I am currently investigating how we can use v4l2 devices from python, and found that python has a binding for ioctl (https://docs.python.org/3/library/fcntl.html).
I done some implemntations in C, but i have a hard time understanding if ioctl is the same as v4l2_ioctl?
They seem to take the exact same arguments, in the official examples i see both wrapped in a function, that is used in the same way:
static void xioctl(int fh, int request, void *arg)
{
int r;
do {
r = v4l2_ioctl(fh, request, arg);
} while (r == -1 && ((errno == EINTR) || (errno == EAGAIN)));
if (r == -1) {
fprintf(stderr, "error %d, %s\\n", errno, strerror(errno));
exit(EXIT_FAILURE);
}
}
And for the normal ioctl:
static int xioctl(int fh, int request, void *arg)
{
int r;
do {
r = ioctl(fh, request, arg);
} while (-1 == r && EINTR == errno);
return r;
}
I looked in the linux repository, but could not figure out the exact difference between the two.
Can i use ioctl and v4l2_ioctl interchangeably?
If so why does both exist?
If not, what is the limitations of ioctl compared to v4l2_ioctl?
Can i use ioctl and v4l2_ioctl interchangeably?
No.
If so why does both exist?
ioctl exists to do some special operations on devices.
v4l2_ioctl is a wrapper from libv4l2 to simplify operations on v4l2 devices.
From README:
libv4l2
This offers functions like v4l2_open, v4l2_ioctl, etc. which can by used to quickly make v4l2 applications work with v4l2 devices with weird formats. libv4l2 mostly passes calls directly through to the v4l2 driver. When the app does a TRY_FMT / S_FMT with a not supported format libv4l2 will get in the middle and emulate the format (if an app wants to know which formats the hardware can really do it should use ENUM_FMT, not randomly try a bunch of S_FMT's). For more details on the v4l2_ functions see libv4l2.h .
And the source found in libv4l project is the ultimate code documentation.