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f73f7f4d |
| 15-Feb-2021 |
Alexandru Ardelean <alexandru.ardelean@analog.com> |
iio: buffer: add ioctl() to support opening extra buffers for IIO device
With this change, an ioctl() call is added to open a character device for a buffer. The ioctl() number is 'i' 0x91, which fol
iio: buffer: add ioctl() to support opening extra buffers for IIO device
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@analog.com> Link: https://lore.kernel.org/r/20210215104043.91251-21-alexandru.ardelean@analog.com Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
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