> > +     ib->indio_dev = indio_dev;
> > +     ib->buffer = buffer;
> > +
> > +     fd = anon_inode_getfd(buf_name, &iio_buffer_chrdev_fileops,
> > +                           ib, O_RDWR | O_CLOEXEC);
> > +     if (fd < 0)
> > +             goto error_free_ib;
> > +
> > +     if (copy_to_user(ival, &fd, sizeof(fd))) {
> > +             fd = -EFAULT;
>
> I suspect the iio_events equivalent of this is wrong, as we should be
> tidying up the fd and we aren't.
>
> put_unused_fd() I think, but not 100% sure on what the right handling is here.

i'm a bit unsure here as well;
been trying to find examples of this clean-up [on error] in other
places, but i couldn't find any clear-to-the-point examples;
so, put_unused_fd() should be it; looks like that should be the one;


>
>
> > +             goto error_free_ib;
> > +     }
> > +
> > +     return fd;
> > +
> > +error_free_ib:
> > +     kfree(ib);
> > +error_iio_dev_put:
> > +     iio_device_put(indio_dev);
> > +     clear_bit(IIO_BUSY_BIT_POS, &buffer->flags);
> > +     return fd;
> > +}
> > +
> > +static long iio_device_buffer_ioctl(struct iio_dev *indio_dev, struct file *filp,
> > +                                 unsigned int cmd, unsigned long arg)
> > +{
> > +     switch (cmd) {
> > +     case IIO_BUFFER_GET_FD_IOCTL:
> > +             return iio_device_buffer_getfd(indio_dev, arg);
> > +     default:
> > +             return IIO_IOCTL_UNHANDLED;
> > +     }
> > +}
> > +
> >  static int __iio_buffer_alloc_sysfs_and_mask(struct iio_buffer *buffer,
> >                                            struct iio_dev *indio_dev,
> >                                            int index)
> > @@ -1472,6 +1584,7 @@ int iio_buffer_alloc_sysfs_and_mask(struct iio_dev *indio_dev)
> >       struct iio_buffer *buffer;
> >       int unwind_idx;
> >       int ret, i;
> > +     size_t sz;
> >
> >       channels = indio_dev->channels;
> >       if (channels) {
> > @@ -1493,6 +1606,18 @@ int iio_buffer_alloc_sysfs_and_mask(struct iio_dev *indio_dev)
> >                       goto error_unwind_sysfs_and_mask;
> >               }
> >       }
> > +     unwind_idx = iio_dev_opaque->attached_buffers_cnt - 1;
> > +
> > +     sz = sizeof(*(iio_dev_opaque->buffer_ioctl_handler));
> > +     iio_dev_opaque->buffer_ioctl_handler = kzalloc(sz, GFP_KERNEL);
> > +     if (!iio_dev_opaque->buffer_ioctl_handler) {
> > +             ret = -ENOMEM;
> > +             goto error_unwind_sysfs_and_mask;
> > +     }
> > +
> > +     iio_dev_opaque->buffer_ioctl_handler->ioctl = iio_device_buffer_ioctl;
> > +     iio_device_ioctl_handler_register(indio_dev,
> > +                                       iio_dev_opaque->buffer_ioctl_handler);
> >
> >       return 0;
> >
> > @@ -1514,6 +1639,9 @@ void iio_buffer_free_sysfs_and_mask(struct iio_dev *indio_dev)
> >       if (!iio_dev_opaque->attached_buffers_cnt)
> >               return;
> >
> > +     iio_device_ioctl_handler_unregister(iio_dev_opaque->buffer_ioctl_handler);
> > +     kfree(iio_dev_opaque->buffer_ioctl_handler);
> > +
> >       iio_buffer_unregister_legacy_sysfs_groups(indio_dev);
> >
> >       for (i = iio_dev_opaque->attached_buffers_cnt - 1; i >= 0; i--) {
> > diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> > index 26b05dddfa71..febb3a0d91f3 100644
> > --- a/drivers/iio/industrialio-core.c
> > +++ b/drivers/iio/industrialio-core.c
> > @@ -1737,6 +1737,7 @@ static int iio_chrdev_release(struct inode *inode, struct file *filp)
> >       struct iio_dev_buffer_pair *ib = filp->private_data;
> >       struct iio_dev *indio_dev = container_of(inode->i_cdev,
> >                                               struct iio_dev, chrdev);
> > +
>
> Stray change that doesn't belong in here.
>
>
> >       clear_bit(IIO_BUSY_BIT_POS, &indio_dev->flags);
> >       iio_device_put(indio_dev);
> >       kfree(ib);
> > diff --git a/include/linux/iio/buffer_impl.h b/include/linux/iio/buffer_impl.h
> > index 768b90c64412..245b32918ae1 100644
> > --- a/include/linux/iio/buffer_impl.h
> > +++ b/include/linux/iio/buffer_impl.h
> > @@ -6,6 +6,8 @@
> >
> >  #ifdef CONFIG_IIO_BUFFER
> >
> > +#include <uapi/linux/iio/buffer.h>
> > +
> >  struct iio_dev;
> >  struct iio_buffer;
> >
> > @@ -72,6 +74,9 @@ struct iio_buffer {
> >       /** @length: Number of datums in buffer. */
> >       unsigned int length;
> >
> > +     /** @flags: File ops flags including busy flag. */
> > +     unsigned long flags;
> > +
> >       /**  @bytes_per_datum: Size of individual datum including timestamp. */
> >       size_t bytes_per_datum;
> >
> > diff --git a/include/linux/iio/iio-opaque.h b/include/linux/iio/iio-opaque.h
> > index c909835b6247..2c3374d465da 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;
> >       struct list_head                buffer_list;
> >       struct list_head                channel_attr_list;
> >       struct attribute_group          chan_attr_group;
> > diff --git a/include/uapi/linux/iio/buffer.h b/include/uapi/linux/iio/buffer.h
> > new file mode 100644
> > index 000000000000..13939032b3f6
> > --- /dev/null
> > +++ b/include/uapi/linux/iio/buffer.h
> > @@ -0,0 +1,10 @@
> > +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> > +/* industrial I/O buffer definitions needed both in and out of kernel
> > + */
> > +
> > +#ifndef _UAPI_IIO_BUFFER_H_
> > +#define _UAPI_IIO_BUFFER_H_
> > +
> > +#define IIO_BUFFER_GET_FD_IOCTL                      _IOWR('i', 0x91, int)
> > +
> > +#endif /* _UAPI_IIO_BUFFER_H_ */
>