V4L problem with VIDIOCGCAP ioctl call

Question

I'm having some issue working with V4L (the API that provides unified access to various video capturing for Linux). I'm tryng to make a VIDIOCGCAP ioctl call, but I get an INVALID ARGUMENT error. Here is an strace:

execve("./test", ["./test"], [/* 26 vars */]) = 0
brk(0)                                  = 0x8d5c000
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
mmap2(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7fc9000
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY)      = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=29703, ...}) = 0
mmap2(NULL, 29703, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7fc1000
close(3)                                = 0
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/lib/i686/cmov/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\260e\1\0004\0\0\0\4"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0755, st_size=1413540, ...}) = 0
mmap2(NULL, 1418864, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb7e66000
mmap2(0xb7fbb000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x155) = 0xb7fbb000
mmap2(0xb7fbe000, 9840, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb7fbe000
close(3)                                = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7e65000
set_thread_area({entry_number:-1 -> 6, base_addr:0xb7e656b0, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0
mprotect(0xb7fbb000, 4096, PROT_READ)   = 0
munmap(0xb7fc1000, 29703)               = 0
open("/dev/video0", O_RDONLY)           = 3
ioctl(3, EXT2_IOC_GETVERSION or VIDIOCGCAP, 0xbf8e4ca4) = -1 EINVAL (Invalid argument)
fstat64(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 0), ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7fc8000
write(1, "err"..., 3err)                   = 3
exit_group(3)                           = ?              = ?

Here is the code:

#include "linux/videodev.h"
#include "fcntl.h"
#include "stdio.h"
int main() {
int fd = open("/dev/video0", O_RDONLY);
struct video_capability chan;
if (ioctl(fd, VIDIOCGCAP, &chan) == -1) printf("err");
}

And:

gcc -o test test.c

More info: I have other video capture software in this machine that use V4L without problems. So, I'm doing something wrong.

Answer 1

Perhaps you need to try using V4L2 instead, namely the VIDIOC_QUERYCAP ioctl.