[PATCH v6 20/24] iio: buffer: add ioctl() to support opening extra buffers for IIO device

From: Alexandru Ardelean
Date: Mon Feb 15 2021 - 05:47:59 EST

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>
---
drivers/iio/iio_core.h | 12 +--
drivers/iio/industrialio-buffer.c | 144 ++++++++++++++++++++++++++++--
include/linux/iio/buffer_impl.h | 5 ++
include/linux/iio/iio-opaque.h | 2 +
include/uapi/linux/iio/buffer.h | 10 +++
5 files changed, 162 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 7990c759f1f5..062fe16c6c49 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_buffers_alloc_sysfs_and_mask(struct iio_dev *indio_dev);
void iio_buffers_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 7b5827b91280..4848932d4394 100644
--- a/drivers/iio/industrialio-buffer.c
+++ b/drivers/iio/industrialio-buffer.c
@@ -9,9 +9,11 @@
* - Better memory allocation techniques?
* - Alternative access techniques?
*/
+#include <linux/anon_inodes.h>
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/device.h>
+#include <linux/file.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/slab.h>
@@ -89,7 +91,7 @@ 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 +103,8 @@ 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 +170,8 @@ 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 +186,32 @@ __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 +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 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);
+
+ kfree(ib);
+ clear_bit(IIO_BUSY_BIT_POS, &buffer->flags);
+ iio_device_put(indio_dev);
+
+ 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,
+ .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;
+ 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 (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);
+ 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;
+ }
+
+ 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;
+}
+
+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 +1590,7 @@ int iio_buffers_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 +1612,18 @@ int iio_buffers_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 +1645,9 @@ void iio_buffers_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/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 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;
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_ */
--
2.17.1