by Alexandru Ardelean

[permalink] [raw]

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

On Sun, Feb 14, 2021 at 4:38 PM Jonathan Cameron <[email protected]> wrote:
>
> On Thu, 11 Feb 2021 14:24:48 +0200
> Alexandru Ardelean <[email protected]> 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 <[email protected]>
>
> 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_ */
>